Breeding

Yellow-headed Parrots nest in tree cavities from 6-15 m above the ground (Juniper and Parr 1998). They have been reported to nest in cavities of large mature trees of Astronium graveolens, Bursera arborea, Ebenopsis ebano, and Sideroxylon palmeri (Renton 2002).

In southeastern coastal Tamaulipas, Mexico, Yellow-headed Parrots nested in both woodlots and pastures and nest cavities were detected more frequently in pastures, although detection biases could not be disproved. They nested in cavities in coma (Bumelia laetevirens) (n = 11), ebony (Ebenopsis ebano) (n = 5), and strangler fig (Ficus cotinifolia) (n = 2), the three dominant tree species on this site. The mean (range) measurements of these nest trees and cavities (n = 17) are as follows: diameter of tree at breast height 80 cm (42-234 cm); height above ground of the cavity entrance 559 cm (280-1150 cm); width of entrance 11 cm (6-19 cm); length of entrance 20 cm (10-59 cm); depth of cavity 140 cm (51-260 cm); and internal diameter of cavity 27 cm (14-52 cm) (Enkerlin-Hoeflich 1995).

In Belize these parrots favor Pinus trees for nest sites (Juniper and Parr 1998). They nest in palm savanna and mangrove forest in Guatemala; they were most abundant in seasonally flooded, open palm savanna dominated by Caribbean royal palm (Roystonea oleracea) and with an understory of tall grass (Eisermann 2003). Most nest cavities were located in snags of royal palm, but some were found in other tree trunks with suitable cavities, such as Salix species and old red mangroves (Rhizophora mangle). Nest cavities were as high as 20 m above ground level.

Yellow-headed Parrots breed from February to May in the south, and until June in the north (e.g. Tamaulipas) (Juniper and Parr 1998). The reproductive period (when nestlings were in the cavity) was in April in Guatemala, with juveniles fledged by May and June (Eisermann 2003). He considered that this population of Yellow-headed Parrots (A. o. "guatemalensis") was exhibiting low reproductive success because 60 adults had been recorded before the breeding season, and only a total of 68 individuals after fledging.

Clutch size is usually 2-3 (Juniper and Parr 1998); in Tamaulipas, mean clutch size was 2.6 (range 2-3; n = 7) (Enkerlin-Hoeflich 1995). Although the sample size was too small for Yellow-headed Parrots in Tamaulipas, Enkerlin-Hoeflich (1995) documented that the sympatric Red-crowned Parrot (Amazonas veridiginalis) hatched asynchronously, with approximately 48 hours between successive eggs, n = 7). It seems likely that this is similar in Yellow-headed Parrots, given that the female initiates incubation with the first egg.

Pairs tend to vocalize for long periods near the nest cavity but rarely approach the nest tree, especially if they perceive the presence of an observer. Unlike some other sympatric Amazona, observers were not able to detect any characteristic calls used by adults when exiting the nest cavity (Enkerlin-Hoeflich 1995).

In Tamaulipas nesting started on approximately the same date and varied little by year; mean clutch initiation days in 1992, 1993, and 1994 were within 6 days which coincided with the last week of March and first week of April (mean clutch initiation date pooled across years was 31 March; n = 6). Yellow-headed Parrots initiated clutches from mid-March to mid-April. The captive parrot literature considers incubation to take 28 days. Females initiated incubation with the first egg, and stayed on the nest nearly continuously except for short interruptions. On average (n = 3) the female stopped brooding 12 days (range 10-14) after the first chick hatched.

Mean adult daily feeding visits to nest was 2.18 (range 0-3); one visit was usually an hour before sunrise, and a second one and a half hours before sunset. Pairs showed a distinctive routine in direction, demeanor and time of arrival at nests; mean arrival times and afternoon activity periods for Yellow-headed Parrots were 0650 hours (n = 12) and 1733 hours (n = 15) (Enkerlin-Hoeflich 1995).

In response to the arrival of the male, the female sometimes came out of the cavity promptly, but more often took a long time to exit the cavity. Feeding of the female by the male occurred at distances of 10 to more than 100 m from the nest tree. Females frequently defecated in the first seconds of flight (Enkerlin-Hoeflich 1995).

Mean age at fledging (n = 2) was 57 days. A few days before fledging parents often skipped feeding sessions. Adults would vocalize softly near the cavity entrance and the nestlings would crowd at the opening. At times, after some begging calls, adults would feed the young at the entrance or enter the cavity to feed them there (Enkerlin-Hoeflich 1995).

The predominant category of reproductive failure in Tamaulipas was "nest failure/abandonment"; one of the failed nests was due to unhatched eggs (either infertile or embryonic mortality). Enkerlin-Hoeflich (1995) speculated that his study may have underestimated the cases of predation as a cause of nest failure; he noted that if he had added suspected cases of predation to the category, total losses to predation could have been as high as 30% of all chicks and eggs. There was also a high proportion of non-reproductive pairs; in 1992 5 of 7 pairs did not nest and in 1993 6 of 10 did not nest, which he noted meant failed before incubation (Enkerlin-Hoeflich 1995).

Although these data appear to be pooled across the three Amazona species studied (Enkerlin-Hoeflich 1995), there was evidence of the reuse of nest cavities between years (15-35%); 83-88% of the reused cavities had successfully fledged young the previous year. In contrast, only 20-28% of the nests that were unused in a subsequent year had fledged young.