Breeding plumage birds have conspicuous pink bills and black on the crown, face, throat and upper breast, contrasting with grey on the sides of the head and neck.

Non-breeding adults are more buffy than grey and brown, with reduced or absent black markings and often have whitish scalloping on the head and throat.

Migrating sparrows may be attracted to marsh elder (Iva annua) and giant ragweed (Ambrosia trifida).

Primary in the diet (66% of stomach contents of breeding birds) are seeds, largely of Carex sedges, grasses and Scirpus bulrush.

[7] Also important in the breeding season diet are fruits, largely black crowberry (Empetrum nigrum), mountain bearberry (Arctostaphylos alpina) and various Vaccinium species.

[6] The principal preferred animal prey includes beetles, flies, bees, ants, moths, butterflies, spiders, cicadas, aphids and leafhoppers.

In winter flocks, Harris's sparrows maintain linear dominance hierarchies that determine access to food and roost sites.

"Jump fights" between males occasionally occur, consisting of birds facing off, then leaping at each other, pecking, clawing and beating each other with wings.

If first winter birds have their feathers dyed black, creating an artificially large bib, they rise in the dominance hierarchy past females and other young males.

From three to five eggs are laid, being variably greenish or greyish in colour with differing degrees of small reddish-brown spot.

The first nest ever found was discovered 1931 in Churchill, Manitoba by ornithologist George M. Sutton, 91 years after the species was initially described.

Canada jays (Perisoreus canadensis), northern shrikes (Lanius excubitor) and merlins (Falco columbarius) can be a serious predators at the nest (including both nestlings and adults).

[6] Shrikes, sharp-shinned hawks (Accipiter striatus) and great horned owls (Bubo virginianus) are known predators of wintering Harris's sparrows.

[5] As an anti-predator adaptation, Harris's sparrows fly up into trees when startled by other animals, usually issuing an alarm call in the process (weenk).

The boreal forest, beyond heavy logging, has been adversely affected by increased wildfire and declining soil quality, both of which are likely correlated to global climate change.