Seasonal Metabolic Variation in Two Populations of an Afrotropical Euplectid Bird

Abstract

Many birds exhibit seasonal phenotypic flexibility in basal metabolic rate (BMR) and summit metabolism (M sum ), but very little information is available for species from subtropical latitudes or for conspecific populations from sites that vary in climate. We measured body mass (M b ), BMR, and M sum in summer and winter in two populations of the southern red bishop Euplectes orix, a passerine that is widespread in southern Africa. One population occurs at a comparatively warmer coastal site (mean daily minimum air temperature [T a ] in midwinter, 8.3ЊC) and the other at a colder inland site (mean daily minimum T a in midwinter, Ϫ2.8ЊC). Bishops from both populations significantly increased M b in winter. However, seasonal metabolic adjustments differed considerably between the populations. The inland population significantly increased BMR by approximately 58%, mass-specific BMR by approximately 31%, and M sum by approximately 15% in winter, although massspecific M sum did not change significantly. In contrast, the coastal population showed no significant seasonal change in BMR and significant winter reductions in mass-specific BMR (∼15%), M sum (∼8%), and mass-specific M sum (∼15%). The interpopulation differences in the magnitude and direction of seasonal mass-specific BMR changes are qualitatively consistent with global patterns, although the increase shown by the inland population is larger than expected. Our data reveal that avian seasonal metabolic adjustments can vary greatly within subtropical species depending on the climatic conditions experienced by the birds, and our findings reiterate the need to better understand metabolic flexibility in species that inhabit lower latitudes.

Summit metabolism and metabolic expansibility in Wahlberg's epauletted fruit bats (Epomophorus wahlbergi): seasonal acclimatisation and effects of captivity

“…The magnitude of the among-population differences in E. wahlbergi is similar to that recently documented in a bird; two southern red bishop (Euplectes orix) populations showed contrasting seasonal changes in both BMR and M sum , with birds at a warmer coastal site showing no significant seasonal variation in BMR, whereas birds from a colder inland site increased BMR by 58% in winter (van de Ven et al, 2013b). However, whereas the two study sites in that study differed by ~10°C in winter minimum air temperature (T a ), Pretoria and Pietermaritzburg are climatically similar, with average minimum and maximum temperatures across all months differing by at most 2°C between them, and with mean annual precipitation differing bỹ 20% (Pretoria: 703 mm; Pietermaritzburg: 832 mm; South African Weather Service).…”

Thermoregulation in African Green Pigeons (Treron calvus) and a re-analysis of insular effects on basal metabolic rate and heterothermy in columbid birds

“…Second, our analysis implicitly assumes that BMR is a fixed, speciesspecific parameter. In reality, avian BMR is a variable trait constantly adjusted in response to environmental conditions (reviewed by McKechnie 2008), including in tropical and subtropical species (Maldonado et al, 2009;Smit and McKechnie, 2010a;van de Ven et al, 2013). Finally, as already mentioned we could not account for fine-scale variation in climatic conditions across the ranges of the species included in the analysis because many of the data were obtained from captive-bred birds, whereas others were from wild-caught individuals.…”

Cross-training in birds: cold and exercise training produce similar changes in maximal metabolic output, muscle masses and myostatin expression in house sparrows,Passer domesticus

“…In contrast, winter BMR is usually higher than that in summer for wild birds in seasonal climates, but it may also be lower or seasonally stable (Dawson and O'Connor, 1996;McKechnie, 2008), although some of this variation is likely explained by differences in climate (van de Ven et al, 2013a). Cold-acclimated birds generally show 5-42% increases in BMR compared with their warm-acclimated counterparts (Klaassen et al, 2004;Vézina et al, 2006;McKechnie, 2008;Peña-Villalobos et al, 2014).…”