Basal Metabolic Rate of the Black-Faced Sheathbill (Chionis minor): Intraspecific Variation in a Phylogenetically Distinct Island Endemic

Abstract

Metabolic rate is a fundamental characteristic of all organisms. It covaries most significantly with activity, body mass, seasonality, and temperature. Nonetheless, substantial additional variation in metabolic rate, especially either resting rate or basal rate, is associated with a range of factors including phylogenetic position, ecological distinctiveness, range position, and diet. Understanding this variation is a key goal of physiological ecology. The black-faced sheathbill is a phylogenetically distinct, highlatitude, island-endemic bird occurring exclusively on several archipelagos in the southern Indian Ocean. Here we examined the idea that the unique phylogenetic position and ecology of the black-faced sheathbill may lead to a basal metabolic rate (BMR) different from that predicted by its body mass. When compared with BMR data available for all birds and a subset of island species, it was clear that the BMR of the black-faced sheathbill on subantarctic Marion Island, estimated at 157C using indirect calorimetry (2.370 5 0.464 W, mean 5 SD; n p 22), for a group of birds with a mean mass of 459 5 64 g, is no different from that expected based on body mass. However, variation in BMR, associated with habitat use and diet, even when correcting for variation in mass, was found. Sheathbills foraging year-round in comparatively resource-rich king penguin colonies have a higher BMR (2.758 5 0.291 W, n p 12) than sheathbills that split their foraging between rockhopper penguin colonies and the intertidal zone (2.047 5 0.303 W, n p 10), which are poorer in resources. Because these populations coexist at relatively small spatial extents (the entire island is 290 km 2 ), other factors seem unlikely as causes of this variation.

How hornbills handle heat: sex-specific thermoregulation in the southern yellow-billed hornbill

“…There is increasing evidence for fine-scale intraspecific variation in the thermal physiology of endotherms (Tieleman et al, 2009;Glanville et al, 2012;McClennand et al, 2016;Noakes and McKechnie, 2019), which may arise from phenotypic flexibility, developmental plasticity (sensu Piersma and Drent, 2003), epigenetic transmission or genotypic adaptation (Merilä and Hendry, 2014). Far less is known about the contributions of these sources of variation to intraspecific variation in the heat tolerance of endotherms compared with that of ectotherms (Ketola et al, 2012;Xue et al, 2019), although recent work suggests that differences in heat tolerance among white-browed sparrow-weaver populations arise from phenotypic flexibility rather than genotypic adaptation (Noakes and McKechnie, 2019).…”

‘Scalping’ of albatross fledglings by introduced mice spreads rapidly at Marion Island

“…2006). In 2008–11, densities in mire habitats on Marion Island reached up to 237 mice ha -1 (McClelland 2013), similar to peak densities on Gough Island (266 mice ha -1 , Cuthbert et al . in press).…”

“…2012), and has not increased since cats were eradicated (Ferreira et al . 2006, McClelland 2013). Indeed, smaller size might make it easier for mice to cling onto the heads of albatross chicks.…”

“…One hypothesis is prey switching by mice, whereby mice supplement the invertebrate component of their diet with seabird chicks, driven by a steady decrease in invertebrate biomass on Marion Island over the last 40 years (Burger 1978, Gleeson & van Rensburg 1982, Smith et al . 2002, McClelland 2013). Another intriguing question is how attacks on albatross chicks commenced at scattered locations all around Marion Island’s ~70km coastline.…”

Geographical variation in the standard physiology of brushtail possums (Trichosurus): implications for conservation translocations

“…However, this approach generally ignores potential variation within a particular taxonomic group, assuming that the trait(s) in question are fixed for each species being studied ( Bozinovic et al , 2009 ). Variation in physiological traits between spatially separated populations of a single or closely related species has been relatively understudied ( Bozinovic and Naya, 2015 ; McClelland et al , 2016 ), but recognition of lower-taxonomic-level physiological variation is gaining prominence along with attempts to identify the underlying mechanisms and functional significance when such variability is found ( Bozinovic et al , 2009 ).…”