the field sparrow (spizella pusilla) is a small new world sparrow in the family emberizidae .
it is about 140 mm (6 in) long and weighs about 12.5 g (0.4 oz) .
the head is grey with a rust-coloured crown , white eye-ring and pink bill .
the upper parts are brown streaked with black and buff , the breast is buff , the belly is white and the tail is forked .
there are two different colour morphs , one being greyer and the other more rufous .
the field sparrow is distributed across eastern canada and the eastern united states , with northern populations migrating southwards to southern united states and mexico in the fall .
the typical habitat of this bird is bushy country with shrubs and grassland .
the nest is a cup-shaped construction built on the ground and hidden beneath a bush or clump of grass .
the birds forage on the ground or in low vegetation , feeding mainly on seeds and insects .
the population is thought to be in slow decline , but it is a common species with a wide range , and the international union for conservation of nature has assessed its conservation status as being of "least concern" .
adults have brown upperparts , a buffy breast , a white belly , two whitish wing bars and a dark-brown forked tail .
they have a grey face , a rusty crown , a white eye ring and a pink bill .
they have rusty markings behind the eye .
there are grey and rufous colour variants .
their breeding habitat is brushy , shrubby fields across eastern north america .
the nest is an open cup on the ground under a clump of grass or in a small thicket .
these birds are permanent residents in the southern parts of their range .
northern birds migrate to the southern united states and mexico .
these birds forage on the ground or in low vegetation , mainly eating insects and seeds .
they may feed in small flocks outside the nesting season .
the male sings from a higher perch , such as a shrub or fencepost , which indicates his ownership of the nesting territory .
the song is a series of sad whistles ending in a trill , often compared to the accelerating sound of a bouncing ball .
this bird's numbers expanded as settlers cleared forests in eastern north america , but may have declined in more recent times .
despite this , it is a common species with a wide range , and the international union for conservation of nature has assessed its conservation status as being of "least concern" .
