Experimental determination of the photoperiodic basis for geographic variation in avian seasonality

Abstract

Geographic variation in the timing of breeding, moult and migration of birds reflects adjustment of their annual cycles to regional differences in environmental conditions. Understanding to what degree this variation results from phenotypic plasticity or from genetic adaptation is important both as a goal of primary research and especially because we need to understand the potential for species to adapt to global environmental change. The annual change in day-length remains invariant, year after year, and birds depend primarily on this environmental information to match breeding and migration schedules with the changing seasons. Here, I review what is known about the role of photoperiodic responses in shaping geographic variation in avian life cycles, focussing on intraspecific comparative studies in passerine birds. Experiments with hand-raised individuals from different populations kept under identical conditions (common-garden experiments) suggest that differences in the timing of events are not photoperiodically determined when trait differences persist. A single common-garden experiment has no neutral testing ground, however. Thus, if birds breeding at different latitudes have evolved (or retained) non-parallel reaction norms, a single test environment is not sufficient to quantify genetic and environmental influences. While reciprocal transplantation may control for this problem, such an extended experimental design has only rarely been considered. More recently, population-specific reaction norms have been studied by assigning full siblings to various photoperiodic regimes. Through this approach, the extent of genotype-by-environment interaction can be estimated, which is essential information when interpreting trait differences among populations under natural conditions and predicting how species or populations will respond to photoperiodic conditions outside present-day geographical ranges.

Variation in Primary Molt in the Least Auklet

“…Second, the timing of primary molt differs by colony and year, and in other auklets both timing and rate vary from year to year (Emslie et al 1990), so it is possible that breeders and nonbreeders molt at different rates in some years, perhaps in response to variation in food availability or other factors. Birds breeding at high latitudes often breed in a briefer period (e.g., Summers et al 2004, Coppack 2007, and molt is often faster at more northerly locations, presumably to minimize overlap of the two life-history stages (Wingfield 2008). Delays in molt can result in an increase in molt rate and decrease in feather quality (Dawson 2004).…”

Rainfall-induced changes in food availability modify the spring departure programme of a migratory bird

“…This mechanism is considered to be particularly important for the timing of spring migration in species than winter in the tropics because potential seasonal environmental cues are thought to be too weak or unpredictable to reliably stimulate migratory behaviour [17,18]. Two recent studies suggest that tropical precipitation may vary enough to influence the timing of spring arrival.…”

Sleepless in Town – Drivers of the Temporal Shift in Dawn Song in Urban European Blackbirds

“…Intensively illuminated structures also cause migrating birds to become disoriented and entrapped in the light cone, thus disturbing migratory behaviour [31], [32], [33], [34]. Furthermore, light pollution is suspected to interfere with avian circannual and circadian rhythmicity, because photoperiod is one of the most important cues in timing seasonal and daily activities [35], [36]. European Blackbirds advance the growth of their testes by one month after experimental exposure to low artificial night light [37].…”