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The Prothonotary Warbler (Protonotaria citrea) is the only wood warbler in the eastern United States that nests in cavities. It readily accepts nest boxes in lieu of natural breeding sites and therefore provides an excellent model for tests of ecological factors associated with reproductive success. During 1987, 300 nest boxes were placed along a 30-km transect along the tidal James River in eastern Virginia, and these nest boxes have been monitored every year through 2000. During the 1999 and 2000 breeding seasons, we collected 2910 measurements of nestling mass, and recorded ages of parental females, dates of clutch initiation and hatching, brood sizes, and the number of young that survived to fledging. Multivariate analysis of variance indicates that nestling mass was a significant function of brood size, hatching date, age of the female, and year, even when the effects of all independent variables were considered simultaneously. Growth rate and fledging mass were significantly lower in larger broods. Two- to three-year-old females fledged nestlings with greater mass than one-year-old females and females older than three years. Frequency of handling nestlings was not significantly associated with changes in their mass. Ambient temperature of the study area during the breeding season was significantly colder during 1999 than during 2000. Growth rate, fledging mass, and rate of survival of nestlings to fledging were lower during 1999 than during 2000. Growth of nestling birds was related to a large suite of intrinsic variables, but application of growth data to environmental concerns requires knowledge of both demographic and ecological factors.
Pneumatization of the skull roof and cerebellum region of the occipital bone was studied in 193 skulls of 18 genera and 56 species in the family Parulidae (wood warblers). The grundtypus type of pneumatization, which closes the windows anteriorly in immatures of migratory species, was present in fall migration and was completed on the wintering grounds during December and January. The only genera to show what I call the geospizid type of skull pneumatization were Basileuterus and Phaeothlypis, supporting their treatment as congeners. The geospizid type of skull pneumatization is typical of all species in the Galapagos Finches (Geospizidae). In this type the skull roof closes posteriorly in the parietal bone; large members of the family exhibited midline pneumatization, and smaller members the peripheral type. Genera Setophaga, Myioborus, and Basileuterus retained cerebellar windows for an extended period after skull roof pneumatization had been completed. Basileuterus is set apart from other parulids by four trenchant characters and is considered primitive.
I studied the reproductive ecology of Loggerhead Shrikes (Lanius ludovicianus) in southcentral Florida from 1991 through 1993. Pairs were sedentary and defended territories year-round. Completed nests were found from late December to mid-May. Nesting peaked during mid-March with second and third nestings attempted from late March to late May. Sixty percent of all nests were built in blackberry bushes (Rubus betulifolius), but cabbage palm (Sabal palmetto) and wax myrtle (Myrica cerifera) also were used frequently. Mean nest height was 1.6 m and mean clutch size was 4.3 eggs. A mean of 17 days was required for incubation and the mean fledging period was 15 days. Nest failure occurred more often during the incubation than the nestling stage. The majority of nest losses were due to predation and inclement weather (49 and 20 nests, respectively). Mean hatching success was 87%, and 81% of chicks fledged successfully. Nesting success (percentage of nests that fledged at least one young) was 55%, and an analysis of other studies that used this measure detected significant clinal variation in Loggerhead Shrike nesting success, with success rate positively correlated with latitude. Unlike conspecifics in northern latitudes where second broods are considered rare, 96% of breeding pairs in Florida attempted second broods.
The migrant race of the Loggerhead Shrike (Lanius ludovicianus migrans) has undergone a severe decline in Canada since the mid-1950s and was designated as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1991. In order to gain a better understanding of the factors that may be associated with the decline of this species in eastern Canada, we studied the breeding biology and nesting success of Loggerhead Shrikes in the three core breeding areas in Ontario, Canada, during 1991 and 1992. We located 27 breeding pairs during 1991 and 50 breeding pairs during 1992. Mean clutch size was 4.9 and 5.6, mean number of eggs hatched per nest was 4.2 and 5.4, and mean number of young fledged per nest was 3.9 and 4.2 in 1991 and 1992, respectively. Only 2.3 and 2.5 young per pair survived to independence in each year. Percent success in fledgling at least one young was 89% and 78%. We believe that predation was the cause of all but one of the nest failures in both years. One pair successfully double brooded in 1991. In 1992 one of three double-brooding attempts was successful. The probability of survival of an egg was 58.6% for nests in isolated red cedars (Juniperus virginiana), 76.2% in isolated hawthorn (Crataegus spp.) shrubs, 88.5% in hawthorn shrubs in hedgerows, and 92.9% for all other species of nest tree. Daily nest survival was 98% for nests in isolated red cedar trees and 100% for nests in isolated hawthorn shrubs, in hawthorn shrubs in hedgerows, and in all other species of nest tree. Nest depth ranged from 11.2–12.4 cm and nest height above ground ranged from 2.1–2.5 m. Most nests in red cedar and other species of trees were located adjacent to the main trunk. Nests in hawthorn shrubs were located adjacent to the main trunk, on a main branch, or in the center of the canopy.
We studied the reproductive success and habitat selection of a migratory population of Loggerhead Shrikes (Lanius ludovicianus migrans) during the nesting season in northwest Missouri. The selection of breeding habitat was investigated at different spatial scales. Thirty-eight (67%) of 57 nests were located in osage orange (Maclura pomifera) trees. Shrike territories (defined as the area ;le 200 m from the nest site) contained significantly more pasture, fenceline, and perch sites, but less corn, alfalfa, and forest than random sites. At larger spatial scales, more grassland was detected ;le300 m of shrike nests than random locations. However, no differences were detected between shrike nests and random sites when larger radii (600, 900, and 1500 m) were analyzed. Nest success (56%) and productivity (3.63 young/successful pair) were similar to other North American means, and specific habitat variables appeared to have little association with nest success. However, nests located ;le15 m of roadways were significantly less successful (39%) than interior nests (76%).
Despite widespread population declines, few studies have sought to quantify nesting habitat and reproductive characteristics of Golden-winged Warblers (Vermivora chrysoptera). We characterized territory and nesting habitat and measured productivity in forest regeneration areas in the Nantahala National Forest, North Carolina, and Cherokee National Forest, Tennessee, during 1997–1998. We located 82 territories and monitored 23 nests. Golden-winged Warblers occupied young stands with low basal area and annually mowed daylit roads (roads mowed wider than the track to facilitate drying), and nested in sites with high herbaceous density compared to unoccupied regeneration areas. Nest sites had fewer saplings and less canopy cover than the surrounding territory. Overall nest success was 72.5% and nests fledged an average of 3.65 young. Recently harvested forest stands (age ;le13 yr) with herbaceous cover on logging roads and log landings provided habitat capable of supporting Golden-winged Warbler reproduction at levels equal to or greater than productivity reported from other study sites across the range of this species.
We compared nest placement and characteristics of nesting habitat used by Red-eyed Vireos (Vireo olivaceous) in deciduous forests of central Pennsylvania during the breeding seasons of 1998 and 1999. Nest patches versus random patches (0.04-ha circular plots centered on nests or random points, respectively) and successful versus unsuccessful nest patches were compared. Vireos selected nest patches in a nonrandom fashion with respect to vegetative characteristics at two strata: canopy level and ground/shrub level (<1.0 m). Nests were located closer to surrounding trees and were found in areas with greater canopy coverage, less ground vegetation, and fewer small (0.5–1.0 m in height) stems than random patches. Of the four microhabitat characteristics that distinguished used from random patches, however, only ground vegetation was associated with nest fate. Successful nests were surrounded by less ground vegetation than failed nests. Nest placement characteristics were not significantly associated with nest fate. We suggest that current nesting success may be independent of patch or site level attributes because the processes responsible for determining what constitutes a suitable nest patch or site characteristic may act at different spatial or temporal scales.
We measured the home ranges and habitat use of 11 Red-shouldered Hawks (Buteo lineatus) during the breeding season and 9 during the nonbreeding season in suburban Ohio, using standard telemetry techniques. Mean home ranges, calculated using the adaptive kernel method (95% isopleth), were 90 ha ;pm 11 SE during the breeding season, 189 ha ;pm 33 SE during the nonbreeding season, and 165 ha ;pm 24 SE for the annual home range. Males and females did not differ significantly in home range size. We examined habitat use by hawks by classifying the habitat where birds were observed perching. Habitat used by hawks differed significantly from that available within home ranges for all birds tested. Most Red-shouldered Hawks used riparian zones and pond edges more than expected, based on availability of such habitats within their home ranges; residential areas and lawns were used less than expected or in proportion to their availability.
We report on studies of four small forest passerines of Saipan, Mariana Islands, Micronesia, in order to characterize the ecological strategies employed in this threatened but virtually unstudied bird assemblage, and to provide a baseline for assessing shifts in foraging and microhabitat use that might follow reestablishment of extirpated populations. Data were gathered on microhabitat selection and foraging behavior, and limited observations are reported on wet-dry season shifts and annual changes in foraging. Two species were primarily canopy species, with one (Bridled White-eye, Zosterops conspicillatus) a live-leaf gleaner using smaller perches of taller trees, particularly Cynometra ramiflora, and the other (Micronesian Honeyeater, Myzomela rubratra) a flower prober using larger perches of taller trees. The remaining two species occupied the canopy and understory, with one (Rufous Fantail, Rhipidura rufifrons) an aerial forager and the other (Golden White-eye, Cleptornis marchei) a more generalized forager that selected larger perches of a wider variety of smaller trees. Hence, the species overlapped ecologically, but were differentiated in use of microhabitat space, including both structural and floristic components, and in manner of foraging. Comparisons of ecological overlap demonstrated that the two white-eye species were the most si