Body Composition of Bar-tailed Godwits (Limosa lapponica)

Bar-tailed Godwits used in analysis were salvaged after accidental death (godwits from Cold Bay; Piersma and Gill 1998), inadvertent trapping mortality (godwits from The Netherlands; Piersma and Gill 1998), seizure from poachers (godwits from New Zealand; Piersma and Gill 1998), or purposely collected with a shotgun (godwits from Egegik Bay; Piersma et al. 2021). External morphology of birds (wing chord, bill, total head, tarsus, tarsus-toe) was measured using calipers, and body mass was weighed using electronic balance.

Compositional analysis of godwits consisted of dissecting birds into relevant organ and muscle groups; see Piersma and Gill (1998) for details related to specimens from Cold Bay and Landys-Ciannelli et al. (2003) and Piersma et al. (2021) for details related to godwits from New Zealand, The Netherlands, and Egegik Bay. The procedures for determining the compositional analysis evolved over time, and thus not all variables were measured in all specimens. The general procedure is detailed as follows: birds were first plucked of feathers. Next, for birds from Cold Bay, the right flight muscle (including the pectoralis and supracoracoideus muscles), heart, gizzard, esophagus and proventriculus, liver, left kidney, and gut were removed and weighed wet to the nearest 0.01 g. The length of the gut was measured to the nearest 1.0 mm, then gently flushed with water and reweighed empty; the gizzard and proventriculus was similarly emptied and reweighed.

To determine the compositional analysis of godwits from Cold Bay, a ground homogenate was made for each bird by passing the entire carcass (less contents of the gut, gizzard, and proventriculus) multiple times through a food grinder. From each godwit, a random sample of the homogenate (~10% of bird body weight) was collected and dried in a vacuum at 100°C for 15 h to determine water content. The lipid content of each sample was determined using Soxhlet extraction with petroleum ether, and nitrogen content was determined via Kjeldahl method, both following procedures described by Horowitz (1984). Results of these analyses were expressed as proportions of fresh body mass from which we determined total fat, water, and fat-free dry masses for each specimen.

For godwit specimens from New Zealand, The Netherlands, and Egegik Bay, the general procedure follows Landys-Ciannelli et al. 2003. After plucking, birds were dissected into relevant organ and muscle groups. Generally the heart, stomach (gizzard and proventriculus), liver, both kidneys, gut, and pectoralis and supracoracoideus muscles (from both sides) were dissected from each bird. Other measures (e.g., skin, leg muscles, spleen, salt glands, etc.) were collected from certain specimens; see data table for such cases. These organs and muscles were weighed wet to the nearest 0.01 g. As with the birds from Cold Bay, the length of the gut was measured to the nearest 1.0 mm, then gently flushed with water and reweighed empty. The stomach was similarly emptied and reweighed. Only the fresh masses of these organs and muscles were recorded in godwits from The Netherlands. For godwits from New Zealand and Egegik Bay, however, each of these discrete organ and muscle groups was then dried along with the carcass at 60°C for ≥24 h and reweighed. Next, these pieces from godwits from New Zealand, The Netherlands, and Egegik Bay were individually wrapped in filter paper and placed in a Soxhlet apparatus from which lipids were extracted using petroleum ether. Samples were again dried at 60°C for ≥24 h and weighed. From each specimen from New Zealand and Egegik Bay, we subtracted the dry mass from the wet mass to determine the water mass, and the fat-free dry mass from the dry mass to determine the fat mass. For godwits from The Netherlands, we did not calculate water mass, but instead calculated fat mass and fat-free dry mass alone. The sex of all specimens was determined based on gonadal inspection during dissections.