If you can’t go north, where can you go?
The yellow-billed cuckoo (Coccyzus americanus) is a culturally and ecologically important species throughout its native breeding range in the eastern United States, but has experienced population declines in recent decades. Climate change is likely to put additional strain on this species by reducing suitable habitat: new research suggests that the yellow-billed cuckoo’s ability to shift northward to track warming temperatures might be limited by other environmental conditions.
Known for its unique call that is often heard on hot summer afternoons before storms, the yellow-billed cuckoo is referred to as the rain crow or storm crow throughout the American south. Its population sizes often track insect outbreaks, especially tent caterpillars, a native pest that builds large unsightly nests and can defoliate entire trees. Although yellow-billed cuckoo abundance fluctuates naturally with insect outbreaks, surveys indicate that there has been a general decline over the last few decades.
To understand how climate change will impact this important species, I used a generalized joint attribute model (gjam) to predict suitable habitat for the yellow-billed cuckoo and over 100 other bird species across the United States based on data from the Breeding Bird Survey. I used environmental conditions including as temperature, rainfall, and elevation to estimate habitat suitability weighted by abundance, meaning maps show not only where each species is expected to live, but also the species’ relative abundance.
Based on estimates of future climate scenarios, the model predicts that overall, the yellow-billed cuckoo’s range will shift northward. However, the model estimates that the greatest increases in abundance will occur in the middle of its range. We know that the larger increases in the middle of the range compared to the northern edge are not due to the species’ inability to move quickly enough to track temperature changes because the model only evaluates habitat suitability, not a species’ capacity to shift its range.
Therefore, this pattern indicates that even as warming temperatures push the species range north, other environmental factors limit the yellow-billed cuckoo’s potential habitat in the north.
We often assume that species can simply move north to track suitable temperatures as the climate warms. However, the results of this model suggest that species’ actual responses are more complicated because habitat suitability is dictated by much more than just temperature. It is critical to consider how environmental conditions change holistically to understand how important species like the yellow-billed cuckoo will respond to climate change.