Annual variation in fat storage by a migrant warbler overwintering in the Indian tropics

Abstract

Summary 0[ We studied fat storage in a population of greenish leaf warblers "Phylloscopus trochiloides# in southern India over four winters "0882Ð86#[ This species breeds in temperate regions and overwinters in India from October to April[ 1[ Diurnal variation in fat scores was comparable to that seen among temperate wintering passerines[ Seasonal variation was slight\ except for premigratory fattening[ There was signi_cant annual variation] in drier winters\ which were also winters of low food supplies\ fat scores were higher[ 2[ Energy metabolized overnight is unlikely to vary across winters\ and annual vari! ation in fat scores is considered a response to uncertainty of food intake on a given day[ Fat scores varied inversely with short!term rainfall\ which drives the abundance of arthropod prey[ 3[ Annual variation in fat scores was not accompanied by changes in total body mass[ This suggests that protein reserves were being compromised by increased fat deposition in dry years and o}ers an explanation for the observed delay in moult during drier winters[ These results suggest that strategies for maximizing short!term probability of survival translate into future _tness costs\ and may shape long!term life!history strategies through simple physiological processes[ Key!words] diurnal variation\ energy reserves\ Phylloscopus\ timing of moult\ winter survival strategies[ Journal of Animal Ecology "0888# 57\ 704Ð712

Sex and Age Differences in Site Fidelity, Food Resource Tracking, and Body Condition of Wintering Kirtland's Warblers (Setophaga Kirtlandii) in the Bahamas

“…data). This continuous diurnal foraging activity coincides with the observed increase in corrected body mass over the course of the day, suggesting that during the night the warblers lose energy, which can not be quickly replaced in the early morning hours (e.g., Katti and Price 1999). By late winter, the occurrence of the warbler's pre-alternate molt (Pyle 1997) further contributes to energetic demands when birds are storing fat for migration and food resources may be low.…”

“…Detecting these patterns, however, may require controlling for changes in physical condition during the day, because condition is known to change during the day in other wintering migrants (e.g., Katti andPrice 1999, Townsend et al 2012).…”

“…These sex and age differences were expected to result in corresponding differences in body condition (Marra and Holmes 2001), which by late winter could affect migration departure schedules (Marra et al 1998;Marra 2007, 2011). Body condition was also expected to vary with rainfall (Katti and Price 1999, Studds and Marra 2007, Smith et al 2010, given the likely effects of rainfall on food resources, especially in late winter, when drought conditions are most likely to occur. Finally, warblers in good body condition were expected to show higher annual return rates than those in poor body condition (Wolfe et al 2013).…”

Fat and pectoral muscle in migrating Sedge WarblersAcrocephalus schoenobaenus

“…This supports an interpretation of the Bardsey data that while increases in fat and pectoral muscle mass are part of the preparation for migration, they are not necessarily linked and can vary independently. Other studies, although not directly related to migration, have shown that fat and lean body mass in birds can vary independently; for example, Great Tits Parus major breeding in marginal habitats maintain fat reserves at the expense of pectoral muscle (Riddington & Gosler 1995), and in Greenish Warblers Phylloscopus trochiloides, fat can be accumulated at the expense of lean body mass to ensure short-term survival under conditions of food shortage (Katti & Price 1999).…”

Seasonal variation in foraging ecology of three species of overwintering Leaf Warblers (genus Phylloscopus) in the Himalayan foothills

“…These changes suggest that, as resources declined, the species were forced to segregate along these dimensions in addition to foraging in different vertical layers in the vegetation in order to avoid competing with their congeners. Such segregation must be particularly necessary in late winter when energetic costs increase to facilitate premigratory fattening (Katti and Price 1999).…”