Date of Award
Master of Science in Zoology
Northern Harriers (Circus cyaneus) have experienced serious population declines throughout their breeding range in North America. In the northeastern United States, destruction and degradation of wetland habitats and the reforestation of open lands are the primary factors responsible for their decline. The breeding biology and hunting habitat selection and behavior of harriers in Coos County, New Hampshire, were studied in 1984 and 1985 to provide baseline data on this population for management purposes.
In Coos County, incubation and egg-laying begins in mid-May, the nestling period ranges from late June to early August, and the young fledge from the end of July to mid-August. Nesting season range sizes of females varied from 1.42 to 4.0 km 2. Data on the range sizes of males were incomplete. Harriers nested in old fields and shrub wetlands, in vegetation composed primarily of meadowsweet (Spiraea latifolia) and red-osier dogwood (Cornus stolonifera). The density of breeding birds in 1984 and 1985 ranged from 1 female per 5.0 to 6.7 km 2. Mean fledgling production for the two-year period ranged from 2.6 to 2.7 young per successful nest.
Harriers were observed hunting in hayfields, edges, shrub habitats and forests. Males preferred hayfields over other habitats; females did not show a preference for any particular habitat. Hunting behaviors were observed which have not been reported in the literature, such as diving between trees, circling, and dipping flight. These behaviors were used by both males and females. Males spent more time using transect behavior than other flight types; females showed a preference for transect, circling and border following. Flight altitude was also determined for hunting harriers. Males exhibited a preference for lower flight altitudes; female appeared to spend slightly more time using higher flight altitudes.
Small mammal populations were sampled by live-trapping in several habitat types in 1985. Capture success was 1.5% for five fields. Small mammal abundance during 1985 appeared low in the habitats sampled. Pellets and prey remains were collected from four nests in 1985. On a qualitative basis, small mammals (subfamily Microtinae) were the most important prey item, with small- and medium-sized birds second.
A management plan for harriers in Coos County would be difficult to implement because most land is privately owned. Landowner agreements may provide some protection to nesting birds. In other parts of New England and the Northeast, suitable breeding habitat should be surveyed for breeding harriers. Where possible, areas which support breeding populations should be protected from development.
Serrentino, Patricia, "The Breeding Ecology and Behavior of Northern Harriers in Coos County, New Hampshire" (1987). Open Access Master's Theses. Paper 970.