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We compared the feeding patterns of Great Egrets (Casmerodius albus) and Snowy Egrets (Egretta thula) in flowing and still aquatic habitats of coastal (New York City) and interior (Wichita, Kansas) locations. These included strike rate, prey capture rate, strike success, “idle time” and diet. We tested the hypothesis that widely-distributed species of wading birds that face different ecological conditions across their geographic range modify their feeding behavior to match local conditions. If this hypothesis is correct, then the feeding patterns of egrets at the coastal site will differ from those in the interior. Great Egrets in coastal habitats had higher capture rates and strike rates than interior birds, but strike success was similar in both areas. The diets of coastal and interior Great Egrets were broadly similar. Great Egrets also spent less “idle time” while foraging at coastal sites than at interior sites. Snowy Egrets had higher capture rates at interior sites, but strike rates did not differ between study areas. Snowy Egrets also had higher strike success at interior sites, but also more “idle time”. Their diets also were similar in both areas.
The distribution and abundance of Red-legged Cormorants (Phalacrocorax gaimardi) were assessed by visiting 42 localities on the mainland and surveying most of the islands along Peru’s 2,500 km coastline between October 1999 and December 2000. Cormorants were distributed in small discrete groups (Mode = 5 birds, range 1-69) from Isla Foca (5°12’S) to Morro Sama (18°0’S). The southern (56% of the total numbers) and central (34%) coast held a larger proportion of cormorants than did the northern region (10%). Birds were mainly located in unprotected areas, either on islands (6%) or on the mainland (51%). The remainder was found in protected areas, either guano bird islands (27%), guano bird headlands (3%) or within the Paracas Reserve (13%). We counted 658 birds (95% adults, 5% juveniles), but based on bird density, availability of suitable habitats and cliff lengths we predicted a total of 1,803 ± 282 birds in Peru. Red-legged Cormorants built their nests on narrow ledges on vertical rocky walls falling sheer to the sea, located, on average, 17.8 m (range = 3-50, N = 56) above the sea level on open cliffs, high-up in sea cave entrances or on small islets. They have undergone a spectacular decline over the last 30 years. Between 1968 and 1999-2000, the numbers at ten localities in the northern and central coast decreased from 3,229 to 69 birds. It is likely that low numbers recorded in this study reflect the devastating effects of the strong El Niño Southern Oscillation (ENSO) of 1997-98, as numbers prior and after this event at eight southern localities decreased by 73%. Because of the inaccessibility of their nesting and roosting sites and the lack of natural predators, Red-legged Cormorants are apparently not in danger at such sites. However, entanglement in fishing nets, competition for food in inshore waters, pollution, human disturbance and harvesting of kelp banks are potential threats at sea and could affect the population recovery.
Killdeer (Charadrius vociferus) is a common and widespread North American species for which there are few studies of residency patterns and movements. We quantified fidelity and movement patterns of 24 radio-tagged Killdeer in the Willamette Valley of Oregon during the winter of 1999-2000. Results from telemetry surveys and census efforts revealed that the group monitored was composed of winter residents (63%), winter transients (26%), and year-round residents (11%). Movements were localized with birds detected at an average distance of 5.15 ± 0.91 (SE) km from the site of capture. Mean home range size (95% kernel) was 7.73 ± 3.19 km2. However, results also indicated periodic exploratory movements, with some birds detected up to 30 km from marking sites. Overall, individuals exhibited a low degree of fidelity to specific sites and were detected at an average of 11.9 ± 1.1 sites. No differences were found in monthly movement patterns. In almost all cases, year-round residents were more sedentary than winter residents and winter transients. Results indicate a complex regional population structure and highlight the need to consider both migrant and resident birds, as well as seasonal differences in habitat needs and space use requirements, in future conservation planning efforts.
Count data for twelve species of seabird from Aride Island Nature Reserve, Seychelles were reviewed from 1988 to 2000. The numbers of six of the ten breeding species remained relatively stable during the period, while those of one species, the White-tailed Tropicbird (Phaethon lepturus) underwent a 60% decline. Roseate Tern (Sterna dougallii) numbers significantly declined between 1987 and 1993, followed by a significant increase between 1994 and 2000. Current count data for Audubon’s Shearwater (Puffinus l’herminieri) and the Wedge-tailed Shearwater (P. pacificus) are insufficient to establish trends. The maximum annual count of roosting non-breeding frigatebirds (Fregrata spp.) increased steadily throughout the period. The island has internationally important numbers of breeding seabirds (330,000-720,000 pairs per annum), including the largest known colony of Audubon’s Shearwater, the largest colony of the declining Roseate Tern in Seychelles, and the largest known colony of the nominate subspecies of Lesser Noddy (Anous tenuirostris).
Rubbish dumps provide an extra and constant food source for many birds. The White Stork (Ciconia ciconia) is one of the species that have taken advantage of these new foraging areas both during breeding season and during the winter. This study analyzes data collected in the Spanish province of Cordoba throughout five years between 1992 and 1998 on the biology and breeding success of the White Stork and the influence of rubbish dumps. Breeding success varied significantly between years and areas in two of the study years. A banding program from 1990 to 1998 resulted in 145 storks being marked as nestlings. Of these, 49 were resighted at least once by May 2001 (34% resighting rate) and 16 of these birds were resighted as breeders at a mean age of 2.87 years. 75% of them were breeding close to rubbish dumps. Fifteen birds were resighted during wintering time, of which twelve were at rubbish dumps.
Double-crested Cormorant (Phalacrocorax auritus) predation on Channel Catfish (Ictalurus punctatus) at commercial farms has been estimated to cost the Mississippi aquaculture industry approximately $5 million annually to replace consumed fingerlings. In 1997, catfish producers assumed responsibility for the dispersal of cormorants in night roosts in the eastern (interior) delta region of Mississippi, where catfish farms are concentrated. We documented movements of 50 cormorants marked with radio transmitters in the delta region from January through March 1997. We obtained 161 post-capture day locations and 176 post-capture night roost locations. Cormorants that were harassed at their night roost flew farther to their next day’s location than birds that were not harassed the previous night. Of the cormorants for which we had more than one night roost location, only 11% of cormorants that were harassed returned to the same roost within 48 hours, compared with an 81% return of cormorants to a previously un-harassed night roost. Moreover, cormorants in the eastern portion of the delta (where all harassment was conducted) changed night roosts more frequently than cormorants in the western (non-harassed) delta. Since cormorants in our study foraged relatively close to their night roosts and only 11% of the birds that we observed roosting in the western delta traveled to the eastern delta to forage the following day, coordinated and intensive dispersal of cormorants from the interior delta may, temporarily, limit cormorant impacts to Mississippi aquaculture.
Nesting adult Seychelles Sooty Terns (Sterna fuscata) were banded in five colonies. Searches for banded birds were made annually during the incubation phase of the breeding cycle. Within the colonies on Bird Island (largely protected from human intrusion) and Desnoeufs Island (from half of which eggs are harvested annually), differences in the tendency to return to nest sites used in earlier years were attributed to the effects of human disturbance, especially egg collecting. On Bird Island, the only colony that was searched intensively for banded birds each year between 1994 and 2001, eighteen birds were found that had formerly nested in other colonies. These inter-colony movements of breeding adults were also attributed to human disturbance in source colonies, but changes in food distribution may have stimulated birds to move from a colony that was protected from human interference. The finding that breeding adult Sooty Terns sometimes switch colonies suggests that these Seychelles colonies should be regarded as units within a metapopulation, with genetic exchange between units. This must be taken into account when estimating the allowable harvest of eggs, for human consumption, undertaken in the Seychelles.
The distribution of the Whiskered Tern (Chlidonias hybridus) is scattered, numbers fluctuate and they are threatened in many regions. Its breeding ecology has only occasionally been studied so far. It is relatively common in some North African wetlands. This study was carried out on Lake Tonga, northern Algeria, south of El-Kala (3651’N; 0820’E) in 1996 and 1997, with 169 and 215 initiated clutches studied, respectively. Basic characteristics of the Whiskered Tern breeding ecology studied were: laying date, clutch size, hatchling number, nest size and shape and egg size. Hatching success differed significantly between 1996 and 1997, probably due to weather. Laying date did not influence breeding parameters. Clutch size and hatching success were correlated with size and shape of nests. Hatchability was also correlated with egg length (negatively) and mass (positively). Relationships between breeding characteristic in relation to weather are discussed.
Post-hatch brood amalgamation is common in many waterfowl species and especially prevalent in the Common Eider (Somateria mollissima). Studies in the temperate region have shown that brood abandonment is influenced both by female body condition and brood size. In this study we tested how these two factors influenced the probability of brood desertion in eiders breeding under harsh conditions in the high Arctic (78N). We found that females in poor body condition were less likely to care for their young, but there was no effects of brood size. We speculate that the differences between southern and northern populations of eiders may be due to different environmental conditions.
The breeding biology of the Slender-billed Gull (Larus genei) is poorly known. Several reproductive parameters have been recorded during ten years (from 1992 to 2001) at the Ebro Delta (northwestern Mediterranean), such as clutch size, egg size and breeding success, as well as the number of breeders during the study and their population dynamics. Average clutch size during the study was 2.57 eggs per nest, with three eggs being the modal size. Slender-billed Gulls can lay a second clutch after egg loss, although clutch size is decreased. Mean egg size for the period 1998-2001 was 38.50 ml (SE 0.11). Although breeding is highly synchronous, females laying first were probably those in best body condition. Average breeding success for the whole period was 0.71 chicks per nest (24% of eggs laid). Compared with other colonies, results suggest that on average, the site may be a high quality colony in terms of availability of food, nest sites and predation rates. However, most of the breeding parameters analyzed showed statistically significant differences between years, and also between breeding areas and sub-colonies within the delta. The number of breeding pairs increased slightly from 388 in 1992 to 468 in 2001 (mean annual growth rate was 1.02 per year), although the rate fluctuated greatly between years, these changes were probably related to emigration-immigration processes at a metapopulation level.
The coastal states of western North America and Mexico are home to a population of Caspian Terns (Sterna caspia) that are geographically disjunct and probably genetically isolated from other Caspian Terns in North America. About 74% of these birds nest at a single colony, East Sand Island, near the mouth of the Columbia River between Washington and Oregon. It is estimated by others that when the terns nested in 1998 on Rice Island, 26 km further east in the Columbia River estuary, they consumed Steelhead smolts (Oncorhynchus mykiss), Coho smolts (O. kisutch), and spring/summer Chinook smolts (O. tshawytscha) that reached the Columbia River estuary, thus involving species listed under the United States Endangered Species Act. In addition, because such a large percentage of the west coast population breeds at a single colony, there is concern that a natural or anthropogenic event at this colony may adversely impact the entire population. As a result, many federal, state, tribal and private natural resource managers are trying to develop a management plan to disperse a fraction of these terns from East Sand Island to other historic and/or newly created nesting sites throughout western North America. Among factors to be considered, managers must assess the potential impact that terns would have on fisheries, especially salmonids, at potential relocation sites before attempts are made to relocate the birds. This study documents the diet of terns in one prospective relocation area, Commencement Bay, Washington. Relative abundance of prey species, including salmonids, delivered to the colony by adults differed significantly from month to month during the breeding season, but overall terns brought an average of 52% juvenile salmonids back to the colony, a higher percentage of salmonids than are consumed by terns on East Sand Island. Therefore, we conclude that Commencement Bay may not be an appropriate relocation site for Caspian Terns.
The inclusion of Spain and Portugal within the European Community has brought about a change in the traditional farming practices in the dehesas of Iberia to intensive cereal and to irrigated crops. Here we use seven-year counts of Common Cranes in 38 wintering sites to evaluate whether habitat structure modified by farming practices in the Holm Oak (Quercus ilex) dehesas is an important determinant of variability in winter crane numbers. We extracted, from a set of nine variables that express different levels of human management in the Holm Oak dehesas, two factors that accounted for the 66% of the variance. The first factor was related to livestock utilization of the dehesas, while the second one reflected Holm Oak presence. We ran a general linear model to analyze the influence of farming practices (PC1 and PC2), landscape heterogeneity and roost site stability on inter- and intra-season variability in numbers of winter cranes. Livestock presence, Holm Oak presence, landscape heterogeneity and roost type stability did not explain intra- and inter- season variability in crane numbers wintering in the Holm Oak dehesas of Spain.
The present wintering range of the Pacific Golden Plover (Pluvialis fulva) includes the northeastern tip of Africa, southern Asia, to Australia and New Zealand and much of the Pacific Ocean. We summarize evidence from the oral history of “wilsternetters” (artisanal hunters using an ancient, specialized netting device to capture grassland-shorebirds in daytime), as well as written records, to suggest that, until quite recently the wintering range of the Pacific Golden Plover may even have included the southern North Sea coast, mainly in the north of The Netherlands. Near the Zuiderzee (a large Dutch estuary that was closed off from the sea in 1932 and is now known as Lake IJsselmeer), the birds came inland to roost during spring tides, often in the company of Dunlin (Calidris alpina). However, Pacific Golden Plover were usually captured much further inland after the onset of severe winter weather, apparently after the birds had started moving away from their normal coastal winter habitat. Uniquely, Pacific Golden Plover wintering so far west and north appeared to show adaptations to cold (a thick and rather downy plumage) and unpredictable feeding conditions (a large fat store in midwinter). These special life-history features may have made it a distinct subspecies. Whether Dutch engineering, i.e. the loss of the Zuiderzee, played a role in their disappearance is probably beyond investigation.
We measured offshore Marbled Murrelet (Brachyramphus marmoratus) abundance from April through October between 1989 and 1998, in northern California and southern Oregon and investigated its relationships with marine and terrestrial habitats. We found that higher murrelet abundance offshore was strongly related to the presence of large, clustered and unfragmented old-growth forests on nearby inland areas. Murrelets were most abundant offshore of contiguous old-growth forest adjacent to relatively abundant medium-sized, second-growth coniferous forests. Compared to the forest habitat, marine habitat was relatively unimportant in determining murrelet abundance offshore; high marine primary productivity and nutrients were not associated with high murrelet numbers. Tidal flat shorelines were weakly associated with more murrelets, independent of inland habitat. Our findings suggest management efforts to conserve the Marbled Murrelet should focus on protecting or creating large, contiguous blocks of old-growth habitat, features which currently are rare in the study area.
Data on the occurrence and frequency of adoption of chicks by adult Pied Avocets (Recurvirostra avosetta) were collected by monitoring individually color-banded chicks on alkaline lakes in the Kiskunság National Park in central Hungary between 1998 and 2000. Fifty-three adoptions were observed, and 22% of the resighted broods (N = 244) contained on average 1.7 (range 1-6) adopted chicks. Ninety-two chicks, or 13% of the color-banded chicks (N = 697) were adopted. The frequency of adoption was similar among years and was positively related to the number of pairs within a colony. At least 60% of the adoptions occurred in the nesting colonies, whereas adoptions during brood movements or in the brood-rearing areas, as well as brood amalgamations, were rare. More than two-thirds (68%) of the adopted chicks in the colony left the natal brood and joined other broods voluntarily. The remaining adopted chicks were the last to hatch in their own brood and were adopted into another brood after being left behind by their parents. Adults did not behave aggressively toward young alien chicks and always accepted them. Adoption appears to be initiated by chicks in Pied Avocets, and it may be associated with small fitness costs, or may even provide benefits, for the adoptees or the adopting adults.
Great Blue Herons (Ardea herodias) and Great Egrets (Casmerodius albus) partitioned feeding habitat based on wetland size at Peltier Lake rookery in east central Minnesota. Great Blue Herons preferred large waterbodies (350 ha), whereas Great Egrets fed most often at small ponds (<25 ha). Forty-nine percent of Great Blue Herons used wetlands 301-400 hectares in size and 83% of Great Egrets fed in wetlands <100 ha in size. Great Blue Herons selected large wetlands more often than expected both at the regional (30-km radius) and local (4-km radius) scales. Habitat use by Great Egrets was in proportion to availability at the regional scale, but they selected smaller wetlands for feeding more often than expected at a local scale. The median flight distance of Great Blue Herons was 2.7 km, similar to distances reported elsewhere. Great Egrets flew farther to feeding sites than Great Blue Herons, and flew farther (median = 13.5 km) than reported in other geographic areas.