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1. Six decades of North American bird banding records reveal plasticity in migration phenology

   https://doi.org/10.1111/1365-2656.13887  

   Horton, Kyle G.; Morris, Sara R.; Van Doren, Benjamin M.; Covino, Kristen M. (March 2023, Journal of Animal Ecology)

   Abstract The timing of avian migration has evolved to exploit critical seasonal resources, yet plasticity within phenological responses may allow adjustments to interannual resource phenology. The diversity of migratory species and changes in underlying resources in response to climate change make it challenging to generalize these relationships.We use bird banding records during spring and fall migration from across North America to examine macroscale phenological responses to interannual fluctuations in temperature and long‐term annual trends in phenology.In total, we examine 19 species of North American wood warblers (family Parulidae), summarizing migration timing from 2,826,588 banded birds from 1961 to 2018 across 46 sites during spring and 124 sites during fall.During spring, warmer spring temperatures at banding locations translated to earlier median passage dates for 16 of 19 species, with an average 0.65‐day advancement in median passage for every 1°C increase in temperature, ranging from 0.25 to 1.26 days °C⁻¹. During the fall, relationships were considerably weaker, with only 3 of 19 species showing a relationship with temperature. In those three cases, later departure dates were associated with warmer fall periods. Projecting these trends forward under climate scenarios of temperature change, we forecast continued spring advancements under shared socioeconomic pathways from 2041 to 2060 and 2081 to 2100 and more muted and variable shifts for fall.These results demonstrate the capacity of long‐distance migrants to respond to interannual fluctuations in temperatures, at least during the spring, and showcase the potential of North American bird banding data understanding phenological trends across a wide diversity of avian species. 

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2. Individual-tree phenology reveals climate-dependent responses to urban thermal heterogeneity across U.S. cities

   https://doi.org/10.64898/2026.08.05.740604  

   Zhu, Jiali; Song, Yiluan; Kong, Juwon; Meng, Lin; Peruzzi, Michele; Zhang, Yiwen; Zhao, Lei; Zhu, Kai (August 2026, bioRxiv)

   Abstract Rapid urbanization is altering the seasonal life cycles, or phenology, of urban trees. Diverse species composition and heterogeneous urban thermal environments can generate pronounced phenological variation within cities, yet such fine-scale seasonality remains poorly understood. This limits the ability to anticipate localized ecosystem services and disservices, including canopy cooling and pollen exposure. Here, we analyzed individual-tree phenology and their response to temperature across 76 cities in the contiguous United States by integrating municipal street-tree inventories, PlanetScope satellite time series, and 1-km near-surface urban air-temperature data. We quantified intra-city and cross-city phenological variation, estimated species-level associations between phenology and fine-scale urban temperature, and tested whether these associations vary with regional climatic context. Intra-city phenological variation rivaled cross-city variation for 33.3% of species in spring and 53.7% in fall. Temperature-phenology associations were widespread: warmer local urban environments were associated with earlier spring onset in 51.5% of cases and delayed fall senescence in 66.5%, with approximately two-thirds of these responses cascading to longer growing seasons. These associations varied with regional climate, generally showing stronger spring advancement and fall delay in cooler and wetter cities, but weaker or reversed responses in hotter or drier cities. Together, these results suggest that urban tree phenology is shaped by interactions among fine-scale urban temperature, species identity, and regional climate. Accounting for this heterogeneity can improve predictions of urban forest function and inform climate-resilient species selection and management. Plain Language SummaryStreet trees within the same city do not all leaf out in spring or lose their leaves in fall at the same time. This seasonal timing, called phenology, affects services such as shade and cooling, as well as disservices such as pollen exposure. We studied individual tree phenology and their temperature response in 76 U.S. cities using street-tree records, satellite observations, and local air-temperature data. We asked how much phenology varies within cities, how it responds to neighborhood-scale temperature differences, and whether these responses depend on regional climate. Variation within a city was often as large as variation among cities, especially in fall. Trees in warmer parts of cities generally leafed out earlier and lost their leaves later, often extending the growing season. However, these responses were stronger in cooler and wetter cities and weaker or sometimes reversed in hotter or drier cities. These findings show that urban tree seasonality depends on local temperature, species identity, and regional climate, which should be considered when selecting and managing trees for future cities. Key PointsSubstantial within-city phenological variation is not captured by city-level averages.Fine-scale temperature shaped phenology and growing-season length, but responses varied across species, cities, and phases.Temperature sensitivity depended on regional climate, weakening or reversing in hotter or drier cities. 

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3. Spatial Nonstationarity in Phenological Responses of Nearctic Birds to Climate Variability

   https://doi.org/10.1111/ele.14526  

   Tonelli, Benjamin A; Youngflesh, Casey; Cox, Tyler; Neate‐Clegg, Montague_H C; Cohen, Emily B; Tingley, Morgan W (October 2024, Ecology Letters)

   Climate change is shifting the phenology of migratory animals earlier; yet an understanding of how climate change leads to variable shifts across populations, species and communities remains hampered by limited spatial and taxonomic sampling. In this study, we used a hierarchical Bayesian model to analyse 88,965 site‐specific arrival dates from 222 bird species over 21 years to investigate the role of temperature, snowpack, precipitation, the El‐Niño/Southern Oscillation and the North Atlantic Oscillation on the spring arrival timing of Nearctic birds. Interannual variation in bird arrival on breeding grounds was most strongly explained by temperature and snowpack, and less strongly by precipitation and climate oscillations. Sensitivity of arrival timing to climatic variation exhibited spatial nonstationarity, being highly variable within and across species. A high degree of heterogeneity in phenological sensitivity suggests diverging responses to ongoing climatic changes at the population, species and community scale, with potentially negative demographic and ecological consequences. 

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4. Migratory strategy drives species-level variation in bird sensitivity to vegetation green-up

   https://doi.org/https://doi.org/10.1038/s41559-021-01442-y  

   Youngflesh, Casey; Socolar, Jacob; Amaral, Bruna R; Arab, Ali; Guralnick, Robert P.; Hurlbert, Allen H.; LaFrance, Raphael; Mayor, Stephen J.; Miller, David A.; Tingley, Morgan W. (January 2021, Nature ecology evolution)

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   Animals and plants are shifting the timing of key life events in response to climate change, yet despite recent documentation of escalating phenological change, scientists lack a full understanding of how and why phenological responses vary across space and among species. Here, we used over 7 million community-contributed bird observations to derive species-specific, spatially explicit estimates of annual spring migration phenology for 56 bird species across eastern North America. We show that changes in the spring arrival of migratory birds are coarsely synchronized with fluctuations in vegetation green-up and that the sensitivity of birds to plant phenology varied extensively. Bird arrival responded more synchronously with vegetation green-up at higher latitudes, where phenological shifts over time are also greater. Critically, species’ migratory traits explained variation in sensitivity to green-up, with species that migrate more slowly, arrive earlier and overwinter further north showing greater responsiveness to earlier springs. Identifying how and why species vary in their ability to shift phenological events is fundamental to predicting species’ vulnerability to climate change. Such variation in sensitivity across taxa, with long-distance neotropical migrants exhibiting reduced synchrony, may help to explain substantial declines in these species over the last several decades. 

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5. Demographic consequences of phenological asynchrony for North American songbirds

   https://doi.org/10.1073/pnas.2221961120  

   Youngflesh, Casey; Montgomery, Graham A.; Saracco, James F.; Miller, David A.; Guralnick, Robert P.; Hurlbert, Allen H.; Siegel, Rodney B.; LaFrance, Raphael; Tingley, Morgan W. (July 2023, Proceedings of the National Academy of Sciences)

   Changes in phenology in response to ongoing climate change have been observed in numerous taxa around the world. Differing rates of phenological shifts across trophic levels have led to concerns that ecological interactions may become increasingly decoupled in time, with potential negative consequences for populations. Despite widespread evidence of phenological change and a broad body of supporting theory, large-scale multitaxa evidence for demographic consequences of phenological asynchrony remains elusive. Using data from a continental-scale bird-banding program, we assess the impact of phenological dynamics on avian breeding productivity in 41 species of migratory and resident North American birds breeding in and around forested areas. We find strong evidence for a phenological optimum where breeding productivity decreases in years with both particularly early or late phenology and when breeding occurs early or late relative to local vegetation phenology. Moreover, we demonstrate that landbird breeding phenology did not keep pace with shifts in the timing of vegetation green-up over a recent 18-y period, even though avian breeding phenology has tracked green-up with greater sensitivity than arrival for migratory species. Species whose breeding phenology more closely tracked green-up tend to migrate shorter distances (or are resident over the entire year) and breed earlier in the season. These results showcase the broadest-scale evidence yet of the demographic impacts of phenological change. Future climate change–associated phenological shifts will likely result in a decrease in breeding productivity for most species, given that bird breeding phenology is failing to keep pace with climate change. 

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