Relative contribution of lipid sources to eggs of lesser scaup

Abstract

Studies of how birds mobilize nutrients to eggs have traditionally considered a continuum of possible allocation strategies ranging from income breeding (rely on food sources found on the breeding grounds) to capital breeding (rely on body reserves stored prior to the breeding season). For capital breeding, stored body reserves can be acquired either on or away from the breeding grounds, but it has been difficult to quantify the relative contribution of each, precluding identification of key habitats for acquiring nutrients for clutch formation. During 2006-2009, we explored the importance of spring-staging habitats versus breeding-area habitats for egg-lipid formation in female lesser scaup Aythya affinis using stable carbon (d 13 C) isotope analyses. Although d 13 C values for abdominal lipid reserves brought to the breeding grounds overlapped those of local amphipods, we were able to quantify the importance of local plant carbohydrates (seeds of emergent wetland plants) to the production of eggs. We compared the importance of local wetland seeds (overall d 13 C: 229.1  0.9‰ SD) to combined lipid stores and lipids from local amphipods (overall d 13 C: 223.8  2.2‰). Local seeds and stored body lipids contributed equally to egg lipid formation across years but we found evidence of annual variation in their relative importance. Wetland seeds contributed 39% (SE  10%) to egg lipid production, and the importance of this source varied by year (90% CI  47-75% in 2006(90% CI  47-75% in , 13-42% in 2007(90% CI  47-75% in , 29-65% in 2008(90% CI  47-75% in , and 7-30% in 2009). In contrast to earlier studies that suggest lesser scaup predominantly employ a capital breeding strategy, our results suggest that in some years females may attain half of their energy for clutch formation from foods on the breeding grounds.

Reproductive Rates in Lesser Scaup (<i>Aythya affinis</i>) in Southwestern Manitoba: Another Look at the Data

“…Captive female scaup have been shown to completely recover from a loss of 11% body mass in only 4 days, and, during migration, some wild-living scaup could increase body mass by about 60 g/day under ideal foraging conditions where abundant natural foods were supplemented by corn (Martin 2007;Anteau and Afton 2008c). In addition, at a high-elevation southern breeding site in Montana, USA, during the lengthy pre-nesting period, a female of average structural size was able to increase her body condition by 2.2 g/day (wet weight) supplementing endogenous reserves (lipids and protein) with nu trients from local dietary sources (Cutting et al , 2014Warren et al 2013). Together, these results suggest that mass loss can be re versed if food supplies are adequate.…”