Active Nest Sites Research Articles

Conservation Value of Private Lands for Crested Caracaras in Florida

Abstract: In southcentral Florida, where agricultural lands are being converted rapidly to urban development, much of the remaining nonurban habitat occurs on privately owned cattle ranches. We studied the Crested Caracara (Caracara cheriway), a threatened bird of prey, to learn the role of private lands in sustaining the population. We investigated patterns of distribution and reproductive activity of breeding pairs of caracaras in relation to patterns of land ownership and use. Eighty‐two percent of 73 active nest sites found were on privately owned cattle ranches. We rarely found breeding pairs on publicly owned lands, most of which are managed as natural areas (no agricultural production and limited livestock grazing) to support native plant and animal communities. In 46 breeding areas with 4 years of known histories of occupancy and reproduction, pairs nesting on lands where the major land use was cattle ranching exhibited higher rates of breeding‐area occupancy, attempted breeding during more years, initiated egg laying earlier, exhibited higher nesting success, and attempted a second brood after successfully fledging a first brood more often than pairs nesting on lands managed as natural areas. Compositional analysis suggested nonrandom selection of habitats by breeding pairs of caracaras in their establishment of a home range in the current landscape of southcentral Florida. Compared with random areas and available habitat in the overall study area, caracara home ranges had higher proportions of improved pasture and lower proportions of forest, woodland, oak scrub, and marsh. Which management activities favor and do not favor caracaras is uncertain, and hypotheses should be formulated and tested to guide future conservation applications. Particular grazing and fire management practices on privately and publicly owned lands may affect the structure of vegetation and prey communities in ways that influence caracaras. Or, replacement of native by exotic grasses may retain structurally suitable plant communities, whereas fertilization and grazing may increase productivity and nutrient cycling in ways that favor caracaras. Given continued conversion of natural habitats and agricultural lands to urban development, it is important to recognize that cattle ranches may provide important resources for wildlife conservation. Although cattle ranching is not likely to benefit all species historically associated with the native prairie ecosystem in Florida, finding ways to retain this land use may be important for the conservation of Florida's population of Crested Caracaras and other organisms of Florida's dry prairies.

Habitat use by Loggerhead Shrikes in Ontario and Quebec

Once common throughout northeastern North America, the migrant race of Loggerhead Shrike (Lanius ludovicianus migrans) has undergone a drastic decline since the middle of the last century. The subspecies was designated as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1991. To gain a better understanding of the factors affecting the decline of this species in eastern Canada, habitat selection by Loggerhead Shrikes breeding in Ontario (Smith's Falls, Napanee, and Carden limestone plains) and southern Quebec was studied in 1991 and 1992. Nest trees used by breeding shrikes were compared with similar arbitrarily identified trees in suitable unoccupied habitat to determine if there was a nest-tree preference. Territories where successful nesting attempts were made (i.e., young fledged from at least one of the eggs laid) were located over a 2-year period; data were not collected for unsuccessful nests or nests used for double-brooding. Thirty-seven nests (50%) were located in hawthorn shrubs (Crataegus spp.) and 29 nests (40%) in red-cedar trees (Juniperus virginianus). White cedar (Thuja occidentalis), buckthorn (Rhamnus catharticus), and ash (Fraxinus spp.) were used infrequently (10%). Sixty-two nests (86%) were located in isolated trees or in a copse. Ten nests (14%) were located in hedgerows. Fifty-one (64%) nest sites were located in an actively grazed pasture. The other nest sites were located in idle pasture, hayfields, or old fields. Nest trees and arbitrarily chosen trees in suitable unoccupied habitat did not differ significantly in average height, width, or canopy concealment. Few differences were detected in the average height of the vegetation or the composition of ground cover within a 10-m radius of nest trees and arbitrarily chosen trees. The average numbers of shrubs per hectare did not differ between breeding sites and suitable unoccupied habitat. Nest trees in the Smith's Falls core breeding area were located significantly closer to roads than arbitrarily chosen trees in suitable unoccupied habitat. Habitat suitability was also assessed according to the density of perches (trees and shrubs), which directly affects the amount of actual utilizable habitat in a territory. Significant differences were found in the amounts of actual habitat and potential habitat. The amount of habitat around active nest sites, historic nest sites, and suitable unoccupied sites was significantly greater around active nest sites. Since few statistically significant differences were found between habitat occupied by shrikes and that which was not used, it is not possible to build a predictive model of suitable breeding habitat for shrikes in this study area.

Azure-winged magpies avoid nest predation by breeding synchronously with Japanese lesser sparrowhawks

Azure-winged magpies, Cyanopica cyana, breed most successfully when nesting near active nest sites of Japanese lesser sparrowhawks, Accipiter gularis. Magpie nests that contain nestlings after the period when sparrowhawks defend their nests suffer predation and the success of magpie breeding depends greatly upon hawk nest defence. To clarify the relationship between the timing of breeding of these two species, I compared the timing of breeding in azure-winged magpie pairs with variation in the level of nest defence by the hawk (as estimated by the nest success and the rate of nest defence of hawks). The date of onset of incubation in magpies was similar to the date that would have maximized the protection they gained from the hawk. Magpies nesting near hawk nests bred synchronously, but magpies far from them did not. The results suggest that magpies breed according to the hawks' breeding schedule in order to avoid nest predation and increase breeding success.

Seasonal patterns of abundance of Kelp Gulls Larus dominicanus at breeding and non-breeding localities in southern Africa

Crawford, R.J.M., Nel, D.C, Williams, A.J. & Scott, A. 1997. Seasonal patterns of abundance of Kelp Gulls Larus dominicanus at breeding and non-breeding localities in southern Africa. Ostrich 68 (1): 37–41. At Malgas Island, Western Cape Province, South Africa, active nest sites of Kelp Gulls were recorded from August to February, but mainly between October and December with a peak in November. In August and September all active sites were recently-made scrapes without eggs or chicks. Eggs were found from early October until January and chicks from late October to early February. At Dassen Island, Western Cape Province, numbers of adult Kelp Gulls are highest during the main October-December breeding season. After breeding, adults disperse from the island, with only 4% remaining by May. First-year birds were observed at Dassen Island from February to July, with mean numbers decreasing after April. At De Hoop, Western Cape Province, numbers of Kelp Gulls were also highest during the breeding season, but the decrease in the non-breeding season was less marked. Near Walvis Bay, central Namibia, at a non-breeding site, numbers of Kelp Gulls were highest outside the breeding season, indicating dispersal of birds away from colonies after completion of breeding.

The Influence of Vegetation Removal by Western Harvester Ants (Pogonomyrmex owyheei) in a Relict Area of Sagebrush-steppe in Central Oregon

-We examined the influence of western harvester ants (Pogonomyrmex owyheei) as vegetation removers in a relict area of semiarid vegetation in central Oregon on The Island Research Natural Area (IRNA). Because IRNA is an almost inaccessible basaltic plateau that has been free of livestock grazing and other significant anthropogenic influences for over 70 years, it serves as an excellent natural laboratory for examining the effects of P owyheei as vegetation removers. Pogonomyrmex owyheei are able to remove plant cover around their nest sites. However, opportunities to study P owyheei in undisturbed areas of the semiarid west are rare. We randomly selected 30 active ant nest sites on IRNA and sampled the vegetation around these nests using line-intercept transects. Comparisons of mean vegetation cover between P owyheei nest site transects and a reference group of nonnest site transects show a significant reduction in total cover on the nest site transects, but no significant difference in total cover when the cleared disc areas on the P owyheei transects are excluded. Our results suggest that vegetation removal by P owyheei reduced the cover of some species (e.g., Artemisia tridentata) and, indirectly, increased the cover of other species (e.g., Stipa thurberiana). We also found significant increases in vegetation cover on the perimeter of the cleared areas surrounding the nest site, a phenomenon described as the border effect. With an estimated density of 28 ant nests per hectare, and a mean cleared area per nest site of 5.9 m2, P owyheei is an important source of vegetation removal on IRNA.

NEST SITES OF THE SOUTHERN GROUND HORNBILL BUCORVUS LEADBEATERI IN THE KRUGER NATIONAL PARK, SOUTH AFRICA, AND CONSERVATION IMPLICATIONS

Summary Kemp, A. C. & Begg, K. S. 1996. Nest sites of the Southern Ground Hornbill Bucorvus leadbeateri in the Kruger National Park, South Africa, and conservation implications. Ostrich 67: 9–14. Details of 56 active and 18 potential nest sites of the Southern Ground Hornbill Bucorvus leadbeateri were recorded in the Kruger National Park, South Africa, over 298 nest-seasons during 1967–95. Nests were natural cavities with a median diameter of about 40 cm, 96% situated in 12 species of trees and 4% in rock faces. Only four species of tree provided 72% of nest sites and 85% of active nest sites were formed by rotting of a damaged branch or trunk. No habitat preference associated with nest sites was detected, but 61% of nests were within 400 m of a tourist road, possibly due to lower predation pressure. Nest attractiveness was correlated positively with nest height, cavity shallowness and proximity to tourist roads, but nest success was not correlated with any measured features of the sites. Average cavity d...

Alloparenting at an Eastern Screech-Owl Nest

Alloparenting at an Eastern Screech-Owl Nest

Nest Placement and Productivity of Ferruginous Hawks in Western Kansas

The nesting ecology of Ferruginous Hawks (Buteo regalis) in western Kansas was studied from 1979 through 1987. During this time 100 nesting areas and 181 different active nest sites were located. Nesting density in the study area was 316.5 km2/pair and was highest (71.5 km2/pair) along the Smoky Hill River, where chalk outcrops were common. On average, 38 nests and 43 percent of nest areas surveyed annually from 1979 were active each year. Nests were large (up to 190 cm wide and 180 cm deep), but averaged 100130 cm across and 30-50 cm deep. Nests were typically composed of old fruit stalks and stems of Yucca as well as bits of Russian thistle (Salsola kali), cow chips, and occasional wire. The majority (71.8%) of active sites were on ledges; butte, tree and ground nest sites were less common. Compass orientation of ledge nests tended to be northwest, but was statistically random. The majority (76.4%) of nesting areas included white or yellow chalk outcrops surrounded by rangeland. Only one nesting area included less than 25 percent rangeland and more than 75 percent cropland. Half of all active sites were considered impossible for quadrupedal predators to access and only 29.2 percent were easily accessed from one or more directions. Most (81.9%) nesting areas were within 8 km of active black-tailed prairie dog (Cynomys ludovicianus) towns, but 86.9 percent of areas were not adjacent to dog towns. Hawks may avoid nesting in cropland sites, ground sites, and easily-accessed sites, suggesting that sites with low levels of human and predator disturbance may be favored. Productivity varied greatly among sites, but was significantly higher at inaccessible sites. Accessible sites within eye-view of prairie dog towns were the least productive, perhaps because unsuccessful predators of prairie dogs turn to hawk eggs and nestlings as alternative prey. Variable nest placement, so typical of this species, may occur because undisturbed sites are actively selected and undisturbed sites have variable characteristics throughout the species' range. This content downloaded from 207.46.13.94 on Mon, 05 Jun 2017 18:26:41 UTC All use subject to http://about.jstor.org/terms VOLUME 92, NUMBERS 3-4 133 The Ferruginous Hawk (Buteo regalis) is a conspicuous inhabitant of semiarid grasslands and sparse woodlands of the western United States and prairie provinces of southern Canada. Formerly one of the most abundant hawks in these regions its populations have declined, primarily because of increased human domination of the land (Bechard, 1981; Houston and Bechard, 1984; Schmutz, 1984). In order to determine the abundance and productivity of Ferruginous Hawks in Kansas (the eastern border of the species' range) this species was monitored beginning in 1978. The objective of this paper is to document utilization of habitat and productivity during the breeding seasons of 1979 through 1987. Nests are described, nest site characteristics quantified and nest placement related to reproductive success.

Characteristics of Northern Hardwood Trees Used by Cavity-Nesting Birds

Characteristics of Northern Hardwood Trees Used by Cavity-Nesting Birds

ASPECTS OF THE POPULATION DYNAMICS OF CAPE VULTURES IN THE CAPE PROVINCE

Summary Robertson, A. S. 1984. Aspects of the population dynamics of Cape Vultures in the Cape Province. Ostrich 55: 196–206. Information gathered in 1981 and 1982 and collated from previous records on the numbers, spatial distribution, proportion of age classes, age and frequency of breeding, breeding success and causes of breeding failure, and the survival of immature and adult Cape Vultures Gyps coprotheres in the southern and southwestern areas of the Cape Province, South Africa, is presented. This sub-population of about 75 birds is apparently isolated from conspecifics in the rest of southern Africa; the implications of this are discussed. At the Potberg colony in both years an average of 85% of birds 5 years and older were involved in breeding attempts. The age of first breeding was 4–6 years. Nest sites were active for about two in every three years. Between 1975 and 1982, 0,51-0,67 nestlings were reared per active nest site (n=165). Four (possible maximum six) of 21 immatures were resighted one y...

Some Winter and Nesting Season Foods of the Common Raven in Virginia

LITTLE is known of the ecology of the Common Raven (Corvus corax) population that inhabits the narrow belt of mountains from north Georgia to northern Pennsylvania. This disjunct group is a remnant of a previously larger, contiguous population (A.O.U. 1957). To our knowledge, only one account of the food habits of this isolated population has been published. Murray (1949) reported the animal remains found below two cliff nests in Rockbridge County, Virginia. Included were the bones of flying squirrels (Glaucomys volans), gray squirrels (Sciurus carolinensis), a Norway rat (Rattus norvegicus), a Mourning Dove (Zenaida macroura), a Blue Jay (Cyanocitta cristata), a Ruffed Grouse (Bonasa umbellus), a snake, and remains of grasshoppers. Reports from other regions indicate that Common Ravens rely heavily on carrion (Ratcliffe 1962, White and Cade 1971, Dorn 1972). Some students believe the raven has considerable potential as a predator (Craighead and Craighead 1956: 339; White and Cade 1971; Dorn 1972). That ravens frequent garbage dumps is well-known (Bent 1946: 227-262). Our objectives of the research were to determine the food habits of Common Ravens in Virginia during two critical periods of the yearwinter and the nesting season. Of particular interest were (1) the importance of prey as a food source, (2) possible economic implications of their food habits, and (3) the importance of garbage dumps as a food source. The study was made possible by the discovery of a nocturnal winter raven roost and the relocation of the apparent nonbreeding segment of the roost following the dispersal of the winter roost at the beginning of the nesting season. A concurrent study of nesting habitat made possible a search of 20 active nest sites for castings. The research was conducted in the Ridge and Valley Physiographic Province of Virginia, a region of parallel ridges that rise 1000 to 2000 feet above the intervening valleys. The ridges are covered by oak forests (Braun 1967) while the valleys are interspersed forest and pastures. The numerous cliffs and remote woodlands have provided a refuge for the species at a time when its numbers were being reduced throughout the eastern United States.

Breeding Success, Numbers, and Movements of House Sparrows at McLeansboro, Illinois

A portion of McLeansboro was censused for breeding birds in 1966 and 1967 by a mapping technique patterned after Williams (1936). The area censused (Figure 1) comprises about 100 acres (40 hectares) and includes the main business district, residential areas, a cattail-bordered pond, a grain elevator, and two feed stores. The locations of active nest sites in 1966 and 1967 were also plotted. Observations on nests were made at three sites (Figure 2) within two miles (3.2 km) of McLeansboro. Two of the sites were farm lots where intensive livestock feeding was done. The third site was my backyard. Nests at the Sneed lot were observed in 1966, 1967, and the early part of 1968. In my backyard, observation of nests was carried out during 1966 and 1967, while at the R. B. Stelle lot nests were observed in 1967 and 1968.