The diet of the pine grosbeak is mainly composed of the seeds and buds of mountain ash (Eucalyptus regnans), box elder (Acer negundo) and ash trees (Fraxinus spp.), as well as the fruits of junipers and spruce (2). Although the pine grosbeak does not truly migrate, it moves through its range in response to food availability (3).
In late May, the female pine grosbeak builds a nest, which is usually between two and four metres from the ground and is well concealed within the dense foliage of the trees. The outer layer of the nest is constructed using conifer twigs, roots and grass stems and is then lined with grass, lichens, feathers and conifer needles (3).
In late May or June (3), the female pine grosbeak lays a clutch of between two and five eggs, which are pale blue with dark brown, purple and black dots and markings (2) (3) (6). The female then incubates the eggs for 13 to 14 days and is fed by her mate during this period (3) (6).
When the eggs have hatched, the male and female pine grosbeak both feed the hatchlings, carrying the food in a pouch on the floor of their mouths (2) (3). This pouch, known as the ‘buccal pouch’, is only developed in breeding adults (2). The diet of nestling pine grosbeaks is mostly insect matter (2) (3). Only one brood is raised per season (6).
In winter, the pine grosbeak is gregarious and can be found in large flocks (2) (3). However, during the breeding season it is very territorial (2) (3), and the male defends its territory by vocalising (3).