Showing papers in "Waterbirds: The International Journal of Waterbird Biology in 2001"
TL;DR: The authors studied American Oystercatchers (Haematopus palliatus) by examining reproductive success and the factors affecting it at one location, and by examining the status and trends of breeding population numbers from Florida to Nova Scotia on the east coast of North America.
Abstract: -We studied American Oystercatchers (Haematopus palliatus) by examining reproductive success and the factors affecting it at one location, and by examining the status and trends of breeding population numbers from Florida to Nova Scotia on the east coast of North America. We conducted our field research on Cape Lookout National Seashore, Carteret County, North Carolina from 1997 to 1999, and we documented larger scale breeding population trends by contacting state biologists and reviewing the literature and historical accounts. Presence of eggs and young were checked two to five times per week (by observing from a distance), and efforts were made to determine the reasons for loss of the nest contents. We monitored a total of 245 nests and found low productivity. At least one egg in 32 (13%) nests hatched and one or more chicks fledged from 12 broods. Overall, 14 chicks successfully fledged (nine from North Core Banks and five from South Core Banks) during the three years of the study. Of the 213 clutches that did not hatch, 163 (76%) failed because of predation, and 46 (22%) because of overwash or severe weather. Our minimum estimate for the number of oystercatchers breeding along the entire Atlantic coast and the Gulf coast of Florida is 1,624 pairs. North of Virginia, numbers appear to be stable or slowly increasing and the species has expanded as far north as Cape Sable Island in Nova Scotia. From Virginia south, breeding numbers show a decline in recent years. The number of oystercatchers breeding on barrier islands in Virginia has decreased by more than 50% in the last 20 years. Given their relatively small numbers and inherently low productivity, American Oystercatchers are at risk in rapidly changing coastal ecosystems. Received 1 June 2000, accepted 11 October 2000.
58 citations
TL;DR: The median density of shorebirds during their non-breeding season on the coast of South America was significantly greater in coastal zones with high primary productivity than in zones with moderate and low primary productivity.
Abstract: -The median density of shorebirds during their non-breeding season on the coast of South America was significantly greater in coastal zones with high primary productivity than in zones with moderate and low primary productivity. A world-wide review showed that sites harboring large numbers of wintering and migratory shorebirds corresponded significantly with regions of high coastal zone productivity. We suggest that the spacing of rich intertidal foraging habitats along the world's coastlines has been an important feature in the evolution of long distance migration by shorebirds. Received 16 November 2000, accepted 20 December 2000.
57 citations
TL;DR: Caziani et al. as discussed by the authors presented a paper on Caziani, Sandra Monica, and Isabela, which was published by the Consejo Nacional de Investigaciones Cientificas and Tecnicas.
Abstract: Fil: Caziani, Sandra Monica. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Salta; Argentina
49 citations
TL;DR: The scarcity of vectors due to the marine environment and the dry conditions around the colonies is the most plausible hypothesis for explaining the apparent absence of blood parasites in the Patagonian seabird community, although other hypotheses should be examined.
Abstract: Fil: Jovani, Roger. Consejo Superior de Investigaciones Cientificas. Estacion Biologica de Donana; Espana
46 citations
TL;DR: The diet of Common Terns, which breed in North America and migrate into the southern hemisphere in winter, show a wide nonbreeding distribution that includes the Atlantic coasts of Argentina and Brazil, was assessed by the analysis of regurgitated pellets collected at Punta Rasa.
Abstract: -Common Terns (Sterna hirundo), which breed in North America and migrate into the southern hemisphere in winter, show a wide nonbreeding distribution that includes the Atlantic coasts of Argentina and Brazil. At Punta Rasa (Samborombon Bay, Argentina), there were about 30,000 Common Terns. Their diet in winter was assessed by the analysis of regurgitated pellets collected at Punta Rasa. Adult Coleoptera, Odonata, Orthoptera and Hemiptera were the main insects found in the diet. A total of 14 species of fishes were identified. Argentine Anchovy (Engraulis anchoita) and Anchovy (Anchoa marinii) (Family Engraulidae), represented 79% by number and the 78% of the consumed biomass of fish prey. The average length of fish prey was 90.0 ? 17.6 mm. Half the prey lived in seawater, while the other half was taken in estuarine or seawater. There was no evidence of fish prey taken by terns foraging in freshwater habitats. Total consumption of food was estimated as 106 tons of fish (most of themjuvenile) during a five month period at Punta Rasa. Received 6 August 2000, accepted 9 December 2000.
32 citations
TL;DR: In this paper, the authors compared shorebird behavior, abundance and prey availability between natural and created wetlands along the Gulf of Mexico, Texas, USA, and found no significant differences in invertebrate density or biomass between sites.
Abstract: -We compared shorebird behavior, abundance and prey availability between natural and created wetlands along the Gulf of Mexico, Texas, USA. Locations included Aransas National Wildlife Refuge, the Nueces River Delta, and Mustang Island. Few significant differences existed in invertebrate density or biomass between sites; greater differences were found seasonally than between natural and created sites. Non-metric multidimensional scaling of avian abundance separated Mustang Island from Nueces Delta. Cluster analysis of behavior of Black-bellied Plover (Pluvialis squatarola), Long-billed Curlew (Numenius americanus), "peeps" (Calidris minutilla, C. pusilla), and Willet (Catoptrophorus semipalmatus), showed no clear differences in their behavior on natural and created sites. Mustang Island sites were more similar to each other than to Nueces Delta. All created sites had natural hydrology and tidal circulation, which appear to facilitate invertebrate and avian recruitment. Received 12 February 2001, accepted 12 August 2001.
30 citations
TL;DR: During 13 visits to the State of Rio Grande do Sul, Brazil outside of the breeding season, stomachs were collected from 144 dead and randomly selected first-year Magellanic Penguins Spheniscus magellanicus and their contents analyzed.
Abstract: -During 13 visits to the State of Rio Grande do Sul, Brazil outside of the breeding season, stomachs were collected from 144 dead and randomly selected first-year Magellanic Penguins Spheniscus magellanicus and their contents analyzed. Cephalopods were an important item in the diet and were found in 76% of the stomachs, averaging five cephalopod beaks per stomach. The following cephalopods were identified from the remains: Illex argentinus, Histioteuthis sp., Loligo sp., L. sanpaulensis, L. plei, Argonauta nodosa and one specimen of family Cranchiidae. Smaller numbers of fish and fish otoliths (less than one per stomach); a few Hydrozoa, Isopoda and Salpa sp. were also found. Parasitic Nematoda were recorded in 80% of the stomachs. Many of the cephalopods were small and were probably planktonic. Maximum size of prey were larger than those reported from the breeding season. Received 1 October 2000, accepted 16January 2001.
29 citations
TL;DR: The worldwide rare Steller's Eider seems to be a specialist with limited ability to exploit different food resources, while the numerous Long-tailed Duck is an opportunistic generalist.
Abstract: -We examined the flexibility in feeding ecology of Steller's Eider (Polysticta stelleri) by comparing its diet to the taxonomically relatively close Long-tailed Duck (Clangula hyemalis) during two winter periods (early and late) when the two species occurred together. Steller's Eider generally fed on the same type of prey in early and late winter, with a dietary overlap of 43% between the two periods (57% among shelled prey). The mean number of prey species per bird was 7.8 in both early winter and late winter. In contrast, the Long-tailed Duck changed completely from feeding on benthic invertebrates in early winter to spawning Capelin (Mallotus villosus) in late winter. The dietary overlap between the two bird species was 38% in early winter. In early winter, the mean number of prey species was 5.5 in the Long-tailed Duck, and not significantly different from the Steller's Eider. Steller's Eider seemed to be restricted to small prey, both compared to availability of sizes and also to the prey size taken by the Long-tailed Duck. Thus the worldwide rare Steller's Eider seems to be a specialist with limited ability to exploit different food resources, while the numerous Long-tailed Duck is an opportunistic generalist. Low flexibility in feeding ecology indicates that winter habitats for Steller's Eider may be limited, and protection of these areas would probably benefit the species. Received 28June 2001, accepted 25 August 2001.
29 citations
TL;DR: Oystercatchers showed stronger site fidelity to territories where chicks were fledged than territories where they failed to raise young.
Abstract: -We compared reproductive success and territory fidelity in Black Oystercatchers (Haematopus bachmani) in the Strait of Georgia, British Columbia. Twenty-four of 34 nesting pairs hatched eggs in at least one year of the study, and of which 16 pairs raised chicks that fledged. Mean fledging production for 34 pairs in 1996 and 1997 was 0.44 fledglings per breeding pair per year. Thirty of the 34 pairs observed used the same territory in 1996 and 1997. Of the 30 pairs that occupied the same territory in both years, 16 pairs failed to raise chicks in both years, seven pairs fledged chicks in one year and seven pairs fledged chicks in both years. Oystercatchers showed stronger site fidelity to territories where chicks were fledged than territories where they failed to raise young. Received 23 October 2000, accepted 23 February 2001.
29 citations
TL;DR: In this article, the authors conducted surveys in five fishing villages in northern Peru to estimate seabird by-catch and 29 fishermen were interviewed and found that over 40% of hooked seabirds were albatrosses.
Abstract: -Longlining has been encouraged in Peru as an opportunity for small-scale fishermen to reduce cetacean mortality in gill nets. Very little is known about seabird by-catch in this longline fishery. In January 1999, we conducted surveys in five fishing villages in northern Peru to estimate seabird by-catch and 29 fishermen were interviewed. Eighty percent of the fishermen used frozen bait, which increases the probability of seabird mortality. Ninety percent of fishermen confirmed that birds are hooked while setting the gear. Additionally, we found that over 40% of hooked seabirds were albatrosses. The most common albatross off northern Peru is the Waved Albatross (Phoebastria irrorata) and about 60% of the population of the Chatham Island Albatross (Thalassarche eremita) winters off Peru. Both species are considered threatened due to their small population sizes. Seabird by-catch in the Peruvian small-scale longline fishery should be of conservation concern; pooled estimates of by-catch rates based on interviews were 1 to 2 birds/1,000 hooks. The estimated by-catch of albatrosses by the entire fleet is likely to lie between 2,370 and 5,610 birds each year, which represents between 5% and 13% of the pooled populations of the Waved and Chatham Island Albatrosses. Even though these numbers are extrapolations, they can be considered a rough indicator of the magnitude of the seabird by-catch by the small-scale longline fishery in Peru. Further research that includes onboard seabird by-catch surveys as well as a larger sample of interviews with fishermen are required. Public awareness that encourages the implementation of by-catch deterrence measures such as bird lines, night setting of hooks, and the use of fresh bait, will help reduce by-catch and bait loss, thus benefiting fishermen and promoting albatross conservation. Received 10 July, accepted 28 September 2000.
26 citations
TL;DR: One American white pelican (Pelecanus erythrorhynchos) was captured and fitted with radiotransmitters in south Louisiana and the delta region of Mississippi during the winter and early spring of 1994-1997 as mentioned in this paper.
Abstract: -Twenty-one American White Pelicans (Pelecanus erythrorhynchos) were captured and fitted with radiotransmitters in south Louisiana and the delta region of Mississippi during the winter and early spring of 1994-1997. The pelicans were monitored to determine their daily activity budgets while using different habitats such as catfish ponds, crawfish ponds, rivers, lakes, and bayous. Pelicans foraging at catfish ponds spent about 4% of their day foraging and 96% loafing, while pelicans foraging in other habitats spent about 28% of their day foraging and 72% loafing. For an individual bird, the mean number of foraging sessions per day was 2.5 (? 0.53 SE) and the mean length of each foraging session was 66.7 min. (?8.08 SE). Aerial censuses were also conducted to determine the numbers of pelicans in the delta region of Mississippi. Each year the numbers of pelicans wintering in the delta region of Mississippi peaked in February and March, corresponding with spring migration. Pelican numbers reached approximately 4,600 during February and March 1996. Pelicans were observed foraging in larger flocks for shorter periods of time on catfish ponds than in other habitats. Received 27 September 2000, accepted 28 November 2000.
TL;DR: Most Purple Herons preferred to forage along rivers but rice fields may be a valuable option, and the relationship between biomass ingested in relation to foraging time was greater on rivers.
Abstract: -Adult Purple Herons (Ardea purpurea) were observed while foraging along rivers and rice fields during the breeding season. Proportion of foraging time was higher in rice fields than on rivers and the relationship between biomass ingested in relation to foraging time was greater on rivers. The success of feeding attempts was similar in both habitats. Most Purple Herons preferred to forage along rivers but rice fields may be a valuable option. Received 12 May 2001, accepted 8July 2001.
TL;DR: Recruitment in ducks is the process by which young birds are added to the breeding population, and the two most commonly used methods to estimate recruitment are pair/brood counts, and fall age ratios based on wings returned by hunters.
Abstract: -Recruitment is the process by which young birds are added to the breeding population. The two most commonly used methods to estimate recruitment in ducks are pair/brood counts, and fall age ratios based on wings returned by hunters. Direct counts on the wintering area to determine the proportion of young males to adult males (age ratios), can be used for species with delayed plumage maturation. This is useful for species that are difficult to study on the breeding grounds and are seldom hunted, such as Harlequin Ducks (Histrionicus histrionicus). Such an approach is only valid if age classes are equally sampled. Between 1994 and 1999, the proportion of male Harlequin Ducks that were immatures in the Strait of Georgia, British Columbia, was estimated at 0.068. The proportions differed across years. Little difference occurred through the winter months until spring, when there was a significant increase in proportions in March. If these age ratios are accurate, then recruitment would not be compensating for annual adult mortality and the population could have been declining during the period of our study. However, if immature males are not distributed evenly among the population, then our assessment may underestimate or overestimate proportions. Delayed breeding means that immature birds experience several additional seasons of mortality prior to breeding, and thus the actual recruitment rate into the breeding population would be lower than that presented here. Received 11 April 2000, accepted 18July 2000.
TL;DR: It is suggested that poor environmental conditions may have caused young or poor quality birds to miss breeding in the El Nifio year, and it is important to undertake more research into the ability and mechanisms of seabirds to cope with them.
Abstract: -In 1997, one of the strongest recorded El Niiio-Southern Oscillation (ENSO) events occurred in the eastern Pacific. It caused strong oceanic and climatic anomalies, such as high sea surface temperatures (SST) and heavy rainfall along the eastern Pacific coast. We investigated the effects of this event on the reproductive ecology of the Neotropic Cormorant (Phalacrocorax brasilianus) in central Chile (36037'S; 73'03'W) by comparing the preEl Nifio season in 1996 with the 1997 El Nifio year. Fish landings immediately prior to the 1997 breeding season were notably lower and rainfall increased. In 1997, the number of breeding pairs declined by 71% from the previous year. During El Nifio, laying started 15 days later, was less synchronized and ended 35 days later. Although egg size, clutch size and hatching success did not differ significantly between the two years, the decrease in the breeding numbers in 1997 would have caused a considerable drop in offspring production. We suggest that poor environmental conditions may have caused young or poor quality birds to miss breeding in the El Nifio year. Since it appears that large El Nifio events are becoming more frequent, it is important to undertake more research into the ability and mechanisms of seabirds to cope with them. Received 12 February 2001, accepted 26June 2001.
TL;DR: Marked differences were observed in the frequency of occurrence and numeric importance of the fish prey species found in the three sampling seasons; while typical marine fishes, such as the Argentine Anchovy, constituted the bulk of the diet during 1998, estuarine juvenile fish prevailed in 1999 and 2000.
Abstract: -We investigated the diet of the Black Skimmer (Rynchops niger) in three consecutive years (autumn 1998, autumn 1999 and summer 2000) by analyzing 642 pellets collected at Punta Rasa, Samborombon Bay, Buenos Aires, Argentina. Fish was the main prey in the diet (occurrence = 100%), while insects were present in only 2.7% of samples. Among the 14 fish species identified, Argentine Anchovies (Engraulis anchoita) (occurrence = 38.7%, N = 31.5%), Silversides (Odontesthes spp.) (occurrence = 38.3%, N = 26.2%) and White Croakers (Micropogoniasfurnieri) (occurrence = 11.6%, N = 20.5%) were the most important prey. Fish prey averaged 77 mm in length (?34 mm, range 15-169 mm, N = 123), and had an average mass of 6.9 g (?7.3 g, range 0.1-31.6 g, N = 123). Marked differences were observed in the frequency of occurrence and numeric importance of the fish prey species found in the three sampling seasons; while typical marine fishes, such as the Argentine Anchovy, constituted the bulk of the diet during 1998, estuarine juvenile fish prevailed in 1999 and 2000. The comparison of size and mass of prey between seasons also revealed large differences. Fishes caught in 1998 were significantly larger and heavier than those caught in other seasons. The diet of skimmers overlapped with that of South American Terns (Sterna hirundinacea), Royal Terns (S. maximus) and Sandwich Terns (S. sandvicensis) in the area during 1998, when prey was mostly marine fish. Received 17 April 2001, accepted 25June 2001.
TL;DR: Consuming soft-bodied prey with high energy densities is likely to allow Longtailed Ducks to successfully winter in the predominately ice-covered Hudson Bay.
Abstract: -We examined the diet of Long-tailed Ducks (Clangula hyemalis) in the autumn and winter of 1998-99 in the Belcher Islands, Nunavut, Canada. Collections were made in early November before sea ice had formed and in February and March, the time of maximum ice cover. Eight birds collected in the autumn and 19 collected in the winter had food items in the proventriculus/esophagus. For birds collected in the fall, 89% (aggregate wet mass) of the diet consisted of the amphipod Calliopius laeviusculus. The remainder consisted of other smaller amphipods (5%) and sandlance (sandeels, Ammodytes sp.; 6%). In winter, Long-tailed Duck diet consisted of the amphipod Ischyrocerus anquipes (69%), fish eggs (probably sandlance; 24%), sandlance (1%) and other amphipods (5%). Longtailed Duck foraging at the landfast ice floe edge along coasts fed mostly on fish and fish eggs, while those in polynyas among islands fed on amphipods. Consuming soft-bodied prey with high energy densities is likely to allow Longtailed Ducks to successfully winter in the predominately ice-covered Hudson Bay. Received 21 December 2000, accepted 10 January 2001.
TL;DR: It is inferred that the ease of capture and physical defenses associated with particular foods affect Great Egret foraging preferences and management of Great Egrets impacts to aquacultural production should focus on dispersing egrets from ponds containing small (<18 cm) Channel Catfish, rather than generalized dispersal at all ponds on all farms.
Abstract: -Several species of fish-eating birds are commonly observed near aquaculture facilities in the southern United States. An understanding of the relationships between these birds and specific commodities is needed to interpret and manage bird impacts to aquacultural production. We conducted two foraging experiments to evaluate the preference of Great Egrets (Ardea alba) for three specific size classes of Channel Catfish (Ictalurus punctatus). During six no-choice feeding trials, egrets consumed significantly more small (7.5-10 cm) fingerlings than medium (1518 cm) or large (23-25 cm) catfish. Egrets captured 19 large catfish, and ingested only two, even when no other fish were available. During two-choice trials, Great Egrets significantly preferred small fingerlings to medium-sized fish, and medium-sized catfish to large fish. Handling time was directly related to the size of catfish ingested. Handling time was inversely related to the number of catfish ingested from each size class, particularly when Great Egrets were given a choice between two catfish size classes. Thus, we infer that the ease of capture and physical defenses (e.g., catfish spines) associated with particular foods affect Great Egret foraging preferences. Management of Great Egret impacts to aquacultural production should focus on dispersing egrets from ponds containing small (<18 cm) Channel Catfish, rather than generalized dispersal at all ponds on all farms. Received 1 October 2000, accepted 18 April 2001.
TL;DR: In this paper, the authors studied the diving behavior of chick-rearing Northern Fulmars ( Fulmarus glacialis ) in Shetland, U.K., in July 1998.
Abstract: We studied the diving behavior of chick-rearing Northern Fulmars ( Fulmarus glacialis ) in Shetland, U.K., in July 1998. Seen birds were caught oil nests and fitted with data loggers attached to a plastic ring on one leg of each bird. Only one data set, spanning tell days was recovered. Dives (N = 972) were generally shallow; the maximum dive depth was 2.6 in. Maximum dive duration was 8 s. Dicing took place most often in the afternoon; hardly any dives occurred during the night. Diving activity was irregular over the study period with a peak activity of 0.9 dives/min over many hours
TL;DR: In this article, the authors spot-mapped Long-billed Curlews (Numenius americanus) at the Elk River estuary, California to examine variation in territory occupancy from May 1999-April 2000.
Abstract: -During the non-breeding season, many shorebirds use coastal habitats where tides influence their dispersion patterns and social systems. We spot-mapped Long-billed Curlews (Numenius americanus) at the Elk River estuary, California to examine variation in territory occupancy from May 1999-April 2000. Curlew abundance was highest (a maximum of 16 territorial and up to 10 non-territorial birds) from July to September, after which time numbers declined progressively to 2-6 in winter. Five curlews were resident on >50% of observation days (N = 133) from June-April; these individuals returned to the estuary earlier and departed later than 11 other territorial curlews that were present 12-37% of occasions and mostly from July-November. Territory occupancy declined in association with precipitation and diurnal low tides ranging between -0.7 and 1.3 m. The absence of two territorial curlews coincided with rainy periods. The absence of curlews from five territories coincided with neap (low) tides; four of these curlews held territories at lower intertidal elevations with gently sloping topographies, such that they were inundated longer than other territories. At the Elk River estuary, territoriality may limit the number of curlews using intertidal habitats, but individual variation in territory residency suggests that numbers, and possibly carrying capacity, changed seasonally with availability of food in intertidal and pasture habitats. Habitat losses, such as those accompanying moderate (25-50 cm) rises in sea level associated with global warming, may reduce the carrying capacity of estuaries where existing levees preclude creation of new intertidal habitat. Received 31 October 2000, accepted 16January 2001.
TL;DR: In this article, the authors studied the nocturnal interactions of waterbirds with a 550v transmission powerline in the flat, open landscape of the Florida Everglades using a combination of surveillance radar to detect incoming birds, and night vision optical equipment to observe flight behavior.
Abstract: -Many birds move at night, and although there is strong potential for collisions with stationary structures, the behavior of birds in response to such structures is poorly understood. We studied the nocturnal interactions of waterbirds with a 550v transmission powerline in the flat, open landscape of the Florida Everglades using a combination of surveillance radar to detect incoming birds, and night vision optical equipment to observe flight behavior. During 118 hours of observation we recorded a total of 285 flocks of ciconiiform birds crossing the powerline during spring 1997. We visually observed 663 birds in 187 flocks, and documented their response to the powerline. We found that the flight directions and the colony site locality strongly suggested regular nocturnal foraging behavior of some species, especially Black-crowned Night Herons (Nycticorax nycticorax) and Wood Storks (Mycteria americana). Birds flying at night were less likely to react to the powerline, suggesting that powerlines may pose more of a collision threat during darkness. However, we also found that waterbirds flew higher at night than during the day and thus came into a zone of potential contact with the powerline much less often than during the day. Received 8 April 2001, accepted 3July 2001.
TL;DR: Bill morphology was related to nest position in the colony, with individuals occupying the central positions having the deeper bills, and this relationship was found in both sexes, suggesting that competition for position within the colony is not an important factor involved in the sexual dimorphism shown by the Chinstrap Penguin.
Abstract: -In most seabirds, breeding success can be related to the ability to obtain a suitable nest-site within the colony, and this may result in competition for the limited number of available sites. Thus, if nest-sites vary in quality, individuals of the same sex are expected to compete for access to the highest quality nest-sites to enhance their own fitness. It is therefore expected that intrasexual competition would result in a correlation between size in the competing sex, or the size of a trait used as a weapon, and nest quality. Chinstrap Penguins (Pygoscelis antarctica) fight with other conspecifics using the bill as a weapon. If bill size provides an advantage for intra-specific combat, we would expect stronger bills in males occupying the best nest sites. We studied patterns of some adult morphological traits in relation with nest position in a colony of Chinstrap Penguins. Bill morphology was related to nest position in the colony, with individuals occupying the central positions having the deeper bills. This relationship was found in both sexes. Our data suggest that competition for position within the colony is not an important factor involved in the sexual dimorphism shown by the Chinstrap Penguin. Received 31 August 2000, accepted 1 October 2000.
TL;DR: If rockweed harvest lowers the canopy height and reduces the time during each tidal cycle that algae floats at the surface, it might adversely affect Common Eider ducklings during the first weeks of life, when they are less able to dive for food.
Abstract: -Common Eider (Somateria mollissima) ducklings and associated females in the Bay of Fundy feed extensively on invertebrates found in association with Knotted Wrack (Ascophyllum nodosum), commonly referred to as rockweed. To assess whether commercial harvest of rockweed, which is occurring in New Brunswick, might adversely affect ducklings, I examined their feeding behavior in relation to rockweed availability and duckling age. Ducklings fed in rockweed whenever it was available. Young ducklings (less than 3 weeks old) spent more time dabbling for invertebrates in the floating rockweed canopy and less time diving than did older birds. Young ducklings fed when rockweed was most available at the surface, whereas rockweed availability had no effect on the feeding rate of older ducklings. When rockweed was unavailable, older ducklings dove for food, while younger birds still attempted some dabbling. These results suggest that if rockweed harvest lowers the canopy height and reduces the time during each tidal cycle that algae floats at the surface, it might adversely affect Common Eider ducklings during the first weeks of life, when they are less able to dive for food. Consequently, in areas where ducklings feed regularly, care should be taken during harvesting to avoid changing the height and structure of the rockweed canopy. Similarly, harvesters should avoid disturbing foraging ducklings, because it could increase the already high predation risk that these birds face in their first few weeks of life. Received 10 March 2000, accepted 16 November 2000.
TL;DR: Blood cells from the adult andjuvenile terns from two Core Sound colonies, Wainwright and Sand Bag Islands, had significantly higher levels of apparent DNA damage than the remaining study sites, a finding contrary to the expected result based on the DNA damage.
Abstract: -We studied possible genotoxic exposure in Royal Terns (Sterna maxima) by collecting blood from adults and juveniles at five breeding colonies in coastal North Carolina in 1999. These colonies are located in three estuarine systems (Core Sound, Pamlico Sound, and Cape Fear River), each subjected to different contaminant loads. DNA in red blood cells was analyzed using the comet assay to determine levels of DNA strand breaks, a technique previously not applied to birds. In addition, we weighed each bird and estimated its fat reserves as an indication of nutritional health. Gross health assessments showed no significant differences between study sites, both for adult and juvenile terns. The comet assay indicated that blood cells from the adult andjuvenile terns from two Core Sound colonies, Wainwright and Sand Bag Islands, had significantly higher levels of apparent DNA damage than the remaining study sites. Based on previously published studies of sediment contaminants, the Core Sound colonies have relatively low overall pollutant loads, a finding contrary to the expected result based on the DNA damage. Plausible explanations for these finding are that birds from the Core Sound are exposed to an undetected genotoxic contaminant(s) or that birds from the more polluted sites have had an adaptive response to the contaminant exposure. Received 30 October 2000, accepted 25 March 2001.
TL;DR: The strict age assortment the authors observed in Black-crowned Night Herons is to be ascribed to active mate selection by age, and Reproductive success was higher for pairs of adults than for those in juvenile plumage, while no difference was found for egg size, chick condition or asymmetry.
Abstract: -Age-assortative mating occurs frequently in birds, and may be produced by active selection for older and more successful mates, but also simply by age-related differences in breeding time, or by mate fidelity, without age-related selection. We describe the occurrence of age-assortative breeding in the Black-crowned Night Heron (Nycticorax nycticorax) near Wuxi, China. Throughout the whole breeding season, 59% of the breeders were adults i.e., birds older than two years, and 41% were younger birds injuvenile plumage i.e., birds in their second year. Most of 206 pairs were strictly assorted by age, and only 2.4% had one adult and one juvenile. A part of this assortment was due to age-related differences in the breeding period, but even when this seasonality is accounted for, the observed frequency of mixed pairs is much lower than expected. Mate fidelity is not likely to account for the observed assortment. We conclude that the strict age assortment we observed in Black-crowned Night Herons is to be ascribed to active mate selection by age. Reproductive success was higher for pairs of adults than for those in juvenile plumage, while no difference was found for egg size, chick condition or asymmetry. Pairing between adults may therefore be adaptive because it enhances reproductive success. The high frequency of Black-crowned Night Herons breeding in juvenile plumage in China (41%) contrasts sharply with the situation in other parts of the species range, where birds injuvenile plumage rarely breed, are even seldom seen near colonies, and are believed to remain in their wintering areas. Received 2 February 2001, accepted 25 March 2001.
TL;DR: This paper studied seven species of waterbirds that nested on Isla Montague, Mexico, at the mouth of the Colorado River, during the 1993 and 1994 breeding seasons: Great Blue Heron (Ardea herodias), Snowy Egret (Egretta thula), Black-crowned Night Heron, Laughing Gull (Larus atricilla), Least Tern (Sterna antillarum), Sterna nilotica), and Black Skimmer (Rynchops niger).
Abstract: -We studied seven species of waterbirds that nested on Isla Montague, Mexico, at the mouth of the Colorado River, during the 1993 and 1994 breeding seasons: Great Blue Heron (Ardea herodias), Snowy Egret (Egretta thula), Black-crowned Night Heron (Nycticorax nycticorax), Laughing Gull (Larus atricilla), Least Tern (Sterna antillarum), Gull-billed Tern (Sterna nilotica), and Black Skimmer (Rynchops niger). Breeding occurred along several tidal channels of the Estero del Chayo and on shell mounds near the lighthouse. There were low levels of predation, by at least one Coyote (Canis latrans), and unknown, but likely avian, predators. Tidal inundation was the major factor affecting the nesting of the birds, as it destroyed almost all nests, eggs and chicks on at least five occasions during one breeding season. It seems likely that the pattern of inundations we recorded does not happen all years. Received 21 August 2000, accepted 20 March 2001.
TL;DR: In this paper, elastic harnesses were used to attach radio transmitters to 49 newly hatched Banded Dotterel chicks, a bird breeding along braided rivers of the South Island, New Zealand.
Abstract: -Radio transmitters have potential for measuring rates and causes of mortality in precocial chicks. To assess their utility, elastic harnesses were used to attach radio transmitters to 49 newly hatched Banded Dotterel (Charadrius bicinctus) chicks, a bird breeding along braided rivers of the South Island, New Zealand. Twelve chicks either lost their transmitters or the transmitters were removed, six chicks survived to fledging, 26 chicks died and the outcome was unclear for the remaining five chicks. A minimum of 18% of chicks that died were taken by predators, but predator identity was clear in only one case. The transmitters did not appear to affect growth rates of radiomarked chicks, but three chicks died from harness entanglement. This technique provided only limited information about causes of mortality in Banded Dotterel chicks, and radio transmitters attached with elastic harnesses are not suitable for young chicks. Received 2 March 2001, accepted 20 April 2001.
TL;DR: In this article, the potential impact of large oil spills on seabird populations are dealt with in the strategic environmental impact assessments (EIA) of oil exploration in the Barents Sea (1988) and the Beaufort Sea (1996).
Abstract: It is analysed, how the potential impact of large oil spills on seabird populations are dealt with in the strategic environmental impact assessments (EIA) of oil exploration in the Barents Sea (1988) and the Beaufort Sea (1996). Current knowledge on the effect of large oil spills on bird populations is reviewed as background information for the analysis. The analysis of the two EIA cases focus on what ecological science can deliver to the EIA process and how the EIAs can manage with what they get. The use of oil spill scenarios and impact indices in the EIA-reports is discussed.
TL;DR: Predation of nestlings was greatest in Delaware Bay for Cattle Egret, but there were no differences between estuaries for other species, and abundance of nesting wading birds and avian predators in most years of study.
Abstract: -We investigated wading bird productivity in four estuaries from Delaware Bay to Boston Harbor in northeastern U.S.A. over the period 1986-1998. To document and characterize reproductive performance of numerically dominant species for use in wildlife and habitat management planning, we recorded 1) number of eggs laid, 2) percent of eggs hatched, 3) percent of hatchlings surviving 10-15 days post-hatch, 4) number of nestlings produced, and 5) factors of offspring mortality in nests of Black-crowned Night Heron (Nycticorax nycticorax), Snowy Egret (Egretta thula), Cattle Egret (Bubulcus ibis), and Glossy Ibis (Plegadisfalcinellus). We randomly selected 30-50 nests of each species (as available) for study at colonies in Delaware Bay (1993-1998), New York Harbor (1986-1994), Cape Cod (1990-94), and Boston Harbor (1993-94). In addition, we recorded abundance of nesting wading birds and avian predators in most years of study. Colony size ranged from 120-8,300 nests. Clutch size of all species was greater at northern-most sites. Loss of eggs varied between estuaries for all species except Glossy Ibis. Hatching success ranged from 75-88% and differed between estuaries for Black-crowned Night Heron and Glossy Ibis. Hatchling survival ranged from 16-87% and was lowest in Delaware Bay for all species. Nestling production was lowest in Delaware Bay for all species. In general, predation was high in Delaware Bay and egg inviability was high in Boston Harbor. Predation of nestlings was greatest in Delaware Bay for Cattle Egret, but there were no differences between estuaries for other species. Proportions of avian predators to nesting herons did not explain high predation rates in Delaware Bay. Received 18 April 2001, accepted 21June 2001.
TL;DR: In this paper, the three South American flamingos, Chilean Flamingo (Phoenicopterus chilensis), Andean and James' Flamingos coexist in Laguna de Pozuelos (ujuy Province, northwestern Argentina), and the authors report changes in the habitat conditions and how they affect the presence and abundance of flamingo species.
Abstract: -The three South American flamingos, Chilean Flamingo (Phoenicopterus chilensis), Andean Flamingo (Phoenicoparrus andinus) and James' Flamingo (Phoenicoparrus jamesi), coexist in Laguna de Pozuelos (ujuy Province, northwestern Argentina). This lake is an important overwintering habitat for Andean and James' Flamingos. The Chilean Flamingo is the predominant species and the only one breeding on the lake. This study was conducted from 1992 to 1995, during a period of drought. I report changes in the habitat conditions and how they affect the presence and abundance of flamingo species. Results indicate that in years of below average rainfall, the number of flamingos decreased appreciably, and their expected seasonal pattern of abundance is affected. Chilean Flamingo abundance showed a positive association with the size of the lake, possibly related to the scarcity of deep foraging areas. Zooplankton was lacking, so the presence of Chilean Flamingo might not be related to it. Diatom density was not a limiting resource for James and Andean Flamingos. James' Flamingo preferred to feed near the banks, and was favored by the availability of shallow foraging habitats as the lake contracted. Flamingos recorded in Laguna de Pozuelos represent a fraction of their entire populations within the high-Andes wetland complex. In this context, Pozuelos is an important habitat for flamingos and one of the main breeding grounds for Chilean Flamingo at high altitudes. Received 20 August 2000, accepted 21 December 2000.
TL;DR: Feeding where there is a high density of potential victims may be advantageous forjuveniles compared to feeding elsewhere because they are not selectively harassed or displaced by older, foraging gulls, which could contribute to juvenile survival and contribute to an increased population size.
Abstract: -We studied kleptoparasitic behavior of Kelp Gulls (Larus dominicanus) feeding on fishery waste at trawl vessels in northern Patagonia, Argentina, by experimentally discarding fish. Intraspecific kleptoparasitism by gulls of all age-classes was recorded at all hauls. During experimental discarding, Kelp Gulls attempted to steal fish from other gulls in 23.5% of 1,915 cases. The length of fish handled differed between age-classes, tending to be larger in younger age classes. The size of fish being carried by victims of kleptoparasitic attempts was similar between age-classes. On the other hand, adult and sub-adult were more frequently attacked when they carried larger fish, while juveniles were victims of kleptoparasitic attempts independent of the size of the fish carried by them. The lengths of successfully stolen fish were similar between victims of different age-classes. Adult and sub-adult were successfully robbed when they carried larger fish, while juveniles were successfully robbed irrespective of the size of the fish carried by them. Gulls of different age-classes were victims of kleptoparasitic attempts, in direct proportion to the number of fish handled by each age-classes. However, juveniles were successfully robbed more often than other age-classes. Juveniles lost prey in 83% of kleptoparasitic attempts, while sub-adults and adults lost their fish in 41 % and 42% of cases, respectively. Although selection of juvenile hosts to attack could be more profitable, attack rate on young birds was not higher than expected, suggesting attacks at trawlers were at random. Feeding where there is a high density of potential victims may be advantageous forjuveniles compared to feeding elsewhere because they are not selectively harassed or displaced by older, foraging gulls. If so, this could contribute to juvenile survival which could contribute to an increased population size. Received 8 March 2000, accepted 8 May 2000.