Unveiling the nesting secrets of the Urubamba Antpitta, Grallaria occabambae (Aves: Grallariidae)

Overall nest description and the nesting biology of Neotropical bird species are poorly known. The recent split of bird species complexes into multiple independent lineages has exacerbated this lack of knowledge. Hence, we describe the nesting biology of Grallaria occabambae, a recent split in the G. rufula complex from south-eastern Peru. Our research was conducted at the Wayqecha Biological Station in the department of Cusco, Peru. We monitored four nests of G. occabambae between 2823 and 2991 m, on mature forest dominated by Chusquea. The cup nests were located in a shallow cavity in a tree or a tree fern. The eggs were pale blue with small reddish flecks and weighed 6.3 ± 0.4 g. Parental birds averaged 4 ± 0.8 off-bout trips per day, with an average duration of 23.9 ± 16.2 min each across incubation. Nocturnal incubation events occurred from 6.20pm to 6.00am, and we recorded on two nights a nocturnal off-bout from 10.00pm to 12.00pm, during which inner nest temperature dropped to an average of 10.2 ± 2.9°C, differing from the average daytime nest temperatures of 28.9 ± 3.2°C. The nestlings were pinkish to orange with pale black natal down on the crown, nape, neck, thigh, and scapulars. Nestlings grow 7.9 g/day and develop fluffy post-natal down until the 17th–19th day when they start growing primary feathers or more adult-like feathering (before leaving the nest). Our findings suggest that G. occabambae has similar nesting habits to other antpittas, particularly those of the G. rufula complex. We provide the first nesting information on G. occabambae and contribute to our understanding of the ecology and conservation of this poorly known species complex.