Climate change and timing of avian breeding and migration: evolutionary versus plastic changes

Abstract

There are multiple observations around the globe showing that in many avian species, both the timing of migration and breeding have advanced, due to warmer springs. Here, we review the literature to disentangle the actions of evolutionary changes in response to selection induced by climate change versus changes due to individual plasticity, that is, the capacity of an individual to adjust its phenology to environmental variables. Within the abundant literature on climate change effects on bird phenology, only a small fraction of studies are based on individual data, yet individual data are required to quantify the relative importance of plastic versus evolutionary responses. While plasticity seems common and often adaptive, no study so far has provided direct evidence for an evolutionary response of bird phenology to current climate change. This assessment leads us to notice the alarming lack of tests for microevolutionary changes in bird phenology in response to climate change, in contrast with the abundant claims on this issue. In short, at present we cannot draw reliable conclusions on the processes underlying the observed patterns of advanced phenology in birds. Rapid improvements in techniques for gathering and analysing individual data offer exciting possibilities that should encourage research activity to fill this knowledge gap.

Keywords: bird; climate change; evolution; phenology; phenotypic plasticity; selection; timing of breeding; timing of migration.

Figure 1

Schematic illustration of phenological ‘mismatch’ taking great tits and their caterpillar food supply as example. The curves indicate frequency distributions of first eggs of clutches (blue), hatching (red) and caterpillar abundance (green). Food demands of great tit chicks are highest approximately 9 days after hatching indicated by the black arrow. In the upper panel describing a scenario before climate change, the birds' breeding is well-timed to the caterpillars, and chick demand coincides with caterpillar abundance. In the lower panel, the timing of both the great tits and the caterpillars has advanced – due to climate change – but the caterpillars have advanced twice as fast. This now has led to a ‘mismatch’ between the chick demands and the phenology of the caterpillars.