COS 75-3
Are there fitness consequences of North American birds mistiming their migrations due to climate change? A test of the phenological mismatch hypothesis at an unprecedented spatial scale
Migratory birds, given their ability to move long distances, might be expected to be among the most adaptable to climate change. However, birds must anticipate climatic conditions of their distant breeding grounds from their wintering grounds, which is complicated by greater climatic change at higher latitudes. While food emergence at the breeding grounds is driven by annually variable climate, birds are driven to migrate primarily instead by hormonal responses to light cues such as photoperiod, which is constant across years.
The phenological mismatch hypothesis predicts that migratory bird populations have been unable to match their migratory arrival times to the timing of spring “green-up”, when food resources become plentiful. If so, we also test if suboptimal migration timing results in negative fitness consequences for individual bird species.
We present a continental scale study testing the phenological mismatch hypothesis and resulting fitness consequences across arrival records (eBird) for 50 common North American bird species over 10 years. Improving on previous studies examining correlations to temperature, we instead use remotely sensed vegetation green-up (MODIS), a close proxy of resource availability, and we link our results to recruitment and reproduction estimates for each bird species (MAPS).
Results/Conclusions
We found that many migratory bird species advanced arrival at their breeding grounds in years with earlier vegetation green-up. However despite this advancement, many species still poorly synchronized arrival dates with green-up. Further, greater asynchrony was observed between green-up date and arrival date in years with earlier and more extreme green-up dates. Longer distance migrants also displayed greater asynchrony. Reduced recruitment and reproduction, but not survivorship, were strongly correlated with asynchrony between arrival and green-up dates.
Our results generally support the phenological mismatch hypothesis, that climate change has resulted in asynchrony between phenology of birds and their food, and that this has resulted in negative fitness consequences. Birds arriving too early at breeding grounds likely experienced colder temperatures and arrived before peak resource abundance, whereas those arriving too late arrived after the resource peak and may have had to choose from less optimal nest sites. Migratory birds, particularly long distance migrants, appear to be susceptible to climate driven phenological mismatches.