Genetically‐based behavioural morph affects stopover refuelling performance in white‐throated sparrows Zonotrichia albicollis

Abstract

Intraspecific competition can influence refuelling at migration stopover sites. White‐throated sparrows Zonotrichia albicollis have genetically‐determined plumage morphs that differ in dominance behaviour and competitive abilities. This study examines the effects of plumage morph, sex and age, three likely indicators of competitive ability, on fall migration timing, body composition, and refuelling rates during stopover at Long Point, Ontario. We used quantitative magnetic resonance analysis and plasma metabolite profiling to determine body composition and refuelling rates, respectively. We determined sex and plumage morph genetically. Competitive ability did not influence migration timing. Controlling for structural size, males had larger lean mass than females, but we found no differences in body fat or lean mass between plumage morphs. Plasma metabolite concentrations indicated that the aggressive white‐stripe morph refuelled faster than the less aggressive tan‐stripe morph, though there were no differences among sex and age groups. We suggest that increased refuelling rates did not result in increased fat or lean mass because 1) individuals categorised as less competitive had longer stopover durations to compensate for slower refuelling rates; or 2) costs of behaving more competitively offset gains from faster refuelling rates.

Stopover refuelling, movement and departure decisions in the white‐throated sparrow: The influence of intrinsic and extrinsic factors during spring migration

“…For example, high-quality stopover locations or years with plentiful resources may enable all migrants to refuel equally well, independent of sex, age, or plumage morph. This may also explain the mixed evidence for morph-specific refuelling rate between past studies (Brown et al, 2014;Hoh et al, 2018) and our own. Age-specific stopover refuelling rate is generally not observed in spring migrating songbirds (Macdade et al, 2011;Morbey et al, 2018), and our findings concur.…”

“…Less is known about differential migration by age or migration distance. Although age differences in fall migration timing were not observed in this species (Brown et al., 2014), second year birds (henceforth: juveniles) have longer stopovers in fall than after second year birds (henceforth: adults) at the same location (Mackenzie, 2010). Males generally spend the non‐breeding season further north than females (Jenkins & Cristol, 2002; Mazerolle & Hobson, 2007; Odum, 1958).…”

“…Sex differences in refuelling rate have yet to be evaluated during migration, and there is mixed evidence that refuelling rate can differ between plumage morphs. During fall migration, Brown, McCabe, Kennedy, and Guglielmo (2014) found a higher refuelling rate in the WS birds during stopover on the north shore of Lake Erie during fall migration. In contrast, Hoh et al.…”

Banding data reveal bias in age-class sampling of songbirds during spring migration

“…), and the energetic condition of migrants (e.g., Brown et al. ). However, my results suggest that these datasets cannot be assumed to be unbiased samples with respect to the age structure of populations during either spring or fall migration.…”

“…Analysis of long-term banding data collected at migration monitoring stations has provided insight concerning migration timing (e.g., Mills 2005), stopover ecology (e.g., Horton and Morris 2012), sex ratios (e.g., Mulvihill et al 1992), population biology (e.g., Osenkowski et al 2012), and the energetic condition of migrants (e.g., Brown et al 2014). However, my results suggest that these datasets cannot be assumed to be unbiased samples with respect to the age structure of populations during either spring or fall migration.…”