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We report the first prehistoric bird bones from the isolated limestone island of Niue, South Pacific. Discovered in a cave known as Anakuli, the bones are Holocene in age but lack cultural association. They represent three extinct species: a night-heron (Nycticorax kalavikai), a new species known thus far only from Niue but closely related to an extinct undescribed species from Tonga; the “Niuafo'ou” Megapode (Megapodius pritchardii), known historically only from Niuafo'ou (Tonga) but recorded from prehistoric sites elsewhere in Tonga; and Gallirallus huiatua, a new species of flightless rail presumably endemic to Niue and distinct from extinct, flightless congeneric species from island groups immediately east (Cook Islands) and west (Tonga) of Niue. The first two species are in accord with the overall biogeographic affinity of the extant avifauna of Niue, which is West Polynesian rather than East Polynesian.
I investigated the roles of intraclutch variation in egg volume and hatching asynchrony in the establishment of mass hierarchies in broods of the Brown Pelican (Pelecanus occidentalis). The second egg averaged 2.6% larger than the first and 1.9% larger than the third. In unmanipulated control broods, first eggs hatched an average of 25 h before second eggs, which hatched 40 h before third eggs. On the day the last egg hatched, first chicks averaged 16% heavier than second chicks and 30% heavier than third chicks. Although chick mass at hatching was strongly correlated with egg volume, differences in mass within broods were almost entirely the result of hatching asynchrony. In broods in which I experimentally reduced hatching intervals, initial nestling mass differences were significantly smaller and strongly correlated with differences in egg volume but not with hatching asynchrony. Intrabrood mass differences remained lower in experimental than control broods throughout the first 2 weeks of the nestling period. Furthermore, mass ranks established at hatching were less likely to persist through this period in experimentally synchronized broods than in asynchronous controls. These results indicate that hatching asynchrony promotes the establishment of a more stable size hierarchy. However, the adaptive significance of nestling size hierarchies in Brown Pelicans remains unresolved.
We studied the breeding biology of the Bicolored Hawk (Accipiter bicolor) in the forest of Tikal National Park of northeastern Guatemala from 1991 to 1994. Bicolored Hawks are year-round residents and establish nesting territories during the breeding season, which coincides with the late dry season and beginning of the wet season. Nest building and courtship spanned 92 days. We documented 17 nesting attempts from February to July 1991–1994. Egg-laying began in April and May, with 36 eggs laid in 15 nests for an average clutch size of 2.4 (range 1–3 eggs). We documented one renesting after failure of the first clutch. Incubation was approximately 35 days (n = 5 clutches). Young hatched asynchronously with a light pinkish natal down. Of 36 eggs laid, 64% hatched. Nearly all hatching occurred during May except one renesting, from which one young hatched on 26 June 1994. Young departed from the nest tree at 30–36 days of age and 100% of the nestlings fledged; thus a total of 1.4 young fledged per breeding attempt and overall nest success was 76%. Most reproductive losses occurred during the incubation period. We found addled eggs in 2 nests and egg predation and nestling predation at 1 nest each. Bicolored Hawk nests averaged 22 m above the ground in living trees 75 cm in diameter. All nests were stick nests, averaging 51 × 44 cm exterior diameter, 26 cm exterior depth, and 3.6 cm interior depth. The Bicolored Hawk diet of 173 identified prey was composed almost exclusively of birds (95%) with relatively few mammals (3%) or reptiles (2%) taken.
We evaluated characteristics at Red-shouldered Hawk (Buteo lineatus) nest sites at two study areas with different topography and forest types in north-central and central Minnesota to identify nest site commonalities across geographically distinct areas. During the breeding seasons of 1994–1995, we located nests of Red-shouldered Hawks at the Camp Ripley Army National Guard Training Site and the Chippewa National Forest using a combination of broadcast surveys, helicopter searches, and systematic foot searches. All 38 nests at Camp Ripley and 18 nests in the Chippewa National Forest were in upland hardwood stands; the remaining two nests in the Chippewa National Forest were in aspen (Populus spp.) stands. We aged cores from 19 nest trees at Camp Ripley and measured habitat characteristics in a 0.04 ha circle centered on each nest tree and at a paired random site within the nest stand. We compared habitat variables at nest and random sites to identify habitat characteristics that were consistent predictors of nest sites versus random sites for each study area and for all nests combined. Compared to random sites, nest sites in the Chippewa National Forest had larger diameters at breast height (dbh) of the nest tree, taller nest tree height, and higher canopy height. At Camp Ripley, nest sites differed from random sites with regard to many more variables; nests were located in portions of the stand with larger trees and closer to surface water. Nest trees ranged in age from 50–89 years. Logistic regression models indicated that, for both study areas combined, nest tree dbh, basal area, canopy height, and distance to water were the most important variables in distinguishing nest sites from random sites.
We trapped more than 23,000 migrating raptors at Cedar Grove, Wisconsin during the autumns of 1953–1996, permitting accurate identification of age and sex. Adults migrated significantly later than juveniles in 8 of 10 species, and males migrated later than females in 7 species. We suggest that it is adaptive for adults and males to remain on breeding territories as long as possible. Adult Peregrine Falcons (Falco peregrinus) migrated before juveniles. There was no age difference in migration of Rough-legged Hawks (Buteo lagopus). Both species breed in the Arctic where the brief breeding season requires that adults leave as soon as possible so adults might then migrate more rapidly than juveniles. We compare our results with those of 16 other studies. Juveniles migrated significantly later than adults in 8 of 13 species at Falsterbo in southern Sweden (Kjellén 1992). Falsterbo is more than 12° latitude (1300 km) north of Cedar Grove and the breeding range of most of the species occurring there extends north of the Arctic Circle, where birds suffer from the same abbreviated breeding seasons as do the Peregrine Falcon and Rough-legged Hawk in North America. Adult females migrated after adult males in the two large species of Accipiter; this may be because the females, not the males, establish and maintain territory in these species.
We studied the nesting ecology of the Chimango Caracara (Milvago chimango), a common yet poorly known raptor on Chiloé Island, southern Chile, during two breeding seasons. Deforestation and land clearing in this landscape may be benefiting this raptor, which is tolerant of open and disturbed habitats and human activity. Chimangos nested at different heights in a variety of trees and shrubs, but nests were always well concealed because they were placed centrally and in dense vegetation within the substrate. Egg laying occurred in most nests in October during both years; the most common clutch sizes were 2 or 3 eggs. The incubation and nestling periods were approximately 5 (2 nests) and 6 (1 nest) weeks, respectively. Nest success (Mayfield) for 72 nests averaged 57% for the two years. Productivity averaged 1.22 ± 0.11 fledglings per active nest and did not differ between years. For nests located during both years (n = 15), productivity was slightly higher in 1997–1998 and more nests failed in 1998–1999. Two pairs attempted to renest after nest failure but were not successful. Habitat and landscape features associated with high productivity of chimango nests included exotic trees and shrubs, tidal flats, linear forest strips, and occupied houses or barns. Successful nesting was associated with exotic trees and shrubs. Nesting density was highest along beaches, although not all pairs that built nests along beaches laid eggs. Successful nests along beaches fledged twice as many young as inland nests. Continued clearing of the rainforest in this region may provide increased foraging opportunities for this raptor but may also result in fewer nest sites.
We report the study of parental care of Wood Thrush (Hylocichla mustelina) fledglings from nest-leaving to independence. From 1993 to 1995, we captured, radio-tagged, and monitored the movements and behavior of 23 fledglings and their parents from 12 broods at the U.S. Marine Corps Base, Quantico, Virginia. For pairs that subsequently renested (n = 5), the family group of male, female, and fledglings, remained within 62 (±5 SE) m of the first nest after fledging. During the period of post-fledging parental care, mean maximum distance between parents was 70 (±14) m. Females attended the young 13 (±1.3) days before initiating the incubation of a second clutch. Males continued attending the fledglings for 6 (±0.7) more days until the young achieved independence and dispersed (28–36 days post-hatching). In final clutches (n = 7), brood care was divided between the parents, and the position of the fledglings relative to the nest depended on the parents' choice of molting site (in the nesting area or elsewhere). Division of the brood by the parents has been thought to be a strategy to reduce predation and increase foraging efficiency. However, in the Wood Thrush and other species, joint attendance of initial broods, but division of final broods, suggest that other factors could be important for the parents' decision of whether or not to split the brood.
We investigated the influence of disturbance type (agriculture and silviculture) within forested landscapes, amount of forest cover within 1 km of the site, and local habitat characteristics on the pairing success of Ovenbirds (Seiurus aurocapillus) in central Pennsylvania during May and June 1998. Because areas with low pairing success often are inferred to have high nest predation, we also examined whether pairing and nesting success were correlated across sites. We determined the pairing status of 116 male Ovenbirds on 10 sites within contiguous mature forest. Percent of males that were paired on each site ranged from 54–92% (mean = 78%). Pairing success was negatively associated with forest cover within 1 km and positively associated with leaf litter depth. Percent bare ground also was positively correlated with forest cover within 1 km of the site. Estimates of pairing success were unrelated to Ovenbird nesting success at each site (based on 48 nests), which suggests that site-level differences in nest predation or reproductive potential are not necessarily associated with the ability of males to acquire mates. Our data suggest that pairing success of Ovenbirds in forested landscapes is not reduced by the amount of habitat loss within 1 km and is determined by local habitat rather than landscape characteristics.
The Eastern Towhee (Pipilo erythrophthalmus) has undergone population declines across much of its range, especially in New England. Despite being a widespread and, at one time, a common species, relatively little is known about its natural history, ecology, or demographics. We conducted baseline research on Eastern Towhees at the Savannah River Site, South Carolina, in 1995 and 1996 to estimate breeding season survival rates, nest success rates, breeding densities, and daily movements. We also were interested in whether towhees had differences in survival and movement rates between young and mature managed pine stands. We found that survival rates during the breeding season of radio-marked towhees did not vary by sex or stand type. Daily nest success rates were very low [0.629 ± 0.088 (SE)] as a result of high predation levels. Abundance estimates adjusted for sampling effort differed between years. In 1995, the abundance estimate was significantly lower in mature stands (7.1 ± 0.47) than in young stands (9.6 ± 0.60) while in 1996, there was no different between mature stands (26.2 ± 5.67) and young stands (16.5 ± 3.39). Average daily movements by radio-marked towhees did not vary by sex or stand type. Movements among adjacent stands were common, and sometimes great distances.
We evaluated the effects of plant succession on habitat use and fruit resource availability for autumn migratory and resident songbirds in 43 ha of abandoned farm fields in central New Jersey. Using fixed net sites, standardized effort, and simultaneous sampling across habitat types, we mist-netted birds to compare habitat use and found that (1) use of three shrub-tree invasion interfaces declined as fruit-bearing shrubs were overgrown by trees, while use of three open shrublands changed little over the same period; (2) use of two pairs of contrasting successional habitats, shrubland and young woodland, was higher in the shrubland with abundant, highly nutritional fruits than in young woodland with sparse fruit; and (3) use of three shrublands at similar successional stages but with different fruit availability differed by bird taxonomic family and migratory strategy. Data on species composition and relative abundance of fruit-bearing shrubs and fruit consumption by birds (assessed by regurgitated and defecated matter) were used to elucidate avian patterns of habitat use. The relative abundance of fruit-bearing species may be more important than habitat structure in determining habitat use by birds. Shrubland dominated by panicled dogwood (Cornus racemosa) was favored over shrubland dominated by red cedar (Juniperus virginianum) or multiflora rose (Rosa multiflora). Favored vines were Japanese honeysuckle (Lonicera japonica), Virginia creeper (Parthenocissus quinquefolia), poison ivy (Toxicodendron radicans), and grape (Vitis spp.).
I studied the frequency with which Emperor Geese (Chen canagica) of known age were observed breeding on the Yukon-Kuskokwim Delta, Alaska. No one- or two-year old geese were observed on nests. Three-year old geese bred at a lower rate than four-year old geese. These data suggest that patterns of age-specific breeding in Emperor Geese are similar to other sympatrically nesting, large bodied geese [Greater White-fronted Geese (Anser albifrons)] but delayed relative to smaller bodied geese [Cackling Canada Geese (Branta canadensis minima) and Pacific Black Brant (B. bernicla nigricans)].
We determined diet composition of Sandhill Cranes (Grus canadensis; n = 136) wintering in 4 regions of Texas during November–January 1996–1997 based exclusively on examination of esophageal and proventricular contents. Wintering Sandhill Cranes were predominately herbivorous, with animal matter representing less than 5% of their diet. Agricultural grains comprised most of the diet of wintering Sandhill Cranes from all regions of Texas except the South Texas Plains where nut-grass (Cyperus spp.) tubers made up a larger proportion of their diet. Cranes used agricultural and native plant matter and animal matter in different proportions among regions. There were no sex or subspecific related differences in frequency of occurrence or proportional dry mass of foods consumed by wintering Sandhill Cranes. Agricultural foods represented a larger proportion of the diets of Sandhill Cranes in this study than in previous studies conducted along the Gulf Coast, probably because of improved sampling methodology and differences in habitat conditions.
Cattle Egrets (Bubulcus ibis) expanded their range greatly during the twentiethth century, making localized food habit studies necessary to determine their impact in newly invaded ecosystems. We examined 44 Cattle Egret stomachs collected in January 1993 from Alexander Hamilton Airport on St. Croix Island, U.S. Virgin Islands. Orthopterans and lepidopterans were the most prevalent invertebrate food items. The St. Croix anole (Anolis acutu) was the major vertebrate prey. Meat scraps and ticks occurred in minor quantities.
Most life history traits of the American Bittern (Botaurus lentiginosus) have not been studied and are poorly understood. The ability of the American Bittern to renest has not been confirmed previously. A second nesting attempt by an American Bittern was observed on Agassiz National Wildlife Refuge on 8 July 1996. This information provides insight into American Bittern fecundity by showing that additional reproductive capability exists when nests are destroyed by predation or weather related events. Future studies of nesting bitterns will need to consider renesting when estimating density of nesting females.
I documented interspecific and intraspecific helping behavior (more than two adults feeding young at a nest) within sapsuckers of the genus Sphyrapicus. Of 120 nests, 97 belonged to Red-breasted (Sphyrapicus ruber), Red-naped (Sphyrapicus nuchalis), or hybrid (Red-breasted × Red-naped) sapsuckers, and 23 to Williamson's Sapsuckers (Sphyrapicus thyroideus). Interspecific helping behavior was observed at two nests (1 with a Red-breasted × Red-naped and hybrid female, 1 with Red-breasted × Red-breasted and Williamson's male) and intraspecific helping behavior (Red-breasted male) was observed at one nest. Given the rarity of helping behavior observed in these species a functional advantage is unlikely; individuals that helped might simply have been responding to a feeding stimulus.
Nest helping has not been reported previously among Cooper's Hawks (Accipiter cooperii). We report a nesting attempt involving three Cooper's Hawks. An adult and subadult male made prey deliveries to an adult female and all three hawks engaged in nest defense. No evidence of intraspecific aggression was observed among the three hawks.
In altricial birds, scramble competition for favorable feeding positions in the nest may cause younger chicks to starve. We studied nestling survival in a population of Tree Swallows (Tachycineta bicolor) breeding in nestboxes near Seattle, Washington, in a year of bad weather. Only a mean of 0.5 chicks fledged per nest (range 0–2, 22 nests). Nestling mortality appeared to be caused by starvation. Video filming showed that when chicks were old enough (largest chick within the brood had reached a wing length of about 55–60 mm), they spent much time in the nestbox opening, calling loudly. This behavior seemed to be driven by hunger because it occurred mainly in broods where chicks had low body masses. Parents fed the chick in the opening and did not try to push it back into the nest cavity or go around it. We suspect that blocking of the nestbox opening accelerated mortality of other young in the nest. Such behavior by dominant chicks may be more readily achieved in hole nesting birds with narrow entrances to their nest site than by open nesting birds.
During June 1999, in Grand Isle, Vermont, four Northern Rough-winged Swallows (Stelgidopteryx serripennis) fed five nestlings at one nest. A second nest 3 m away had been depredated. The four swallows continued their unusual cooperative behavior until the young had fledged.
Nests and nesting behavior of the Nightingale Wren (Microcerculus marginatus) in Panama are described. Two nests were found at the ends of horizontal burrows in dirt banks, presumably excavated by other species. The nest chambers were lined with dead leaf fragments. Clutch sizes were two and three eggs. Incubation period was 19 or 20 days for one nest, and the nestling period was 16 or 17 days for the second nest. A comparison of nests in the Troglodytidae shows the nests of M. marginatus to be most similar to those of the genera Salpinctes, Catherpes, and Hylorchilus, all of which are secondary cavity nesters. If nest type is a phylogenetically conserved characteristic, then these four genera may be more closely related than is reflected in current classifications.
During June and July, 1999, we observed two male Ovenbirds (Seiurus aurocapillus) caring for recently fledged Ovenbird chicks from the same nest in what we believe was the outcome of a polyandrous relationship. If so, the circumstances surrounding this observation are similar to the only other published account of polyandry in this species. We suggest that the reason for the adoption of this behavior may be related to a shortage of females. If this is the case, then polyandry may be more widespread in Ovenbirds than previously thought because we regularly observed unmated male Ovenbirds on our study plots, indicating that the conditions favoring polyandry (limited access to females) occur relatively frequently.
We conducted unlimited radius point counts from March–July 1999 at sunrise, dusk, and night to document the relative frequency of nocturnal singing by grassland birds at Prairie Ridge State Natural Area, Jasper County, Illinois. Most grassland species were recorded singing at all times of day, but least commonly at night. Short-eared Owls (Asio flammeus) and American Woodcock (Scolopax minor) were only recorded at dusk and night. Sedge Wrens (Cistothorus platensis) and Henslow's Sparrows (Ammodramus henslowii) were most frequently recorded at night and least frequently at sunrise. Only 57% of all the breeding species recorded by our surveys were detected on June sunrise counts corresponding to the timing of the North American Breeding Bird Survey.
I report a predation rate of 24 birds from 3707 total captures of birds caught in mist-nets in fragmented upland forests in Kenya. Predation was highly concentrated in specific forest fragments, with multiple birds simultaneously found killed in more than half of the predation events. Predators were probably attracted to the mist-nets by the noise and activity of the netted birds because the capture rate of predated nets was more than three times the mean for the survey as a whole. The most common victims were Yellow-whiskered Greenbuls (Andropadus latirostris), and the most common predators were blue monkeys (Cercopithecus mitis). Although 20% of all our mist-net captures were in Kakamega, a large forest, not a single bird was taken from our nets there, suggesting that predation rates on mist-netted birds are higher in small forest fragments.