Widespread shifts in bird migration phenology are decoupled from parallel shifts in morphology

Authors: Marketa Zimova, David E. Willard, Benjamin M. Winger, Brian C. Weeks

Year: 2021

Publication: Journal of Animal Ecology

Publication Link: https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2656.13543

Keywords: adaptation, biotic responses, body size, climate change, migration speed, migratory birds, museum collections, wing length


1. Advancements in phenology and changes in morphology, including body size reductions,
are among the most commonly described responses to globally warming
temperatures. Although these dynamics are routinely explored independently, the
relationships among them and how their interactions facilitate or constrain adaptation
to climate change are poorly understood.
2. In migratory species, advancing phenology may impose selection on morphological
traits to increase migration speed. Advancing spring phenology might also
expose species to cooler temperatures during the breeding season, potentially
mitigating the effect of a warming global environment on body size.
3. We use a dataset of birds that died after colliding with buildings in Chicago, IL to
test whether changes in migration phenology are related to documented declines
in body size and increases in wing length in 52 North American migratory bird
species between 1978 and 2016. For each species, we estimate temporal trends in
morphology and changes in the timing of migration. We then test for associations
between species-specific
rates of phenological and morphological changes while
assessing the potential effects of migratory distance and breeding latitude.
4. We show that spring migration through Chicago has advanced while the timing of
fall migration has broadened as a result of early fall migrants advancing their migrations
and late migrants delaying their migrations. Within species, we found that
longer wing length was linked to earlier spring migration within years. However,
we found no evidence that rates of phenological change across years, or migratory
distance and breeding latitude, are predictive of rates of concurrent changes in
morphological traits.
5. These findings suggest that biotic responses to climate change are highly multidimensional
and the extent to which those responses interact and influence adaptation
to climate change requires careful examination.

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