Little Tern (Sternula albifrons) prey composition was studied on a sandy islet in inland Andong Lake, Republic of Korea, during the breeding season (April to July 2018). Two remote-control video cameras with 4K-resolution were set on the islet to identify prey and determine whether prey species composition or size differed among breeding stages. On still images in which terns had prey in their bills (n = 1,275), prey species were identified, classified to five length-categories, and compared among breeding stages. Freshwater fishes dominated the observed diet (100%; 11 species overall), where the landlocked pond smelt (Hypomesus nipponensis; 80.8%) and largemouth bass (Micropterus salmoides; 13.7%) were main prey species. The mean prey length was 51.0 ± 20.89 mm, where 50.1–75.0 mm prey was the most frequent in the diet (42.2%) and varied significantly among breeding stages; 50.1–75.0 mm prey were most frequent during courtship and incubation stages, whereas 1.0–25.0 mm prey were most frequent at the chick-rearing stage. Surface water temperatures exceeded the upper thermal tolerance of the primary prey species at a date coincidental with tern departure from the colony.

The number of breeding pairs is an essential indicator for assessing waterbird colony status. Accurate estimates require distinguishing stationary adults (likely to be breeders on nests) from nonstationary adults (likely to be loafing or foraging breeders or non-breeders). High-resolution multi-temporal aerial imagery obtained from manned aircraft, satellites, or unmanned aircraft systems (UAS) can be analyzed to determine bird movements and derive estimates of the number of stationary adults, which corresponds to the number of active nests, and thereby breeding pairs. Automated detection of stationary objects, such as nesting waterbirds, can be complicated by small positional changes of objects, either because of image co-registration errors or because the object slightly shifts position. A non-parametric, point-based approach was developed to distinguish stationary birds from moving birds using sequences of either two or three consecutive remotely-sensed images. This approach was tested with simulated data and during a case study of nesting American White Pelicans (Pelecanus erythrorhynchos). In both cases, the non-parametric point-based approach had higher accuracy than other established methods such as ground counts. Using two consecutive images had higher sensitivity (correct classification of stationary birds) while using three consecutive images had higher specificity (correct classification of nonstationary birds). This novel, multi-temporal nearest-neighbor method is most useful when positional shifts of stationary animals is low between consecutive images.

Birds have been monitored as indicators of ecosystem health in both the freshwater and marine habitats of south Florida, USA for decades. This study reports on nine years (2010-2018) of monthly systematic surveys of breeding waterbird colonies in Biscayne National Park. Overall, 89% of active nests in the park belonged to Double-crested Cormorants (Phalacrocorax auritus). The annual sum of nest counts within the study area grew by 58% over the course of the study. This growth in the nesting population is driven by a 61% growth in northern colonies. During this same time period, the southern colonies declined to less than half their original size. These opposing trends coincide with differences in habitat quality (salinity, chlorophyll, sea grass density, and/or prey abundance) between the two regions. In addition, Hurricane Irma strongly impacted the nesting Double-crested Cormorants, suggesting a loss of nearly 400 nests, although four months post-storm nesting was back to normal levels. Finally, two colonies appear to have started during the study period in close proximity to recently completed Biscayne Bay Coastal Wetlands restoration projects. One of these colonies supported a maximum of over 350 nests.

Although studying the diet of threatened species is crucial in terms of conservation, the diet of the Madeiran Storm Petrel (Hydrobates castro) and the vulnerable, Azores-endemic Monteiro's Storm Petrel (H. monteiroi) is mostly unknown. The only information available to date comes from anecdotal observations, analysis of mercury levels and stable isotopes. Here is presented the first insights into prey consumption by adults and chicks from the two species breeding in the Azores Archipelago, Portugal, in the mid-Atlantic Ocean. The rapidly developing field of metabarcoding was used to identify dietary items from fecal samples, to species level where possible. A total of thirteen fish, five cephalopod, one crustacean and two oligochaete operational taxonomic units (OTUs) were detected. Results suggest that both petrel species feed mainly on myctophid fish. However, differences were detected between the prey species consumed by (i) H. monteiroi and H. castro, (ii) two distinct H. castro populations (Vila and Praia islets), and (iii) chicks and adults within the same population.

Although the River Tern (Sterna aurantia) has been widely distributed across south and southeast Asia, its population is declining and was classified as Vulnerable in the 2020 IUCN Red List of Threatened Species. Insufficient information is available on its breeding ecology. This study reports the breeding ecology and factors affecting breeding of the River Tern over three years (2017-2019) along the Mahanadi River in Odisha, eastern India. Breeding was observed between February and May, with peak activity in April. The mean clutch size was 2.4 ± 0.06 SE and incubation period was 22.1 ± 0.06 days. Out of 163 nests, 68 nests succeeded in hatching at least one egg and apparent nesting success rate varied between 2.6% (2018) and 62.3% (2017). Factors affecting nesting success (95 nests) were predation (37.9%), flooding (32.6%), a cyclone (28.4%) and nest desertion (1.1%). Overall, of 124 chicks hatched, 58 were estimated to have fledged. Factors affecting chick survival were a cyclone (43.9%), predation (39.4%), and unknown causes (16.7%). A cyclone in May 2019 wiped out all eggs and chicks. Development and implementation of an evidence-based multi-species conservation action plan to protect River Tern and other globally threatened riverine ground nesters is urgently required.

Common Loons (Gavia immer) are migratory, piscivorous waterbirds that exhibit high wintering site fidelity. Forty-three immature loons were captured in 2013, 2015–2017, in southwest coastal Louisiana, an area moderately to heavily exposed to oil from the Deepwater Horizon oil spill of 2010. We analyzed blood from loons to examine associations between exposure to polycyclic aromatic hydrocarbons (PAH) and 25 blood analytes. Overall, 60% (26/43) of the loons had detectable concentrations of PAHs, with an average concentration of 55.3 ± 10.3 ng/g. After controlling for body weight, loons with detectable blood PAHs had higher concentrations of absolute eosinophils, lymphocytes, or monocytes compared to loons without PAH exposure. This study provides evidence of subclinical inflammation in Common Loons wintering in coastal Louisiana and identifies exposure to PAHs as a stressor, raising concern for potential impaired fitness in this population resulting from low-level exposure to PAHs.

This study investigated if morphological measurements made from digital photographs of banded adult Black Skimmers (Rynchops niger), using alphanumeric field readable leg bands as a scale reference, can be used to determine their sex. Black Skimmers are known for their extreme sexual dimorophism and make an excellent study subject. Measurements made in the field using calipers to determine length of the exposed culmen of skimmer chicks were significantly correlated to measurements made by three technicians using open-source software (ImageJ) measuring the culmen from photographs, with little variability among technicians. To determine sex, ImageJ was used to measure the culmen, bill depth at base, lower mandible and head + culmen lengths from photographs of 24 known sex adult skimmers (11 female, 13 male). Males were significantly larger than females for all four measurements and a stepwise Discriminant Function Analysis (DFA) using all 4 measurements retained exposed culmen and bill depth as the best predictor variables. This model correctly classified 100% of known sex males and females. Using the DFA equation, 40 additional banded skimmers were classified, and it was determined that 46 of the banded skimmers that were photographed as adults were male and 18 were female. Using a field readable band as a reference scale for other measurements may prove useful for research on other sexually dimorphic species that are banded and later photographed in the wild.

The Harlequin Duck (Histrionicus histrionicus) is a species of conservation priority in western North America. Harlequin Ducks breed in small, isolated populations and have specific nesting requirements. Archival, light-level geolocators are increasingly being used as a low-cost, non-invasive tracking technology to explore migratory connectivity. From 2015-2019, geolocators were deployed on 70 Harlequin Ducks in breeding streams of the Rocky Mountains, Canada and USA, to obtain information on connectivity (breeding to non-breeding), molt-winter sites, dispersal, and breeding phenology. Twenty-two of the 70 geolocators were retrieved from locations in the Rocky Mountains (Alberta, Canada; Montana and Wyoming, USA) and analyzed using the TwGeos and FLightR R packages. Harlequin Ducks from the warmer climate of northwest Montana migrated in spring and started incubation one to two weeks earlier than ducks in west-central Alberta and the greater Yellowstone area. During the non-breeding period, individuals dispersed along the Pacific coast, from Oregon to the Alaskan Panhandle, independent of breeding site. Females that incubated successfully spent 32-34 days incubating, which is several days longer than what is in the literature. Use of geolocators provided detailed information about migration connectivity and breeding behavior in a cost effective and relatively non-invasive manner.

In an effort to quantify the value of wetland habitats, GPS technology was used to document the movement patterns of 16 Great Egrets (Ardea alba) in North America. Patterns in daily flight distances and utilization distributions (UD; estimates of area occupied on the ground) were documented throughout the annual cycle. Maximum Daily Displacement (MDD), the farthest distance occupied by a bird from colony/roost (central place) in 24 hr was greatest (4.3 ± 0.1 km) during breeding season and lowest (3.3 ± 0.1) during post-breeding season. As birds visited multiple foraging sites and made multiple round trips to central places, this Total Daily Distance (TDD) was also measured. It increased from a mean of about 12 km during the incubation phase to about 35 km at the time of fledging. Average TDD was greatest during breeding season (14.2 ± 0.3 km) and lowest during winter (11.0 ± 0.2 km). The utilization distribution increased from 128 (± 21.3) ha during breeding season to 179 (±32.6) ha during winter. Birds that foraged at tidal sites used 183.3 (± 22.2) ha, twice as much area as birds that foraged strictly in freshwater sites (89.6 ± 21.3 ha).

This study aims to describe the breeding biology of Ibisbill (Ibidorhyncha struthersii), a poorly studied wader nesting on the River Sindh in Kashmir Himalayan region of India. A total of 16 nests were monitored during the breeding seasons (late February to late July) of Ibisbill in 2018 and 2019. Nest building was completed in 21-28 days on bare ground by tossing small pebbles into a shallow depression that had no special markings to the human eye (mean pebble size = 4.09 mm ± 1.26 SD x 6.23 ± 3.71 mm, n = 42). Nests measured 28.45 ± 1.75 cm × 18.91 ± 0.99 cm (n = 12). Eggs were laid in the first week of April with clutch size ranging from 2 to 4 eggs. Eggs were 50.58 ± 1.07 mm in length and 36.77 ± 0.85 mm in breadth (n = 5), with egg shape index of 72.23 ± 2.58 (range: 69.23 to 76.42). Incubation lasted 28-32 days, with 3 out of 19 observable eggs successfully hatched (15.79% hatching success). Fledging success was zero due to predation. Defensive behavior was directly observed for 16 nesting pairs during two breeding seasons. A total of 407 defensive incidents were recorded during incubation and chick stage, with both parents engaging in defense together and individually.

Pheasant-tailed Jacana (Hydrophasianus chirurgus) have a polyandrous mating system, with females defending larger territories within which males compete for and defend smaller territories. The role of the sexes in territorial defense is therefore potentially complex yet remains poorly known. The sex-roles of defensive responses to intruders were monitored at Anawilundawa Ramsar site, North-Western Province, Sri Lanka, where birds encountered conspecifics and other potential predators: Purple Coots (Porphyrio porphyrio), aerial predators, and other waterbirds. Females contributed to defense, though males performed most defense. Females increased their propensity to defend as breeding progressed; by the chick-rearing phase defense was shared more or less equitably between the sexes. Females were more likely to defend against aerial predators than males, and males were more likely to defend against conspecifics than they were to other intruders. When defending against conspecifics, most male defense was directed at intruding males, and most female defense at intruding females. Defense in this polyandrous species relied on cooperation between the sexes but also on some defense specialization whereby females focussed on defending against aerial predators and conspecific females, perhaps because of their larger body size. Both female and male Pheasant-tailed Jacanas therefore contribute to parental care via their defensive activities.

Information on resident and wintering waterbirds in Haiti is particularly scarce, limiting knowledge needed to inform waterbird conservation across the Caribbean. Here, results from a winter census of waterbirds at five major wetland sites in Haiti in 2019 are presented. Overall, 10,265 waterbirds belonging to 34 species and 12 families were counted. Richness per site varied between 8 and 26 species, and the Shannon diversity index ranged from 2.69 to 8.54. Only 17.6% of observed species were recorded at more than three sites, and there was no significant relationship between the overall number of individuals counted per species and the number of sites where the species was observed. This was reflected in the moderate degree of similarity between the five sites in terms of shared species as calculated with Horn index. Although the species observed during the survey are currently listed as Least Concern (LC) in the Global IUCN Red List, at the local level several of them are considered threatened: White-cheeked Pintail (Anas bahamensis) and American Coot (Fulica americana); or rare: Mallard (Anas platyrhynchos) and Wilson's Phalarope (Phalaropus tricolori). Results are discussed relative to previous records of waterbirds in Haiti and need to develop ornithological research based on local expertise.

This work aims to provide information regarding the behavioral ecology of the least studied of the two sheathbill species, the Snowy Sheathbill (Chionis albus), wintering in northern Argentina in a male South American Sea Lion (Otaria flavescens) haul-out. Data about bird abundances and time allocated to behaviors was gathered during the final stage of three consecutive non-breeding seasons. Significant differences were found in the abundance between and within seasons. Overall, sheathbills allocated most of their time to foraging, followed by resting and self-maintaining, with the least of the time allocated to agonistic behaviors. The results obtained by the authors demonstrated that the Snowy Sheathbill recurrently used the local sea-lion haul-out as a foraging ground, with steady numbers throughout the non-breeding seasons.

Bangladesh hosts most of what is left of Indian Skimmer (Rhynchops albicollis) populations, a globally endangered species. Each October-March from 2015-2020, 21 surveys of nonbreeding birds were made in Nijhum Dweep National Park, Bangladesh. High tide or evening roosts were counted from vantage points whenever a buildup or breakdown of skimmer concentrations was noticed, and site use noted by marking all observations of presence and activity on maps. The largest single count was 3,108 skimmers on 18 February 2020, constituting 30-50% of the known global population. Indian Skimmers mostly occurred in Damar Char West and at the tip of the Majher Char. Throughout the day with incoming tide, skimmers moved between preferred roosting areas to forage in the shallows. We describe a unique group-foraging strategy in which skimmers chase fish from deep water to shallow water along the shoreline. Circling high over the tidal channel, the flock of skimmers dives down in unison to just above the water surface, then spreading like a net towards the shore. Raptors caused disturbances to roosting skimmers, and we observed one instance of predation of a skimmer by a White-bellied Sea Eagle (Haliaeetus leucogaster). Human fishing activities disturbed nearshore foraging and shoreline roosting skimmers. We suggest protecting Damar Char West by regulating human activities to minimize disturbance from December to March.