Seasonal and directional dispersal behavior in an ongoing dove invasion

Range expansions require the dispersal of individual organisms, but dispersal behavior is notoriously difficult to study. Eurasian collared-doves have colonized both Europe and North America this century, with both initial invasions proceeding northwestward via 'jump' dispersal. The European population has reached carrying capacity, but in the Americas, where exponential population growth continues, little is known about dispersal behavior. I queried citizen science field notes to investigate Eurasian collared-dove dispersal behavior in North America along the Pacific Ocean, a natural barrier to northwestward landbird dispersal. I examined coastal and pelagic records of Eurasian collared-doves to determine the seasonality and directionality of dispersal flights and to assess changes in the frequency of dispersal-related behavior across years. Most reports of Eurasian collared-doves flying in flocks along the coast and most pelagic sightings were in March-May, mirroring the spring natal dispersal documented during the European invasion. Almost all spring coastal flocks were flying north, consistent with the overall northwestward direction of the initial North American invasion and northward deflection of northwest-bound birds upon encountering the Pacific Ocean. Spring flying flock observations showed no significant change in frequency from 2010 to 2018 after controlling for overall increases in spring collared-dove reports. This refined understanding of Eurasian collared-dove dispersal behavior informs full life cycle management of this rapidly increasing invader in the Americas, raises new questions about evolutionary mechanisms driving this spectacular invasion, and illustrates the potential power of citizen science field notes for documenting dispersal behavior, a longstanding challenge in ecology.