Behavioral and physiological traits of migrant and resident White-crowned Sparrows: a common garden approach

Abstract

To accommodate a migratory life history, migrants express a greater number of physiological and behavioral stages per annum than residents and are thus considered to have higher finite state diversity (FSD). To investigate the physiological mechanisms and constraints associated with migration, direct comparison of two subspecies of white-crowned sparrow -migrant, Zonotrichia leucophrys gambelii, and resident, Z. l. nuttalli -were made under common garden conditions of photoperiod and housing, as birds progressed from winter through the vernal life history stages. We tested the hypothesis that migrants (higher FSD) respond differently than residents (lower FSD) to the initial predictive cue, photoperiod, to initiate and integrate the progression of vernal stages of prenuptial molt, migration and development of breeding. If differences in vernal phenology were noted, then the basis for the distinctions was considered genetic. Results indicate that (1) residents had a lower threshold to vernal photoperiod with elevations of plasma androgen, growth and development of reproductive structures preceding those of migrants; (2) only migrants displayed prenuptial molt, preparations for migration and migratory restlessness; and (3) neither baseline nor stress-induced plasma corticosterone differed across subspecies, suggesting energetic demands of the common garden were insufficient to induce a differential adrenocortical response in either subspecies, highlighting the impact of environmental conditions on corticosterone secretion. Thus, in a common garden experiment, Z. l. gambelii responds differently to the initial predictive cue, photoperiod, to initiate and execute the vernal stages of molt, migration and development of breeding in comparison to the shared stage of breeding with Z. l. nuttalli, confirming a genetic basis for the subspecies differences.

Increasing photoperiod stimulates the initiation of spring migratory behaviour and physiology in a facultative migrant, the pine siskin

“…Here, we found a significant increase in haematocrit in natural-day birds, occurring shortly before they increased nocturnal activity. Natural-day birds also had a significant increase in flight muscle size, again consistent with migratory preparations [1,53]. Finally, the observed changes in flight muscle coloration were somewhat surprising.…”

“…In both experiments, these birds displayed significant increases in body condition, indicating increases in body mass and fat. These changes in body condition mirror the physiological changes displayed by obligate migrants during spring migratory preparations [1,15,53,54], with stored fat serving as the main fuel during migratory flight [55,56]. Obligate migrants also cope with the increased energetic demands of migratory flight by increasing haematocrit levels, which increases the oxygen carrying capacity of the blood [57,58].…”

“…We caution, however, that interpretation of our results may be limited as blood samples were collected during morning hours, not during the night. In at least two species of obligate migrants, corticosterone levels during the dark phase show the strongest relationship with nocturnal migratory restlessness [16,53,54]. Thus, it remains to be determined whether there is a relationship between corticosterone levels during the dark phase and migratory restlessness in pine siskins.…”

Mechanisms Associated with an Advance in the Timing of Seasonal Reproduction in an Urban Songbird

“…Heteropatry-where closely related populations coexist during the non-breeding season (e.g., fall, winter, and /or early spring) yet pursue independent phenological and geographical trajectories during breeding-provides a unique opportunity to address the physiological mechanisms that underlie reproductive timing differences between populations (Winker, 2010;Ketterson et al, 2015;Bauer et al, 2016;Fudickar et al, 2016a,b;Greives et al, 2016;Ramenofsky et al, 2017). Broadly distributed avian species often have heteropatric distributions, in which some populations migrate while others do not (Winker, 2010).…”

Contrasting seasonal and aseasonal environments across stages of the annual cycle in the rufous‐collared sparrow, Zonotrichia capensis: Differences in endocrine function, proteome and body condition

“…Thus, temporally appropriate expression of the annual stages allows animals to match their energetic expenditures with resource availability (Lack, ; Ashmole , #712; Ricklefs, ). For example, in seasonal environments birds coordinate migration and breeding to utilize seasonal peaks in primary productivity (Cornelius, Boswell, Jenni‐Eiermann, Breuner, & Ramenofsky, ; Ramenofsky, Campion, Perez, Krause, & Nemeth, ; Slagsvold, ). Considering that some stages of the annual cycle are associated with high energy costs, minimal overlap of LHSs of the annual cycle avoids detrimental energetic fitness costs (Echeverry‐Galvis & Hau, ; Zera & Harshman, ;).…”