Studying the breeding patterns and diet of conspicuous predators is a useful way to understand the structure of marine coastal food webs. The Banc d'Arguin, Mauritania, hosts a significant portion of the West African population of a widespread and conspicuous fish predator, the Caspian Tern Hydroprogne caspia. At two small islands, the relatively offshore Arel and the inshore Zira, in the Parc National du Banc d'Arguin, the size of the colonies and the timing of the first wave of breeding were measured during the breeding seasons 2015–2018. At Arel, the summed number of nests counted varied between 128 in 2015 to 306 in 2018 and at Zira between 375 in 2015 to 279 in 2018. Breeding at Arel commenced about a month later than at Zira. During the breeding season of 2016, the diet of Caspian Terns was assessed by the identification of hard items found in pellets collected near nests. All of these appeared to be parts of fish (e.g., otoliths, bones, vertebrae, scales, bullae and atlas). Despite the effort, for Arel 47% and for Zira 45% of the fish parts remained unidentified. Nevertheless, diet composition differed in interesting ways between the two colonies. At offshore Arel, the identifiable part of the diet consisted primarily of pelagic species, namely Hemiramphidae, while at inshore Zira, pellets consisted primarily of bentho-pelagic prey, namely Cichlids. Repeated sampling across years may show whether the evidence for earlier inshore breeding holds up and is consistently correlated with dietary differences.

Most seabirds delay reproduction for multiple years. The standing hypothesis is that seabirds delay reproduction while they develop foraging skills. Here, I clarify an old but understudied alternative hypothesis: young seabirds also undergo a phase of social development before beginning reproduction. I then provide a prefatory, but necessary, test of this hypothesis with American Herring Gulls (Larus argentatus smithsonianus), asking whether young gulls have an opportunity for social development at colonies before breeding. A corresponding set of predictions is that young gulls are (A) present at breeding colonies, (B) socially engaged, and (C) not breeding. I conducted census counts and behavioral observations at a northwest Atlantic breeding colony on Kent Island, New Brunswick, Canada during summers 2022–3, along with supplementary observations at Great Duck Island, Maine, USA. Immature gulls in an advanced predefinitive plumage stage were common (2.5–6.2% of a total census of ∼4,000 birds). Younger birds, identified via less-advanced predefinitive plumage stages, were nearly absent (generally <1% of census). Immature birds were socially engaged around foreign territories. Yet only 1–4 immature birds held territories or nests of their own. This phenomenon suggests the social conditions at breeding colonies may set the stage for forms of social development that, in turn, set the stage for life history and plumage evolution.

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 Atlantic coast of South America supports many Nearctic shorebirds during their non-breeding season where they use a network of stop-over and wintering sites. To quantify the importance of French Guiana among those sites, we surveyed and resighted banded birds in the Kourou River estuary during two periods: 1989–1997 and 2005–2008. Twenty species were recorded, among which 15 were observed every year, during migration and/or boreal wintering. The most abundant species was Semipalmated Sandpiper (Calidris pusilla), accounting for 57% of all observations. In most Nearctic shorebird species, we observed dramatic changes in numbers and phenology between both survey periods. In the 1990s, the Kourou River estuary was mainly a post-breeding stop-over site; in the common shorebird species the largest numbers were observed in September and October. In the 2000s, only few species still occurred in significant post-breeding numbers, and migration peaks occured later for some of them. Observations of 304 banded individuals of five shorebird species indicated that some staging birds stopped in southern Canada and over-wintered in Brazil or Argentina. Many of our resighted birds stopped over in Delaware Bay in spring. Our results indicate the importance of French Guiana as a fall stop-over for Nearctic shorebirds using Western Atlantic Flyway.

Black Skimmers (Rynchops niger) are sexually monochromatic seabirds that are dimorphic in size. Although most dimorphic seabird adults can be accurately sexed using non-invasive techniques, determining the sex of pre-fledglings is more challenging. Schew and Collins (1990) developed an equation to estimate chick age from wing chord and used body mass of chicks ≥ 24 days old to evaluate the sex of skimmers in California; however, this was not verified on known-sexed individuals. Our objective was to assess the accuracy of their methodology on banded skimmer chicks from southwest Florida whose sexes were confirmed during adulthood. Out of 32 skimmers, Schew and Collins' (1990) method only classified 44% of males and 81% of females correctly. While males on average were larger than females, there was considerable overlap between the sexes when measurements of body mass, culmen and tarsus length were plotted against wing chord. It appears our Florida chicks grow slower than those in the California study and do not asymptote until after they are flight capable. As Black Skimmer populations decline, further research is needed to determine the most effective chick sexing method as knowledge of survival rates of pre-fledglings by sex will be critical for evaluating management efforts.

Increases in population size and reductions in suitable migration stopover habitat associated with drought, water development, and agricultural practices, along with conspecific attraction, are hypothesized mechanisms for increasing flock sizes of migrating Whooping Cranes. During autumn 2021, we observed such a phenomenon during a period of drought in the central Great Plains when 46 Whooping Cranes gathered as a single flock in the central Platte River valley. We provide a detailed account of how this larger aggregation formed from 5 smaller groups, behavioral observations, and environmental conditions experienced during this event including river flow, ambient temperature, and wind and drought conditions. Here, we report considerations for environmental and hydrologic conditions preceding and during this event as well as use patterns and behaviors we observed while the largest single flock of Whooping Cranes ever documented in the United States portion of the migration corridor was in the central Platte River valley.

Wetlands in arid and semiarid regions are recognized as priority ecosystems for conservation of wetland-dependent species in these systems. Evaluation of habitat selection is necessary for effective habitat management and, consequently, population management. The Lower Colorado River Valley population of Greater Sandhill Cranes (Antigone canadensis tabida), winters exclusively in portions of southwestern Arizona and southeastern California. Therefore, there is a need for information pertaining to winter habitat selection to guide management decisions. We attached solar-powered satellite platform transmitter terminals to greater Sandhill Cranes and used daily global positioning system locations. Each used location paired with 10 randomly generated locations had equal probability of drawing any of the randomly generated locations. We evaluated habitat selection and found the model that included land use type (β = –5.85, SE = 0.23, P < 0.001) and distance to roost (β = –4.61, SE = 0.16, P < 0.001) as interactive effects was the most supported model in the candidate set. Our results emphasize the importance of maintaining wetlands in close proximity (∼ 5 km) to selected land use types, which can be challenging to manage for in arid systems but are particularly necessary for this high conservation priority population of greater Sandhill Cranes.