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At least 595 records · Page 33Linked to original sources
USGS1999

Predicting chick survival and productivity of Roseate Terns from data on early growth

Early growth of Roseate Tern (Sterna dougallii) chicks is a strong predictor of chick survival and hence of productivity. We developed discriminant functions to predict chick survival from body-masses measured during the first 3 days of life. Productivity is estimated by assuming that almost all A-chicks (first-hatched in each brood) survive to fledging, and using the discriminant functions to predict survival of B-chicks (second-hatched in each brood). A relation between survival rates and classification rates is derived, allowing discriminant function results to be used in predicting survival rates. In the absence of predation, the resulting estimates of chick survival and productivity are almost as good as those obtained by more intensive methods, but require much less effort and much less disturbance. This approach might be useful for other seabird species in which chick survival is determined primarily by parental performance.

Waterbirds↗
USGS2006

Nest fate and productivity of American Oystercatchers, Cumberland Island National Seashore, Georgia

The American Oystercatcher (Haematopus palliatus) is listed as a species of high priority by the U.S. Shorebird Conservation Plan and is state-listed as rare in Georgia; however, biologists have not focused on identifying the causes of egg and hatchling losses. In 2003 and 2004, continuous video monitoring was used to document reproductive success of American Oystercatchers and identify causes of nest failure at Cumberland Island National Seashore, Georgia. The modified Mayfield method and program CONTRAST were used to determine and compare survival of eggs and nestlings. Eleven pairs made 32 nest attempts during two seasons. Nine attempts were successful, fledging 15 chicks. Daily survival of clutches was 0.973 (95% CI = 0.960-0.987) for 2003, 0.985 (95% CI = 0.974-0.995) for 2004, and 0.979 (95% CI = 0.970-0.987) for combined years. Daily survival was greater on the North End, than on the South End of the island (X21 = 7.211, P = 0.007). Eighteen of 20 nest failures during the egg stage and one of eight chick losses were documented. Egg predators included raccoon (Procyon lotor, N = 9), bobcat (Lynx rufus, N = 3), and American Crow (Corvus brachyrhynchos, N = 1). A ghost crab (Ocypode quadata) preyed on one chick. Other causes of nest failure were tidal overwash (N = 1), horse trampling (N = 1), abandonment (N = 2), and human destruction (N = 1). The North End of the island has one of the highest reproductive rates reported along the Atlantic coast. Predator control may be an effective means of increasing reproductive success on the South End of the island.

Waterbirds↗
USGS2008

Effects of human activity of breeding American Oystercatchers, Cumberland Island National Seashore, Georgia, USA

Abstract.-Increased human use of coastal areas threatens the United States population of American Oystercatchers (Haematopus palliatus), a species of special concern. Biologists often attribute its low numbers and reproductive success to human disturbance, but the mechanism by which human presence reduces reproductive success is not well understood. During the 2003 and 2004 breeding seasons, 32 nesting attempts of American Oystercatchers were studied on Cumberland Island National Seashore (CINS). Behavior was examined with and without human activity in the area to determine how human activity affected behavior. The oystercatchers' behavioral responses (proportion time) were analyzed with and without human or intraspecific disturbances using mixed models regression analysis. Proportions of time human activities were present (< 300 m from oystercatchers) during observations averaged 0.14 (N = 32, 95% CI = 0.08-0.20). During incubation, pedestrian activity near (< 137 m) oystercatchers reduced the frequency of occurrence of reproductive behavior, but pedestrian activity far (138-300 m) from oystercatchers had no effect. Vehicular and boat activities (< 300 m) had minimal effects on behavior during incubation. During brood rearing, an effect of pedestrian activity near oystercatchers was not evident; however, pedestrian activity far from oystercatchers increased the frequency of reproductive behavior. Vehicular and boat activity had no effects on behavior during brood rearing. Of 32 nesting attempts, two failed (<10%) because of human disturbance and were located in areas of greater human activity (south end). Managers on CINS should minimize pedestrian activity near nests (< 137 m) during incubation. During brood rearing, protection from pedestrian activity should be increased, when possible, to >137 m and vehicular activity should be minimized at current levels or less.

Waterbirds↗
USGS2008

Temporal variation in adult survival rates of Roseate Terns during periods of increasing and declining populations

We used 19 years of mark-recapture/resighting data collected on 11, 020 birds from 1988-2006 at five colony sites in Massachusetts, New York, and Connecticut, USA, to examine temporal variation in the survival rates of adult Roseate Terns (Sterna dougallii) during periods of overall population increase (1988-2000) and decline (2000-2006). Roseate Terns nested at only one colony site in Buzzards Bay, Massachusetts at the start of this period, but two more sites in this area were recolonized as the study progressed. Adult survival rates varied temporally in overall population increase (0.835 +/- 0.006 SE) and the period of population decline (0.835 +/- 0.008 SE). As expected based on previous work, adult survival from 1991 to 1992 was lowered as a result of a severe hurricane in August 1991. An oil spill in Buzzards Bay in April 2003 did not appear to result in lower survival of the birds nesting at the variation in other vital rates of this species (such as postfledging survival) needs to be examined to determine the likely cause(s) of the recent population decline.

Waterbirds↗
USGS1997

Numbers and distribution of Double-crested Cormorants on the upper Mississippi river

Historic records indicate that Double-crested Cormorants (Phalacrocorax auritus) were common breeders and abundant during migration on the Upper Mississippi River from St. Paul, Minnesota, to St. Louis, Missouri, during the 1940s and 1950s. Their numbers declined in the mid- to late-1950s, remained low through the 1970s, and began to increase somewhat in the late 1980s. Aerial surveys of migrating cormorants and ground surveys at cormorant colonies during 1991-1993, indicate that numbers have not returned to historic levels. Only 500-2,000 cormorants were seen during spring migration 1992-1993; and 5,000-7,000 during fall migration 1991-1992; whereas, tens of thousands were reported in the 1940s and 1950s. Four hundred ninety-six nests were counted at 4 colonies in 1992, and 545 nests were counted in 9 colonies in 1993; whereas, during the 1940s and 1950s, about 2,500 birds were reported nesting in 4 locations. Pools 6 and 13 have always attracted breeding and migrating cormorants, currently attract the largest numbers of cormorants during migration, and still support breeding colonies.

Waterbirds↗
USGS1997

Population trends of Black Terns from the North American Breeding Bird Survey, 1966-1996

Data from the North American Breeding Bird Survey indicate a survey-wide decline in Black Terns (Chlidonias niger) at an average rate of 3.1% annually during 1966-1996. Black Terns in Canada decreased at an average annual rate of 3.5% during this interval, while the United States population showed no significant trends. These long-term declines largely reflect trends prior to 1980, when the continental, Canadian, and United States populations decreased at average annual rates of 7.5%, 5.6%, and 11.9%, respectively. Most population trends were reversed during the 1990s, causing trend estimates over the 1980-1996 interval to become more positive. Associations between patterns of change in Black Terns, Mallards (Anas platyrhynchos), and numbers of ponds in the northern Great Plains suggest some relationships exist between habitat availability and the population trajectories.

Waterbirds↗
USGS1997

Spring prey use by double-crested cormorants on the Penobscot River, Maine, USA

We analyzed 2 sets of data for Double-crested Cormorant (Phalacrocorax auritus) stomach contents (including esophageal contents) that were collected from April through June of 1986-1988 (N = 580) and 1992-1993 (N = 200) on the Penobscot River, Maine. Our objectives were to examine temporal and spatial variation in the spring diet and estimate the importance of Atlantic salmon (Salmo salar) smolts to the cormorant diet. We analyzed stomach contents relative to samples from 3 river sections: 5 mainstem dams collectively, above the head of tide, and free-flowing areas above and below the head of tide. Between years composition of taxa lists were compared (P = 0.05) relative to time and river section. We estimated taxon importance for data collected during 1992-1993 by ranking taxa according to 3 statistics: frequency of occurrence, mean percent volume, and numerical abundance. Data from 1986-88 were analyzed by frequency of occurrence only. Across the 3 river sections, the number of prey species recovered from cormorant stomachs increased from 15 in late April to at least 31 through May. Cormorants collected above the head of tide consumed 12 fish species (including freshwater, anadromous, and catadromous types), whereas birds collected below the head of tide consumed 28 freshwater and seasonally-available estuarine, marine benthic, and pelagic species. Salmon smolts were not recovered from stomachs collected in April, rare in stomach samples during the first week of June, and absent from the diet thereafter. In contrast, smolts were among the 5 most frequently occurring (1986-88) and highest ranking (1992-1993) prey taxa across the 3 river sections through May.

Waterbirds↗
USGS1997

Nesting season food habits of 4 species of Herons and Egrets at Lake Okeechobee, Florida

Based on the composition of nestling regurgitations collected during 3 breeding seasons, fish were the most important prey group for Great Egrets (Ardea alba: N = 200 nest-day samples; aggregate percent biomass [APB] = 73.4%), Snowy Egrets (Egretta thula: N = 115; APB = 91.4%), and Tricolored Herons (E. tricolor. N = 68; APB = 97.3%). For Little Blue Herons (E. caerulerr. N = 57), grass shrimp (Palaemoneles paludosus; APB = 39.7%) ranked higher in overall importance than all fishes combined (APB = 36.5%). Dietary overlap, as measured by Schoener's Similarity Index, was greatest between Snowy Egrets and Tricolored Herons (77%) and lowest between Tricolored Herons and Little Blue Herons (30%). Diet diversity, as measured by Shannon's Index, was highest for Great Egrets (2.04), intermediate for Snowy Egrets (1.71) and Tricolored Herons (1.68), and lowest for Little Blue Herons (1.60). Great Egrets ate a wider variety of fish species and sizes, especially larger fishes, and more crayfish than the other species. Little Blue Herons ate fewer fish and more grass shrimp and insects, and ate smaller forage fishes than Tricolored Herons but similar-sized fish as Snowy Egrets. The coarse-scale trophic composition of Snowy Egret and Tricolored Heron diets did not differ significantly, but Tricolored Herons ate larger forage fishes than Snowy Egrets. Pronounced interannual and intercolony variation in diet composition suggested that Great Egrets and Little Blue Herons switched prey types as hydrologic conditions and habitat availability changed. Conversely, lack of such variation suggested that Snowy Egrets and Tricolored Herons adjusted their foraging tactics to ensure contin-ued encounters with preferred prey despite changing habitat conditions. These results are generally consistent with other published data, help confirm some generalizations about foraging strategies and patterns of niche differentiation among these ecologically similar species, and have implications for managing the Lake Okeechobce ecosystem.

Waterbirds↗
USGS1997

Female Roseate Tern fledges a chick following the death of her mate during the incubation period

Despite the death of her mate during the incubation period and a shortage (or lack of availability) of food in nearby waters, a female Roseate Tern (Sterna dougallii) nesting at the Falkner Island Unit of the Stewart B. McKinney National Wildlife Refuge in Connecticut was able to raise a chick to fledging in 1995 without human assistance. The growth and development of this chick was slower than that of other single chicks in the colony; it never weighed more than 90 g and did not fledge until 32 days of age. Despite this exceptional female's ability to rear a chick on her own, this observation supports the idea that biparental care is important in Roseate Terns, particularly during years of food shortage.

Waterbirds↗
USGS1997

Evidence of secondary consumption of invertebrate prey by Double-crested Cormorants

The piscivorous nature of the Double-crested Cormorant (Phalacrocorax auritus) is well documented. However, many researchers who have used regurgitated pellets to describe the diet of cormorants report that invertebrates compose a small but consistent portion of the diet. We examined the hypothesis that invertebrates found in pellets are primarily the result of secondary consumption. We used odds ratio analysis to examine associations in 2,846 individual pellets between the presence of specific invertebrate prey and the presence of fish species known to consume those invertebrate taxa. Significant (P < 0.05) relationships occurred between gastropods and pumpkinseed (Lepomis gibbosus) and ictalurids, and between decapods and rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu). Significant (P < 0.05) relationships were also found between pelecypods and pumpkinseed and ictalurids. We suggest that the invertebrate prey we observed in pellets were present in the digestive tracts of fish that were consumed by Double-crested Cormorants and hence represent secondary consumption by cormorants. We conclude that consumption of invertebrates by Double-crested Cormorants may be overestimated in the literature in instances where the diet was described using pellets.

Waterbirds↗
USGS1998

History and status of introduced mammals and impacts to breeding seabirds on the California channel and Northwestern Baja California Islands

The California Channel Islands, U.S.A., and Northwestern Baja California Islands, Mexico, host important breeding populations of several seabird species, including the endemic Black-vented Shearwater (Puffinus opisthomelas) and Xantus' Murrelet (Synthliboramphus hypoleucus). Mammals introduced to nearly all of the islands beginning in the late 1800s to early 1900s include: cats (Felis catus), dogs (Canis familiaris), Black Rats (Rattus rattus), rabbits and hares (Leporidae), goats (Capra hirca), sheep (Ovis ones), and other grazers. Cats, dogs and rats are seabird predators, grazers such as goats and sheep cause habitat degredation, and rabbits destroy habitat and compete with hole-nesting seabirds. Cats, which were introduced to at least 19 islands and currently occur on ten islands, have had the greatest impacts on seabirds, including the extinction of the endemic Guadalupe Storm-Petrel (Oceanodroma macrodactyla). Cats are known to have eliminated or severely reduced colonies of Black-vented Shearwaters, Cassin's Auklets (Ptychoramphus aleuticus) and Xantus' Murrelets. Black Rats have occurred on a minimum of seven islands and have reduced numbers of small, hole-nesting alcids on at least one island. At many islands, defoliation and erosion caused by rabbits and large grazing mammals has been severe. Their effects on seabirds are not well documented but potentially are serious. Impacts from introduced mammals have been most severe on islands with no native mammalian predators. On the Northwestern Baja California Islands, temporary and permanent human settlements have led to a greater diversity and source of introductions. Programs to remove introduced mammals and to reduce the possibility of future introductions are needed to restore seabird populations and to preserve the biodiversity of the region. Surveys are needed particularly on the Northwestern Baja California Islands to update the status and distribution of seabirds and to further assess impacts from introduced mammals.

Waterbirds↗
USGS1998

Status of the White-faced Ibis: Breeding colony dynamics of the Great Basin population, 1985-1997

The status of the White-faced Ibis (Plegadis chihi) in the Great Basin is of concern because of its small population size and the limited and dynamic nature of its breeding habitat. We analyzed existing annual survey data for the White-faced Ibis breeding in the Great Basin and surrounding area for 1985-1997. Methods varied among colonies and included flight-line counts and fixed-wing aircraft and helicopter surveys. The number of White-faced Ibis breeding pairs in the Great Basin area has nearly tripled since 1985, despite years of severe flooding and drought at major breeding areas. This growth is reflected in both peripheral (i.e., Oregon, California, Idaho) and core (i.e., Nevada and Utah) components of the population. Our data on colony dynamics in Oregon and Nevada illustrate the ability of the highly nomadic White-faced Ibis to compensate for poor conditions at traditional colony sites by moving among colonies and rapidly colonizing newly available wetlands. We suggest that the White-faced Ibis would benefit from a landscape mosaic of well-distributed peripheral wetlands and persistent colony sites. The nomadic nature of the White-faced Ibis and the dynamic nature of their breeding habitat necessitates that wetland management decisions and population monitoring be conducted in a regional context.

Waterbirds↗
USGS1998

Diets of nestling Gull-billed Terns in coastal Virginia

We studied the diets of nestling Gull-billed Terns (Sterna nilotica) at colonies in coastal Virginia during the breeding seasons of 1995 and 1996 as part of a long-term study of the species. No previous quantitative assessments had been made of diets of this species anywhere along the Atlantic Coast, and only a few observations had been reported from other coastal areas in the southern United States. During 80 h of observations over the two seasons, 757 feeding observations were made, primarily at two colony sites. We examined how prey type (fish, marine invertebrates, terrestrial prey) and size were influenced by year, tide cycle, season (early and late) and age of the young (small chicks <7 d old versus large chicks >7 d). We did not find significant year differences, but all other factors revealed statistically significant results. Older (>7 d) chicks were fed relatively more terrestrial and marine invertebrate prey than were younger chicks. In June (early season), fewer fish and terrestrial prey were fed to chicks than later (July-August). Most prey were less than one bill length in size, with the majority of the smallest prey being marine invertebrates. Tide cycle influenced prey delivered with terrestrial prey becoming relatively more important during high and ebb periods than during low and flood tides when aquatic prey dominated. The major marine invertebrate prey taken was the fiddler crab (Uca spp.). Terrestrial prey consisted mostly of large odonates and orthopterans. Unlike earlier reports from Europe, we found no regurgitated food pellets in any of the colonies in either year. This study confirms that the Gull-billed Tern is an extremely opportunistic feeder and has adapted to a variety of habitats, helping to explain its cosmopolitan distribution.

Waterbirds↗
USGS1998

Key areas for wintering North American herons

Nearly all North American heron populations are migratory, but details of where they winter are little known. Locations where North American herons winter were identified using banding recovery data. North American herons winter from Canada through northern South America but especially in eastern North America south of New York, Florida, California, Louisiana, Texas, Mexico and Cuba, these areas accounting for 63% of winter recoveries. We identified regions where recoveries for various species clustered as "key areas." These forty-three areas constitute a network of areas that hold sites that likely are important to wintering North American herons. Within each area, we identify specific sites that are potentially important to wintering herons. The relative importance of each area and site within the network must be evaluated by further on the ground inventory. Because of biases inherent in the available data, these hypothesized key areas are indicative rather than exhaustive. As a first cut, this network of areas can serve to inform further inventory activities and can provide an initial basis to begin planning for the year-round conservation of North American heron populations.

Waterbirds↗
USGS1999

Seasonal movements, migration, and range sizes of subadult and adult Bamforth Lake California Gulls

We investigated seasonal migration patterns of three age classes of California Gulls (Larus californicus). Using band recovery data and reported sightings of patagially marked gulls, we constructed location maps for fledglings, one to two-year-old gulls, and breeding-age adult gulls during five time periods: spring migration, breeding season, early and late fall migration, and winter. Using repeated observations, we also produced a location map with directional vector plots. Gulls followed a triangular pattern of movements. At the conclusion of breeding, gulls migrated west and northwest to the Pacific coast, distributing themselves mainly between San Francisco and British Columbia. During winter, gulls moved south along the Pacific coast and by spring were concentrated in southern California and northern Mexico. The range size was largest among fledgings which provided the northernmost and southernmost observations for the population. Few subadult gulls migrated to the breeding colony. During the breeding season, a substantial portion of breeding-aged adults remained on the Pacific coast and throughout the intermountain west but were not observed at other California gull colonies. While fledgings moved directly toward the Pacific coast at the end of the breeding season, many adults lingered near the colony site at aquatic habitats south of the colony. We suggest that adults remain longer in the area to feed and to rejuvenate before attempting migration.

Waterbirds↗
USGS2000

Performance of implantable satellite transmitters in diving seabirds

We report on the first deployment of satellite transmitters in large alcids. In 1995 and 1996, we surgically implanted 51 transmitters in Common and Thick-billed murres ( Uria aalge and U. lomvia ) and Tufted Puffins ( Fratercula cirrhata ) at three colonies in Alaska. These devices furnished more than 2,900 locations over succeeding months (eight months maximum transmitter life), some 30-40% of which had calculated errors of <1,000 m. We considered other data to be reliable if locations were repetitive within a short period of time. As measures of data collection efficiency, we calculated location indices (number of locations per hour of transmission) of 0.44 during the breeding season and 0.35 overall. Those values compared favorably with satellite transmitters previously deployed on large mammals at similar latitudes. Transmitters did not last as long as expected because lithium batteries tended to self-discharge when kept at the high internal temperature of a bird. Most importantly, we encountered high mortality of instrumented birds, especially in the interval from 11-20 days after release. Our results suggest that radio transmission itself somehow impaired normal feeding behavior or otherwise compromised the birds' health. Those two problems (battery life and bird mortality) will need to be solved before implantable devices can be applied effectively to the same or similar species in the future.

Alaska↗
USGS2000

Do male breeding displays function to attract mates or defend territories? The explanatory role of mate and site fidelity

Many shorebirds show elaborate breeding displays that include aerial flights and ground displays accompanied by song. The mate attraction hypothesis suggests that breeding displays function to attract mates and maintain pair bonds, whereas the territory defense hypothesis suggests breeding displays function in defining and defending nesting and feeding territories. We tested these hypotheses in the Western Sandpiper ( Calidris mauri ) by contrasting the duration and level of male breeding displays among pairs that differed in their mate and site fidelity. As predicted by the mate attraction hypothesis, males performed the highest number of song sequences during pair formation, and males paired with their mate of a prior year sang less than males paired to new mates. Further, sitefaithful males mated to a new but experienced mate displayed significantly more than remated males or males new to the area. This suggests a male's prior familiarity with an area and his neighbors does not lessen his display rate as was predicted under the territory defense hypothesis. Limited support for the territory defense hypothesis came from observations of males performing breeding displays with neighboring males along nest territory boundaries. This behavior was short-lived, however, as males abandoned nesting areas after pair-formation and used adjacent or disjointed feeding areas during egg-laying and incubation. Male aggression (i.e., aerial and ground chases), as opposed to breeding displays, appeared to be the principal means of maintaining territory boundaries. Indeed, the rate at which males chased other males remained fairly constant and high throughout the breeding season. Male chasing behavior may also serve as a paternity guard to protect against extra-pair copulations. Our study also found that a female's prior breeding experience in an area correlated with a reduced display rate by her mate, particularly if that mate was new to the area. This indicates female characteristics may not only drive nest initiation, as has been shown in other studies, but are important in determining the duration and extent of male display.

Alaska↗
USGS2001

Selection of habitats by Emperor Geese during brood rearing

Although forage quality strongly affects gosling growth and consequently juvenile survival, the relative use of different plant communities by brood rearing geese has been poorly studied. On the Yukon-Kuskokwim Delta, Alaska, population growth and juvenile recruitment of Emperor Geese (Chen canagica) are comparatively low, and it is unknown whether their selection of habitats during brood rearing differs from other goose species. Radio-telemetry was used to document the use of habitats by 56 families of Emperor Geese in a 70 km2 portion of the Yukon-Kuskokwim Delta during brood rearing in 1994-1996. When contrasted with available habitats (a set of six habitat classes), as estimated from 398 random sampling locations, Emperor Geese strongly selected Saline Ponds, Mudflat, and Ramenskii Meadow habitats and avoided Levee Meadow, Bog Meadow, and Sedge Meadow. These selected habitats were the most saline, comprised one-third of the study area, and 43% of all locations were in Ramenskii Meadow. I contrasted these Emperor Goose locations with habitats used by the composite goose community, as inferred from the presence of goose feces at random locations. The marked difference between groups in this comparison implied that Cackling Canada Geese (Branta canadensis minima) and Greater White-fronted Geese (Anser albifrons) collectively selected much different brood rearing habitats than Emperor Geese. Received 20 February 2001, accepted 18 April 2001.

Waterbirds↗