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

Abstract

The transition to a migratory state involves coordinated changes in physiology and behaviour. In species with regular, predictable (obligate) migrations, increasing day length triggers the expression of a spring migratory state and androgens play an important role in stimulating its development. By contrast, we know little about the environmental cues and endocrine mechanisms that regulate migration in species with less predictable (facultative) migrations. Here, we tested whether photoperiod stimulates a migratory state in a facultative nomadic migrant, the pine siskin (Spinus pinus). We exposed wintering birds to either a naturally increasing or short-day photoperiod and measured physiological and behavioural changes indicative of a migratory state. We also examined changes in circulating hormones that may play a role in the migratory transition. Natural-day, but not short-day, birds displayed physiological preparations for migration, including increases in fat deposition, and showed increased levels of migratory restlessness. We found no evidence for a role of corticosterone in the migratory transition, but testosterone may be important. This study is the first experimental test of the role of photoperiod in regulating facultative migration and demonstrates that the predictive cue used by many obligate migrants to time spring migration is also important in a facultative migrant.

Seasonal Patterns of Fat Deposits in Relation to Migratory Strategy in Facultative Migrants

“…Seasonal cycles in fat stores consistent with premigratory fattening have been observed in populations of facultative migrants under both natural conditions (Newton, 1972;Summers et al, 1996;Marquiss and Rae, 2002;; but see Alonso and Arizaga (2011) and controlled captive conditions with unlimited food (Berthold and Gwinner, 1978;Hahn, 1995;Babushkina and Bojarinova, 2011;Newton and Dawson, 2011;Robart et al, 2018). Further, the timing of premigratory fattening in the irruptive long-tailed tit and pine siskin (Spinus pinus) responds to experimental manipulations of photoperiod in captivity (Babushkina and Bojarinova, 2011;Robart et al, 2018), although apparently not in Eurasian siskins (Spinus spinus) (Newton and Dawson, 2011). These studies suggest that even those species with highly flexible migratory behaviors may sometimes utilize endogenous programs and predictive cues to prepare for movements.…”

“…All birds were sexed and aged according to plumage, bill and skull characteristics or reproductive characteristics (Pyle et al, 1997). Birds for which characteristics were not sexually dimorphic at the time of capture (e.g., non-breeding pine siskins) were either molecularly sexed (as in Robart et al, 2018) or categorized as unknown sex and excluded from these analyses.…”

“…The responsiveness of facultative migrants to dwindling food resources has led some to speculate that facultative migrants may struggle to meet energy demands during migration or to store sufficient fat (Tiainen, 1980;Silverin, 2003), but others challenge that hypothesis given that facultative migrants often carry large fat deposits and maintain high body mass even during mass irruptions when resources should be most limiting (Bojarinova and Babushkina, 2010). Seasonal cycles in fat stores consistent with premigratory fattening have been observed in populations of facultative migrants under both natural conditions (Newton, 1972;Summers et al, 1996;Marquiss and Rae, 2002;; but see Alonso and Arizaga (2011) and controlled captive conditions with unlimited food (Berthold and Gwinner, 1978;Hahn, 1995;Babushkina and Bojarinova, 2011;Newton and Dawson, 2011;Robart et al, 2018). Further, the timing of premigratory fattening in the irruptive long-tailed tit and pine siskin (Spinus pinus) responds to experimental manipulations of photoperiod in captivity (Babushkina and Bojarinova, 2011;Robart et al, 2018), although apparently not in Eurasian siskins (Spinus spinus) (Newton and Dawson, 2011).…”

Variation in chronotype is associated with migratory timing in a songbird

“…Data for this study came from three previous experiments investigating the use of environmental cues to time spring migration: the 'photoperiod' and 'timing' experiments from Robart et al [32] and the 'males-only' experiment from Robart and Watts (A. R. Robarts, H. E. Watts 2017, unpublished data). In all experiments, wild-caught siskins were held in individual cages on photoperiods mimicking naturally increasing daylengths at a northtemperate latitude (table 1).…”

Bright artificial light at night is associated with increased body mass, poor reproductive success and compromised disease tolerance in Australian budgerigars (Melopsittacus undulatus)

“…Like all mammals, many avian species use the natural photoperiod to predict environmental changes and to regulate various adaptive physiological and behavioral functions, such as reproduction, growth, energy intake, metabolism, immunity and migration (Wang et al 2016;Schultz et al 2017;Dixit & Byrsat 2018;Robart et al 2018). The effects of ALAN on variant physiological, behavioral and ecological functions in birds have been reviewed (Navara & Nelson 2007).…”