Body mass variation in breeding Florida Scrub-Jays

Abstract

Many birds lose mass when feeding dependent young and multiple hypotheses have been proposed to explain this loss. The reproductive-stress hypothesis suggests that mass loss results from an energy deficit. The flight-efficiency hypothesis suggests that breeders lose mass in advance of feeding young to save energy during flight. The reserve-mobilization hypothesis suggests that female breeders accumulate energy reserves during egg production and incubation and mobilize those reserves to meet their own energy needs after eggs hatch. Finally, birds may lose mass due to gonadal regression. From 1999 to 2001, we attracted Florida Scrub-Jays (Aphelocoma coerulescens), sedentary cooperative breeders, to a portable electronic balance. Our objective was to determine which hypotheses might best explain mass variation during breeding. Both male and female Florida Scrub-Jays lost mass during the period of nestling care (males, 3.2%; females, 6.5%), but not when feeding fledglings, despite this being the period of peak effort. Such results are consistent with both the flight-efficiency and reserve-mobilization (females only) hypotheses. We also found a significant negative influence of brood size on mass change in males, providing support for the reproductive-stress hypothesis, and we conclude that, for males, both the flight-efficiency and reproductive-stress hypotheses apply. For female scrub-jays, our results were consistent with the flight-efficiency and energy-reserve mobilization hypotheses, both of which view mass loss as beneficial. RESUMEN. Variación en la masa corporal en individuos reproductivos de Aphelocoma coerulescensMuchas aves pierden masa corporal cuando alimentan a sus pichones y se han propuesto varias hipótesis para explicar dicha pérdida. La hipótesis de "estrés reproductivo" sugiere que la pérdida de masa es el resultado de un déficit energético. La hipótesis de "eficiencia de vuelo" sugiere que en los reproductores la pérdida en masa es en antelación a la alimentación de los pichones, en aras de ahorrar energía para el vuelo. La hipótesis de "movilización de reserva" sugiere que las hembras reproductoras acumulan reservas de energía durante la producción de huevos e incubación y luego movilizan dichas reservas para cumplir con la demanda energética luego del eclosionamiento. Finalmente, las aves pueden perder masa corporal debido a la regresión de la gónada. De 1999 al 2001, atrajimos a una balanza electrónica a individuos del Azulejón (Aphelocoma coerulescens), que son reproductores sedentarios cooperativos. Nuestro objetivo fue determinar que hipótesis pudiera explicar la variación en masa durante el periodo reproductivo. Ambos, hembras y machos, perdieron masa durante el periodo de atención a los pichones (machos, 3.2%; hembras, 6.5%), pero no durante el periodo de alimentar a los volantones, siendo este el periodo de mayor esfuerzo. Estos resultados son consistentes con ambas hipótesis, la de eficiencia de vuelo y la de movilización de reservas (solo en las hembras). Además encontramos una influenc...

Mass fluctuation in breeding females, males, and helpers of the Florida scrub-jay Aphelocoma coerulescens

“…Their weigh fluctuated and showed some significant difference when comparing different stages or fortnights, but the differences were small (<1 g). The patterns of mass variation for female and male breeders in this study are consistent with mass data for an adjacent study population of the Florida scrub-jay collected over three years during the building, incubation and nestling stages ( Schoech, 1998 ) and to data collected in the same population in different years ( Brand & Bowman, 2012 ). However, in these studies the patterns of mass variation in helpers were never examined in detail before.…”

“…A recent study on long term mass variation for females and males breeders throughout the breeding season showed that both sexes lost mass during the period of nestling care, but not when feeding fledglings. Although post-fledging is a period of peak effort ( Brand & Bowman, 2012 ) this is also the period during which contributions by helpers is at its highest, suggesting that their contributions might buffer mass losses by breeders. Despite this, few studies have examined mass loss in non-breeding helpers of cooperative species.…”

Experimental evidence and 43 years of monitoring data show that food limits reproduction in a food‐caching passerine

“…It is well established in a wide range of animals that reproduction is energetically costly (Gittleman and Thompson 1988, Olsson et al 1997, Watson et al 1998, Hendry and Berg 1999, Ferna´ndez et al 2000, Brand and Bowman 2012. High energy demands are associated with multiple stages of the reproductive cycle, for example the construction of nests (Gauthier and Thomas 1993, Nilsson and Ra˚berg 2001, Mikheyev and Tschinkel 2004, the production of eggs in oviparous species (Fitzpatrick 1973, Vance 1973, Tallamy and Denno 1982, Ve´zina and Williams 2005, brooding and incubating (Fitzpatrick 1973, Tallamy and Denno 1982, Ferna´ndez et al 2000, Hanssen et al 2003, Lardies et al 2004), gestation and lactation in mammals (Gittleman andThompson 1988, Clutton-Brock et al 1989), and care of young until independence in altricial species (Gittleman and Thompson 1988, Daan et al 1990, Steinhart et al 2005.…”

Physiological costs of prospecting in a resident cooperative breeder, the Florida scrub-jay

“…We used field measures of body condition and assays of oxidative status alongside estimates of prospecting effort. Previous studies on Florida scrub-jays have demonstrated mass changes (Brand & Bowman, 2012;Cucco & Bowman, 2018) as well as oxidative damage (Heiss & Schoech, 2012) in relation to breeding season and reproductive effort. However, the relationship between such proxies of body condition and prospecting effort remains unknown owing to limited information on prospecting We hypothesised that prospecting entails physiological costs in Florida scrub-jays, potentially constraining prospecting effort and leading to individual differences.…”