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Selection of a nest site that affords camouflage of eggs or incubating adults is thought to be strongly influenced by predation, especially for ground-nesting birds. Data from 115 Snowy Plover (Charadrius nivosus) nests were used to model relationships between nest survival, habitat characteristics, predator activity and human activity on four sandy, ocean-fronting beaches in coastal northern California from 2007–2009. Plover daily nest survival was higher at two southern sites (South Spit range = 0.98–0.99; Eel River Wildlife Area range = 0.91–0.96) compared with two northern sites (Mad River Beach range = 0.77–0.88; Clam Beach range = 0.79–0.89) where predator activity was appreciably higher. Nest survival was positively related to debris heterogeneity and negatively related to the amount of debris near the nest, but these relationships were weaker than the site-level effect. Although plovers select nest sites among cryptic debris in sparsely vegetated areas, restoration that creates and enhances such habitats may have limited utility at sites where predators are abundant. Thus, managers must carefully consider predator activity at the landscape level in order to maximize the effectiveness of fine-scale restoration efforts.
The present study describes the selection of breeding habitat by Little Terns (Sternula albifrons) nesting on sandy beaches in southern Portugal and the consequences of nest site selection for breeding performance. A range of physical and biological factors were used to assess the reproductive consequences of the birds' decisions, using three complementary approaches: 1) the characteristics of individual nest sites were compared with those of random points within a colony, 2) a Binomial Generalised Linear Model was used to examine which nest-site characteristics, including proximity to conspecific nests, might explain the success of Little Tern nests, and 3) a field experiment with artificial nests was conducted to test whether avoiding nesting near vegetation improves nesting success. Little Terns generally placed their nests approximately two thirds of the distance between mean high water and the seaward edge of the dunes, with a tendency to avoid vegetated areas but with a preference for a higher coverage of debris. Nesting success was about 35% higher in coarse sand compared to fine sand and was higher for nests closer to their nearest neighbor. Nests placed up to about 20 m distant from the nearest neighbor were about 5% more likely to succeed earlier in the season but nests at distances of 30 m or more to the nearest conspecific had a much higher probability of success later in the season. The combination of interacting abiotic and biotic factors identified as explaining Little Terns' nest site selection and nesting success provide insights relevant to the conservation management of birds breeding on sandy beaches.
Given historical patterns of decline, the American Black Duck (Anas rubripes) has long been a species of concern. To support the identification of core Maritime habitat, the distribution of breeding ducks was mapped at the landscape scale through the combination of GIS-based land cover information and five years of intensive aerial surveys (2006–2010). A predictive, mixed effects model was used to generate the maps, based on the weighted average of coefficients for the top 95% of all-possible models (as measured by AIC weights). The results of the averaged mixed model indicated that annual variation (YEAR), availability of surface water (WET_AREA, LAKE_AREA and WET_DIVERSITY) and occurrence of active agricultural landscapes (AG_PROP and ROAD_DENSITY) were strongly associated with the number of breeding pairs. The presence of larger numbers of breeding ducks in agricultural landscapes represents a departure from studies conducted in more intensively utilized regions (e.g. southern Ontario and Quebec), and suggest that the benefits of breeding in Maritime agricultural areas outweigh potential costs. Using 34,659 prediction points, duck distribution was modeled in relatively high and low years (2008 and 2006, respectively), resulting in detailed maps suitable for the identification of priority areas for habitat restoration and enhancement. In order to help refine conservation management plans, future work should more closely examine the impact of different types and combinations of Maritime agricultural production to better understand the way these landscapes attract breeding ducks.
The migratory population of the King Rail (Rallus elegans) has declined dramatically during the past 50 years, emphasizing the need to document the distribution and status of this species to help guide conservation efforts. In an effort to guide King Rail breeding habitat protection and restoration, a landscape suitability index (LSI) model was developed for the Upper Mississippi River and Great Lakes Region Joint Venture (JV). To validate this model, 264 sites were surveyed across the JV region in 2008 and 2009 using the National Marshbird Monitoring protocol. Two other similarly collected data sets from Wisconsin (250 sites) and Ohio (259 sites) as well as data from the Cornell Laboratory of Ornithology's eBird database were added to our data set. Sampling effort was not uniform across the study area. King Rails were detected at 29 sites with the greatest concentration in southeastern Wisconsin and northeastern Illinois. Too few detections were made to validate the LSI model. King Rail detection sites tended to have microtopographic heterogeneity, more emergent herbaceous wetland vegetation and less woody vegetation. The migrant population of the King Rail is rare and warrants additional conservation efforts to achieve stated conservation population targets.
In the first comprehensive survey of post-breeding shorebirds conducted along the remote deltaic mudflat habitats on the coastline of the Arctic National Wildlife Refuge, six species of shorebirds were documented aggregating prior to southbound migration. Energy reserves gained while foraging in these areas may be critical for southbound migration of long-distance migrant shorebirds, but these habitats are vulnerable to potential effects of oil and gas development and climate change. The study objective was to assess the relative density and species composition of shorebirds . Surveys were conducted at 13 major river deltas on the coast between late July and mid-August each year from 2006 to 2010. Double-observer methods were used in 2010 to estimate the detection rate in surveys of randomly-selected transect sections. Shorebird density varied significantly between years and among river deltas. Peak relative density estimates at three deltas, the Jago (247.8 birds/km2), the Kongakut (100.6 birds/km2) and the Hulahula (49.5 birds/km2), were significantly higher than the estimate for the Canning (16.0 birds/km2). Because shorebird density and abundance vary significantly among sites and years, and individuals likely move among multiple sites within a given year, shorebird conservation strategies for these habitats should consider them to be spatially and temporally interconnected.
In the Camargue (southern France), drastic changes in wetlands have occurred (notably extension of agriculture and salt extraction) since the 1960s, which affect the resources available to migratory waterbirds. Winter diets of Mallard (Anas platyrhynchos) and Teal (A. crecca) in 2006–2008 were assessed by analyses of gullet contents. Using PCA-based methods, duck diets were described and the main feeding habitats used by each duck species were then determined with a typology analysis. The same four food items were most important (in terms of occurrence and average dry weight) in the diet of Mallard and Teal: Oryza sativa (rice), Echinochloa sp., Scirpus maritimus and Potamogeton pusillus seeds. However, Teal diet was more diversified, with eleven feeding habitat types, compared to only five in Mallard. Both species were found to be dependent on ricefields and ricefield-like habitats. Compared to previous studies in the same area between 1964 and 1981, permanent freshwater habitats now appear to be used more intensively by Mallard and Teal, while temporary marshes are used to a lesser extent. Since the 1960s, temporary marshes have been partially replaced by permanent freshwater in order to attract more ducks, mostly for hunting. The flexibility of duck diet in response to changing food availability may explain why duck populations have not decreased in the Camargue or in Europe despite changes in land use.
Quantifying variation in diet over time and space is important for understanding patterns of habitat use in marine birds. Diet composition of adult male White-winged Scoters (Melanitta fusca) was quantified at five study sites in coastal British Columbia and Washington during mid-winter (December) and late winter (February-— March). At four sites where White-winged Scoters fed in nearshore areas, diet varied little between winter periods and birds fed almost exclusively on large infaunal bivalves (≥85% of mean ash-free dry mass of esophagus contents for each season × site combination). The main prey of White-winged Scoters in intertidal foraging areas (N = 3 of 5 study sites) were Varnish clams (Nuttalia obscurata), which were introduced to the region within the last 25 years. At an offshore site, diet consisted mainly of bivalves except during one period when White-winged Scoters had consumed mainly fish, crustaceans, polychaetes and echinoderms. Greater temporal variation in diet at the offshore site may have been an effect of reduced time available to locate preferred prey items and lower predictability of prey distributions owing to this site's greater exposure to wind and waves. However, neither exposure nor water depth received appreciable support in models of the dietary fraction of bivalves across sites and periods. Our results underscore the importance of marine areas with high densities of infaunal bivalves to White-winged Scoters, but also show that White-winged Scoters exhibit flexibility to adjust diet in response to differences in prey composition across habitats.
The study aim was to describe and explain the distribution of waterbird breeding colonies in the vicinity of one of Uganda's largest rice schemes, Doho, a major feeding site for waterbirds. A total of 18 colonies were identified in which six species bred and two others were found roosting. Colony size ranged from seven to 588 breeding pairs. All colonies were located within human settlements, contrasting with patterns seen in typical waterbird colonies in Europe and America. Seventy-five percent of waterbirds placed their nests on Mvule trees (Milicia excelsea) while the number of breeding pairs was positively correlated to the number of trees at colonies. Contrary to expectations, colony size was not correlated with distance from the Doho rice scheme, or with the amount of foraging area within one, five and 10 km from the colony. These results suggest that nesting, rather than foraging habitat could be restricting the distribution and potentially population sizes of tree-nesting waterbirds in our study area. They also highlight the importance of the Mvule as nesting habitat for waterbirds, a tree species that is in great need of protection throughout Uganda, and presumably throughout other parts of Africa.
To understand the adaptive significance of colonial breeding, evaluating the costs and benefits that colonial breeding provides to individuals is necessary. To study some of these costs and benefits of colonial breeding, over 24,000 nest-hour observations of kleptoparasitism (stealing of food being fed to young), intraspecific attacks on and killing of chicks, and chick adoption were conducted in colonial breeding Black-tailed Gulls (Larus crassirostris) during two breeding seasons. Although kleptoparasitism was rarely observed (under 0.001 events/ nest/observational hour), the occurrence of chick-attacks was 5–10 times higher (0.005–0.01 events/nest/observational hour) than that of kleptoparasitism, with over 10% of the attacks resulting in the death or disappearance of chicks. More than 60% of all attacks on chicks were by failed breeders and non-breeding adult floaters. The survival of attacked chicks reached 98–100% if they escaped into other nests and were accepted by “foster” adults, or if they were defended by non-parental adults. Chick adoption and non-parental defense were more likely to be observed among breeding neighbors (52–60% of chick adoptions and almost all examples of non-parental defense) than among non-neighbors. An increased chick survival rate, resulting from nesting in close to proximity to conspecific neighbors, was considered as a factor promoting colonial breeding among the Laridae.
KEYWORDS: egrets, herons, monitoring, North American Waterbird Conservation Plan, pelicans, seabirds, wading birds, Waterbird Conservation for the Americas
The commentary follows the story of colonial waterbird conservation in the United States over the past 150 years. Colonial waterbirds, especially egrets and pelicans, played an important role in the founding of the American bird conservation movement. At the beginning of the 20th Century, bird conservation activity self-organized, inspired creation of refuges for colonial waterbirds, protected colonies with wardens, and secured passage of conservation laws. Thereafter Federal and state governments slowly grew in their authorities and commitment to bird conservation. Successes achieved, colonial waterbirds fell from priority during the remainder of the first half of the 20th Century, although legislative, administrative and academic progress was made of considerable subsequent value. In the 1960s and 1970s, colonial waterbirds resumed a significant role, first in contaminant studies and then in population inventories. This engagement encouraged maturation of a colonial waterbird research and conservation agenda in the United States, including founding of the Waterbird Society, which facilitated a blossoming of colonial waterbird research in the succeeding decades. In the national conservation planning initiatives of the 1990s, colonial waterbirds were represented by the North American Waterbird Conservation Plan, later Waterbird Conservation for the Americas. Waterbirds are now well integrated in bird conservation planning and action at multiple scales in the United States. Conservation biology, assessment, protection and site management have progressed well, while population estimation, monitoring and data archiving have not. Appropriate direction seems clear, involving regional coordination of the actions of local stakeholders.
The Socotra Cormorant Phalacrocorax nigroogularis is a little studied, regional endemic seabird restricted to the Arabian Gulf region threatened by anthropogenic disturbance. The global population is estimated at 110,000 breeding pairs. The Siniya Island colony, the largest in the United Arab Emirates (∼ 15,500 breeding pairs), was studied during the 2011 breeding season to determine baseline reproductive parameters and the effect of exotic trees on reproductive performance. Mean nesting density was 0.92 nests/m2 and shaded areas had significantly higher density (1.05/m2) compared to unshaded areas (0.75/m2). Mean clutch size was 2.4 eggs/nest and did not differ between shaded and unshaded areas. Mean egg volume was significantly higher in shaded (49.56 cm3) compared to unshaded areas (48.5 cm3). Hatching success was significantly higher in shaded (65.1%) compared to unshaded areas (46.6%). Fledging success was 65.6% and did not differ between shaded and unshaded areas. Chicks crèched under trees soon after leaving their nests and this likely increased fledging success, regardless of whether chicks came from shaded or unshaded areas. Overall reproductive success was 1.7 chicks/nest. Higher egg volumes and hatching success under shaded areas suggest that plantations had a beneficial effect on the cormorants on Siniya Island and could be of conservation value. Further studies are required to determine what habitat features linked with these trees specifically aid in enhancing reproductive performance.
Using mark-recapture models, apparent survival was estimated from older banding and re-sighting data (1978–1983) of American Oystercatchers (Haematopus palliatus) nesting on beaches and in salt marshes of coastal Virginia, USA. Oystercatchers nesting in salt marshes exhibited higher apparent survival (0.94 ±0.03) than birds nesting on beaches (0.81 ±0.06), a difference due to variation in mortality, permanent emigration, or both. Nesting on exposed barrier beaches may subject adults and young to higher risk of predation. These early estimates of adult survival for a species that is heavily monitored along the Atlantic and Gulf Coasts can be used to (1) develop demographic models to determine population stability, (2) compare with estimates of adult survival from populations that have reached carrying capacity, and (3) compare with estimates of survival from other oystercatcher populations and species.
Seasonal (semestral) counts of aquatic birds at five Andean lakes in Ecuador (Colta, La Mica, Yambo, Yahuarcocha and San Pablo) were analyzed to detect trends in population size between 2004 and 2011. Trends of four abundant species (Ardea alba, Anas georgica, Fulica ardesiaca and Oxyura jamaicensis) and those of five functional groups (based upon body size and diet) were tested using generalized additive mixed modeling. In total, 19 bird species were consistently recorded over the whole period. The Andean Coot (F. ardesiaca) was found in highest densities (c. 3 birds per ha at Colta and Yambo). No significant trends were detected. However, the counts of functional groups exhibited a seasonal pattern (higher counts in February than in July), possibly due to lower resource availability in the dry season. Piscivorous species were relatively abundant at one lake (Yahuarcocha), which might be related to the introduction of Tilapiine cichlid fishes.
There are two recognized subspecies of the Piping Plover (Charadrius melodus): the Atlantic coast United States and Canada (‘Atlantic’) subspecies and the Great Lakes and Northern Great Plains (‘Interior’) subspecies. More than 7,000 Piping Plovers have been banded and monitored since 1982, yet no individual marked as a hatchling or breeding adult in the range of one subspecies has been reported breeding in the range of the other. Recent molecular genetic analyses further support subspecific taxonomic classification of Atlantic and Interior breeding populations. On 22 May 2011, a banded Piping Plover and unbanded mate were observed nesting on North Core Banks, Cape Lookout National Seashore, North Carolina, USA. The uniquely-banded adult was a female captured as a chick at Wasaga Beach, Georgian Bay, Ontario, Canada; the female nested unsuccessfully in its first breeding year at Tawas Point State Park, Michigan, USA and then successfully fledged two chicks in its second breeding year at North Core Banks, North Carolina, USA. The observation is the first confirmed record of a Piping Plover dispersing from its subspecies' range and successfully breeding in the range of the other subspecies.
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