Data from: Variation in chronotype is associated with migratory timing in a songbird

Like many organisms, birds exhibit daily (circadian) and seasonal
biological rhythms, and within populations both daily and seasonal timing
often vary among individuals. Because photoperiod interacts with the
circadian rhythms of many organisms to induce seasonal changes in behavior
and physiology, it is hypothesized that differences in daily timing,
called chronotypes, underpin differences among individuals in the timing
of seasonal events. For seasonal events stimulated by increasing
daylength, this hypothesis predicts a positive relationship between the
timing of daily and seasonal activities of individuals, with advanced
chronotypes expressing events earlier in the year. The few previous tests
of this hypothesis have focused on seasonal reproductive timing in birds.
However, the hypothesis predicts that this relationship should extend to
other photoinduced seasonal events. Therefore, we tested whether variation
in chronotype was associated with variation in spring migratory timing in
a captive songbird model, the pine siskin (Spinus pinus). We found that
pine siskins expressing migratory restlessness exhibited repeatable
chronotypes in their timing of nocturnal activity. Further, chronotype was
significantly associated with the onset date of migratory behavior,
consistent with the hypothesized relationship between chronotype and
seasonal timing.