Continental patterns of bird migration linked to climate variability

For ˜100 years, the continental patterns of avian migration in North America have been described in the context of three or four primary flyways. This spatial compartmentalization often fails to adequately reflect a critical characterization of migration — phenology. This shortcoming has been partly due to the lack of reliable continental-scale data, a gap filled by our current study. Here, we leveraged unique radar-based data quantifying migration phenology and used an objective regionalization approach to introduce a new spatial framework that reflects interannual variability. Therefore, the resulting spatial classification is intrinsically different from the “flyway concept”. We identified two regions with distinct interannual variability of spring migration across the contiguous U.S. This data-driven framework enabled us to explore the climatic cues affecting the interannual variability of migration phenology, “specific to each region” across North America. For example, our “two-region” approach allowed us to identify an east-west dipole pattern in migratory behavior linked to atmospheric Rossby waves. Also, we revealed that migration movements over the western U.S. was inversely related to interannual and low-frequency variability of regional temperature. A similar link but weaker and only for interannual variability was evident for the eastern region. However, this region was more strongly tied to climate teleconnections, particularly to the East Pacific-North Pacific (EP-NP) pattern. The results suggest that oceanic forcing in the tropical Pacific—through a chain of processes including Rossby wave trains—controls the climatic conditions, associated with bird migration over the eastern U.S. Our spatial platform would facilitate better understanding of the mechanisms responsible for broad-scale migration phenology and its potential future changes.

Ontogenetic shifts from social to experiential learning drive avian migration timing

Migrating animals may benefit from social or experiential learning, yet whether and how these learning processes interact or change over time to produce observed migration patterns remains unexplored. Using 16 years of satellite-tracking data from 105 reintroduced whooping cranes, we reveal an interplay between social and experiential learning in migration timing. Both processes dramatically improved individuals’ abilities to dynamically adjust their timing to track environmental conditions along the migration path. However, results revealed an ontogenetic shift in the dominant learning process, whereby subadult birds relied on social information, while mature birds primarily relied on experiential information. These results indicate that the adjustment of migration phenology in response to the environment is a learned skill that depends on both social context and individual age. Assessing how animals successfully learn to time migrations as environmental conditions change is critical for understanding intraspecific differences in migration patterns and for anticipating responses to global change.

A Novel Locality for the Observation of Thousands of Passerine Birds during Spring Migration in Los Angeles County, California

Avian migration is a spectacular phenomenon, representing the annual movements of billions of birds globally. Because the greatest diversity and numbers of birds migrate at night, opportunities to observe active migration are rare. At a number of localities in North America, however, observers can quantify movements of many typically nocturnal migrants during daylight where they continue after dawn. Such locations have provided much information about species-specific phenology, status, and orientation during migration. Localities where morning flights of land birds can be observed are unevenly distributed, however, and are little reported along the Pacific coast. Here we describe a novel location for the observation of spectacular morning flights of nocturnal migrants during spring migration at Bear Divide, in the western San Gabriel Mountains, Los Angeles County, California. In two years of informal surveys at the site, we have recorded at least one morning with an estimated ~13,500 individual birds passing. Our preliminary analyses suggest that the peak of a species’ migration at Bear Divide is correlated with the latitude of a species’ breeding, being later in the spring as that latitude increases. Our data from Bear Divide provide an independent perspective on migration as quantified by local radar. Further work at this locality may help inform our knowledge of migration phenology and population trends.

No general shift in spring migration phenology by eastern North American birds since 1970

We studied the phenology of spring bird migration from eBird and ÉPOQ checklist programs South of 49°N in the province of Quebec, Canada, between 1970 and 2020. 152 species were grouped into Arctic, long-distance, and short-distance migrants. Among those species, 75 significantly changed their migration dates, after accounting for temporal variability in observation effort, species abundance, and latitude. But in contrast to most studies on the subject, we found no general advance in spring migration dates, with 36 species advancing and 39 species delaying their migration. Several early-migrant species associated to open water advanced their spring migration, possibly due to decreasing early-spring ice cover in the Great Lakes and the St-Lawrence river since 1970. Arctic breeders and short-distance migrants advanced their first arrival dates more than long-distance migrants not breeding in the arctic. However, there was no difference among migrant groups when median arrival dates were considered. We conclude that general claims about advances in spring migration dates in eastern North America are misleading due to large taxonomic variation.

Temporal patterns and ecosystem correlates of chum salmon (Oncorhynchus keta) migration phenology in the Pacific Northwest

Understanding and quantifying migration phenology of commercially harvested Pacific salmon (Oncorhynchus spp.) is a cornerstone for managing sustainable populations. Here, we use a multi-decadal data timeseries together with a hypothesis driven framework to evaluate migration phenology in adult fall and winter ecotype chum salmon (O. keta) in a poorly studied but highly managed system – the South Puget Sound (SPS) of Washington State, USA. Using generalized additive mixed models that accounted for temporal autoregressive dynamics, we examined the effect of commercial harvest, climate variation, intraspecific density dependence, and predator buffering on migration timing and run duration. SPS chum salmon are migrating earlier over time, especially the winter ecotype that showed the strongest temporal shift from historical timing. Migration timing shifts were closely associated with regional-scale marine climate regimes, local-scale freshwater availability, and statewide pinniped abundance. In conclusion, there is potential for the winter ecotype migration converging with that of the fall ecotype, and that directional change in migration phenology may be driven by a unique combination of ecosystem factors.