Evaluating indices of lipid and protein content in lesser snow and Ross's geese during spring migration

Abstract

Assessing nutrient stores in avian species is important for understanding the extent to which body condition influences success or failure in life-history events. We evaluated predictive models using morphometric characteristics to estimate total body lipids (TBL) and total body protein (TBP), based on traditional proximate analyses, in spring migrating lesser snow geese (Anser caerulescens caerulescens) and Ross's geese (A. rossii). We also compared performance of our lipid model with a previously derived predictive equation for TBL developed for nesting lesser snow geese. We used external and internal measurements on 612 lesser snow and 125 Ross's geese collected during spring migration in 2015 and 2016 within the Central and Mississippi flyways to derive and evaluate predictive models. Using a validation data set, our best performing lipid model for snow geese better predicted TBL (root mean square error [RMSE] of 23.56) compared with a model derived from nesting individuals (RMSE ¼ 48.60), suggesting the importance of season-specific models for accurate lipid estimation. Models that included body mass and abdominal fat deposit best predicted TBL determined by proximate analysis in both species (lesser snow goose, R 2 ¼ 0.87, RMSE ¼ 23.56: Ross's geese, R 2 ¼ 0.89, RMSE ¼ 13.75). Models incorporating a combination of external structural measurements in addition to internal muscle and body mass best predicted protein values (R 2 ¼ 0.85, RMSE ¼ 19.39 and R 2 ¼ 0.85, RMSE ¼ 7.65, lesser snow and Ross's geese, respectively), but protein models including only body mass and body size were also competitive and provided extended utility to our equations for field applications. Therefore, our models indicated the importance of specimen dissection and measurement of the abdominal fat pad to provide the most accurate lipid estimates and provide alternative dissection-free methods for estimating protein. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Condition Bias of Decoy‐Harvested Light Geese During the Conservation Order

“…We weighed thawed individuals to the nearest 0.5 g. We measured head length, culmen length, and total tarsus length to the nearest 0.1 mm, and measured body length and un‐flattened wing chord to the nearest mm using a measuring board (Dzubin and Cooch ). A complete description of dissection methods and chemical analyses for collected geese is detailed in Fowler et al (), but in brief, we shaved individuals of feathers to estimate muscular and cardiac protein and weighed and removed ingesta‐contents to obtain ingesta‐free body mass (g). We ground individual carcasses (whole bird minus feather and ingesta contents) through an industrial meat grinder (Hobart 4146, Toledo, OH, USA) and then dried a subsample (50.0 g) to a constant mass.…”

Winter carry-over effects on spring body condition driven by agricultural subsidies to Lesser Snow Geese (Anser caerulescens caerulescens)

“…Therefore, we collected birds in these states to ensure a heterogeneous sample range of nutrient reserves among sex and age classes representative of snow goose populations during spring migration. We obtained individuals harvested over decoys from participants in the Light Goose Conservation Order as well as those that were collected using jump shooting techniques (Fowler et al 2018).…”

“…A complete description of methods for dissection and chemical analyses of geese are detailed in Fowler et al (2018), but in brief, we shaved individuals of their feathers to estimate muscular and cardiac protein and weighed and removed ingesta-contents to achieve an ingesta-free body mass (g). To infer winter habitat use, we extracted 1 cm 3 sample of bicep muscle from one wing for isotopic analysis (details below).…”

“…Subsequently, we submitted pulverized homogenate samples to the University of Missouri Agricultural Experiment Station Chemical Laboratory for proximate analysis of crude lipid and protein following standardized procedures (Alisauskas 2002, Horwitz 2006. Total body lipids and protein were then scaled to body size as described in Alisauskas (2002) and Fowler et al (2018).…”

Heterogeneity in body condition, survival, and seasonal origins among lesser snow and Ross's geese

“…Therefore, we collected birds in these states to ensure a heterogeneous sample range of nutrient reserves among sex and age classes representative of lesser snow goose populations during spring migration. We obtained individuals harvested over decoys from participants in the Light Goose Conservation Order as well as those that were randomly collected using jump shooting techniques (Fowler et al 2018b For individuals collected during spring, we aged snow geese as hatch-year or after hatch-year (HY or AHY, respectively) using plumage characteristics and foot color and recorded sex based on reproductive organs during dissections (Baldassare 2014). We weighed thawed individuals to the nearest 0.5 g with an electronic scale.…”