Decoupling of bird migration from the changing phenology of spring green-up

Shifts in avian migration phenologies do not compensate for changes to conditions en route in spring and fall

Several factors are known to affect bird migration timing, but no study has simultaneously compared the effects of temperature, land surface phenology, vegetation greenness, and relative humidity in both spring and fall. In addition, it is unclear whether long-term shifts in migration phenologies have kept pace with changing climates. For example, if migration shifts earlier in the spring, temperatures on migration dates may remain stable over time despite spring warming trends. If the phenologies of birds, plants, and insects shift asynchronously in response to changing climates, then birds may encounter reduced resource availability during migration. We estimated spring and fall 10%, 50%, and 90% cumulative migratory passage dates at 53 weather surveillance radar stations across the US Central Flyway. We determined which conditions (temperature, timing of green-up and dormancy, relative humidity, and enhanced vegetation index [EVI]) explained annual variation in migration phenologies. We also described decadal trends in environmental conditions and whether shifts in migration phenologies were sufficient to compensate for these changes. Annual changes to spring migration phenologies were best explained by anomalies in temperature, with earlier passage in warmer years. Fall migration occurred later on warmer, more humid years with higher EVI and later dormancy. Long-term adjustments in bird migration phenologies did not mitigate their exposure to changing environmental conditions. Although passage dates for all spring migration quantiles advanced significantly (~0.6 days/decade), temperatures on spring 10% passage dates increased, while 50% and 90% passage occurred closer to green-up. In the fall, temperatures increased on 50% and 90% passage dates. By contrast, the advancement of 10% passage (~1 day/decade) prevented early migrants from experiencing the cooling late-summer temperature trend. Warmer temperatures in mid to late fall may lead to earlier fruiting phenology and asynchronies with migratory passage, which occurred later in warmer years. Changes in temperature and land surface phenophases experienced by migrants suggest that resource availability during migration has changed and that adjustments to migration phenologies have not compensated for the effects of changing climates.

Chasing the Niche: Escaping Climate Change Threats in Place, Time, and Space

Climate change is creating mismatches between species' current environments and their historical niches. Locations that once had the abiotic and biotic conditions to support the persistence of a species may now be too warm, too dry, or simply too different, to meet their niche requirements. Changes in behaviors, altered phenology, and range shifts are common responses to climate change. Though these responses are often studied in isolation by scientists from disparate subfields of ecology, they all represent variants of the same solution-strategies to realign the conditions populations experience with their niche. Here, we aim to (1) identify the physiological and ecological effects, and potential alignment, of these three ecological responses: shifts in behavior, phenology, or ranges, (2) determine the circumstances under which each type of response may be more or less effective at mitigating the effects of climate change, and (3) consider how these strategies might interact with each other. Each response has been previously reviewed, but efforts to consider relationships between ecological (or with evolutionary) responses have been limited. A synthetic perspective that considers the similarities among ecological responses and how they interact with each other and with evolutionary responses offers a more robust view on species' resilience to climate change.

Influence of local (air temperature) and wide-scale (North Atlantic Oscillation) climate indices on the first arrival dates of the Common Wood Pigeon (Columba palumbus) at breeding site in SE Poland

In this study, a relationship between climate indices (local - air temperatures, and wide-scale - North Atlantic Oscillation) and first arrival dates (FAD) of a short-distant migratory bird, the Common Wood Pigeon (Columba palumbus) at a breeding site in SE Poland (Lublin) was investigated. Temporal patterns of FAD on a multi-year scale (20 years within 39 years between 1982 and 2020) were also studied. Additionally, correlations between mean air temperature at Lublin and sites along the spring migration route with various distances from the breeding site and various time lags were searched for. A significant temporal trend in arrival dates was found, indicating the advancing of FADs by 9.5 days compared to the 1980s. It was found that FAD in the studied period was affected by North Atlantic Oscillation (NAO) in February and among daily indices by mean air temperature in Lublin 12 days and by NAO - 7 days before arrival. As expected, the highest correlation between air temperatures in Lublin and sites along the spring migration route of the studied population for locations < 500 km from Lublin and a few days' travel before arrival were found. Studying FADs and climatic indices in the breeding areas and en route of migration helps to understand factors affecting the phenology of spring avian migration.

Potential for bird-insect phenological mismatch in a tri-trophic system

Climate change is altering the seasonal timing of biological events across the tree of life. Phenological asynchrony has the potential to hasten population declines and disrupt ecosystem function. However, we lack broad comparisons of the degree of sensitivity to common phenological cues across multiple trophic levels. Overcoming the complexity of integrating data across trophic levels is essential for identifying spatial locations and species for which mismatches are most likely to occur. Here, we synthesized over 15 years of data across three trophic levels to estimate the timing of four interacting phenological events in eastern North America: the green-up of forest canopy trees, emergence of adult Lepidoptera and arrival and subsequent breeding of migratory birds. We next quantified the magnitude of phenological shift per one unit change of springtime temperature accumulation as measured by accumulated growing degree days (GDD). We expected trophic responses to spring temperature accumulation to be related to physiology, thus predicting a weaker response of birds to GDD than that of insects and plants. We found that insect and plant phenology indeed had similarly strong sensitivity to GDD, while bird phenology had lower sensitivity. We also found that vegetation green-up and bird arrival were more sensitive to GDD in higher latitudes, but the timing of bird breeding was less sensitive to GDD in higher latitudes. Migratory bird species with slow migration pace, early arrivals and more northerly wintering grounds shifted their arrival the most. Across Eastern Temperate Forests, the similar responses of vegetation green-up and Lepidoptera emergence to temperature shifts support the use of remotely sensed green-up to track how the timing of bird food resources is shifting in response to climate change. Our results indicate that, across our plant-insect-bird system, the bird-insect phenological link has a greater potential for phenological mismatch than the insect-plant link, with a higher risk of decoupling at higher latitudes.

Among-species variation in six decades of changing migration timings explained through ecology, life-history and local migratory abundance

Species exploiting seasonal environments must alter timings of key life-history events in response to large-scale climatic changes in order to maintain trophic synchrony with required resources. Yet, substantial among-species variation in long-term phenological changes has been observed. Advancing from simply describing such variation towards predicting future phenological responses requires studies that rigorously quantify and explain variation in the direction and magnitude of changing timings across diverse species in relation to key ecological and life-history variables. Accordingly, we fitted multi-quantile regressions to 59 years of multi-species data on spring and autumn bird migration timings through northern Scotland. We demonstrate substantial variation in changes in timings among 72 species, and tested whether such variation can be explained by species ecology, life-history and changes in local abundance. Consistent with predictions, species that advanced their migration timing in one or both seasons had more seasonally restricted diet types, fewer suitable breeding habitat types, shorter generation lengths and capability to produce multiple offspring broods per year. In contrast, species with less seasonally restricted diet types and that produce single annual offspring broods, showed no change. Meanwhile, contrary to prediction, long-distance and short-distance migrants advanced migration timings similarly. Changes in migration timing also varied with changes in local migratory abundance, such that species with increasing seasonal abundance apparently altered their migration timing, whilst species with decreasing abundance did not. Such patterns broadly concur with expectation given adaptive changes in migration timing. However, we demonstrate that similar patterns can be generated by numerical sampling given changing local abundances. Any apparent phenology-abundance relationships should, therefore, be carefully validated and interpreted. Overall, our results show that migrant bird species with differing ecologies and life-histories showed systematically differing phenological changes over six decades contextualised by large-scale environmental changes, potentially facilitating future predictions and altering temporal dynamics of seasonal species co-occurrences.