EBird records show substantial growth of the Allen's Hummingbird (Selasphorus sasin sedentarius) population in urban Southern California

Abstract

ABSTRACT The sedentary subspecies of Allen's Hummingbird (Selasphorus sasin sedentarius) was originally endemic to the Channel Islands off the coast of Southern California, but it colonized the mainland at the Palos Verdes Peninsula sometime before 1966. In the decades since, its population has expanded in Southern California. I tracked its growth using eBird checklists. The mainland range of S. s. sedentarius has grown from ∼70 km2 in 1970 to ∼13,000 km2 today, representing an increase of ≤23% in the total range of the species as a whole. Its main habitat within Los Angeles, Orange, San Diego, and western Riverside counties is urban parks, gardens, and campuses. The range expansion of S. s. sedentarius seems to be driven by food availability—although, given that it is found in urban habitats that the other subspecies, S. s. sasin, does not seem to utilize, a subtle change in the ecology of the 2 subspecies is also implied. Analysis of eBird data suggests that breeding S. s. sedentarius met S. s. sasin ne...