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The feeding and vigilance behavior of the Black-tailed Godwit (Limosa limosa) were studied in an intertidal area of the Ría de Huelva, Spain, during the autumn migration. During diurnal low-tide periods, feeding was the predominant activity (80-85% of birds sampled). No significant negative relationship was observed between conspecific density and vigilance variables, and this may be related to the increases observed with group size in the intraspecific aggression and probe rates. The godwits showed greater vigilance in the presence of Black-headed Gulls (Larus ridibundus), possibly because of the kleptoparasitic activity of this species. The godwits ingested more worms during the period around low tide and fewer prey items when the air temperature was rising. The feeding rate did not decrease with the conspecific density.
This study examines predatory threats to Piping Plovers (Charadrius melodus) nesting at Breezy Point, Gateway National Recreation Area, New York. Several methods used include: 1) an evaluation of reproductive success data with documentation of predation to eggs and chicks, 2) predator surveys, and 3) an artificial nest study. The range of breeding pairs nesting from 1988-1996 was 11-19, with an average of 15.8 (SE ± 0.79) pairs/season. The average number of eggs hatched and chicks fledged per year for pairs was 2.2 ± 0.23 and 0.8 ± 0.16 respectively. Reasons for egg losses often went undetected (68%) but known sources included: tidal flooding (2%), human disturbance (4%), and predation (26%). Reasons for chick loss were generally not detected (99%). For eggs in artificial nests, overall egg removal was 84% and the two main predators based on visible footprints in sand were avian: gulls and crows. Results suggested that gulls predated significantly fewer eggs at artificial nests than crows, although they were more numerous in the area. With artificial nests, the highest egg removal occurred at a gull colony (100%), although losses were similarly high on adjacent beaches and at interior locations (greater than 90%). During the nesting season, highest removal occurred early in the field season (April - 93%) when nesting Common Terns (Sterna hirundo), which mob potential predators, had yet to arrive. Once terns arrived, rates of egg loss at artificial nests in their colony were significantly lower than that at other habitats. It is suggested that crow control, including nest removal, be added to the existing management plan that already involves gull control.
Aerial surveys of American White Pelicans (Pelecanus erythrorhynchos) were conducted over coastal Louisiana and the delta region of Mississippi on 1-2 days during December, February, and April each year from 1997 to 1999. Additional surveys were conducted in coastal Texas and Mexico during January 1998 and 1999. The numbers, location, and habitat of all pelicans observed were recorded. The coastal zone of Louisiana consistently had higher numbers of pelicans (18,000 to 35,000 birds) than other areas surveyed (3,000 to 8,000 birds), indicating that Louisiana may be the most important wintering area for American White Pelicans east of the Rocky Mountains. Among the four regions surveyed, the average size of pelican flocks was largest in Mississippi during January-February, particularly in 1999 (x̄ = 245 birds/flock). Pelican numbers in Mississippi peaked in February but in Louisiana they were more variable. Pelicans in the delta region of Mississippi were found most often in fresh water and sand bar habitats during December, flooded field habitats during February, and catfish ponds in April. In Louisiana, pelicans used fresh, intermediate, and brackish marshes during December, but showed a preference for brackish and saline marshes in February and April.
Prey taken by breeding White Storks (Ciconia ciconia) were studied using pellets collected from 1993 to 1995 within its breeding area in Greece. Prey consisted of orthopterans, coleopterans, other insects, mollusks and vertebrates. The difference in the proportions of these taxa was significant among major foraging habitats (lakes, rivers, deltas and dry habitats). With the exception of the rivers, major habitats tended to group together in clusters, suggesting that similar prey types were available to the storks in common habitat types.
The food of immature White Storks (Ciconia ciconia) feeding in meadows in Poland was studied by pellet analysis. The most important food items by numbers were insects, mainly beetles, which constituted 83% of all prey items (N = 5,958 items) and were found in all pellets (N = 163). However, by biomass, 58% of food consisted of small mammals, mainly voles Microtus sp. Insects (22%) and earthworms (11.5%) were secondary resources. Literature on White Stork diet in Europe also showed that voles, insects and earthworms were the dominant food of breeding White Storks. Their roles changed with latitude, habitat, time, as well as method of data analysis. Generally, the diet of non-breeding storks was similar to breeding birds, but more of the prey was obtained in dry habitats.
We documented roosting and foraging habitat use by Wood Storks during the post-breeding season in the coastal zone of Georgia from 1994-1998. Larger, more persistent aggregations of roosting storks typically occurred in enclosed wetlands on large estuarine islands. Smaller, more ephemeral aggregations tended to occur on salt marsh/upland ecotones, where storks appeared to be waiting for local conditions (tide levels) to become suitable for foraging. Examination of habitat types within a 2-km radius of the larger (mean >10 storks/survey) vs. smaller (mean <10 storks/survey) roosts showed that surrounding habitat structure, including those used for foraging, were similar. Foraging storks typically fed in close proximity (median = 0.5 km) to large roosts, much closer than storks using coastal wetlands during the breeding season. Tidal creeks were used almost exclusively as foraging habitat (92%). Storks and other wading birds were almost always present when the study bird arrived. The foraging patterns of study birds and four storks carrying radios suggested that storks often used the same foraging sites and/or marsh systems in the non-breeding season. Coastal Wood Storks apparently selected roosting sites based on the presence of conspecifics, abundant local prey, or possibly as shelter from adverse weather conditions.
We describe the kleptoparasitic behavior of ten adult Roseate Terns (Sterna dougallii) breeding at a colony at Falkner Island, Connecticut, USA between 1995 and 1998. These birds were considered habitual kleptoparasites because they stole fish repeatedly from other terns in every year they were observed at the site. No other breeding individuals were observed attempting to steal fish during our study. Kleptoparasitic techniques included aerial piracy, ground-based attacks, and deceptive behavior, but with one exception, each individual used one method exclusively. Success varied among individuals, but overall, kleptoparasites obtained prey at a significantly higher rate than did “honest” foragers. Eight of the ten kleptoparasites were females, suggesting a sex-biased tendency in Roseate Terns to engage in this behavior. Our observations indicate that kleptoparasitism by Roseate Terns is a specialized behavior, used regularly by only a few individuals at this breeding colony. This conclusion is consistent with a recent theoretical prediction regarding kleptoparasitism in birds.
In the east Atlantic during the latter part of the 20th century, small colonies of Northern Gannets (Morus bassanus) grew at a faster rate than big ones. In this species, colony growth occurs largely at the perimeter. Hence, the relative growth rate of a colony should be inversely proportional to the square root of its size. Data from 34 colonies confirmed this expectation. Modelling based on observed population parameters suggested that small colonies could sustain their faster growth rate only by recruiting birds from other colonies. Conversely, while large colonies grew more slowly, they reared more young than they could recruit. This implied net movement of young birds from big colonies to small ones, and showed how a population of gannets could sustain fast growth by founding new colonies.
We developed a satellite transmitter attachment technique for adult Common Loons (Gavia immer) that would help in identifying important migration routes, staging areas, and the location of wintering grounds of birds that breed in the north central United States. During the autumn and winter of 1998, the migration of six adult loons that were radio marked in northern Wisconsin and Minnesota was monitored. The results of this work offer insight into autumn movement patterns of Common Loons. Timing of autumn staging and migration to wintering grounds appeared to be related to low pressure systems that delivered winter weather to the Upper Midwest. Most of the radiomarked birds staged on the Great Lakes and then followed one of two distinct migration routes to the Gulf of Mexico and Atlantic coasts. Several of the birds used lakes and reservoirs in the southeastern United States during migration. This study provides a basis for more extensive studies of Common Loon migration.
We report the southernmost recoveries of Common Terns (Sterna hirundo) banded in the Azores archipelago, North Atlantic. Two birds banded as chicks and one bird banded as an adult were recovered at Punta Rasa, Argentina, adding support to the hypothesis of a regular movement of Common Terns between the Azores and the South American coast rather than to the African coast.
Results of surveys in the last ten years have produced more information on the wintering of the Scaly-sided Merganser (Mergus squamatus), showing that the species is dispersed widely in mainland China, with the majority of the wintering flocks of birds along the lower branch of the Yangtze River.
The relationships between wetland water conditions and breeding numbers of Mallard (Anas platyrhynchos), Northern Pintail (A. acuta), Blue-winged Teal (A. discors), and Northern Shoveler (A. clypeata) during May of 1992-1995, were examined on twelve study areas in the eastern Prairie Pothole Region. Data were collected on water levels (by wetland class [temporary, seasonal, semipermanent]), pond density (density of wet basins), and numbers of indicated pairs for each species from weekly roadside transect surveys. Comparison of models relating duck numbers to wetlands using Akaike’s Information Criterion indicated that measures of water condition generally were of similar value for explaining duck numbers. The model containing effects of semipermanent wetland water levels was among the best in explaining duck numbers for all species. Inclusion of temporary and seasonal wetland water levels in models for Mallard and Northern Pintail was not strongly supported by the data. Variation in duck numbers was much higher among areas than among years. Water conditions accounted for nearly all among-year variation for individual sites, but a large proportion of residual variation remained unexplained. Water condition measures (excluding spatial and temporal factors) explained 9-49% of variation in duck numbers, leaving 51-91% unexplained. Comparisons of these results to those of studies conducted at local or regional scale indicated that the relationship between duck numbers and pond numbers varied with scale, and suggested that other area-related factors should be considered at smaller landscape scales.
The Port of Long Beach is currently developing the former U.S. Naval Station Long Beach into a marine container terminal. When the Naval Station was operational, a large Black-crowned Night Heron (Nycticorax nycticorax) colony (up to 500 pairs) occupied mature Indian Laurel (Ficus microcarpa) and Olive (Olea europaea) trees that lined the Station streets. Although Black-crowned Night Herons are abundant throughout southern California, a nesting colony of this size is unusual. As part of an agreement with the U.S. Fish and Wildlife Service under the Migratory Bird Treaty Act, the Port agreed to relocate the colony prior to construction of the terminal. In 1999, 50 mature Indian Laurel, Olive, and Paperbark (Melaleuca sp.) trees were boxed and transported to a location in the port approximately two km from the original site. The relocated trees supplemented approximately 70 trees and bushes already at the location, formerly a park. Black-crowned Night Heron decoys were placed in the trees, heron vocalizations recorded from the original colony site were played twice per day, and public access to the site was eliminated. Three years of monitoring have shown that nesting has been successful and has increased at the relocation site; in 2000, 1,128 young were produced from 423 nests. Three years remain in the monitoring plan. No other documented relocation of an entire Black-crowned Night Heron colony of this size is recorded.
Magellanic Penguins (Spheniscus magellanicus) show little sexual dimorphism, and although males are usually larger than females, sexing by direct observation may be difficult, especially in the case of chicks. In this paper we evaluate the utility of four different PCR-based sex determination techniques using genomic DNA for sexing Magellanic Penguins. We found that the primer set designed for sex determination in Collared Flycatcher (Ficedula albicollis) also provided a reliable, simple and convenient sexing procedure for Magellanic Penguins. Additionally, we obtained discriminant functions for sexing adults and chicks, sampled at six colonies differing in size and other ecological characteristics. Discriminant function for adults used two variables, bill length and bill depth that correctly classified 97% of the birds. Discriminant function for chicks included bill length and flipper length and correctly classified 78% of the individuals. Although molecular and biometric approaches could be useful for sexing adult Magellanic Penguins, only molecular procedures proved appropriate for accurately sexing chicks.
Miniaturized temperature loggers placed in Red-necked Grebe (Podiceps grisegina) nests revealed that 16 of the 32 monitored pairs abandoned their nests for extended periods lasting 3-9 h during at least two of the three nights that they were monitored. When incubating pairs left their nests unattended, temperatures of the thermistored egg usually dropped precipitously to below 30°C within 15-25 min. Duration of a pair’s incubation period was positively associated with the number of minutes that the thermistored egg was below 30°C in our 3-day samples, yet nesting success remained high. Embryos appeared to be tolerant of this cooling; 26 of the 32 monitored nests hatched young, and there was no detectable increase in the failure of eggs to hatch for pairs neglecting their clutches more than 3 h per night. We suggest Red-necked Grebes preemptively leave their nests at night to avoid predation on their eggs or themselves.
The richness and abundance of waterbird species were compared in active and abandoned saltpans in southeastern Spain. The effects of traditional methods of salt extraction in Mediterranean wetlands on the avian community were evaluated, as well as the effects of the abandonment of coastal salinas in Europe due to their present low profitability. Major changes in the waterbird community were found in disused saltpans, which were mainly due to environmental changes after salt production ceased. The diversity of bird species and the abundance of the diving species increased following abandonment, but the number of Greater Flamingo (Phoenicopterus ruber) and some shorebirds declined. Management measures required to improve the ornithological diversity in abandoned saltpans are proposed.
This study examines the survival of first and second hatched White-faced Ibis (Plegadis chihi) nestlings from fledging until colony dispersal (age 8-42 days) in Lahontan Valley, Nevada, using the Kaplan-Meier method. Out of 81 radiomarked nestlings sampled from six colonies during a two-year period (1995 and 1997), 18 died before reaching the age of 42 days and eleven were excluded from consideration. No evidence was found to suggest that survival rates of first and second hatched nestlings were different within or among years. The overall nestling survival rate was 76% ± 0.05 SE. The primary mortality source was inclement weather exposure. Weekly conditional survival rates were highest during the first week (99% ± 0.01 SE), and lowest in the second (87% ± 0.04 SE) and fourth (93% ± 0.03 SE) weeks of life.
Capture techniques were developed to study the American Bittern (Botaurus lentiginosus). Mirror traps, mist nets, landing nets, night capture, funnel traps and net gun techniques were evaluated. Mirror traps and mist nets were used with a tape recording of the pumping call of the male bittern. Mist nets were also used to capture females at nest sites. Long-handled fish landing nets were used to capture molting birds and females on nests. Funnel traps were set at feeding sites. Mirror traps had a 50% success rate and were the most efficient means of capturing males. Mist nets were versatile with success rates of 40% on males and 50% on females. Landing net success was 76% on males and 70% on females but restricted to specific situations. Night capture was successful 33% of the time and only on molting birds. Net guns had limited success (6%) due to lack of skill and difficult to get close to birds. Funnel traps were not fully tested.