Calculating food production in the subsistence harvest of birds and eggs.
ABSTRACT. Subsistence harvest studies use number-to-mass conversion factors (CFn-m) to transform numbers of animals harvested into food production (CFn-m = body mass x recovery rate; where recovery rate is the percentage of the body mass represented by the processed carcass). Also, if egg harvest was reported as volume (e.g., a bucket), volume- to-number conversion factors (CFv-n) are needed to calculate the number of eggs taken. Conversion factors (CF) for subsistence harvest of birds and eggs have been based on unclear assumptions. We calculated a mean recovery rate (65%) by weighing and processing wild birds, compiled data on bird and egg mass, developed an egg CFv-n equation, and presented CF for 88 bird species, 13 subspecies or populations, and 25 species categories likely to be harvested in Alaska. We also made recommendations on how to apply and adjust CF according to study objectives. We recommend that subsistence harvest studies (1) collect egg harvest data as egg numbers (not volume); (2) clearly explain considerations and assumptions used in CF; (3) report recovery rates and mass of birds and eggs; and (4) cite original sources when referring to CF from previous studies. Attention to these points of method will improve the accuracy of food production estimates and the validity of food production comparisons across time and geographic areas.Key words: bird; egg; subsistence harvest; subsistence hunt; harvest survey; food production; edible mass; recovery rate; number-to-mass conversion factor; volume-to-number conversion factor; Alaska
RESUME. Les etudes sur la recolte de subsistance utilisent des facteurs de conversion nombre-masse (CFn-m) pour transformer le nombre d'animaux chasses en production alimentaire (CFn-m = masse corporelle x taux de recuperation; le taux de recuperation etant le pourcentage de la masse corporelle representee par la carcasse transformee). De plus, si la recolte des ceufs etait rapportee en volume (p. ex. un seau), les facteurs de conversion volume/nombre (CFv-n) s'averent necessaires pour calculer le nombre d'ceufs preleves. Les facteurs de conversion (FC) pour la recolte de subsistance d'oiseaux et d'ceufs s'appuient sur des hypotheses floues. Nous avons calcule une moyenne du taux de recuperation (65 %) en pesant et en transformant des oiseaux sauvages, recueilli des donnees sur la masse des oiseaux et des ceufs, trouve une equation pour les facteurs de conversion volume/nombre pour les ceufs et presente des FC pour 88 especes d'oiseaux, 13 sous-especes ou populations et 25 categories d'especes susceptibles d'etre chassees en Alaska. Nous avons egalement formule des recommandations sur la fafon d'appliquer et d'ajuster les FC selon les objectifs de I'etude. Nous recommandons que les etudes sur la recolte de subsistance (1) recueillent les donnees sur la recolte des ceufs en nombre d'ceufs (et non en volume); (2) expliquent clairement les considerations et les hypotheses utilisees pour les FC; (3) rendent compte des taux de recuperation et de la masse des oiseaux et des ceufs; et (4) citent les sources originales quand elles font reference aux FC d'etudes precedentes. L'attention portee a ces elements methodologiques ameliorera la precision des estimations de la production alimentaire et la validite des comparaisons en matiere de production alimentaire en fonction des periodes et des regions geographiques.
Mots cles : oiseau; ceuf; recolte de subsistance; chasse de subsistance; enquete sur les recoltes; production alimentaire; masse comestible; taux de recuperation; facteur de conversion nombre/masse; facteur de conversion volume/nombre; Alaska
Traduit pour la revue Arctic par Nicole Giguere.
INTRODUCTION
Number-to-Mass Conversion Factors for Birds and Eggs
Studies of subsistence uses of wild resources report harvest as the number of animals taken and as the amount of food produced (edible mass). Estimates of the number of animals taken are used to document subsistence activities, to assess harvest impacts on fish and wildlife populations, and to allocate harvestable amounts among user groups (Usher and Wenzel, 1987). Food production data are used to depict the relative importance of resources (e.g., moose, salmon, geese) and their role in subsistence economies (Brown and Burch, 1992), to assess exposure to contaminants derived from wild foods (Usher, 2000), and to estimate the monetary (replacement) value of harvest. Food production estimates do not account for the nutritional and cultural importance of different resources (Usher, 1976; Behnke, 1982). But these data are also important in adjudicating disputes among stakeholders, quantifying ecological services provided by resources and ecosystems, assessing food security, and prioritizing human activities on the basis of their socioeconomic contribution to communities' well-being (Jones, 1997; Magdanz et al., 2011; Hoover et al., 2013).
Food production is calculated by multiplying the number of animals taken by a number-to-mass conversion factor (CFn-m). A CFn-m integrates two variables: the live (whole, round) body mass of individual species or multi-species categories and the recovery (yield) rate, which is the percentage of the live mass represented by the processed carcass. Studies have commonly failed to explain assumptions used in CFn-m and to report body mass and recovery rates (Table 1). Over the decades, CFn-m developed in earlier studies have often been reused without critical evaluation or clear reference to original sources. Thus, it is difficult to evaluate discrepancies in CFn-m and food production estimates across studies. For instance, conversion factors (CF) used for Sandhill Crane Grus canadensis harvested in Alaska (CFn-m = 10-15 lb/bird) (4536-6804 g/bird) (Patterson, 1974; Wolfe, 1981; Ikuta et al., 2014) appear overestimated when compared to body mass of the subspecies occurring in Alaska (8.17-9.82 lb) (3705-4455 g) (Rodewald, 2015).
To inform stakeholders who rely on accurate food production data, studies need to clearly report considerations and variables used to derive CF. From subsistence users' perspectives, biased-low recovery rates conflict with the non-waste principle that is intrinsic to their cultural values (Zavaleta, 1999). Biased-low recovery rates also lead to underestimating the importance of wild resources in subsistence economies. On the other hand, biased-high recovery rates can discredit food production assessments and their use in mitigation and litigation.
Birds and eggs are a small proportion of the subsistence harvest, but data on their food production help address complex management issues (Fienup-Riordan, 1999; Zavaleta, 1999). In Alaska, the subsistence harvest (about 34 million edible pounds per year) is composed of fish (53%), land and marine mammals (23% and 14%), plants (4%), shellfish (3%), and birds and eggs (3%) (Fall, 2016). Developing CF for each of these resource categories involves diverse challenges. Previous efforts to consolidate information and clarify CF have addressed all resource categories (JBNQHRC, 1982; Usher, 2000; Ashley, 2002), and because this task is immense, some issues pertaining to bird and egg CF remained unresolved.
For wild birds, body mass depends on species, subspecies, population, sex, and age. Within these categories, body mass also varies because of ecological conditions and breeding, migration, and feather molting cycles (Piersma and Lindstrom, 1997). Because of difficulties in species identification, harvest surveys use species categories, which also complicate CFn-m because the species within a category may differ in body mass. Some studies have defined CFn-m for categories that include species with considerable size difference (Patterson, 1974). For instance, surveys have used one category for gull eggs, but eggs of large gulls are at least twice the size of those of small gulls (Rodewald, 2015). Social science researchers and other staff working on harvest surveys are often unfamiliar with the identification (including size), distribution ranges, and relative abundance of the dozens of bird species that may be harvested in a region. Thus, it is often difficult for them to critically evaluate bird and egg CF used in previous studies and to generate new CF.
Recovery rates in subsistence harvests depend on harvesting and processing conditions, cultural practices, species, and food preferences (Burch, 1985; Usher, 2000). Assumptions underlying recovery rates used for subsistence bird harvest are sometimes unclear, and rates have ranged from 40% to 75% (Table 1). Although in Alaska Native cultures birds have not been widely used as dog food, recovery rates in some earlier studies considered harvest for such use (Usher, 1970) and likely differ from rates that consider human consumption only. In many studies, recovery rates for egg harvest do not indicate whether the shell mass was included as edible mass.
Volume-to-Number Conversion Factors far Eggs
To facilitate accurate recall of harvest events and minimize burden on respondents, harvest surveys may use reporting units that are meaningful to harvesters (fish tub, truckload of wood, bucket of eggs) (Tobias and Kay, 1994). Even when respondents are asked to report their harvest in number of eggs, some values may instead be recorded in volume. For such cases, volume-to-number conversion factors (CFv-n) allow calculating the number of eggs taken. A method to estimate egg CFv-n involves comparing the mass (as a proxy for volume) of wild bird eggs to that of chicken eggs (J. Magdanz, pers. comm. in Naves, 2010). But CFv-n estimated in this way seemed high compared to CFv-n based on researcher or key respondent information (Burch, 1985; Fall et al., 1995). Use of padding material (e.g., grass, moss) to protect eggs reduces the total volume of eggs in a given container (Hunn et al., 2003). To clarify assumptions and refine this estimation method, we considered the use of padding material and the fact that full containers may not be filled to the brim to prevent egg damage during harvesting and transporting.
Study Objectives
It is impractical to account precisely for all sources of variation in recovery rate and wild bird body and egg mass that may affect CF (Usher, 1976; Burch, 1985). Thus, rather than defining highly precise and detailed CF, the objectives of this study were (a) to develop CFn-m and CFv-n equations based on clear variables and assumptions that can be easily adjusted depending on the study objectives and context and (b) to provide recommendations on the development and use of CF that will increase the accuracy of food production estimates and the validity of food production comparisons across time and geographic areas.
To achieve these objectives, we first collected ethnographic information from key respondents on subsistence practices in bird processing and egg harvesting. Information on bird parts usually consumed was needed to clarify which parts should be included as edible mass when calculating a recovery rate reflecting subsistence practices. Information on use of containers and padding material in egg harvesting was needed to refine the CFv-n estimation method. Second, we processed and weighed wild birds to calculate a recovery rate. Third, we compiled data on bird and egg mass, as well as distribution ranges and population sizes, for species likely to be harvested in Alaska. We integrated these social science and biological data to develop CFn-m and CFv-n equations and calculated CF for use in harvest studies. Although we addressed bird species composition and subsistence practices in Alaska, our approach and recommendations also apply to food production studies of other resources and regions.
METHODS
Ethnographic Information on Bird Processing and Egg Harvesting
To calculate the bird recovery rate, the first step was to determine which bird parts should be included as edible mass, depending on how birds are processed and which parts are usually consumed. Also, refining the CFv-n equation required information on egg harvesting (see below). To gather this ethnographic information, we designed 14 questions on bird and egg harvesting and processing related to CF (online Appendix S1). The questions asked for information about general harvesting and processing in a region, as opposed to individual practices. We identified 27 Alaska Native people as key respondents who could provide information on the subsistence harvest and culture in their region of origin. Rather than a random selection of individuals within a sampling universe, key respondents are particularly knowledgeable people who can provide expert opinion on a domain (Huntington, 1998; Bernard, 2011). Participation in the Alaska Migratory Bird Co-Management Council (AMBCC, 2016) and in the U.S. Fish and Wildlife Service Refuge Information Technician Program were the main criteria used to identify such individuals. Participation in these programs served as an index of key respondents' extensive experience as subsistence resource users and community leaders, including their engagement in harvest management.
In April-May 2015, printed copies of the questionnaire were distributed in person or via postal mail to the potential respondents. Pre-stamped, pre-addressed envelopes were provided for return of completed questionnaires. We followed ethical principles for social science research, including informed consent and voluntary participation (ARCUS, 1999). One month after the questionnaire was first distributed, a reminder was mailed to people who had not yet returned responses. We received 16 completed questionnaires (a 59% response rate). In results pertaining to the questionnaire, "n" refers to the number of responses to individual questions or the number of times respondents indicated a categorical answer (yes, no, sometimes).
Respondents were instructed to leave fields for answers blank if they did not know the answer or if some species categories did not occur or were not used in their region. Most responses referred to species categories commonly harvested across Alaska (ducks, geese, grouse, and ptarmigan). Fewer responses were obtained to questions related to egg harvest than to those about bird harvest.
Definition of Edible Mass
On the basis of key respondent information (see Results), we defined the edible mass as including the carcass mass (meat, bones, skin, fat, and other tissues remaining after removal of feathers, feet, head, and viscera), as well as the heart and gizzard mass because these parts were also usually consumed by subsistence users. Although some responses indicated that other parts are sometimes consumed (e.g., liver, blood, intestine, stomach; see Results), these responses were infrequent, and the exclusion of these parts from the edible mass was inconsequential for the calculation of the recovery rate. While the exclusion of these parts may have resulted in a minor underestimation of the recovery rate, such underestimation was likely offset by the inclusion of skin and bones, which are sometimes not consumed. In Alaska, wild birds and eggs cannot be bought of sold and therefore have no defined market value. To facilitate assessments of the monetary value of wild foods, the definition of edible mass must be comparable to likely replacement products available in grocery stores. For bird eggs, we used a recovery rate of 100% (whole egg including the shell). Although the shell is not consumed, chicken eggs are a likely replacement product and are sold whole and by the dozen (not directly by weight).
Processing and Weighing Wild Birds to Calculate Bird Recovery Rate
To calculate the mean bird recovery rate according to our definition of edible mass, we weighed and processed wild birds harvested for home use in September-October 2015 and September 2016. This sample included ducks (n = 18), geese (n = 9), and ptarmigan (n = 2) harvested at several locations in south-central Alaska and the Alaska Peninsula. Mass measurements were obtained using an electronic scale with precision of one gram. We weighed the whole body mass of freshly killed birds. We plucked and singed the birds, removed the head, wing tips (cut at the metacarpus and ulna-radius joint), feet (cut at the tarsometatarsus and tibia-fibula joint), and all viscera. The skin-on, bone-in mass of birds thus processed constituted the carcass mass. After the carcass mass was recorded, we cut out and weighed the breast fillets (boneless, skin-on outer and inner fillets, or pectoralis and supracoracoideus muscles) and the whole leg (bone-in, skin-on thigh and drumstick, or tibia-fibula and tarsus sections). We also weighed the heart and clean gizzard (opened to remove food remains and its tough inner lining) to be included as edible mass. Weights were presented as arithmetic means of proportions of the live mass including all species. The bird recovery rate was calculated as the mean proportion of the carcass, heart, and gizzard mass relative to the live mass.
Breast fillets and whole legs are common cuts in sport hunting and poultry processing. Mass data for these cuts are useful to gauge recovery rates used in previous subsistence harvest studies, to generate alternative recovery rates based on different processing methods, and to allow comparisons with potential replacement poultry products.
Bird and Egg Mass Data
We compiled body and egg mass data for bird species, subspecies, and populations occurring in Alaska from Rodewald (2015) unless otherwise noted. Data on sex and age composition of Alaska subsistence bird harvest were unavailable. Thus, it was impossible to account for variation in body mass among sex and age categories in the harvest. We calculated the arithmetic mean body mass including data for males, females, adults, and immatures (as available) to represent sex and age categories potentially harvested. Mass data referred to Alaska-breeding populations in spring (as available) because at least 51% of the annual bird subsistence harvest occurs in spring (Paige and Wolfe, 1997). We used mass of freshly laid eggs because water loss during incubation decreases egg mass.
Mean body and egg mass were calculated based on all items (species, subspecies, populations) within categories. Population size data were used to weight mass means. Population size data were sometimes unavailable because (a) populations have not been monitored; (b) surveys have not differentiated among species (goldeneyes, mergansers, scoters, scaups) (Stehn et al., 2013; Platte and Stehn, 2015); and (c) estimates of abundance were not directly comparable among items within categories. If mass data were unavailable for one or more items within a category, means or reference values were defined by considering data for similar species and species distributions (online Appendix S2).
Body and egg mass data were reported both in grams (as rounded numbers with no decimal places) and in pounds (body mass data with two decimal places and egg mass data with three decimal places). Rather than displaying excessive precision, this level of detail when dealing with mass data in pounds was needed to properly represent mass of small birds and eggs.
Number-to-Mass Conversion Factors for Birds and Eggs
Using the recovery rates defined in this study and the bird and egg mass data compiled, we calculated CFn-m as:
Bird CFn-m = 0.65 x body mass (see Results). (1)
Egg CFn-m = 1.00 x egg mass (shell included). (2)
Volume-to-Number Conversion Factors for Eggs
To refine the CFv-n estimation method based on comparison of chicken and wild bird egg mass, we considered how the volume of eggs in a container is affected by (1) use of padding material and (2) not filling the container to the brim. First, to assess whether these considerations reflect egg harvesting practices, the key respondent questionnaire included questions on characteristics of containers used, frequency of use of padding material, and whether containers are only partially filled to avoid egg loss and damage during transport (questions 8-11, online Appendix S1). On the basis of information from key respondents (see Results), we assumed that padding material is always used and that full containers are filled to 80% of their capacity.
To quantify the reduction of the volume of eggs in a container resulting from use of padding material, we packed large chicken eggs (24 ounces or 680 g per dozen) (U.S. Department of Agriculture, 2000) in a one-gallon (3.8 L) bucket, filling it without any padding material and then adding dry grass between egg layers. We repeated packing with and without grass three times and counted the number of eggs needed to fill the bucket to the brim. With grass, the number of eggs needed to fill the bucket in the three measurements was 37, 36, and 33 eggs (mean = 35.3). Without grass, in each of the three measurements, 48 large chicken eggs were needed to fill the bucket.
We then developed a CFv-n equation including four variables: (a) number of chicken eggs needed to fill a 1-gallon (3.8 L) bucket; (b) proportion of container volume filled; (c) mass of a chicken egg; and (d) mass of a wild bird egg [CFv-n = (a x b) x (c / d)]. Considering our assumptions:
Number of eggs/gallon: CFv-n = (35.3 x 0.8) x 0.126 / mass of wild bird egg, in pounds). (3)
Number of eggs/L: CFv-n = (9.3 x 0.8) x (57.0 / mass of wild bird egg, in grams). (4)
RESULTS
Number-to-Mass Conversion Factors for Birds and Eggs
The following ethnographic information was used to identify bird parts that should be included as edible mass when calculating the recovery rate. Key respondents reported that Alaska subsistence users consumed wild birds as bone-in, skin-on preparations, usually as a roast or soup (see also Mishler, 2003; Unger, 2014). Birds were consumed fresh or preserved by freezing, drying, or canning. Bird processing involved plucking, singeing, and gutting birds.
Meat from the breast, legs, neck, head, back, and wings was usually consumed, as well as skin, fat, heart, and gizzard (Table 2). The liver was indicated as consumed in more than half of responses. Other parts were identified as not usually consumed, but some respondents indicated consumption of blood, intestine (ptarmigan, ducks, and geese), stomach (ducks and geese), kidney, and tongue. Bones were boiled to render broth, and bone marrow was sometimes consumed. We did not ask about non-food uses, but respondents reported that sometimes goose down was used and that the viscera and wings of harvested birds were used as bait in traps for fur animals.
Plucking seemed a preferred processing method among subsistence users, although skinning was sometimes used as a quicker option. To facilitate plucking, birds whose feathers are difficult to remove (swan, crane, seabirds, sea ducks) may be dipped in hot water. Such birds were sometimes skinned. The thin skin of grouse and ptarmigan often tears off during plucking, so these birds were commonly skinned. Plucking allowed consumption of the skin and associated fat. We asked respondents what proportion of the bird's body weight they thought is usually consumed when birds are plucked or skinned (the recovery rate) (questions 5 and 6, online Appendix S1). Responses ranged from 50% to 100%, but some seemed to refer to total mass after processing [recovery rate = 100% (n = 2) and "90% minus guts and bones"]. Because this question seemed unclear to respondents, we based the recovery rate solely on the data from wild birds processed in this study.
Using our data from processed wild birds (n = 29), the mean carcass mass was 60% of the live mass (range = 54%-66%), the heart was 1% (range = 0.5%-1.2%), and the gizzard, 4% (range = l%-7%), resulting in a mean bird recovery rate of 65% (range = 56%-70%) (Table 3). Breast fillets were 22% (range = 18%-28%) and the legs were 10% (range = 7%-13%) of the live mass.
Using a recovery rate of 65% for birds and 100% for eggs and the mass data compiled, we calculated bird and egg CFn-m for 88 bird species, 13 subspecies or populations, and 25 species categories (Table 4 and online Appendix S2).
Volume-to-Number Conversion Factors for Eggs
The key respondent questionnaire indicated that five-gallon (19 L; n = 7) and one-gallon (3.8 L; n = 5) buckets were commonly used for egg harvesting, but that any available container may be used (basket, tea pot, bag, cooler; n = 8). In areas where eggs were commonly harvested, padding material was almost always used (question 9.a, online Appendix SI: "every time" n = 7, "three out of four times" n = 2). Padding was sometimes not used in murre egg harvesting because murre eggs are sturdy. Responses indicating infrequent use of padding material occurred for regions where eggs are harvested occasionally and in small numbers ("two out of four times" n = 2, "one out of four times" n = 1, "do not use moss, grass" n = 1).
Some responses to the question on whether containers are only partially filled to avoid egg loss and damage during transport considered (1) the volume of padding material separately from the volume of eggs; (2) whether eggs were abundant enough to fill containers; or (3) the number of eggs that people needed and intended to harvest (question 10.a: "yes" n = 7, "no" n = 2; question 10.b: "yes" n = 6, "no" n = 7; question 10.c: mean = 69%, range = 30%-100%). Although these questions may have been understood differently by some respondents, responses indicated that, even if reports refer to full containers (e.g., two buckets), these were often not filled to the brim.
We asked the number of eggs packed in a five-gallon bucket (question 11, online Appendix S1). Only one respondent provided direct information on the number of eggs per gallon, and the answer indicated a range (36-60 large gull eggs in a five-gallon bucket). Three respondents indicated proportions of volume, which suggested that this question was not clear for them. Two respondents specified that they did not know the answer (e.g., "1 never count them"). This question was left blank in the remaining 10 completed questionnaires.
DISCUSSION
Bird Recovery Rate
Although the composition of our wild bird sample reflected species availability at a limited set of locations and time of the year, our results were consistent with diverse data sources, including previous subsistence harvest studies, poultry production, and biological data on the relative mass of bird body parts. Considering the range of recovery rates used in previous subsistence harvest studies (40%-75%; Table 1), 40% was likely an underestimate, because it was little more than the percentage (32%) that we measured for only the breast fillets and legs. A recovery rate of 75% was likely an overestimate, because (1) it would involve including as edible mass bird parts other than those identified in this study as commonly consumed, and (2) it is higher than our recommended recovery rate (65%), which included the skin and bones, although the skin is sometimes removed during processing. Our recommended recovery rate (65%) agreed with several subsistence harvest studies in which the rate was based on assumptions by researchers. Even if not explained, recovery rates in some studies were likely based on information from local, Native experts and from researchers with wide experience in ethnographic work involving participant observation and residency in subsistence communities.
Selective breeding and commercial production conditions may result in differences in body composition between poultry and wild birds, but recovery rates in wild birds and poultry were similar. For poultry, the recovery rate for a carcass processed for removal of blood, feathers, head, feet, and all viscera was 65% (range = 58%-72%) of the body mass (Watt and Merrill, 1963; Fanatico, 2003; Lessler et al., 2007; Poltowicz and Doktor, 2011). The breast and legs were about 38% of the body mass (Solomon et al., 2006; Haslinger et al., 2007). In wild birds, the breast and legs were 32% of the body mass in our sample and 28% in other sources (Raveling, 1979; Thompson and Drobney, 1996; Jacobs et al., 2011).
Both our study and other sources reported the heart as 1% of the body mass of wild birds (Thompson and Drobney, 1996; Piersma and Gill, 1998; Jacobs et al., 2011). The gizzard was 1%-2% of the body mass in seabirds and shorebirds (Piersma and Gill, 1998; Jacobs et al., 2011), 5%-7% in geese (Raveling, 1979; Barnes and Thomas, 1987), and 2%-5% in ducks (Barnes and Thomas, 1987; Goudie and Ryan, 1991; Thompson and Drobney, 1996). The relative gizzard mass we obtained (4%) was at the mean for ducks and geese. Using this mean was appropriate because it was in accordance with the overall species composition of subsistence harvest in Alaska (ducks were 58% and geese were 31% of the number of birds annually taken; Paige and Wolfe, 1997).
Using the allometric equation of Prange et al. (1979), bone mass for wild bird species likely harvested in Alaska accounted for 7%-9% of the body mass (results not presented here). Because some bone mass is removed during processing (head, feet, wing tips), the lower end of this range could be used to adjust the recovery rate when exclusion of bones is appropriate.
Recovery rates must reflect prevailing processing practices, which may differ among hunting traditions. A characterization of bird processing by sport users was beyond the scope of this study. In Alaska, bird sport hunting generally applies to harvest in non-subsistence areas as defined by the Joint Board of Fisheries and Game, which are primarily urban areas (State of Alaska, 2015:5 AAC 99.015). Sport hunters pluck birds for bone-in, skin-on preparations, and a recovery rate of 60% is likely adequate for this use (if the heart and gizzard are not usually consumed). But sport hunters also commonly skin birds, and only the breast (recovery rate = 22% for skin-on processing) or the breast and legs (recovery rate = 32%) may be consumed (Shaw, 2013). These three values could be combined to generate a recovery rate for sport hunting. In contrast to subsistence harvest studies, sport hunting economic valuations have focused on hunting activities and expenditures rather than food production (Gan and Luzar, 1993; ECONorthwest, 2014). A better understanding of food production in bird sport hunting as well as other differences and similarities between sport and subsistence bird hunting traditions could help alleviate conflict between user groups and promote positive outcomes in management and conservation issues.
Egg Recovery Rate
Studies have often assumed an egg recovery rate of 100% (e.g., Georgette and Loon, 1993), although this assumption may not be clearly stated. The eggshell is 8%-14% of the total egg mass (Williams et al., 1982). Across species, larger eggs have proportionally thicker shells and higher shell mass (Rahn and Paganelli, 1989). Murre eggs are an important subsistence resource, and their shells are about 14% of the total egg mass (Williams et al., 1982). Whether to include eggshell mass within edible mass depends on the study objectives. In replacement cost evaluation, eggshell should be included as edible mass (recovery rate = 100%) because a likely store-bought replacement product (chicken eggs) would include shells. When assessing exposure to contaminants, eggshells should be excluded from the edible mass because they are not consumed. If discounting shell mass, we recommend a recovery rate of 90% for all egg harvest.
Volume-to-Number Conversion Factors for Eggs
It is possible that the previous attempt to calculate CFv-n based on 48 chicken eggs/gallon (12.6 eggs/L) (J. Magdanz, pers. comm. in Naves, 2010) assumed that padding material was not used and that containers were filled to the brim. Estimates based on these assumptions were likely too high and resulted in numbers of eggs about 40% higher than ours. For murre eggs, the CFv-n calculated using our equation (16.0 eggs/gallon) (4.0 eggs/L) was half of that estimated by Burch (1985) (32 eggs/gallon) (8.4 eggs/L). Considerations used by Burch (1985) were unknown, but this difference may be related to the fact that we assumed use of padding material. For large gull eggs, our CFv-n (17.5 eggs/gallon) (4.3 eggs/L) was higher than (a) empirical data in Hunn et al. (2003) (12 eggs/gallon) (3.2 eggs/L); (b) the range provided by a key respondent in this study (7-12 eggs/gallon) (1.8-3.2 eggs/L); and (c) the value for "gull (unidentified)" provided by a key respondent in Fall et al. (1995) (10 eggs/gallon) (2.6 eggs/L). Although our CFv-n equation relied on simple assumptions, these were clearly stated and their variables can be easily adjusted to suit different study objectives and contexts. For example, if it is known that padding was not used, the equation could consider 35 chicken eggs/gallon (9.2 eggs/L).
In harvest survey interviews, considering individual harvest events, respondents can provide the best data on the number of eggs harvested. If respondents report eggs as volume, surveyors can assist respondents by sequentially asking (1) the kind of eggs harvested (species); (2) the size of containers used; and (3) whether padding material was used. Then, respondents may be asked to estimate how many eggs were harvested. For egg harvest reported as volume, the unit used in the original report must be reported so that standard CFv-n can be applied. Undocumented conversions of egg volume to number make it difficult to compare results among studies.
Species Categories, Regional, and Seasonal Conversion Factors
Mean body and egg mass used in CFn-m should approximate the harvest composition in a given geographic area and season of the year. In this study, we calculated mean mass for species categories weighted by Alaska-wide populations. Using the same principle, the mean mass for species categories may be adjusted for smaller geographic scales. Use of means weighted by population size is relevant for categories that include species of very different sizes. However, to simplify the application of CF and facilitate comparison among studies, whenever appropriate, CF should refer to relatively large geographic areas and encompass all seasons of the year.
Regardless of the level of analytical complexity researchers can implement when using CF, we offer four recommendations for this method. First, surveyors must be prepared to assist respondents in accurately reporting the number of eggs harvested, instead of volume. Second, considerations and assumptions used in CF must be clearly explained. Third, recovery rates and mass of birds and eggs used to generate CF must be reported (with citation of the source) so that users can assess which of these two variables accounts for potential differences from CF in other studies. Fourth, if using CF from previous studies, citations must refer to original sources, avoiding second-hand citations. Attention to these points will improve the accuracy of food production estimates and our ability to compare them across time and geographic areas.
ACKNOWLEDGEMENTS
This study was funded by the Alaska Department of Fish and Game, Division of Wildlife Conservation (RSA-1155353), as a component of the Harvest Assessment Program of the Alaska Migratory Bird Co-Management Council. We thank the key respondents for sharing information on bird processing and egg harvesting; Andrew Ramey and Txai-the Tundra Drummer for providing wild birds for weighing and processing; and Christian Dau (U.S. Fish and Wildlife Service) and Craig Ely (U.S. Geological Service, Alaska Science Center) for providing unpublished data on swan body mass. We also thank Jim Magdanz, Tom Rothe, Julian Fischer, and two anonymous reviewers for suggesting improvements to manuscript drafts.
APPENDICES
The following appendices are available as supplementary files to the online version of this article at: https://arctic.journalhosting.ucalgary.ca/arctic/index.php/ arctic/rt/suppFiles/4630/0
APPENDIX S1. Key respondent questionnaire to collect ethnographic information on subsistence harvesting and processing of birds and eggs in Alaska.
APPENDIX S2. Notes to accompany TABLE 4. Conversion factors to estimate food production in subsistence harvest of birds and eggs in Alaska.
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Liliana C. Naves (1,2) and James A. Fall (1)
(1) Alaska Department of Fish and Game, Division of Subsistence, 333 Raspberry Road, Anchorage, Alaska 99502, USA
(2) Corresponding author: [email protected]
(Received 31 March 2016; accepted in revisedform 4 September 2016)
TABLE 1. Recovery rates used in conversion factors for
subsistence bird harvest.
Recovery Information used to define Study (2)
rate1 the recovery rate or
reference cited
70% Proportion of live mass of White, 1953
domesticated pigs (heavy-
bodied, short-legged
animals)
70% White (1953) Foote, 1965
70% White (1953) cited in Usher, 1970
Foote (1965)
70% Carcass mass determined Patterson, 1974
in consultation with village
representatives
70% Not explained Wolfe, 1981; Behnke,
1982; Georgette and
Loon, 1993
60%-70% White (1953) and poultry JBNQNHRC, 1982
carcass yield (Watt and
Merrill, 1963), including
meat, edible organs, half
of the bone mass, and two-
thirds of the mass of
blood and feathers
60%-70% JBNQNHRC (1982) Berkes et al., 1994;
Tobias and Kay, 1994
70% Poultry carcass yield, Usher, 2000
White (1953); JBNQNHRC
(1982); Georgette and
Loon (1993)
60% Poultry carcass yield Gambell, 1984
40% Researcher estimate Fall and Morris,
1987; Fall et
al., 1995
65% Researcher estimate Kristensen, 2011
68% Poultry carcass yield Goldstein et
al., 2014
75% Not explained Wolfe et al., 1990;
Wentworth, 2007
Unknown Wolfe (1981); Braund & Fuller and George,
Associates (1993); CSIS 1997; Brower et
(2016a) al., 2000
Unknown Wolfe (1981); CSIS Braund & Associates,
(2016a) 1993; Ahmasuk et
al., 2008
Unknown Not explained Whiting, 2006
(1) Percentage of live mass.
(2) This table summarizes our review of literature on the
development and use of conversion factors for birds and other
subsistence resources. It does not present all documents we
consulted. It includes examples of application of conversion
factors and issues related to these factors.
TABLE 2. Consumption of bird parts by subsistence
users in Alaska. (1)
Breast Legs Neck Head Back
Usually consumed:
Ducks 15 14 13 11 14
Geese 15 13 13 9 14
Swans 10 9 8 7 10
Crane 9 8 7 6 9
Gulls, murres, puffins 1 1 1 1 1
Loons 2 2 1 1 2
Snipe, godwit, whimbrel 2 2 1 1 2
Grouse, ptarmigan 12 11 10 8 11
Sometimes consumed:
Ducks -- 1 1 -- --
Geese -- -- -- 1 --
Swans -- -- 1 -- --
Crane -- -- 1 1 --
Gulls, murres, puffins -- -- -- --
Loons -- -- 1 1 --
Snipe, godwit, whimbrel -- -- -- -- --
Grouse, ptarmigan -- -- -- -- --
Usually not consumed:
Ducks -- -- 2 -- 2
Geese -- -- -- 3 --
Swans -- -- 1 3 --
Crane -- -- 1 3 --
Gulls, murres, puffins -- -- -- -- --
Loons -- -- -- -- --
Snipe, godwit, whimbrel -- -- 1 1 --
Grouse, ptarmigan -- -- 2 4 1
Wings Skin Fat Heart
Usually consumed:
Ducks 12 14 14 11
Geese 12 13 13 10
Swans 8 7 9 8
Crane 8 6 7 7
Gulls, murres, puffins -- -- -- 1
Loons 1 -- -- 1
Snipe, godwit, whimbrel 2 1 2 2
Grouse, ptarmigan 11 10 11 9
Sometimes consumed:
Ducks -- -- -- 1
Geese -- -- -- --
Swans -- 2 -- --
Crane -- 2 2 --
Gulls, murres, puffins -- 1 1 --
Loons -- -- -- --
Snipe, godwit, whimbrel -- 1 -- --
Grouse, ptarmigan -- 2 1-- 1
Usually not consumed:
Ducks 1 -- 3 7
Geese 1 -- -- 3
Swans 2 2 1 2
Crane 1 1 -- 2
Gulls, murres, puffins 1 1 -- --
Loons 1 3 1 --
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan 1 -- -- 2
Feet Gizzard Liver Bone
marrow
Usually consumed:
Ducks 4 13 9 4
Geese 3 12 8 4
Swans 2 9 7 5
Crane 2 7 6 3
Gulls, murres, puffins -- -- 1 --
Loons -- -- -- --
Snipe, godwit, whimbrel 1 1 2 1
Grouse, ptarmigan 3 10 8 3
Sometimes consumed:
Ducks -- -- -- 1
Geese 1 -- -- --
Swans 2 -- -- --
Crane -- -- -- --
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan -- -- 1 1
Usually not consumed:
Ducks 1 5 7 7
Geese 7 1 5 7
Swans 6 1 3 4
Crane 6 2 3 5
Gulls, murres, puffins 1 1 -- 1
Loons 1 1 1 1
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan 7 2 3 4
Blood Intestines Pancreas Stomach
Usually consumed:
Ducks 2 1 -- 1
Geese 2 1 -- 1
Swans 2 -- -- --
Crane 2 -- -- --
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel 1 -- -- --
Grouse, ptarmigan 2 1 -- --
Sometimes consumed:
Ducks 1 -- -- --
Geese 1 1 -- --
Swans 1 1 -- --
Crane 1 1 -- --
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan 1 -- " ~
Usually not consumed:
Ducks 9 11 10 8
Geese 6 8 10 9
Swans 4 6 7 7
Crane 5 6 7 7
Gulls, murres, puffins 1 1 1 1
Loons 1 1 1 1
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan 5 8 11 10
Kidneys Lungs Bones Tongue
Usually consumed:
Ducks 2 -- -- 1
Geese 2 -- -- 1
Swans 1 -- -- 1
Crane 1 -- -- 1
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan 2 -- -- 1
Sometimes consumed:
Ducks -- -- -- --
Geese -- -- -- --
Swans -- -- -- --
Crane -- -- -- --
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel -- -- -- --
Grouse, ptarmigan
Usually not consumed:
Ducks 11 2 -- --
Geese 7 8 2 --
Swans 5 7 2 --
Crane 5 7 2 --
Gulls, murres, puffins -- -- -- --
Loons -- -- -- --
Snipe, godwit, whimbrel -- 1 -- --
Grouse, ptarmigan 7 10 2 --
(1) Values are number of key respondents that indicated bird parts as
usually, "sometimes," and "usually not" consumed in this study's
questionnaire (online Appendix SI).
-- : Consumption not indicated by key respondents.
TABLE 3. Mass (g) of wild birds and common cuts in harvest processing
of birds harvested in south-central Alaska and the Alaska
Peninsula in September--October 2015 and September 2016.
Species Live mass Carcass Heart Gizzard
(1)
American 922 563 6 22
Wigeon Anas 919 492 8 25
americana 738 423 8 31
901 533 7 31
766 437 7 43
566 307 3 35
777 426 7 53
598 349 6 39
Mallard A. 1157 721 11 45
platyrhynchos 1080 679 9 54
1307 814 11 57
1055 609 9 47
1149 669 9 49
Northern Pintail 1167 752 9 32
A. acuta 848 527 8 44
948 627 8 28
686 424 8 30
Green-winged 386 243 2 3
Teal A. crecca
Black Brant 1952 1153 16 89
Branta bernicla
Canada/Cackling 1485 882 13 82
Goose Branta spp. 1732 1000 14 84
1677 1010 13 64
2549 1491 17 110
1685 1097 12 75
1471 851 10 71
1602 919 9 87
2493 1494 16 129
Willow Ptarmigan 590 378 7 14
Lagopus lagopus 611 372 7 16
Mean proportion 100% 60% 1% 4%
of live mass
Range of proportions 54%-66% 0.5%-1.2% l%-7%
of live mass
Species Total Breast Whole
edible (2) fillets (3) legs (4)
American 591 213 84
Wigeon Anas 525 211 71
americana 462 160 56
571 193 71
487 167 57
345 113 39
486 162 58
394 119 45
Mallard A. 777 285 102
platyrhynchos 742 267 95
882 305 141
665 214 92
727 251 106
Northern Pintail 793 256 95
A. acuta 579 206 76
663 228 97
462 164 59
Green-winged 248 95 45
Teal A. crecca
Black Brant 1258 412 202
Branta bernicla
Canada/Cackling 977 301 179
Goose Branta spp. 1098 336 186
1087 342 204
1618 507 312
1184 350 220
932 287 155
1015 305 186
1639 452 287
Willow Ptarmigan 399 166 69
Lagopus lagopus 395 163 71
Mean proportion 65% 22% 10%
of live mass
Range of proportions 56%-70% 18%-28% 7%-13%
of live mass
(1) Bone-in, skin-on. Feathers, wing tips, feet,
head, and viscera removed (see Methods).
(2) Edible mass included the carcass, heart, and gizzard.
(3) Boneless, skin-on, outer and inner fillets, right and left sides.
(4) Bone-in, skin-on thigh and drumstick, right and left sides.
TABLE 4. Conversion factors to estimate food production in subsistence
harvest of birds and eggs in Alaska. Source for body and egg mass was
Rodewald (2015) unless otherwise noted. To calculate CF for
multi-species or multi-population categories, we weighted body and
egg mass by population size whenever possible. Asterisks indicate
species or categories for which further information is available in
online Appendix S2- continued:
Bird
Body Relative CFn-m (2)
mass (g) mass1 (g)
American Wigeon 735 478
Anas americana
Gadwall Anas strepera 859 558
Teal (unidentified) * 328 213
Green-winged Teal 328 12% 213
A. crecca
Blue-winged Teal A. 371 241
discors
Mallard A. platyrhynchos 1122 729
Northern Pintail A. acuta 820 533
Northern Shoveler 603 392
A. clypeata
Black Scoter 1052 684
Melanitta nigra
Surf Scoter M. 1022 664
perspicillata
White-winged 1825 1186
Scoter M. fusca
Bufflehead 397 258
Bucephala albeola
Goldeneye 887 577
(unidentified) *
Common Goldeneye 863 5% 561
Bucephala clangula
Barrow's Goldeneye 910 592
B. islandica
Canvasback Aythya 1210 787
valisineria
Scaup (unidentified) * 943 613
Greater Scaup Aythya 943 613
marila
Lesser Scaup A. affinis 751 20% 488
Common Eider Somateria 2288 1487
moliissima v-nigrum *
King Eider 5. 1570 1021
spectabilis *
Spectacled Eider S. 1466 953
fischeri *
Steller's Eider 833 541
Polysticta stelleri *
Harlequin Duck 588 382
Histrionicus histrionicus
Long-tailed Duck 814 529
Clangula hyemalis *
Merganser 1209 786
(unidentified) *
Common Merganser 1472 957
Mergus merganser
Red-breasted Merganser 946 36% 615
M. serrator
Black Brant 1321 859
Branta bernicla
Canada/Cackling Goose 1972 1282
(unidentified) *
Lesser Canada Goose 3060 9% 1989
Branta canadensis
parvipes
Dusky Canada Goose B. 2936 13% 1908
c. occidentalis
Vancouver Canada Goose 3366 2188
B. c. fulva
Taverner's Cackling 2514 25% 1634
Goose B. hutchinsii
taverneri
Aleutian Cackling Goose 1825 46% 1186
B. h. leucopareia
Cackling Cackling Goose 1429 58% 929
B. h. minima
Greater White-fronted 2218 1442
Goose Anser albifrons *
Tundra Greater White- 2420 4% 1573
fronted Goose A. a.
gambelli
Pacific Greater White- 2015 20% 1310
fronted Goose A. a.
sponsa
Tule Greater White- 2510 1632
fronted Goose A.
a. elgasi
Emperor Goose 2148 1396
Chen canagica
Lesser Snow Goose 1955 1271
C. caerulescens
Swan (unidentified) * 7662 4980
Tundra Swan Cygnus 7111 34% 4622
columbianus
Eastern population 7014 3% 4559
Western population 7207 4685
Trumpeter Swan C. 10 700 6955
buccinator
Sandhill Crane 3763 2446
Grus canadensis *
G. c. canadensis 3705 17% 2408
G. c. rowani 4455 2896
Ptarmigan 542 352
(unidentified) *
White-tailed Ptarmigan 355 34% 231
Lagopus leucura *
Rock Ptarmigan L. muta * 420 23% 273
Willow Ptarmigan L. 542 352
lagopus *
Grouse 635 413
(unidentified) *
Ruffed Grouse Bonasa 591 41% 384
umbellus *
Spruce Grouse 595 41% 387
Falcipennis canadensis *
Sooty Grouse 1004 653
Dendragapus fuliginosus
Sharp-tailed Grouse 720 468
Tympanuchusphasianellus *
Short-tailed Shearwater 527 343
Puffinus tenuirostris *
Cormorant 1985 1290
(unidentified) *
Double-crested Cormorant 2330 1515
Phalacrocorax auritus
Red-faced Cormorant 2138 8% 1390
P. urile
Pelagic Cormorant 1868 20% 1214
P. pelagicus
Bonaparte's/Sabine's 185 120
Gull (unidentified) *
Bonaparte's Gull 180 5% 117
Chroicocephalus
philadelphia
Sabine's Gull Xema sabini 190 124
Mew Gull Larus canus * 389 253
Large gull 1199 779
(unidentified) *
Herring Gull L. 1085 24% 705
argentatus
Glaucous-winged Gull 1077 25% 700
L. glaucescens
Glaucous Gull L. 1434 932
hyperboreus
Black-legged Kittiwake 429 279
Rissa tridactyla
Red-legged Kittiwake 377 245
R. brevirostris
Tern (unidentified) * 112 73
Arctic Tern Sterna 112 7% 73
paradisea
Aleutian Tern 120 78
Onychoprion aleuticus
Murre (unidentified) * 965 627
Common Murre Uria aalge 966 628
Thick-billed Murre V. 963 <1% 626
lomvia
Guillemot 505 328
(unidentified) *
Black Guillemot Cepphus 378 25% 246
grille
Pigeon Guillemot 507 330
C. columba
Auklet (unidentified) * 171 111
Least Auklet Aethia 84 83% 55
pusilla
Crested Auklet A. 255 50% 166
cristatella
Least/Crested Auklet 170 111
Cassin's Auklet 185 63% 120
Ptychoramphus aleuticus
Parakeet Auklet 262 48% 170
Aethiapsittacula
Whiskered Auklet 120 76% 78
A. pygmaea
Rhinoceros Auklet 507 330
Cerorhinca monocerata
Puffin (unidentified) * 707 460
Horned Puffin 537 31% 349
Fratercula corniculata
Tufted Puffin F. 774 503
cirrhata
Black Oystercatcher 535 348
Haematopus bachmani
Whimbrel/Curlew 399 259
(unidentified) *
Whimbrel Numenius 391 10% 254
phaeopus rufiventris
Bristle-thighed Curlew 433 281
N. tahitiensis
Godwit (unidentified) * 421 274
Bar-tailed Godwit Limosa 464 302
tapponica baueri
Hudsonian Godwit L. 241 48% 157
haemastica
Marbled Godwit L. fedoa 368 21% 239
beringiae
Golden/Black-bellie 162 105
Plover (unidentified) *
American Golden Plover 133 39% 86
Pluvialis dominica
Pacific Golden Plover 148 32% 96
P. fulva
Black-bellied Plover 219 142
P. squatarola squatarola
Turnstone 122 79
(unidentified) *
Ruddy Turnstone Arenaria 107 14% 70
interpres interpres
Black Turnstone A. 125 81
melanocephata
Phalarope 42 27
(unidentified) *
Red-necked Phalarope 35 33% 23
Phalaropus lobatus
Red Phalarope P. 53 34
fulicarius
Small shorebird 37 24
(unidentified) *
Western Sandpiper 28 60% 18
Calidris mauri
Dunlin C. alpina 65 42
arcticola
Wilson's Snipe 99 64
Gallinago delicata
Loon (unidentified) * 2513 1633
Red-throated Loon 1759 65% 1143
Gavia stellata
Arctic Loon G. arctica 3101 39% 2016
Pacific Loon G. pacifica 2232 56% 1451
Common Loon G. immer 5015 1% 3260
Yellow-billed Loon G. 5056 3286
adamsii
Grebe (unidentified) * 799 519
Horned Grebe Podiceps 405 66% 263
auritus
Red-necked Grebe P. 1192 775
griseana
Snowy Owl Bubo 1873 1217
scandiacus
Bird Egg
Body mass CFn-m (2) CFn-m
(pound) (pound) = egg mass
(3) (g)
American Wigeon 1.62 1.05 43
Anas americana
Gadwall Anas strepera 1.89 1.23 43
Teal (unidentified) * 0.72 0.47 28
Green-winged Teal 0.72 0.47 --
A. crecca
Blue-winged Teal A. 0.82 0.53 28
discors
Mallard A. platyrhynchos 2.47 1.61 52
Northern Pintail A. acuta 1.81 1.18 43
Northern Shoveler 1.33 0.86 38
A. clypeata
Black Scoter 2.32 1.51 67
Melanitta nigra
Surf Scoter M. 2.25 1.46 78
perspicillata
White-winged 4.02 2.61 82
Scoter M. fusca
Bufflehead 0.88 0.57 37
Bucephala albeola
Goldeneye 1.96 1.27 66
(unidentified) *
Common Goldeneye 1.90 1.24 64
Bucephala clangula
Barrow's Goldeneye 2.01 1.31 68
B. islandica
Canvasback Aythya 2.67 1.74 68
valisineria
Scaup (unidentified) * 2.08 1.35 63
Greater Scaup Aythya 2.08 1.35 63
marila
Lesser Scaup A. affinis 1.66 1.08 48
Common Eider Somateria 5.04 3.28 101
moliissima v-nigrum *
King Eider 5. 3.46 2.25 69
spectabilis *
Spectacled Eider S. 3.23 2.10 71
fischeri *
Steller's Eider 1.84 1.20 55
Polysticta stelleri *
Harlequin Duck 1.30 0.85 53
Histrionicus histrionicus
Long-tailed Duck 1.79 1.16 43
Clangula hyemalis *
Merganser 2.67 1.74 69
(unidentified) *
Common Merganser 3.25 2.11 70
Mergus merganser
Red-breasted Merganser 2.09 1.36 68
M. serrator
Black Brant 2.91 1.89 100
Branta bernicla
Canada/Cackling Goose 4.35 2.83 113
(unidentified) *
Lesser Canada Goose 6.75 4.39 --
Branta canadensis
parvipes
Dusky Canada Goose B. 6.47 4.21 --
c. occidentalis
Vancouver Canada Goose 7.42 4.82 --
B. c. fulva
Taverner's Cackling 5.54 3.60 124
Goose B. hutchinsii
taverneri
Aleutian Cackling Goose 4.02 2.61 --
B. h. leucopareia
Cackling Cackling Goose 3.15 2.05 101
B. h. minima
Greater White-fronted 4.89 3.18 129
Goose Anser albifrons *
Tundra Greater White- 5.34 3.47 129
fronted Goose A. a.
gambelli
Pacific Greater White- 4.44 2.89 128
fronted Goose A. a.
sponsa
Tule Greater White- 5.53 3.59 --
fronted Goose A.
a. elgasi
Emperor Goose 4.74 3.08 122
Chen canagica
Lesser Snow Goose 4.31 2.80 122
C. caerulescens
Swan (unidentified) * 16.89 10.98 287
Tundra Swan Cygnus 15.68 10.19 273
columbianus
Eastern population 15.46 10.05 273
Western population 15.89 10.33 --
Trumpeter Swan C. 23.59 15.33 363
buccinator
Sandhill Crane 8.30 5.40 151
Grus canadensis *
G. c. canadensis 8.17 5.31 150
G. c. rowani 9.82 6.38 161
Ptarmigan 1.19 0.77 22
(unidentified) *
White-tailed Ptarmigan 0.78 0.51 19
Lagopus leucura *
Rock Ptarmigan L. muta * 0.93 0.60 21
Willow Ptarmigan L. 1.19 0.77 22
lagopus *
Grouse 1.40 0.91 21
(unidentified) *
Ruffed Grouse Bonasa 1.30 0.85 20
umbellus *
Spruce Grouse 1.31 0.85 22
Falcipennis canadensis *
Sooty Grouse 2.21 1.44 36
Dendragapus fuliginosus
Sharp-tailed Grouse 1.59 1.03 --
Tympanuchusphasianellus *
Short-tailed Shearwater 1.16 0.75 NA
Puffinus tenuirostris *
Cormorant 4.38 2.85 45
(unidentified) *
Double-crested Cormorant 5.14 3.34 47
Phalacrocorax auritus
Red-faced Cormorant 4.71 3.06 --
P. urile
Pelagic Cormorant 4.12 2.68 45
P. pelagicus
Bonaparte's/Sabine's 0.41 0.27 26
Gull (unidentified) *
Bonaparte's Gull 0.40 0.26 --
Chroicocephalus
philadelphia
Sabine's Gull Xema sabini 0.42 0.27 26
Mew Gull Larus canus * 0.86 0.56 52
Large gull 2.64 1.72 97
(unidentified) *
Herring Gull L. 2.39 1.55 95
argentatus
Glaucous-winged Gull 2.37 1.54 92
L. glaucescens
Glaucous Gull L. 3.16 2.05 105
hyperboreus
Black-legged Kittiwake 0.95 0.62 52
Rissa tridactyla
Red-legged Kittiwake 0.83 0.54 49
R. brevirostris
Tern (unidentified) * 0.25 0.16 19
Arctic Tern Sterna 0.25 0.16 19
paradisea
Aleutian Tern 0.26 0.17 20
Onychoprion aleuticus
Murre (unidentified) * 2.13 1.38 105
Common Murre Uria aalge 2.13 1.38 106
Thick-billed Murre V. 2.12 1.38 103
lomvia
Guillemot 1.11 0.72 54
(unidentified) *
Black Guillemot Cepphus 0.83 0.54 54
grille
Pigeon Guillemot 1.12 0.73 54
C. columba
Auklet (unidentified) * 0.38 0.25 25
Least Auklet Aethia 0.19 0.12 18
pusilla
Crested Auklet A. 0.56 0.36 36
cristatella
Least/Crested Auklet 0.37 0.24 27
Cassin's Auklet 0.41 0.27 25
Ptychoramphus aleuticus
Parakeet Auklet 0.58 0.38 34
Aethiapsittacula
Whiskered Auklet 0.26 0.17 --
A. pygmaea
Rhinoceros Auklet 1.12 0.73 78
Cerorhinca monocerata
Puffin (unidentified) * 1.56 1.01 87
Horned Puffin 1.18 0.77 76
Fratercula corniculata
Tufted Puffin F. 1.71 1.11 91
cirrhata
Black Oystercatcher 1.18 0.77 46
Haematopus bachmani
Whimbrel/Curlew 0.88 0.57 50
(unidentified) *
Whimbrel Numenius 0.86 0.56 49
phaeopus rufiventris
Bristle-thighed Curlew 0.95 0.62 56
N. tahitiensis
Godwit (unidentified) * 0.93 0.60 36
Bar-tailed Godwit Limosa 1.02 0.66 37
tapponica baueri
Hudsonian Godwit L. 0.53 0.34 32
haemastica
Marbled Godwit L. fedoa 0.81 0.53 48
beringiae
Golden/Black-bellie 0.36 0.23 30
Plover (unidentified) *
American Golden Plover 0.29 0.19 27
Pluvialis dominica
Pacific Golden Plover 0.33 0.21 27
P. fulva
Black-bellied Plover 0.48 0.31 35
P. squatarola squatarola
Turnstone 0.27 0.18 18
(unidentified) *
Ruddy Turnstone Arenaria 0.24 0.16 17
interpres interpres
Black Turnstone A. 0.28 0.18 18
melanocephata
Phalarope 0.09 0.06 7
(unidentified) *
Red-necked Phalarope 0.08 0.05 6
Phalaropus lobatus
Red Phalarope P. 0.12 0.08 8
fulicarius
Small shorebird 0.08 0.05 8
(unidentified) *
Western Sandpiper 0.06 0.04 7
Calidris mauri
Dunlin C. alpina 0.14 0.09 11
arcticola
Wilson's Snipe 0.22 0.14 15
Gallinago delicata
Loon (unidentified) * 5.54 3.60 103
Red-throated Loon 3.88 2.52 77
Gavia stellata
Arctic Loon G. arctica 6.84 4.45 --
Pacific Loon G. pacifica 4.92 3.20 101
Common Loon G. immer 11.06 7.19 143
Yellow-billed Loon G. 11.15 7.25 154
adamsii
Grebe (unidentified) * 1.76 1.14 30
Horned Grebe Podiceps 0.89 0.58 21
auritus
Red-necked Grebe P. 2.63 1.71 38
griseana
Snowy Owl Bubo 4.13 2.68 57
scandiacus
Egg
CFv-n (4) CFn-m = egg CFv-n (4)
(eggs/L) mass (3) (eggs/gallon)
(pound)
American Wigeon 9.8 0.095 37.5
Anas americana
Gadwall Anas strepera 9.8 0.095 37.5
Teal (unidentified) * 15.1 0.062 57.4
Green-winged Teal -- -- --
A. crecca
Blue-winged Teal A. 15.1 0.062 57.4
discors
Mallard A. platyrhynchos 8.1 0.115 30.9
Northern Pintail A. acuta 9.8 0.095 37.5
Northern Shoveler 11.1 0.084 42.4
A. clypeata
Black Scoter 6.3 0.148 24.0
Melanitta nigra
Surf Scoter M. 5.4 0.172 20.7
perspicillata
White-winged 5.1 0.181 19.7
Scoter M. fusca
Bufflehead 11.4 0.082 43.4
Bucephala albeola
Goldeneye 6.4 0.146 24.4
(unidentified) *
Common Goldeneye 6.6 0.141 25.2
Bucephala clangula
Barrow's Goldeneye 6.2 0.150 23.7
B. islandica
Canvasback Aythya 6.2 0.150 23.7
valisineria
Scaup (unidentified) * 6.7 0.139 25.6
Greater Scaup Aythya 6.7 0.139 25.6
marila
Lesser Scaup A. affinis 8.8 0.106 33.6
Common Eider Somateria 4.2 0.223 16.0
moliissima v-nigrum *
King Eider 5. 6.1 0.152 23.4
spectabilis *
Spectacled Eider S. 5.9 0.157 22.7
fischeri *
Steller's Eider 7.7 0.121 29.4
Polysticta stelleri *
Harlequin Duck 8.0 0.117 30.4
Histrionicus histrionicus
Long-tailed Duck 9.8 0.095 37.5
Clangula hyemalis *
Merganser 6.1 0.152 23.4
(unidentified) *
Common Merganser 6.0 0.154 23.1
Mergus merganser
Red-breasted Merganser 6.2 0.150 23.7
M. serrator
Black Brant 4.2 0.220 16.2
Branta bernicla
Canada/Cackling Goose 3.7 0.249 14.3
(unidentified) *
Lesser Canada Goose -- -- --
Branta canadensis
parvipes
Dusky Canada Goose B. -- -- --
c. occidentalis
Vancouver Canada Goose -- -- --
B. c. fulva
Taverner's Cackling 3.4 0.273 13.0
Goose B. hutchinsii
taverneri
Aleutian Cackling Goose -- -- --
B. h. leucopareia
Cackling Cackling Goose 4.2 0.223 16.0
B. h. minima
Greater White-fronted 3.3 0.284 12.5
Goose Anser albifrons *
Tundra Greater White- 3.3 0.284 12.5
fronted Goose A. a.
gambelli
Pacific Greater White- 3.3 0.282 12.6
fronted Goose A. a.
sponsa
Tule Greater White- -- -- --
fronted Goose A.
a. elgasi
Emperor Goose 3.5 0.269 13.2
Chen canagica
Lesser Snow Goose 3.5 0.269 13.2
C. caerulescens
Swan (unidentified) * 1.5 0.633 5.6
Tundra Swan Cygnus 1.5 0.602 5.9
columbianus
Eastern population 1.5 0.602 5.9
Western population -- -- --
Trumpeter Swan C. 1.2 0.800 4.4
buccinator
Sandhill Crane 2.8 0.333 10.7
Grus canadensis *
G. c. canadensis 2.8 0.331 10.7
G. c. rowani 2.6 0.355 10.0
Ptarmigan 19.2 0.049 72.6
(unidentified) *
White-tailed Ptarmigan 22.2 0.042 84.7
Lagopus leucura *
Rock Ptarmigan L. muta * 20.1 0.046 77.4
Willow Ptarmigan L. 19.2 0.049 72.6
lagopus *
Grouse 20.1 0.046 77.4
(unidentified) *
Ruffed Grouse Bonasa 21.1 0.044 80.9
umbellus *
Spruce Grouse 19.2 0.049 72.6
Falcipennis canadensis *
Sooty Grouse 11.7 0.079 45.0
Dendragapus fuliginosus
Sharp-tailed Grouse -- -- --
Tympanuchusphasianellus *
Short-tailed Shearwater NA NA NA
Puffinus tenuirostris *
Cormorant 9.4 0.099 35.9
(unidentified) *
Double-crested Cormorant 9.0 0.104 34.2
Phalacrocorax auritus
Red-faced Cormorant -- -- --
P. urile
Pelagic Cormorant 9.4 0.099 35.9
P. pelagicus
Bonaparte's/Sabine's 16.2 0.057 62.4
Gull (unidentified) *
Bonaparte's Gull -- -- --
Chroicocephalus
philadelphia
Sabine's Gull Xema sabini 16.2 0.057 62.4
Mew Gull Larus canus * 8.1 0.115 30.9
Large gull 4.3 0.214 16.6
(unidentified) *
Herring Gull L. 4.4 0.209 17.0
argentatus
Glaucous-winged Gull 4.6 0.203 17.5
L. glaucescens
Glaucous Gull L. 4.0 0.231 15.4
hyperboreus
Black-legged Kittiwake 8.1 0.115 30.9
Rissa tridactyla
Red-legged Kittiwake 8.6 0.108 32.9
R. brevirostris
Tern (unidentified) * 22.2 0.042 84.7
Arctic Tern Sterna 22.2 0.042 84.7
paradisea
Aleutian Tern 21.1 0.044 80.9
Onychoprion aleuticus
Murre (unidentified) * 4.0 0.231 15.4
Common Murre Uria aalge 4.0 0.234 15.2
Thick-billed Murre V. 4.1 0.227 15.7
lomvia
Guillemot 7.8 0.119 29.9
(unidentified) *
Black Guillemot Cepphus 7.8 0.119 29.9
grille
Pigeon Guillemot 7.8 0.119 29.9
C. columba
Auklet (unidentified) * 16.9 0.055 64.7
Least Auklet Aethia 23.4 0.040 89.0
pusilla
Crested Auklet A. 11.7 0.079 45.0
cristatella
Least/Crested Auklet 15.6 0.060 59.3
Cassin's Auklet 16.9 0.055 64.7
Ptychoramphus aleuticus
Parakeet Auklet 12.4 0.075 47.4
Aethiapsittacula
Whiskered Auklet -- -- --
A. pygmaea
Rhinoceros Auklet 5.4 0.172 20.7
Cerorhinca monocerata
Puffin (unidentified) * 4.8 0.192 18.5
Horned Puffin 5.6 0.168 21.2
Fratercula corniculata
Tufted Puffin F. 4.6 0.201 17.7
cirrhata
Black Oystercatcher 9.2 0.101 35.2
Haematopus bachmani
Whimbrel/Curlew 8.4 0.110 32.3
(unidentified) *
Whimbrel Numenius 8.6 0.108 32.9
phaeopus rufiventris
Bristle-thighed Curlew 7.5 0.123 28.9
N. tahitiensis
Godwit (unidentified) * 11.7 0.079 45.0
Bar-tailed Godwit Limosa 11.4 0.082 43.4
tapponica baueri
Hudsonian Godwit L. 13.2 0.071 50.1
haemastica
Marbled Godwit L. fedoa 8.8 0.106 33.6
beringiae
Golden/Black-bellie 14.1 0.066 53.9
Plover (unidentified) *
American Golden Plover 15.6 0.060 59.3
Pluvialis dominica
Pacific Golden Plover 15.6 0.060 59.3
P. fulva
Black-bellied Plover 12.1 0.077 46.2
P. squatarola squatarola
Turnstone 23.4 0.040 89.0
(unidentified) *
Ruddy Turnstone Arenaria 24.8 0.037 96.2
interpres interpres
Black Turnstone A. 23.4 0.040 89.0
melanocephata
Phalarope 60.3 0.015 237.2
(unidentified) *
Red-necked Phalarope 70.3 0.013 273.7
Phalaropus lobatus
Red Phalarope P. 52.7 0.018 197.7
fulicarius
Small shorebird 52.7 0.018 197.7
(unidentified) *
Western Sandpiper 60.3 0.015 237.2
Calidris mauri
Dunlin C. alpina 38.3 0.024 148.3
arcticola
Wilson's Snipe 28.1 0.033 107.8
Gallinago delicata
Loon (unidentified) * 4.1 0.227 15.7
Red-throated Loon 5.5 0.170 20.9
Gavia stellata
Arctic Loon G. arctica -- -- --
Pacific Loon G. pacifica 4.2 0.223 16.0
Common Loon G. immer 2.9 0.315 11.3
Yellow-billed Loon G. 2.7 0.340 10.5
adamsii
Grebe (unidentified) * 14.1 0.066 53.9
Horned Grebe Podiceps 20.1 0.046 77.4
auritus
Red-necked Grebe P. 11.1 0.084 42.4
griseana
Snowy Owl Bubo 7.4 0.126 28.2
scandiacus
(1) Relative mass is the percent difference in body mass (g)
between a given species and the heaviest species, subspecies, or
population within the same category. That is, relative mass = [1 -
(focal item heaviest item in category)] x 100.
(2) Bird CFn-m (number-to-mass conversion factor) = recovery rate
(65%) x body mass.
(3) Egg CFn-m (number-to-mass conversion factor) = recovery rate
(100%) x egg mass.
(4) Egg CFv-n: volume-to-number conversion factor.
Number of eggs/gallon: CFv-n = (35.3 x 0.8) * (0.126 / mass of wild
bird egg, in pounds).
Number of eggs/L: CFv-n = (9.3 x 0.8) x (57.0 / mass of wild bird
egg, in grams).
--: Data unavailable.
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| Author: | Naves, Liliana C.; Fall, James A. |
|---|---|
| Publication: | Arctic |
| Article Type: | Report |
| Geographic Code: | 1U9AK |
| Date: | Mar 1, 2017 |
| Words: | 12954 |
| Previous Article: | Farming muskoxen for qiviut in Alaska: a feasibility study. |
| Next Article: | An Intimate Wilderness: Arctic Voices in a Land of Vast Horizons. |
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