In birds, pre-hatching calls are part of the communication behavior between parents and offspring, and may serve multiple functions. The Clark's Grebe (Aechmophorus clarkii) has a wide distribution in Mexico, and in 2015 we monitored a reproductive colony in the lagoon of Zumpango in central Mexico. We describe and measure the pre-hatching calls of two individuals from two different clutches. Eggs were about 22–25 days old. We obtained 5.16 minutes of recordings, with 81 calls made up by a frequency-modulated note and with an average call duration of 8.05 milliseconds and a peak dominant frequency of 828.20 Hertz (max 870.40; min 771.38). Calls were emitted at intervals of 1.38 seconds. This is the first description of pre-hatching calls in the Clark's Grebe, a poorly studied waterbird in Mexico.

There is often substantial variation in habitat type and quality within species ranges and management units, especially in wetland ecosystems. This variation necessitates quantifying behavioral and habitat associations to inform conservation of wetland-dependent species. This study explored drivers of American Avocet (Recurvirostra americana) energy expenditure to evaluate patterns of habitat use during the non-breeding season at Mustang Island in Texas, U.S.A. and Rockefeller Wildlife Refuge in Louisiana, U.S.A., on the coast of the Gulf of Mexico. A Bayesian linear mixed model was used to analyze GPS-acceleration data from tracking devices on 31 American Avocets, with overall dynamic body acceleration (a proxy for energy expenditure) as a response variable and tide, time of day, day of year, and landcover as hypothesized drivers. Results suggested that landcover, tide amplitude, and time of day explained substantial variation in energy expenditure, and each site showed unique patterns in these relationships. For example, the interaction of landcover and tide was heavily influential at Rockefeller, whereas Mustang Island birds showed a substantial dichotomy in energy expenditure between day and night. Using energy expenditure to understand habitat associations could be helpful to better understand variation in habitat use and behavior and customize conservation planning in dynamic ecosystems.

In birds, sexual selection on plumage may promote sexual dichromatism and male ornamentation. However, even in drab species without obvious sexual dichromatism, plumage may still be used for mate choice. A previous study found weak but significant sexual size dimorphism in North American Black Terns (Chlidonias niger surinamensis), but no assortative mating based on morphology. However, the relevance of plumage variation to mate choice in this species is yet untested. Here, using reflectance spectrometry and avian visual modeling, we revealed that Black Tern males and females exhibited a subtle but significant difference in brightness (males darker) in a midwestern USA population. Importantly, the achromatic contrast between the sexes was perceptible during mate choice. Moreover, there was evidence of disassortative mating for plumage color as measured by hue and saturation, but not brightness. There was no relationship between plumage color or brightness and body mass. This finding suggests that visual signals unrelated to body condition may be relevant to Black Tern mate choice. The pattern of disassortative mating was unexpected, and potential benefits of choosing a mate dissimilar from oneself are discussed. This study highlights the importance of considering the avian visual system when studying plumage variation elusive to human observers.

The Black Skimmer (Rynchops niger) is a charismatic representative of coastal-nesting waterbird communities in North America and freshwater riverine and coastal systems in South America. Skimmers are at high risk of decline due to threats including habitat loss, human activity, and climate change throughout the annual cycle. To understand range-wide population connectivity, eight microsatellite loci were used to reveal genetic differentiation between North American Pacific and Atlantic Coasts, including the Gulf of Mexico, and very strong differentiation between the North American sites and a site in Peru, South America. A reduced dataset, incorporating previously published data from South America, documented strong inter-continental differentiation and moderate differentiation among sites within South America in a pattern inconsistent with current subspecies designations, and suggesting a more complex pattern of dispersal. We recommend combined use of telemetry and genomic tools to assist in future delineation of skimmer subspecies ranges and non-breeding habitat use in South America. Because genetic diversity was relatively low in North America and higher in South America, genetics could determine whether skimmers in South America represent the ancestral population now expanding along the Atlantic and Pacific Coasts of North America. Detailed knowledge of seasonal movement and non-breeding habitat use that can be obtained by telemetry and population-wide molecular analyses will be essential to informing effective management across the Americas.

Sexual dimorphism in bill size can lead to sex-specific foraging strategies. All 12 extant species of oystercatchers (Haematopus spp.) have sexually dimorphic bills, and most oystercatcher species show intersexual niche partitioning in diet, where males and females eat different prey species in different proportions. Intersexual niche partitioning in diet has not been examined in American Oystercatchers (Haematopus palliatus). This study tested for intersexual niche partitioning in diet in a population of American Oystercatchers breeding on two barrier islands in coastal Virginia, U.S.A. in 2022 and 2023. Diet composition, prey size selection, and foraging areas were compared between the sexes (n = 31 males and n = 28 females). Unlike other oystercatcher species, male and female American Oystercatcher diets overlapped by 99%. Both sexes took similar-sized prey across the seven prey species and shared use of 59% of feeding areas. Previous studies on other oystercatcher species may have found intersexual niche partitioning in diet because of highly competitive environments due to high population density or low prey availability. In contrast, the present study in the Virginia barrier islands that found diet overlap between the sexes may be due to a low competitive environment from low breeding densities and sufficient prey abundance.

Examining prey choice is important for understanding the drivers of survival, breeding success and population change of tropical seabirds. We analysed spontaneous regurgitations from Red-billed Tropicbirds (Phaethon aethereus), at St Helena, South Atlantic between 2013 to 2018. Squid from four families, eight fish families, and one octopus species were identified. Dietary composition and diversity revealed Red-billed Tropicbirds fed predominantly on epipelagic juvenile squid, especially neon flying squid (Ommastrephes cylindraceus). Commercially exploited fish and species commonly used as bait and/or discarded, had a low frequency of occurrence (8.8%) and by number (3.5%) in regurgitations, indicating tropicbirds may have a low risk of mortality by bycatch. The consumption and size of squid varied among years; 2017 had significantly smaller squid consumed in greater proportions than in the other years observed. Chicks had larger meals (by ∼41 g ± 39 g SD) and higher diversity of prey compared to adults, suggesting adults favoured selecting higher quality, heavier prey as a provisioning strategy for their chicks. The high frequency of occurrence of juvenile squid, and reliance on neon flying squid, suggests future dietary measures may provide valuable information about juvenile squid abundance and development, before they are mature and become commercially important to fisheries.

The Eastern Black Rail (Laterallus jamaicensis jamaicensis) is a subspecies that winters mainly along the Gulf and Atlantic Coasts of the United States. Declines in Eastern Black Rail populations throughout its range raised its federal status to Threatened, amplifying the need to monitor the species year-round. Due to the species' reduced detection probability in the winter, documenting and monitoring individuals during the non-breeding season is challenging and thus information on the early breeding phenology of Black Rails remains limited. In February of 2023 while conducting a multi-species rail monitoring project, we documented three male-female Black Rail pairs on the Texas Gulf Coast when using an unoccupied aerial vehicle (drone) equipped with a thermal camera. During drone flights in April, we recorded the earliest documented fledgling Black Rail. In this note, we outline our detailed observations of Black Rail winter pair formation, summarize our detections of a Black Rail fledgling, and discuss management and conservation concerns regarding early-season pair formation and egg-laying of Black Rails in coastal Texas.

Population data on the African Openbill (Anastomus lamelligerus, hereafter Openbill) are largely lacking. We surveyed Openbill colonies on the Barotse Floodplain of the Zambezi River in western Zambia, describing nest site characteristics, clutch size, and brood sex ratios. We also monitored the movements of a male with the first telemetry transmitter deployed on the species. He travelled an average of 16.4 ± 9.6 (SD) km roundtrip during 73 foraging trips from its nesting colony. In July 2023, we surveyed colonies and estimated nest abundance from the air, identifying three large colonies in dense Phragmites spp. reedbeds along the Zambezi River channel. There were approximately 70,000 Openbill nests in the three colonies combined, with the largest colony estimated to have 57,884 nests. This colony also had 546 African Spoonbill (Platalea alba) nests, making it the largest known Openbill and African Spoonbill breeding site in Africa and one of the world's largest known long-legged wading bird nesting sites. Our study provides a snapshot of a globally significant Openbill population but also shows that much more research is needed.

Closely related sympatric species achieve sympatry using multiple strategies, which includes avoiding competition by sharing some habitats (>1 species using the same habitat at the same time; “syntopy”) while using other habitats exclusively (“allotopy”). The extent to which sympatric species use the syntopy-allotopy strategy relative to other strategies, especially with relation to changing land use and season on agricultural landscapes, is poorly documented in waterbirds. We measured year-long abundance and habitat use of three ibis species on a starkly seasonal semi-arid landscape using an a-priori design covering areas with two dominating land uses (wetlands and agriculture) in north-west India. We hypothesized that ibis abundance and allotopy would be higher in wetter areas and seasons (lower competition, higher resource availability) and that drier areas and seasons (higher competition, scarce resources) would have lower ibis abundance and increased syntopy. Ibis abundance varied by species (Red-naped > Black-headed > Glossy), season (Summer > Winter > Monsoon) and land use (wetland > agriculture). Ibises largely avoided inter-species competition (81% of observations were of single species), one species showed year-long allotopy (Red-naped Ibis used crop fields) and the other two species preferred wetland habitats. Syntopy was rare and occurred mostly in areas with more wetlands (91%) and during summer (63%). Ibises achieved sympatry by employing multiple strategies – avoiding direct competition, divergence in species' habitat use, and increased syntopy during summer. Ibis behavioural plasticity favoured their sympatry across changing landscapes and seasons, but retaining wetlands appears key to their year-long coexistence on mixed use landscapes.

Saddle-billed Storks (Ephippiorhynchus senegalensis) invariably build stick nests on the tops of trees ranging from 4.5 to 25 metres above ground, usually near water, but never in water. We detail the species' first reported floating ground nest in Bangweulu Wetlands Game Management Area, Zambia. The nest was observed on 09 September 2022. It was constructed almost entirely of dried sedges and papyrus with a few sticks, was surrounded by shallow water, and contained two nestlings. Fire posed an imminent threat to the nest.

A Common Grackle (Quiscalus quiscula) was observed consuming eggs from an exclosed (protected) Great Lakes Piping Plover (Charadrius melodus) nest in the lower bay of Green Bay, Lake Michigan in Wisconsin, USA during June 2023. The observation, captured by a trail camera, is the first photographic documentation of grackle predation in any of the three Piping Plover breeding populations. This behavior adds Common Grackle to the suite of egg predators and has critical implications for this shorebird species, particularly in the Great Lakes region where Piping Plover is listed as federally endangered and Common Grackles are relatively abundant. Given that current nest protection efforts rely on exclosures with openings that enable access by grackles, we recommend (1) identification of Piping Plover nesting locations across the Great Lakes region that are frequently used by Common Grackle, and (2) subsequent alteration of exclosure use (e.g., omission to prevent cueing by grackles or possible structural modification to prevent access) and/or habitat or predator management at locations where grackles are particularly problematic. In addition, increased deployment of trail cameras at Great Lakes sites will help elucidate the extent to which Common Grackle predation of Piping Plover nests is a population-wide threat.

Incidence of hybridization, the interbreeding of species, is poorly-understood but believed to be comparatively prevalent in avian communities. In the Outer Islands of Seychelles, at St François Atoll, a Roseate Tern (Sterna dougallii) was first observed to have formed a pair with a Black-naped Tern in 2009. Subsequently, in 2015 conservation staff recorded an adult with intermediate characteristics, presumed to be a hybrid of the mixed-pair seen previously. The suspected hybrid proved fertile, backcrossing with the Black-naped Tern colony and producing offspring of its own. The resultant juvenile had red legs, exhibiting intermediate morphology. Presented here is an assembly of field observations and photographic evidence collected over 15 years which document mixed pairs; displaying defensive nest behavior, mate-feeding, incubating eggs, copulating and parenting chicks. Findings strongly indicate hybridization has taken place, which constitutes only the second example of such an event with this species combination worldwide. We also uncovered evidence for backcrossing, possibly compromising the genetic integrity of the Black-naped Tern colony which is of increased conservation value due to the relative scarcity of the mathewsi sub species.