1. The seasonal movement of animals has been linked to seasonal variation in ecological productivity, and it has been hypothesized that primary consumers synchronize migration with vegetation phenology. Within temperate regions of the Northern Hemisphere, herbivorous bird species often track the phenology of vegetation greenness during spring migration. Phenological synchronization with vegetation greenness by migratory birds in other dietary guilds, across the full extent of their annual distributions during both spring and autumn migration, has not been explored.

2. Here, we document population-level associations with a remotely sensed measure of vegetation greenness for 230 North American migratory bird species in seven dietary guilds across the full annual cycle using eBird occurrence information for the combined period 2006-2018.

3. Evidence of phenological synchronization was strongest for omnivores, herbivores, herbivore-granivores, and granivores during spring and autumn migration, except for omnivores in the west during spring migration. Strong evidence of synchronization was also observed for insectivores during spring migration and carnivores during spring and autumn migration that migrated across the entire breadth of the continent. The level of evidence declined for insectivores in the west and east during spring migration, and for nectarivores in the west during spring and autumn migration. Limited evidence was also found for insectivores in the east during autumn migration, insectivores in the west and the center of the continent during spring and autumn migration, and carnivores in the west during spring migration. Carnivores in the west during autumn migration showed the weakest evidence of synchronization.

4. We found broad support across an array of dietary guilds for phenological coupling between vegetation greenness and seasonal bird migration within North America. Our results highlight the potential for many migratory bird species to encounter phenological mismatches as vegetation phenology responds to climate change. Our findings emphasize the need to better understand the environmental cues that regulate migratory behavior across dietary guilds, consumer levels, and migration tactics.

We compiled bird occurrence information from the eBird database from 1 January 2006 to 31 December 2018 within the Western Hemisphere. We querried the database on 1 February 2019. eBird contains bird obervations in checklist format where species detected by sight or sound are recorded during a sampling event. eBird represents a semi-structured database where each observer selects a predefined sampling protocol and survey effort is determined by the observer. We used occurrence information from single observer checklists and combined occurrence information across checklists that were identified as group sampling events into single checklists. A total of 28,520,138 checklists were available for analysis within our study area containing a total of 4,577 unique species.

A zip file containing 152 RData files organized by month (1-12) and year (2006-2018). Each RData files contains one R data frame (ebrd) containing all the eBird checkists submitted within the Western Hemisphere (170W-30W Longitude, 60S-90N Latitude) during that month and year. The fields in the data frame include the YEAR and DAY the checklists were compiled, the LATITUDE and LONGITUDE where the checklists were compiled, the common name of the bird species in each checklist (PRIMARY_COM_NAME), and the unique identifying number assigned to each checklist (SUB_ID).