The Breeding Ecology and Behavior of Northern Harriers in Coos County, New Hampshire

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 midMay, the nestling period ranges from late June to early August, and the young fledge from the end of July to midAugust. Nesting season range sizes of females varied from 2 1.42 to 4.0 km . 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 bet~een trees, circling, and dipping flight.
These beha v iors 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.

INTRODUCTION
Recent studies of Northern Harrier breeding biology have been conducted in North and South Dakota (Duebbert and Lokemoen 1977), New Jersey (Dunne 1984), Missouri (Toland 1985), Massachusetts (Holt and Melvin 1986;Tate and Melvin 1987) and New York (England, in prep.), where harriers have experienced serious population declines. In New Hampshire, between 1969 and 1979, only seven breeding season records for harriers were reported, most from the northern parts of the state (Smith 1979 Ratcliffe (1977), Newton (1979) and Olendorff et al. (1982) stressed that the first phase of raptor management involves collecting data on population parameters such as density, reproductive success, nest site and hunting habitat selection, prey base and other factors. The objective of this chapter is to provide baseline data on the breeding chronology, nest ecology , size of nesting season ranges, breeding density and fledgling production of harriers in Coos County.

STUDY AREA
My study was conducted in Coos County, New Hampshire, from May to August in 1984 and1985. Coos  County contains three major landforms: rolling hills or plateaus, narrow river valleys , and steep mountains. The higher elevations average between 690 and 750 meters above sea level (Williams et al. 1943). and paper birch (~ papyrifera) and aspen (Populus spp.) (Westveld et al. 1956;Frieswyk and Malley 1985).
Coos County has long cold winters and short cool summers. Because of the differences in elevation in the region, local weather conditions can vary greatly (Williams et al. 1943;Baldwin 1973).

Breeding Chronology
The length and onset of each breeding stage was determined using two methods: back-dating from fledging periods, and by observing the behaviors characteristic of each breeding stage. Both of these methods were used to prevent disturbance to nesting birds. Hamerstrom (1969) reported that females were prone to nest abandonment if disturbed during incubation. Because harriers are listed as a threatened species in New Hampshire, I was unable to visit nests until the young had fledged.
Incubation and hatching periods were estimated by observing the behavior of pairs at nests during May, June and July. During incubation, and continuing into approximately the middle of the nestling stage, the female rarely leaves the nest (Watson 1977). At this time the male supplies most of the food to the female and young (Hecht 1951;Schipper 1973;Picozzi 1978Picozzi , 1980. The male provides the f ema 1 e with food by dropping prey to her in mid-air, either near or above the nest site. After the eggs hatch, the number of prey exchanges between the male and the female increases. As the young develop further, the female leaves the nest more frequently to hunt (Hecht 1951;Schipper 1973).
Hatching dates can be estimated by noting an increase in the number of prey exchanges between the male and female, and an increase in the number of hunting trips by the female.
Newly-fledged harriers remain near their nests for several weeks (Hamerstrom 1969;Watson 1977). I noted the presence of juvenile harriers during nest observations from the end of July and into August. I defined fledge as occurring when the young birds were capable of short flights.

Nesting Season Range Size
I defined nesting season range as the area which encompassed all the activities of a pair of breeding harriers, including their hunting range and the area surrounding the nest site (Craighead and Craighead 1956, p. 247;Newton 1979, p. 40).
The sizes of harrier nesting season ranges were determined by observing nest sites from several observation points within a range. I chose points which afforded the widest view of the area surrounding the nest, allowing me to follow birds over fairly large distances. When possible, birds were followed by automobile or on foot when they left the nest to hunt. Because harriers were not marked, I did not include sightings of individuals unless I was positive of their identity (e.g., birds were followed as they left or returned to their nest).
I used the method outlined by Craighead and Craighead (1956)

Nest Ecology
Nest sites were located by watching for food transfers between male and female harriers (Hamerstrom 1969)  Fledgling production was determined by counting the number of fledglings observed at each successful nest.
Because it was not possible to visit nest sites before fledge occurred, the above method was used to determine the 9 number of fledglings produced per nest.
Juvenile harriers remain near nest sites for approximately one to three weeks after fledging (Hamerstrom 1969;Watson 1977).

RESULTS
Tables 1 and 2 contain a list of localities within th e study area where either fledglings were observed and/ or breeding behavior was seen during 1984 and 1985. The table also contains sites where breeding behavior was seen but nests apparently were abandoned for unknown reasons.
Breeding behavior refers to all or one of the following, occurring over potential breeding habitat: 1) a prey exchange between the male and female, 2) the male and female flying together over suitable breeding habitat, and 3) defensive behavior by a bird toward avian or human intruders.

Breeding Chronology
The data collecte d from six nests were used to determine the breeding chronology of harriers within the study area, including: 1984, DP and FH;1985 I used a range of 29 to 39 days to estimate the time period for both the egg-laying and incubation stages (Brown and Amadon 1968). Eggs are laid at two-day interva ls (Ham e rstrom 1969) . At the study area, egg laying and incubation occurred from approximatel y mid-May , through   I  I   I  I   I   I   I I I I I I I I I I I I I June, and into July. Because sightings of females were rare during the month of June, I assumed that incubation was in progress.
During the second and third week of July, the number of prey exchanges from males to females increased from one per observation period (approximately six hours) to five or six per observation period in 1984. At the same time the number of sightings of hunting females increased and I assumed that the young at the DP-84 and FH-84 nests had hatched between the end of June and the beginning of July. Hammond and Henry (1949) report that hatch takes place over a period of three to eight days.  Urner (1925), Breckenridge (1935) and Hamerstrom (1969

Nesting Season Range Size
I e stimated th e siz es of n e sting season ranges for fiv e f e mal e s: DP andFH in 1984, andDP, FH andMM in 1985 (

Nest Ecology
Although no nests were found in 1984, the general location of three (DP, FH, GB,   In 1985 the mean number of fledglings per successful nest was 2.6 (N=5), and for all nests was 1.9 (N=7).

Breeding Chronology
From the data collected in 1984 and 1985, I estimated that egg laying occurred from mid-May to early June.
Incubation took place from early June to the beginning of July.
Hatch occurred from approximately the last week in June and into mid-July, and the young fledged from the end of July until mid-August.
These calculations are approximations because nests could not be visited until the young had fledged. In addition, differences between years and among nests would be expected because of weather conditions and variation among birds. Egg-laying may b e delayed by cool weather in the spring (Watson 1977). Both Hammond and Henry (1949) and Watson (1977)

Nesting Season Range Size
The sizes of female nesting season ranges in Coos County were similar to those reported in previous studies.
In Minnesota, the ranges of two harrier pairs were approximately 2.6 km 2 (Breckenridge 1935), and in Michigan the ranges for 11 pairs varied from 1.0 to 5.6 km 2 (Craighead and Craighead 1956).
In the Netherlands, Schipper (1977) separated males from females when determining range sizes for the Hen Harrier, ~ ~ cyaneus.
He reported that female range size varied from 0.1 to 5.4 km 2 ; range sizes for males were larger. Hecht (1951), MacDonald (1970), Schipper (1977) and Picozzi (1978) stated that females hunted closer to the nest than males; the same phenomenon occurred in Coos County. Although males were observed hunting near nests, the number of observations for females was much higher.
The estimates of nesting season range size for female harriers are conservative because the terrain was hilly and it was easy to lose sight of hunting birds, and birds were not marked. I conclude that breeding females in Coos County have minimum range sizes of 1.42 to 4.16 km 2 .

Nest Ecology
Northern Harriers nest in a wide variety of habitats and plant associations throughout North America: in stands of reeds and shrubs in salt and freshwater marshes (Hecht 1951;Dunne 1985), in raspberry bushes in shrubby uplands (Toland 1985) and in sphagnum bogs among shrubs and small trees (Bent 1937). Of the four nests discovered in 1985, all were located in dense clumps of red-osier dogwood or meadowsweet, in old fields or shrub wetlands. Harriers at the study area appeared to prefer plant associations similar to those reported by Hamerstrom and Kopeny (1981) in Wisconsin and Toland (1985) in Missouri, i.e., dense patches of shrubs and grasses. The nests were well-hidden from all sides except above, as described in other studies (Duebbert and Lokemoen 1977;Hamerstrom and Kopeny 1981;Toland 1985). Hamerstrom
The density of breeding harriers in Coos County varied from 5.0 to 6.7 km 2 per female ( I conclude that the density and fledgling production   Ne sts were f ound in shrub wetlands and old f i e lds .
All were located in dense patches of shrubs, either meadowsweet or red-osier dogwood. Nests were composed of dead grasses and twigs.
The density of breeding harriers in Coos County varied from 5.0 to 6.7 km 2 per female, and fledgling production range d from 2.6 to 2.7 per succe ssful nest, and from 1.
Many studies have attempted to correlate habitat selection with several variables, such as vegetation cover, prey availability and abundance, morphology of the raptor species, and foraging behavior (Marquiss and Newton 1981;Bechard 1982;Kenward 1982;Janes 1985;Temeles 1986;Collopy and Bildstein 1987;and others).
Although habitat selection in wintering Circus cyaneus has been studied (Schipper et al. 1975;Bildstein 1978;Marquiss 1980;Temeles 1986;Collopy and Bildstein 1987), only Schipper (1973Schipper ( , 1977 and Martin (1987)  Because harriers are assigned threatened status throughout New England~ the data collected on hunting habitat selection can be used for planning management strategies for this raptor.

Hunting Habitat Selection and Hunting Behavior
Hunting habitat selection and behavior were observed near harrier nest sites. I also collected data on hunting birds whose breeding status was unknown. I used focal animal sampling (Altmann 1974) (Robinson and Holmes 1982;Beissinger 1983).
At each observation point, at one-hour intervals, I recorded air temperature, wind speed and direction, relative humidity, cloud cover and precipitation.
Hunting habitats were classified on the basis of structural characteristics of the vegetation. Table 1 contains the habitat types observed at the study area.
Habitats which were used by harriers only once were omitted. General habitat types were hayfields, forests, edge habitats, shrub wetlands, logged areas, pastures and old fields. Habitats with similiar vegetati on structure (e.g., cut vs uncut hayfields) were identified as subdivisions within a particular general habitat type. The flight altitude of hunting harriers was estimated by sight. Because of the irregular topography (many hills and valleys) and the variable heights of different vegetation types, I classified flight altitude into the following ranges: 1) low altitude: the bird flying 1 m or less above the ground; 2) medium altitude: the bird flying from 1 to 9 m above the ground; 3) tree-top altitude: the bird flying from 9 to 2 5 m above the ground, depending on the tree species; 4) above the trees: the bird fl y ing above the tallest trees in the habitat (approximately 12 m and above).
Vegetation heights were determined to provide estimates of the flight altitude of hunting harriers.  observations were recorded on tape and used for anal y sis.
Eight different hunting behaviors were recognized in this study; transect, quartering, border following, hover flying, ground hunting, circling, diving bet~een trees and dipping flight. Transect, quartering, border following and hover flying were observed in the harri e rs studied by Bildstein (1978, p. 179). My definition of ground hunting in harriers was modified from Craighead and Craighead (1956, p. 53).
During a hunting bout, harriers landed on the ground for periods ranging from several seconds to several minutes. I assumed that an individual landing on the ground without capturing prey during a hunting bout, and remaining there for more than ten seconds, was ground hunting (scanning the ground for prey).
Circling, diving bet~een trees and dipping flight were additional hunting behaviors I observed.
Circling flight was defined as flight over a small area in tight circles.
Diving between trees was defined as flying between trees, at varying heights from the ground. Dives toward the trees or the ground frequently occurred. Dipping flight was similar to transect flight in that the bird flew in a fairly straight line; however, flight altitude varied.
For data analyses I interpreted harrier hunting behaviors conservatively, to avoid including those that were associated with breeding or were merely movements of birds to other areas. I omitted the following behaviors: 1) circling of males or females over nest sites, 2) soaring flight, and 3) observations of harriers carrying prey.

Mammal Abundance
To determine the abundance of small mammals at the study area, rodents were live-trapped in six fields from Before dissection, pellets were air-dried and prey remains were dried in an oven when neccessary. Each pellet was then dry-dissected and the contents recorded.
In addition to animal remains, the presence of insects and vegetation was also noted. Dissected pellets and prey remains were examined under a dissecting microscope and compared with museum specimens from the University of Rhode Island and University of Maine mammal and bird collections.
Mammal skulls were identified with the aid of keys (Glass 1951;Hall 1981) and museum specimens.
Pellets were analyzed according to the method recommended by Errington (1932). Fragmented pellets from one area, specific nest or ground site were dissected together.
The frequency of each item (animal) in the pellets was recorded (Balfour and MacDonald 1970).
Quantitative data were recorded only if a skull or par t of the skull was found intact. Remains were id entified to species whenever possible . Other habitats were also surveyed for hunting harriers, and were included in the data analysis under unknown birds (e.g., birds whose breeding status was unknown).

Habitat Selection
To determine whether males or females preferred one habitat over another, I performed a Friedman's test (Conover 1980)    * Denotes significant differences between the rank sums a t the p < .05 level .
Hill (FH-84) pairs were used for this analysis because the most complete data were collected from these pairs.
Because males and females of each pair did not exhibit significant differences in their use of the habitats around nests when compared with each other (Chi square test, p < .05), the data from both sexes were analyzed together.
I found highly significant differences between the  Tables 5 and 7. For the DP pair (Table 5), no significant difference in the use of old fields, pastures, and edges based on their availability was found. Forests were used significantly less than expected and hayfields significantly more than expected. The FH pair (Table 7) did not use hayfield any more or less than expected.

Hunting Behavior
The Friedman test was used to determine whether males or females preferred a particular hunting behavior. These analyses were conducted on duration data. Female use of circling, diving bet~een trees, transect, ground hunt, hover fl_y, dipping and border following was tested.
Quartering flight was not included because females were never observed using this behavior. The results of the pairwise comparison (Table 9) showed that females spent significantly more time using border following and circling behaviors than ground hunting; transect flight was used for significantly longer periods than either diving bet~een trees or ground hunting (Friedman's pairwise test, p < • 0 5 ) ) • Males were tested for differences in use between the same behaviors as females with two exceptions; males were never observed using ground hunting behavior but did use quartering behavior.
The results of the pairwise    that; 1) significantly more time was spent using medium altitude than medium / tree-top; 2) significantly more time was spent using tree-top altitude than low / medium,  * De note s sig nificant d i ff e r e nc e be tw ee n the rank sums at the p < .0 5 l eve l.
Ab b rev i a tions g i ve n i n Table 9 .  * Denotes significant difference between the rank sums at the p < .05 l eve l.

Explanation of abbreviations:
Med : medium height Tree: tree-top Ab. Tr.: above -tree L/ M: low/ medium M/ T: medium/ tree-top T/A: tree-top/above-tree medium/tree-top, and tree-top/above-tree; and ) that significantly more time was spent using ab ove -tree than medium/tree-top (Friedman's pairwise test, p < .05).
Males did not spend equal amounts of t im e in each flight altitude category (Table 12). Medium/t re e-top altitude was omitted from the analysis because of the low number of observations for this category. The r esults of the pair-wise comparison showed that males spert significantly more time using low altitude fli cht than above-tree and tree-top/above-tree altitud e s (~iedman's pair-wise test, p < .05).
To determine whether males and female s se iect flight altitude categories differently, a Wilcoxon tw -sample test was performed, using duration data from al l categories except medium/tree-top (this category was o mit ted because of the lack of data for males and females). Fenales spent significantly more time than males using above-: ree altitude, and males spent significantly more t i ne using low/medium altitude than females (p < .05). The amount of time birds spent using each flight altitude is presented in Appendix F3.

Pellet Analysis
The results of the analysis of the prey remains and pellets collected at the four nest sites in 1985 (DP, MM, FH, AL) are contained in Appendices Hl-H4. Data from these Foss, Bushwack, Shrew and Access were analyzed for vegetation cover and species density and frequency (Appendix C).

Habitat Selection
Intersexual differences in the hunting habitat selection of f..:_ cyaneus has been observed in both breeding and non-breeding populations in North America (Bildstein 1978;Temeles 1986;Martin 1987) and Europe (Schipper et ~-1975;Schipper 1977). The factors responsible for these differences in habitat use were related to the following: utilization of different prey species by each sex during the breeding and non-breeding season (Schipper 1973;Bildstein 1978;Picozzi 1978Picozzi , 1980; smaller nesting season ranges of females compared to males, resulting in female preference for the habitats surrounding nest sites (Schipper 1977;Martin 1987); and female exclusion of males from preferred hunting habitats during the winter (Temeles 1986).
To evaluate prey selection, hunting behavior and habitat selection in raptors, the difference in size between the sexes should be considered. In most raptor species the female is larger than the male, a phenomenon referred to as reversed sexual size dimorphism. The degree of the size dimorphism increases with th e amount of fastmoving prey species present in the diet. As a result, carrion feeders exhibit little size dimorphism, and raptors belonging to the genus Accipiter, which feed almost entirely on birds, are the most strongly dimorphic (Newton 1979).

The harriers, including both the Northern and Hen
Harriers, are also strongly dimorphic. The male Northern Harrier averages 367 grams, and the female 530 grams (Hamerstrom 1986). The male Hen Harrier averages 340 grams and the female 500 grams (Schipper 1973).
Male and female harriers also exhibit differences in wing structure (Nieboer in Bildstein 1978). In ~ cyaneus, the male is considered more agile than the female because males have shorter wings and lower wing-loading ratios (Brown and Amadon 1968;Temeles 1986). Wing-loading is defined as the ratio of body weight to surface area of wings. Shorter wings and lower wing-loading are advantageous for short bursts of flight and increased maneuverability between trees. Males have been found to capture more agile prey than females (songbirds) and use a more "accipi ter-1 ike" f 1 ight style (Schipper et al. 19 7 5;Bildstein 1978). Members of the genus Accipiter feed primarily on avian prey and inhabit woodlands.
In Coos County I did not find significant differences between male and female use of four habitats: hayfield, forest, shrub and edges . When habitat preferen ce within each sex was analyzed, females did not show any preference for a particular habitat. Males spent significantly more time over hayfields than forest, shrub habitats and edges.
In the Netherlands, Schipper (1977) stated that Hen Harriers nested and hunted in coastal dunes and reeds.
Females usually hunted in the habitats adjacent to nest sites. Males also hunted near nests, but were seen more frequently than females in the habitats situated outside of nesting areas (reeds, cultivated fields and grasslands).
In Idaho, Martin (1987)  In two European studies (Schipper 1973(Schipper , 1977Picozzi 1978), breeding males and females selected different prey species. Males usually took lighter prey than females, such as small and medium-sized birds and voles. Females preyed upon a wider range of animals, but were able to take larger prey than males, e.g. grouse, pheasants, and young rabbits. Schipper (1977) found that differences between males and females with respect to habitat selection were related to differences in prey selection. I was unable to collect data on the prey selection of males and females, therefore, the effect of this parameter on the habitat selection of harriers in Coos County is unknown.

The habitat preference of two pairs of harriers in Coos
County, based on the availability of habitat types within their hunting ranges, resulted in both the avoidance and preference of some areas. I found that harriers preferred open habitats, such as hayfields and edges, over forest and shrub. When all male harriers were pooled, they spent significantly more time over hayfields than shrub, forest or edges. Shrub and forest habitats may not have been strongly pref erred because of the dense cover of the vegetation compared to hayfields. The selection of habitats by hunting raptors is often related to vegetation cover and not prey density (Southern and Lowe 1968;Wakeley 1979;Bechard 1982;Martin 1987). In Idaho, Martin (1987) found that male harriers shifted from alfalfa fields, where  (Schipper 1977;Watson 1977;Bildstein 1978). Schipper (1977) infrequently observed males hunting over conifer plantations outside of nest sites. Watson (1977), Because the open habitats within the study area have been reverting to forest and brushy habitats since the early 1900 ' s, it is possible that harriers are being forced to hunt in less-preferred habitats and/or because these habitats were located adjacent to nest sites.

Hunting Behavior and Flight Altitude
Harriers in Coos County exhibited several hunting behaviors which have not been reported in the literatur e , such as circling, diving bet~een trees (DBT) and dipping flight.
In addition, I found that quartering flight was only observed in males, and was infrequently used (1.7 % of all males total hunting time).
Quartering flight has been observed more frequently in females than in males (Schipper 1977;Bildstein 1978; Temel es 1986); males used border folowing (BFL) and transect flight more than females, according to Schipper (1977) and Temeles (1986). In Coos Count y , females exhibited a preference for transect, circling and BFL over other hunting behaviors; males spent more time using transect flight than other flight types. Females spent significantly more time than males using circling flight.
Similarities between both circling and DBT with quartering behavior can be seen. When DBT was observed, the birds often dived toward the ground while "quartering" over trees. Bildstein (1978)  I found that males exhibited a preference for l ow altitude flight, and spent significantl y more time u sing low/ medium flight altitude than females. Females appea r ea to show a slight pre ference for higher flight altitudes than males; they spent more time using medium, tree-top and above-tree height over other flight altitudes, and spent significantly more time than males using above-tree altitude.
In Europe, during the breeding season, male harriers used low flight altitude most frequently (Schipper 1977). Data on female flight altitude selection was not provided. Schipper et al. (1975) and Temeles (1986) Schipper et al. (1975) and Schipper (1977) observed the same response to vegetation height by hunting Hen Harriers in both winter and breeding season studies.
By increasing flight altitude as vegetation height increases, the harrier maintains its field of view into the vegetation.
For hunting harriers, and other raptors, a complex relationship exists among the hunting behavior used, flight altitude, the structure and height of the vegetation, the sex of the bird, prey abundance and vulnerability, and weather conditions (Schipper 1973(Schipper , 1977Schipper et al. 1975;Bildstein 1978;Janes 1985;Collopy and Bildstein 1987). Schipper et al. (1975)  Forested habitats either were not used by harriers or were unavailable (Schipper 1977;Bildstein 1978;Temeles 1986).
Elevations in Ohio ranged from 229 to 335 meters above sea level (Bildstein 1978), and in Coos County, from approximately 270 to 750 meters (Williams et al. 1943).
Vegetation heights in the Netherlands (Schipper 1977) varied from .20 to 2.50 meters. In California, Temeles (1986) does not give the heights of the tallest vegetation, however, the study area was composed primarily of cropland.
Harriers in Coos County may have selected a variety of behaviors and flight altitude combinations to take advantage of the patchy and complex topography at the study area.

Mammal Abundance
Although the various habitats sampled for small mammal abundance appeared able to support high numbers of mammals, only Moose Field, which was trapped along the edges, showed a high trap success. Meadow voles (!i.:_ pennsylvanicus) were not abundant on any of the fields sampled at the study area. Northern Harriers have been found to prey heavily on these voles during the breeding season (Hamerstrom 1969(Hamerstrom , 1979Simmons et al. 1986a.b.). Abandoned fields and other disturbed habitats, with vegetation cover composed primarily of dense grasses or weeds, may support high densities of meadow voles and other small mammals (Craighead and Craighead 1956;Birney et al. 1976;Phelan and Robertson 1978;Baker and Brooks 1981;Hamerstrom 1986).
Other than trapping results, high vole densities may be indicated by the fol lowing; 1) a high number of runways and holes present, 2) frequent piles of scats and / or cut grasses, 3) girdling of trees and shrubs, and 4) frequent sightings of voles when an area is surveyed on foot (Craighead and Craighead 1956;Hamerstrom 1986). Although runways were found in some fields, voles were never observed in them and were rarely seen when investigators were trapping or moving through fields to observe harriers.
Some of the factors which may have accounted for the low number of animals trapped at the study area were that meadow voles were abundant but were reluctant to enter the traps (i.e. were trap-shy) and food was abundant (P. August, pers. comm., 1985); voles were at the low part of a population cycle or decline; and some habitats did not provide enough cover for voles to occur in high densities (Birney~! ~l· (1976).
In Coos County, hunting harriers did not prefer old fields over other habitat types. Hayfields were used significantly more than expected when all males were pooled, and by the Diamond Pond pair. Although small mammal abundance appeared low in both hayfields and old fields, harriers may have found prey more vulnerable in hayfields because cover was not as dense. More data are needed on mammal abundance in old fields and hayfields, in addition to prey selection of harriers in these habitats.

Pellet Analysis
Microtine rodents and small-and medium-sized birds were found with the highest frequency in pellets and as prey remains at nests and ground roosts. The remains of snakes were more difficult to assess with respect to their importance in harrier diets because skeletal remains were rarely found. These results were similar to European and North American studies of harriers where both mammal and bird prey were important in harrier diets (Craighead and Craighead 1956;Schipper 1973;Picozzi 1978Picozzi , 1984Toland 1985). Data from additional nests are needed to adequately assess the prey selection of harriers during the breeding season. Data on prey selection and mammal abundance was limited, but it appeared from pellet analyses that the diet of harriers was varied.

SUMMARY
Microtine rodents and small-and medium-sized birds were most frequently seen in pellets and as prey remains.
CHAPTER THREE:

Introduction
The purpose of this chapter is twofold: to determine the status of the population of Northern Harriers breeding in Coos County, and to discuss management strategies which can be used at the study area and throughout New England.
These subjects will be evaluated by investigating the following: 1) a comparison between the historic and current  (Hamerstrom 1969;Fyfe and Armbruster 1977;Watson 1977;Newton 1979;Grubb et al. 1983;Dunne 1984).

The Historic Distribution of Northern Harriers in New England
The Northern Harrier was a common breeding raptor in New England and other northeastern coastal states in the mid-1800's and early 1900's (Baird et al. 1860(Baird et al. , 1874Bendire 1892;Cory 1899;Hoffman 1910). Forbush (1929) noted that the number of breeding harriers was beginning to decrease in New England during the early 1900's, although the species was still considered fairly common. During the summer months harriers were found in extensive meadows, swampy uplands (Cory 1899; Hoffman 1910), and in salt marshes and river valleys (Forbush 1929 Hampshire in the early 1900's (Smith and Choate 1985) which coincided with the declines in farming (Williams et al. 1943;Russell 1982). After this initial decrease, harrier populations continued to decline because of pesticide poisoning and further reductions in habitat quality and quantity (Smith and Choate 1985).

The Current Status of the Northern Harrier in North Americ~ with Special Reference to New England
According to population assessments in recent years (Arbib 1973;Tate 1981;Evans 1982;Tate and Tate 1982), Northern Harrier populations have declined or are unstable in many parts of North America. The harrier has been on the Blue List (an "early warning" system published by American Birds and used to identify species which have experienced serious, noncyclical population declines) since 197 2. Northern Harrier populations continue to decrease (Tate 1986).
Reports of declines have been received from several parts of the United States and Canada, including the Northeastern Maritime region, the grasslands of the Midwest and West, and the southern part of the West Coast.
In addition to New England, harriers have been placed on lists of special concern in Missouri (Toland 1985) and New York (M. England, Long Island University, pers. comm., 1987), and have experienced serious declines in New Jersey (Dunne 1984) and North and South Dakota (Duebbert and Lokomoen 1977).
Although the factors contributing to the decrease in breeding harriers vary from region to region, habitat destruction throughout their range and the reforestation of open land in New England are considered the most significant (Evans 1982;Dunne 1984;Laughlin and Kibbe 1985;Hamerstrom 1986). Since the mid-1950's, losses of wetlands have increased dramatically because of agricultural expansion, and residential and industrial development (Tiner 1984). In New York, Connecticut and New Jersey, where harrier numbers have declined, losses of ~oastal wetlands are especially significant (Frayer et al. 1983;Niering in Tiner 1984). Inland wetlands are also vulnerable in New England and the Northeast, although coastal wetlands are now protected.
In the Midwest, agricultural development still threatens inland wetlands (Tiner 1984).
In New England, much of the open habitats created by the farming industry since the 1800's have reverted to forest (Williams et ~· 1943;Russell 1982;Frieswyk and Malley 1985;Laughlin and Kibbe 1985). In the midwestern and western United States (Duebbert and Lokomoen 1977;Toland 1985;Hamerstrom 1986), the overgrazing of pastures and conversion of grasslands to crops has destroyed nesting habitat and decreased populations of prey species such as smal 1 mammals.
Pesticide use in Wisconsin in the mid-1960's caused sharp decreases in the number of breeding harriers (Hamerstrom 1969(Hamerstrom , 1979. Increased recreational use of the New Jersey coast was reported by Dunne (1984) to contribute to a decrease in breeding harriers. Human disturbance may also be important in heavily-used areas of the New England coast, such as Rhode Island, Massachusetts and the offshore islands (P. Serrentino, pers. obs.). Arbib (1973)

An Evaluation of the Breeding Biology of the Northern Harrier in Coos County
The density and fledgling production of breeding harriers in Coos County was determined for comparison with data collected on other populations in North America and Europe. The mean number of young fledged for all nests (includes suspected failures and successful nests) was 1.9 to 2.3, and for successful nests only was 2.6 to 2.7, for 1984 and 1985.
The density of breeding harriers ranged from 5.0 to 6. 7 km 2 per female. Although more data are needed, the fledgling production and density of breeding harriers in Coos County does not appear to be signf icantly lower than that reported from studies of harrier populations which were not suffering from severe population declines Cadbury 1975, 1979;Picozzi 1978;Hamerstrom et al. 1985;Simmons et al. 1986a.b.).
Harriers have nested in the same general location at the study area from year to year (Table 1). Because birds were not marked, I could not be sure if the same female or male was involved.

The factors responsible for nest site selection by
Northern Harriers in Coos County are unknown. Data collected in other studies suggest that safety from terrestrial predators (Hamerstrom and Kopeny 1981;Simmons and Smith 1985), the density of prey in nearby areas (Simmons and Smith 1985) and the distribution of suitable nesting habitat (Balfour and Cadbury 1979)

Possible Management Plans for Harriers in Coos County
According to Olendorff and Kochert (1977), the protection of key habitats should be the first step in maintaining a declining or threatened population. Negative impacts to nesting raptors, such as desertion of nests, from human activities should be lessened or stopped compl e tely. Newton (p. 264, 1979)   Early successional stages could be maintained through prescribed burning and grazing, which has been recommended by Duebbert and Lokomoen (1977), Kirsch et al. (1978), and Hamerstrom ( 19 86).
In other regions where harriers breed in disturbed habitats, such as drained marshes and farming areas, these raptors have continued to breed, provided that nesting habitats were plentiful and an adequate prey base was available (Hamerstrom 1979;Hamerstrom et al. 1986;Simmons et al. 1986b (Hamerstrom 1969).
Buffer zones around nest sites have been recommended for the protection of threatened raptor species in other studies (Bednarz and Dinsmore 1981;White and Thurow 1985).
Buffer zones around harrier nests would prevent disturbance from logging activities, off-road vehicle use and other detrimental human activities. Studies on buffer zones for harrier nests have not been published.
Although an arbitrary cut-off zone may be helpful, the response to disturbance by breeding harriers varies individually (Schipper 1973;P. Serrentino , pers. obs.). In Alaska, the buffer zones around raptor nests varied from 3.22 km in diameter for Peregrine Falcons to 0.8 km for Rough-legged Hawks (Olendorff and Kochert 1977). Harriers have bred in agricultural areas in New Brunswick (Simmons et al. 1986b), Michigan (Craighead and Craighead 1956), and the Netherlands (Schipper 1973).
In similar regions throughout New England, harriers either do not breed in high numbers (Tom French, Massachusetts Natural Heritage Program, pers. comm., 1987), or these areas have not been sufficiently surveyed for birds. In upstate New York (M. England, Long Island University, pers. comm., 1987), harriers are uncommon in farming areas.

Harriers may not breed in other farming areas in New
England because of several factors: crops, such as corn, are more frequently grown; hayfields are cut more often; and breeding habitats may be unavailable. Extensive croplands and several hay cuttings may depress populations of small mammals by reducing cover (Birney et al. 1976;Baker and Brooks 1981;Gilmer and Stewart 1983).
Ferruginous hawks in North Dakota (Gilmer and Stewart 1983) maintained the highest nest densities in areas where less than 50 % of the agricultural land was under cultivation.
Harriers are slim, long-tailed and long-legged hawks which often hunt close to the ground, over open habitats.
The male and female harrier are sexually dimorphic with respect to size and color. The female is larger than the male. She is dark brown above and buffy below, whereas the male is pale grey above and white below. Adult and immature birds of both sexes have a distinctive white rump patch.
Immatures are similar in color to the female, but have cinnamon-colored, streaked breasts (Bent 1937;Watson 1977;Terres 1980).
The courtship flight of the Northern Harrier consists of a series of conspicuous, U-shaped dives, which fr eque ntl y occur above the nesting grounds . This display is usually performed by the male only (Breckenridge 1935;Bent 1937;Watson 1977).
Northern Harriers nest on the ground, in a variety of habitats such as salt marshes, sphagnum bogs, shrubdominated swamps and slopes, and wet, grassy hollows (Urner 1925;Bent 1937). Eggs are laid from March to July.
Incubation is performed by the female and takes approximately 31 to 32 days; the young fledge at 30 to 35 days after hatching (Hamerstrom 1969). During the nesting cycle, the female is supplied with food by the male. This is accomplished by a prey exchange, in which the male flies over the nest site and passes prey to the female while both are in mid-air (Breckenridge 1935;Hecht 1951).
The Northern Harrier winters as far north as southern Canada, along the coast of southern New England, and as far south as Cuba. It breeds from Alaska south to California, Texas and Virginia (Heintzelman 1979;Terres 1980).

Methods
The fields were first characterized qualitatively by the amount of woody and grass cover present: old field, early successional stage (plant cover primarily grasses and forbs, little woody vegetation), or late successional stage (grasses and forbs still present, but woody vegetation common). These fields were then sampled to determine if differences among fields occurred with respect to the following parameters: 1) percent cover of grasses, forbs and woody plants less than 1 meter in height, and 2) species composition, relative frequency and relative density of woody plants greater than 1 meter in height.
Old fields were analyzed using the point-centered quarter method (Cottam et al. 1953;Mueller-Dombois and Ellenberg 1974)  The percent cover of grasses, herbaceous forbs and shrubs less than 1 m tall in each field was calculated using the quadrat-charting method. At the same sampling point, a one meter-squared quadrat was placed over the vegetation and the fraction of each type of plant cover estimated.
* Field number in parentheses .
Fields 1, 3 a nd 5 were early successional fields; fields 2, 4 and 6 were late successi onal fields. Fields 1, 2, 4 and 5 were censused for small mamma l abundance (Tabl e 15). no significant differences among any fields from the results of Tukey's test, although the results of the ANOVA indicated a significant difference (p < .05).
It appeared that the differences in woody cover among fields were too close to be detected by Tukey's test.
Importance values or IV's (Cottam and Curtis 1956;Mueller-Dombois and Ellenberg 1974) were calculated for all species of woody plants greater than 1 min height in the six fields sampled by the point-centered quarter method. These values were determined by summing the relative density and relative frequency of each species. Species with the highest IV's in a field were considered the most "important" species, with respect to frequency and density.
The plant species with the highest IV's were fairly similar among fields, regardless of whether the field was labeled early or late successional stage (Table C3)   The data collected on percent cover of vegetation less than 1 m in height suggested that the primary differences between early and late successional fields were in the amount of grass cover present. Although these fields also differed with respect to woody, forb and dead cover, these differences were not related to the successional stage of the field (e.g., early or late successional stage).
For vegetation greater than one meter in height, the species with the highest IV's in both early and late successional fields were often similar, in addition to the number of species present. I conclude that the primary difference between early and late successional fields at the study area was in the amount of grass cover present.  * Th e category of unknown birds repres e nts the minimum number of individuals sampled. Because the birds were not marked, the number of unknown birds is considered an estimate.  Grand Total : 8944 * The category of unkn own b i rds represen t s t he mi nimum number of individuals samp l ed . Because the birds were not marked , t he number of u nknown birds i s con sidered an estima t e .  Grand Total : 9019 * The category of unknown birds represen t s t he minimum number of individuals samp l ed . Because the birds were not marked , the number of unknown birds is considered an estimate .             C. Prey Remains: Young Tamiasciurus hudsonicus, feathers from unidentified birds, feathers from full-grown Common Flicker and Ruffed Grouse (Bonasa umbellus), feathers from young Ruffed Grouse, partial skeleton and feath e rs from small passerine; feet, legs and s y nsacrum from medium-sized passerine, keels and beak from small birds, synsacrum from medium-sized bird, pectoral girdle of small passerine, skull and beak of full-grown Bobolink (Dolichonyx oryzivorus), skin and scal e s from snake .
Note: most fragments contained varying amounts of insect and plant fragments.