As a cooperative breeder, this jay normally has groups of fewer than 10 birds working together to help an adult pair raise young.
Nests are within 5 m of the forest edge and about 2-5 m below the forest canopy. They are between 4.3 and 9.1 m above the ground. The nest is a flimsy platform with a shallow cup made of sticks inlaid with some coarse plant fiber. The eggs or nestlings can often be seen from below. In captive birds, the lead male and female appear to build the nest with the helper birds being tolerated or chased off. In the wild, 3 different birds were found to be involved in building a nest found partially built on the 23 of June. By the 30th of June, the nest was complete and an adult was sitting in it for long periods.
The eggs are mottled pale to medium pinkish-buff with reddish-buff speckles. A full clutch consists of 4-6 eggs in the wild nests examined.
Data on incubation of wild birds is lacking. Raitt and Hardy found that it appeared as though 1 bird was responsible for incubation at each nest they watched. However, birds were unmarked and although birds were never observed trading incubation duties, adults look the same. On a few occasions, when the incubating bird was fed it would depart immediately, leaving the nest under the close watch of the other bird. In 1974 Jorge Orejuela collected an incubating female from a nest and in Hardy's captive birds the female did almost all of the incubation.
During incubation, the sitting bird is present 90% of the time and leaves for an average of 5.4 minutes, with 10/22 being less than 3 minutes and only 2 for longer than 10 minutes. Sitting birds are fed about every 45 minutes. Sometimes the incubator begs for food with open gape and fluttering wings. Begging behavior does not increase during incubation. Incubation lasts for 17 days.
Hatching appears to be synchronous and the young are brooded almost continually immediately after they hatch. At least 2 adult black-billed birds participated in brooding at nests observed by Raitt and Hardy, but because they were unmarked individual identity was unknown. Fecal sacs are quickly removed or eaten.
Yucatan Jays have an interesting behavior often seen in the adult attending birds called "nest inspecting," where much time is spent probing the nest above and below, picking and probing with the bill. Raitt and Hardy assumed this to be the attending birds removing the larvae of parasitic flies which parasitize nestlings, as the behavior was not seen before hatching.
Feeding of nestlings is a communal effort and the method of food delivery differs. Sometimes bird bringing food give it directly to nestlings. Other times, they deliver it to an intermediary which feeds the young. There is a lack of data for fledging time.
Nesting success (eggs to fledged young) is about 41%, or 2.1 young fledged per nesting attempt. In total, about 2.7-3.2 young are produced per flock per year due to multiple nesting attempts.
(Raitt and Hardy 1976)