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At least 469 records · Page 26Linked to original sources
USGS1990

Colony attendance and population monitoring of Least and Crested auklets on St. Lawrence Island, Alaska

Diurnal and seasonal patterns of attendance of Least Auklets ( Aethia pusilla ) and Crested Auklets ( A. cristatella ) were studied in 1987 at breeding colonies on St. Lawrence Island, Alaska. Numbers of auklets attending eight 200-m 2 plots on talus slopes were counted throughout the day by observers on 11 occasions through the breeding season. Numbers attending smaller plots were recorded on time-lapse film on 71 different days. Another 16 200-m 2 plots were censused for auklets using surface counts. Within-day patterns of attendance were extremely variable over small and large temporal scales. Peaks of attendance occurred in late morning and late evening, with a 7- to 12-hr period of absence in the middle of the day. Attendance varied markedly between days, and numbers were negatively correlated with wind speed and the magnitude of tidal oscillations. Patterns of attendance also varied with stage of breeding, and counts were least variable during incubation and early chick rearing. Whereas Least Auklet numbers peaked during prelaying, Crested Auklet numbers peaked during incubation. Counts indicated that auklets at Kongkok Bay have increased about twofold since studies in the mid-1960s. Recommendations are made for future monitoring of auklet populations.

Alaska↗
USGS1990

Extra-pair copulations in Black Brant

Monogamy is the primary mating system among waterfowl, but extra-pair copulations (EPCs) have been documented in at least 39 species (McKinney et al. 1983). Extra-pair copulations occur in most Holarctic species of dabbling ducks ( Anas spp.), but have been recorded in only three species of geese: Lesser Snow Geese, Chen caerulescens caerulescens (Mineau and Cooke 1979a), Ross’ Geese, C. rossii (J. Ryder in McKinney et al. 1984), and Greater White-fronted Geese, Anser albifrons frontalis (C.R. Ely, pers. comm.). In colonial Lesser Snow Geese, the close proximity of nesting conspecifics may enable males to pursue EPCs as a secondary reproductive strategy (Mineau and Cooke, 1979a, 1979b). Copulatory behavior of other geese has not been studied in sufficient detail to permit comparison with Lesser Sone Geese. Here we report on timing and rates of pair copulations (PCs) and EPCs, and describe behaviors associated with EPCs in colonially nesting Black Brant ( Branta bernicla nigricans ).

The Condor↗
USGS1988

A high incidence of brown-headed cowbird parasitism of willow flycatchers

Brown-headed Cowbirds ( Molothrus ater ) parasitize both Willow ( Empidonax traillii ) and Alder ( E. alnorum ) flycatchers (Friedmann et al. 1977, Friedmann and Kiff 1985). These two flycatchers were considered a single species until 1973 (AOU 1973), which has masked information about the frequency with which each is parasitized. Whereas several studies of the superspecies (Traill's Flycatcher) have focused on or included details of cowbird parasitism, most were of eastern populations, and most reported frequencies of parasitism ≤21% (Hicks 1934, Berger 1951, Berger and Parmalee 1952, Walkinshaw 1966, Holcomb 1972). Friedmann et al. (1977:13) suggested that western populations (Willow Flycatchers) are parasitized only about half as much (ca. 10%) as eastern populations (Traill's Flycatcher superspecies). This note described a high rate of cowbird parasitism within a population of Willow Flycatchers in northcentral Colorado. We include details of responses to parasitism and host vs. cowbird fledgling success.

The Condor↗
USGS1987

Aggressive encounters between tundra swans and greater white-fronted geese during brood rearing

Interspecific aggression in waterfowl (Anatidae) is relatively common (McKinney 1965; Kear 1972; Savard 1982, 1984), but interactions leading to mortality of one of the combatants are rarely-observed in the wild. A recent debate (Livezey and Humphrey 1985a, 1985b; Nuechterlein and Storer 1985a, 1985b; Murray 1985) has centered on the proximate and ultimate causes of interspecific territoriality and killing in steamer-ducks ( Tachyeres spp.), a group of large-bodies antids. We report here aggressive encounters between Greater White-fronted Geese ( Anser albifrons ) and Tundra Swans ( Cygnus columbianus ) during brood rearing on the Yukon-Kuskokwim Delta, Alaska, which on two occasions resulted in the death of a White-fronted Goose gosling.

Alaska↗
USGS1987

Winter diets of common murres and marbled murrelets in Kachemak Bay, Alaska

Knowledge of the winter diets of seabirds in high latitudes like Alaskan waters has been an elusive aspect of their biology. Scanty information on winter diets of Common Murres ( Uria aalge ) are available from the Pribilof Islands (Preble and McAtee 1923), California (Baltz and Morejohn 1977), Kodiak Island (Kraznow and Sanger 1986), Newfoundland (Tuck 1960), and the North Sea (Blake 1984), and for Marbled Murrelets ( Brachyramphus marmoratus ) from British Columbia (Munro and Clemens 1931, Carter 1984) and Kodiak (Krasnow and sanger 1986). This paper summarizes the diets of these two species, as observed during the winter season of 1977-1978 in Kachemak Bay, Alaska, as a part fo the Alaskan Outer Continental Shelf Environmental Assessment Program, OCSEAP (Sanger and Jones 1982; Krasnow and Sanger 1986; Fukuyama, Sanger, and Hironaka, unpubl.) and provides further interpretation of the data.

Alaska↗
USGS1987

Adult survival and productivity of Northern Fulmars in Alaska

The population dynamics of Northern Fulmars ( Fulmarus glacialis ) were studied at the Semidi Islands in the western Gulf of Alaska. Fulmars occurred in a broad range of color phases, and annual survival was estimated from the return of birds in the rarer plumage classes. A raw estimate of mean annual survival over a 5-year period was 0.963, but a removal experiment indicated the raw value was probably biased downward. The estimate of annual survival adjusted accordingly was 0.969. Mortality during the breeding season was less than 10% of the annual total, and postbreeding mortality of failed breeders was three to four times higher than that of successful breeders. Breeding success averaged 41% over 9 years. About 5% of experienced birds failed to breed each year due to physical destruction of their breeding sites, mate-loss, or other causes. An estimated 30% of the birds near the colony in one year were of prebreeding age. A comparison of population parameters in Pacific and Atlantic fulmars indicates that higher survival in the prebreeding years is the likely basis for population growth in the northeastern Atlantic. The correlation of breeding success and survival suggests both parameters may decline with age.

Alaska↗
USGS1987

Latent population responses of summer birds to a catastrophic, climatological event

Catastrophic events can create ecological crunches for avian populations. Ornithologists generally assume that such events elicit immediate, dramatic declines in populations followed by rapid recolonization of a site with habitat recovery. Despite total inundation of habitats within the South Platte floodplain of eastern Colorado during the 1983 breeding season, populations of Brown Thrashers (Toxostoma rufum) and Rufoussided Towhees (Pipilo erythrophthalmus) did not decline significantly from 1982 densities. However, populations of both species declined significantly in 1984 and towhee populations remained low in 1985. These observations support speculations from recent studies of shrubsteppe bird populations that site tenacity may play a stronger role in determining annual densities of breeding birds than previously realized.

The Condor↗
USGS1988

Host selection by the shiny cowbird

Factors important in Shiny Cowbird (Molothrus bonariensis) host selection were examined within the mangrove community in Puerto Rico. Cowbirds did not parasitize birds in proportion to their abundance. The cowbird breeding season coincided with those of its major hosts, which were 'high-quality' foster species (i.e., species that fledge .gtoreq. 55% of cowbirds hatched: Yellow Warbler, Dendroica petechia; Yellow-shouldered Blackbird, Agelaius xanthomus; Black-whiskered Vireo, Vireo altiloquus; Black-cowled Oriole, Icterus dominicensis; Peurto Rican Flycatcher, Myiarchus antillarum; Troupial, Icterus icterus), and did not extend into other periods even though nests of 'low-quality: species (i.e., species that fledge < 55% of cowbird chicks that hatched: Bronze Mannikin, Lonchura cucullata; Greater Antillean Grackle, Quiscalus niger; Gray Kingbird, Tyrannus dominicensis; Northern Mockingbird, Mimus polyglottos; Red-legged Thrush, Turdus plumbeus) were available. Shiny Cowbird food habits and egg size were similar to those of their hosts, suggesting that cowbirds choose hosts partly on the basis of this combination. Cowbirds located host nests primarily by cryptically watching activities of birds in likely habitats. Other nest locating strategies were active searching of suitable habitat and 'flushing' of hosts by the cowbird's noisy approach. Cowbirds closely monitored nest status with frequent visits that peaked on the host's first day of egg laying. Hosts using covered nests (e.g., cavities, domed nests) were as vulnerable to cowbird parasitism as those building open nests.

Condor↗
USGS1988

Geographic variation in the yellow-billed cuckoo

Populations of the Yellow-billed Cuckoo, Coocyzus americanus, west of the Rocky Mountains have average wing lengths slightly greater than those of eastern North America, but the difference is not sufficient for taxonomic recognition. There is no geographically oriented variation in bill size or color, and the species is best considered monotypic.

Condor↗
USGS1991

Reproductive vulnerability: Parental attendance around hatching in roseate (Sterna dougallii) and common (S. hirundo) terns

Presence of one or both members of a pair at the nest site during the incubation and early chick stage reduces reproductive losses due to predation and weather stresses. The authors monitored the presence of pair members by the temporary removal of one member of several pairs of Roseate (Sterna dougallii ) and Common (Sterna hirundo ) Terns at nests at Cedar Beach, New York, to determine if vulnerability varies by reproductive stage, to compare species differences that might partially account for declines in Roseate Tern populations, and to examine their response to trapping. There were significant differences between species in the time to return to the nest following an initial disturbance, and Roseate Terns that were trapped and released took longer to return to the nest and resume incubating than did Common Terns. The nests of Roseate Terns were vulnerable (neither adult in attendance) for longer time than were the nests of Common Terns.

Condor↗
USGS1991

Seasonal pattern of reverse mounting in the groove-billed ani (Crotophaga sulcirostris)

We observed reverse mounting behavior in a color-banded population of Groove-billed Anis (Crotophaga sulcirostris) in Costa Rica. Sex was determined with measurements and laparotomies. Reverse mounting appeared nearly identical to mounting by males. Of 27 mountings in which at least one bird was banded, 15 were reverse mountings. Only reverse mountings (11 observations) were observed in the pre-breeding period. During the breeding season males mounted females in 12 of 16 mountings; one of the reverse mountings followed nest predation. The timing of reverse mounting in anis suggests that it has an adaptive function in courtship. The proximate mechanism may be differential timing between partners in the development of breeding condition or of sexual motivation.

Condor↗
USGS1987

Feeding methods and efficiencies of selected frugivorous birds

I report on handling methods and efficiencies of 26 species of Paraguayan birds freeding on fruits of Allophyllus edulis (Sapindaceae). A bird may swallow fruits whole (Type I: pluck and swallow feeders), hold a fruit and cut the pulp from the seed with the edge of the bill, swallowing the pulp but not the seed (Type II: cut or mash feeders), or take bites of pulp from a fruit that hangs from the tree or that is held and manipulated against a branch (Type III: push and bite feeders). In terms of absolute amount of pulp obtained from a fruit, and amount obtained per unit time. Type I species are far more efficient than Type II and III species. Bill morphology influences feeding methods but is not the only important factor. Diet breadth does not appear to be significant. Consideration of feeding efficiency relative to the needs of the birds indicates that these species need to spend relatively little time feeding to meet their estimated energetic needs, and that handling time has a relatively trivial effect on the time/energy budges of the bird species observed.

Condor↗
USGS1990

The importance of subarctic intertidal habitats to shorebirds: A study of the central Yukon-Kuskokwim Delta, Alaska

A 6-year study of shorebird use of intertidal habitats of the Yukon-Kuskokwim Delta revealed this area to be one of the premiere sites for shorebirds throughout the Holarctic and worthy of designation as a Hemispheric Shorebird Reserve in the Western Hemisphere Shorebird Reserve Network. The study area, which covered 10% (300 km 2 ) of the delta's intertidal flats, regularly hosted 17 species of shorebirds between late April and mid-October. The greatest use was during the postbreeding period (late June-October), when Dunlins ( Calidris alpina ), Western Sandpipers ( C. mauri ), and Rock Sandpipers ( C. ptilocnemis ), each with large local nesting populations, accounted for 95% of the shorebirds recorded. Peak counts during autumn approached 300,000 birds. Considering the seasonal occurrence and turnover of populations, we estimate 1-2 million shorebirds use the central delta each year. The delta supports large fractions of the Pacific Rim or world populations of Bar-tailed Godwits ( Limosa lapponica ), Black Turnstones ( Arenaria melanocephala ), Red Knots ( C. canutus ), Western Sandpipers, Dunlins, and Rock Sandpipers. Densities of shorebirds using the central delta's four major bays and connecting coastal areas peaked at 950 shorebirds/km 2 in early September. Hazen Bay frequently hosted more than 1,200 shorebirds/km 2 . Postbreeding shorebirds used intertidal habitats in three distinct patterns according to age class. For most species (n = 7), there was a period when adults appeared first, followed by a brief interval when adults and juveniles mixed, then by a prolonged period when only juveniles remained. In the second pattern (n = 3 species), adults moved onto the intertidal flats first, were later joined by juveniles for a prolonged staging period, then migrated with them. In the third pattern (n = 3 species), only juveniles used the delta's intertidal habitat. Temporal segregation among species and age groups may minimize competition for food and thereby allow the delta to support high diversity and numbers of shorebirds.

Alaska↗
USGS1990

Taxonomic status of the rufous-bellied chachalaca (Ortalis wagleri)

The Rufous-bellied Chachalaca, Ortalis wagleri, of northwestern Mexico was merged with the morphologically different West Mexican Chachalaca, Ortalis poliocephala, on the basis of hybrids taken in the vicinity of Puerto Vallarta, Jalisco (Moore and Medina 1957). Eight specimens from that vicinity vary in appearance chronologically, from an individual similar to wagleri in 1892 through skins appearing to be F1 hybrids in 1955 to birds nearly indistinguishable from poliocephala in 1961. There is no other evidence of contact between the two forms. This is deemed insufficient evidence for considering the forms conspecific, and I recommend that Ortalis wagleri be restored to the status of species.

Condor↗
USGS1990

Water-vapor pressure in nests of the San Miguel Island Song Sparrow

The water-vapor pressure (P N ) in nests of the San Miguel Island race of Song Sparrows ( Melospiza melodia micronyx ) averaged 16 torr, but varied considerable between nests and within individual nests during successive days of incubation. Large daily fluctuations occurred throughout the incubation period and did not parallel concurrent changes in ambien vapor pressure (P 1 ). Daily rates of water loss from nest eggs (M H 2 O ) averaged 28 mg day -1 , but also varied considerable within and between nests and did not correlate with changes in P 1 . M H 2 O increased 6-33% after the third day of incubation. P N was significantly higher and M H 2 O significantly lower in nests located in sheltered gullies than in nests from a windswept slope. These data suggest that Song Sparrows do not regulate P N to achieve hatching success.

California↗
USGS1990

Factors influencing bird foraging preferences among conspecific fruit trees

The rates at which birds visit fruiting individuals of Allophylus edulis (Sapindaceae) differ substantially among trees. Such avian feeding preferences are well-known, but usually involve fruits and trees of different species. Factors controlling avian preferences for particular trees in a population of conspecifics are generally undocumented. To address this issue, I attempted to correlate rates at which individual birds and species fed in trees of Allophylus with 27 fruit or plant characteristics. Birds that swallow fruits whole were considered separately from those that feed in other ways. Plant characters were selected on the basis of their potential influence on feeding efficiency or predation risk, assuming that birds would select feeding trees so as to maximize the net rate of energy or nutrient intake and to minimize predation. Correlations were found between feeding visits by some groups of birds and percent water in the pulp, milligrams of mineral ash in the pulp, and crop size. No character was correlated with feeding visits by all groups of birds in both years of the study. The correlations with water and mineral ash are unexplained and may be artifacts. The correlation with crop size may represent a tactic to minimize predation.

Condor↗
USGS1990

Breeding biology and nesting success of palila

We studied the breeding biology of Palila (Loxioides bailleui ) at 85 nests from 20 April to 14 September 1988. Eggs were laid over a 139-day period and incubation averaged 16.6 days. The female incubated 85.2% of daylight hours and males fed incubating females. Modal clutch size was 2 (x super(-) = 2.0) and an average of 1.4 nestlings fledged per successful nest. Nestlings were in the nest an average of 25.3 days. Both females and males fed nestlings with the rate of feeding decreasing as the nestlings grew older. Palila nesting success was 25%, reduced primarily by hatching failure and depredation of nestlings. Hatching failure, due to inviable eggs or desertion, occurred in 41% of nests with eggs (55% of nest mortality). Egg depredation was rare (5% of nest mortality). Inbreeding and low food availability are postulated as the major causes for poor hatching success.

Condor↗
USGS1987

Ecology, behavior, and conservation of the Maui parrotbill

The distribution, habitat response, sexual dimorphism, foraging, breeding, and flocking behavior of Maui Parrotbills (Pseudonestor xanthophrys ) were studied over a five year period. The species' present range is confined to montane rainforest on eastern Maui, but dry lowland habitats on Maui and Molokai were occupied before Polynesian contact. Birds occurred from 1,250 to 2,150 m elevation, becoming most abundant at 1,750 to 2,000 m. In Kipahulu Valley, birds moved to lower elevations in some seasons. Birds tended to forage in the subcanopy and understory, with 66% of the prey captured 1 to 5 m above ground. Plant species use deviated from expectations based on availability. The most frequent means of prey capture was excavation for timber-boring insects in dead branches on live plants. Foraging accounted for 39% of the diurnal time budget; an average prey item appeared to account for 1% of the daily energy intake. The principal limiting factors appeared to be habitat loss, avian disease, habitat degradation, predation, and competition from exotic species. Control of pig populations is a needed management action.

Condor↗