Linking pre-laying energy allocation and timing of breeding in a migratory arctic raptor

Abstract

For migratory species, acquisition and allocation of energy after arrival on the breeding grounds largely determine reproductive decisions. Few studies have investigated underlying physiological mechanisms driving variation in breeding phenology so far. We linked physiological state to individual timing of breeding in pre-laying arctic-nesting female peregrine falcons (Falco peregrinus tundrius). We captured females from two populations 2-20 days before egg-laying to assess plasma concentration of β-hydroxybutyric acid (BUTY) and triglyceride (TRIG), two metabolites known to reflect short-term changes in fasting and fattening rate, respectively. We also assessed baseline corticosterone (CORTb), a hormone that mediates energy allocation, and the scaled mass index (SMI) as an indicator of somatic body reserves. Plasma BUTY was slightly higher during the pre-recruiting period compared to the period of rapid follicular growth, indicating a reduction in catabolism of lipid reserves before investment in follicle development. Conversely, TRIG levels increased in pre-recruiting females, and best-predicted individual variation in pre-laying interval and lay date. A marked increase in CORTb occurred concomitantly with the onset of rapid follicle growth. SMI was highly variable possibly reflecting variation in food availability or individuals at different stages. Results suggest that (1) lower rates of pre-laying fattening and/or lower mobilization rate of lipoproteins to ovarian follicles delayed laying, and (2) an elevation in pre-laying CORTb may result from, or be required to compensate for, the energetic costs of egg production. Results of this study illustrate how variation in the allocation of energy before laying can influence individual fitness-related reproductive decisions.

Body condition and reproductive phenology

“…Plasma TRIG is positively correlated with short-term increases in body mass, and provides an estimate of fattening rate, even in birds captured only once (Anteau and Afton 2008). Plasma TRIG levels also increase during the period of rapid follicle growth prior to laying (Hennin et al 2015, Lamarre et al 2017, when ovarian follicles quickly increase in size as they accumulate large amounts of yolk precursors, including yolktargeted TRIG (Challenger et al 2001, Gorman et al 2009. Hence, assessment of plasma TRIG prior to the period of rapid follicle growth provides insight into individual fattening rate, whereas assessment during the period of rapid follicle growth reflects a combination of lipid mobilization for egg production and possibly fattening.…”

“…This is a good example of the use of physiology to predict crucial fitness metrics related to reproductive phenology in birds. Nonetheless, to date few studies have been able to measure (Challenger et al 2001, Hennin et al 2015, Lamarre et al 2017 or manipulate (Goutte et al 2011) physiological condition during the pre-laying period to investigate the relationships between individual physiological condition and reproductive decisions (Goutte et al 2014, Hennin et al 2016a, Lamarre et al 2017. The challenges associated with capturing individuals during the pre-laying period, collecting blood within three minutes of capture, and relating physiological condition to relevant fitness-related metrics explain the scarcity of such studies.…”

“…Using markers that are important underlying drivers of reproductive decisions, Lamarre et al (2017) linked individual physiological condition to the timing of reproduction in a migratory and Arctic-nesting raptor, the Peregrine Falcon (Falco peregrinus tundrius). The role of these markers of energy demand and allocation (Hennin et al 2015(Hennin et al , 2016a is described in the following sections using the Peregrine Falcon as an example for potentially undertaking a similar study in Gyrfalcons, either in captivity or in the wild.…”

Foraging tactics in dynamic sea‐ice habitats affect individual state in a long‐ranging seabird

“…Physiological markers of energetic demand, energy acquisition and energy used (i.e. baseline corticosterone, triacylglycerols and β-hydroxybutyrate, respectively) were measured in the plasma using previously validated laboratory procedures (Hennin, Bêty, et al, 2016;Lamarre, Franke, Love, Legagneux, & Bêty, 2017). Details on the laboratory analyses performed are in Appendix S4.…”

“…The most supported model explained 15% of the deviance (Table 2) and included an effect of the ISU in interaction with sex and breeding stage (Table 3; Figure 6a,b). During incubation the ISU had no effect on the males' Δ bc (Figure 6a) and only a slight positive effect on the females' (Cherel et al, 1988;Lamarre et al, 2017) Stable nitrogen isotopic ratios in plasma (Figure 6b), with the 95% Confidence Interval overlapping zero (+0.06 g/mm; 95% CI = [−0.05; 017]; Table 3). During brooding however, the ISU had a negative effect on the Δ bc of both males and females (Figure 6a,b).…”