Henslow's sparrow

In New Jersey the Henslow’s sparrow is a rare migrant. Fall migrants may occur from October to early December and spring migrants from mid-April to mid-May.

Open fallow and grassy fields, sedge meadows, and pastures are home to breeding and migrating Henslow’s sparrows. Henslow’s sparrows prefer habitats of high, dense vegetation and a thick layer of ground litter. Unmowed agricultural fields or ungrazed pastures are preferred for their thick cover. Henslow’s sparrows tolerate a variety of moisture regimes and will occupy wet and dry habitats. Large open areas are preferred; fields of 25 to 250 acres may be needed to support breeding populations.

The diet of the Henslow’s sparrow is comprised of invertebrates and seeds. The bird consumes crickets, grasshoppers, and other invertebrates. In addition, these sparrows forage on seeds of grass, sedge, and weeds. Young sparrows are primarily fed insects.

During late April and May, Henslow’s sparrows arrive on their breeding grounds. Singing males perch atop tall forbs to define their territory boundaries and advertise for mates. Often, only a single pair will nest at one site. However, this species may nest semi-colonially if sufficient habitat exists. Henslow’s sparrow territories average 102 acres per pair.

The female constructs a cup nest of grasses, and dead leaves lined with fine grasses and hair. The nest is located either at the base of a clump of grass on the ground or within vegetation above the ground. Overhanging grasses conceal the nest.

In late May or early June, the female lays a clutch of three to five pale eggs with reddish brown spotting. Incubation is conducted solely by the female for 10 to 11 days. Both adults care for the young, which fledge at 9 to 10 days of age. Henslow’s sparrows may raise two broods per season, provided that sufficient time and food resources exist.

Habitat loss and fragmentation have contributed to the decline of Henslow’s sparrows and continue to limit breeding populations. Vegetative succession, development, the draining and filling of wetlands, and the invasion of phragmites have reduced the availability and quality of breeding habitat. Few agricultural areas or pastures remain idle, limiting nesting habitat. Intensive mowing and overgrazing can reduce the ground cover required for nesting. In addition, early mowing can destroy nests, eggs, and young.

Grasslands should be actively managed to provide breeding habitat for Henslow’s sparrows and other grassland birds. Active management, through mowing or grazing, is necessary to maintain an early successional stage and prevent the eventual transition to forest. Mowing should not be conducted during the breeding season, cattle should be present prior to the birds’ arrival so that they may select an alternative breeding site. Each year some pasture fields should be allowed to go fallow while others are actively grazed. These fallow fields will provide future feeding grounds for cattle while offering breeding habitat to grassland birds in the interim.

Cooperative efforts and incentive programs must be implemented to provide habitat for grassland birds and preserve open space and farmland in New Jersey. If available, large tracts of suitable habitat should be acquired as public land, rather than be lost to development.