Spring is definitely the best time to see Costa's Hummingbirds (Calypte costae) here in southeastern Arizona. Costa's Hummingbirds are common here from early February through May because this is when our spring wildflowers bloom and the temperatures haven't yet grown too hot. With the blazing heat of the Sonoran Desert summer, Costa's Hummingbirds move northward into the cooler, higher elevation uplands and mountains of Arizona and California. They spend their winters in Mexico.
Male Costa's Hummingbirds are iridescent green above and white below with green flanks, a straight, black bill, and an iridescent purple crown and gorget that extends far onto the sides of the neck. The females are similar but do not have a purple crown or gorget.
Here in my Tucson yard, Costa's Hummingbirds are regular early spring visitors to my hummingbird feeders and blooming garden plants like these Parry's Beardtongue (Penstemon parryi).
These small hummingbirds somehow manage to sneak in and get some nectar even though they are often bullied and driven away by the larger and more aggressive male Anna's Hummingbirds (Calypte anna) and Broad-billed Hummingbirds (Cynanthus latirostris) that are also common visitors to my Tucson yard.
Costa's Hummingbirds come here in the springtime in order to breed. The males and females do not pair up to raise their young, and the showy males' only part in reproduction is to attract and mate with the females. During the breeding season, the males use large, looping aerial displays to attract females. Male Costa's Hummingbirds will call to the females just as they dive during their aerial displays, and their distinctive high-pitched "Zee-ee" calls with their curious Doppler effect are a common sound of spring here in the Sonoran Desert.