Failure to advance migratory phenology in response to climate change may pose a significant threat to a declining Nearctic-Neotropical songbird.

Populations of long-distance migrants that breed in seasonal habitats can be significantly impacted by climate change. We examined the migratory and breeding phenologies of the cerulean warbler (Setophaga cerulea), a declining long-distance Nearctic-Neotropical migrant that breeds in deciduous forests of Indiana. Our primary objectives were to determine temporal trends in cerulean warbler migratory timing, and to identify climate variables that explain variation in this species' migratory and breeding phenologies. We reviewed trends in cerulean warbler first arrival to Indiana from 1982 to 2019, and compared them to several explanatory climate variables: spring temperature, growing degree days (GDD), North Atlantic Oscillation (NAO) index, and Oceanic Niño Index (ONI). We also compared the timing of cerulean warbler first lay dates from 2012 to 2019 with the aforementioned climate variables and annual spring precipitation. Cerulean warblers exhibited a minimal advance in first arrival timing (≤4 days in 38 years). Arrival timing was best predicted by GDD and a null model, but trends in GDD indicate that spring warming in Indiana has advanced by a greater margin, approximately 14 days. Climate variables did not predict first lay timing better than a null model. Springtime in Indiana is occurring earlier, but cerulean warblers are advancing their migratory timing to a much smaller degree. This failure to adapt may have a detrimental effect on warbler populations if it results in an asynchronization of important biological timings between them and their prey. Further studies of cerulean warbler breeding and prey phenologies are necessary to determine how climate change is impacting this species' reproductive success.

Changes in spring arrival dates and temperature sensitivity of migratory birds over two centuries.

Long-term phenological data have been crucial at documenting the effects of climate change in organisms. However, in most animal taxa, time series length seldom exceeds 35 years. Therefore, we have limited evidence on animal responses to climate prior to the recent warm period. To fill in this gap, we present time series of mean first arrival dates to Central Europe for 13 bird species spanning 183 years (1828-2010). We found a uniform trend of arrival dates advancing in the most recent decades (since the late 1970s). Interestingly, birds were arriving earlier during the cooler early part of the nineteenth century than in the recent warm period. Temperature sensitivity was slightly stronger in the warmest 30-year period (-1.70 ± SD 0.47 day °C-1) than in the coldest period (-1.42 ± SD 0.89 day °C-1); however, the difference was not statistically significant. In the most recent decades, the temperature sensitivity of both short- and long-distance migrants significantly increased. Our results demonstrate how centennial time series can provide a much more comprehensive perspective on avian responses to climate change.

Significantly Earlier Spring Migration in Most Bird Species at the Eastern Limit of Europe.

The first arrival dates of 31 species of migrant birds in the Tatarstan Republic of Russia were monitored for the 34-year period from 1989-2022. Trends in first arrival date were evaluated using regression against the year value. Patterns in arrival data with respect to species traits (habitat, migration distance, body weight, etc.) were evaluated using redundancy analysis. Relationships between first arrival dates and Tatarstan temperatures were also evaluated using regression methods of first-arrival date on monthly mean temperatures. Almost all (28 of 31) species revealed a significantly earlier migration arrival date; however, associations between arrival patterns and species traits were equivocal. Warmer temperatures were significantly associated with earlier arrival in 26 of the 31 species, but the relationship was insufficient to explain the average 11-day advance in species. For these species and in this location only the timing and location of arrival are well recorded; the exact wintering areas and migration routes, and the timing of these phases are less well understood. When these become better known, an investigation of the influence of environmental conditions (including temperature) on departure timing and passage timing and speed is recommended.