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.