White-necked Jacobin

The white-necked jacobin is 11 to 12 cm (4.3 to 4.7 in) long. Males weigh 7.4 to 9 g (0.26 to 0.32 oz) and females 6 to 9.2 g (0.21 to 0.32 oz). The male is unmistakable with its dark blue head and chest and white belly and tail; the tail feathers have black tips. A white band on the nape separates the blue head from the bright green back and long uppertail coverts. Females are highly variable, and may resemble adult or immature males. The majority of females have green upperparts, a blue-green throat and breast with white "scales", a white belly, and a mostly green tail with a blue end. Immature males vary from female-like, but with more white in the tail, to male-like with more black there. Immature females also vary but usually have less white in the tail and are somewhat bronzy on the throat and chest.