Yucatan jay

The Yucatan jay (Cyanocorax yucatanicus) is a species of bird in the family Corvidae, the crows and their allies. It is native to the Yucatán Peninsula where its habitats are subtropical or tropical dry forest, plantations and cleared areas at altitudes up to 250 m (820 ft). Adults are about 30 cm (12 in) long, black, with blue wings, mantle, and tail, black bills, yellow eye rings and legs. Immature birds have yellow bills. This is a common species of jay with a wide range and the International Union for Conservation of Nature has rated its conservation status as being of "least concern".

The adult Yucatan jay has a black head, nape, and underparts. The back, wings, and tail are a sharp blue colour. It has black irises, black eye rings, a black beak, and yellow legs and feet. There is no difference between the sexes.

The Yucatan jay has several distinct plumages throughout its life cycle. Juvenile Yucatan jays have a white head, body, and tail tip. The back is a soft blue, and the wings and tail are a soft grey, aside from the outer retrices which are white. The beak, legs, and feet are a soft yellow tinged with pink. The inside of the beak is white and the irises are dark brown. These features start to fade a few weeks after they fledge. At this point, the legs, feet, beak, and eye ring become more distinctly yellow. The prebasic moult also begins at this point, with the white head and body feathers being replaced with black ones.

During the first year, the Yucatan jay has an entirely black head and body. The legs, feet, and eye rings remain yellow. The inside of the beak remains white, but takes on a glaucous tone. The wings become bluer, and the tail becomes a purplish blue colour. The back and tail turn a deeper grey, and the retrices are tipped with white. In June or August, the bill may start to develop dark patches, while remaining overall yellow. In September, the dark patches expand further.

In its second year, the Yucatan jay's plumage is the same as that of the adult. The beak is still mottled, and by March it is primarily black with only some yellow marks, becoming entirely black within the second year. The legs and feet remain yellow. The eye ring is still distinctive of age, with some black marks appearing on the otherwise yellow flesh. By the third year, this eye ring is almost entirely black. The darkening of the beak and eye ring usually progress at the same rate. The inside of the beak starts to darken at this point as well. Any trace of yellow on both the beak and eye rings are gone by January of the third year. In the fourth year and later, the Yucatan jay has reached its full adult plumage.

The Yucatan jay is a medium sized jay, averaging 31–33 cm (12–13 in) long. There is some variation in size between the sexes. The average wing length for adults is 141 mm (5.6 in) for males and 139.5 mm (5.49 in) for females, and the average tail length is 142.5 mm (5.61 in) for males and 141.5 mm (5.57 in) for females. Both sexes have an average beak length of 22.5 mm (0.89 in), an average beak depth of 12.7 mm (0.50 in), and average tarsus length of 41 mm (1.6 in), and an average middle toe length of 25 mm (0.98 in). The male is also slightly heavier, weighing 114.4–127.8 g (4.04–4.51 oz) compared to the female who weighs 105.4–121 g (3.72–4.27 oz).

The Yucatan jay is visually unique within its range, with no similar species. Outside of its range, it is similar to the San Blas jay, the purplish-backed jay, and the bushy-crested jay. All three have a yellow iris whereas the Yucatan jay has a black iris, and are a brighter shade of blue on their upperparts.