To identify potential threats and prioritize areas for protection, modern conservation efforts rely on spatial data. While it is often impossible to study the movements of entire populations, we can examine patterns among individuals and groups to better understand populations as a whole. We used geolocator tags to determine where Atlantic Puffins (Fratercula arctica) at the southern edge of their range, vulnerable to warming waters and anthropogenic influence, spend the nonbreeding season, and whether birds from different colonies or parts of the same colony used different overwintering strategies. Between 2013 and 2017, tags were deployed on 97 puffins breeding on three islands in the Gulf of Maine: Machias Seal Island, Matinicus Rock, and Seal Island National Wildlife Refuge. Most tagged puffins remained in or near the Gulf of Maine throughout the autumn and early winter months, venturing as far south as Cape Hatteras (ca. 35°N) in February, March, and April, before returning to their respective colonies. Three individuals travelled north to the Gulf of St. Lawrence and waters around Newfoundland immediately after breeding, returning to the Gulf of Maine in mid-winter. We found no evidence of inter- or intra-colony differences in overwinter movement. This is the first study focusing on overwinter movements of puffins breeding at the southern edge of their range in North America and can assist in the development of policy regarding management and protection of important marine areas for puffins and other species.

Common Loons (Gavia immer) wintering in watercourses of Barataria Bay, in coastal Louisiana were sampled in 2011–2014 following the Deepwater Horizon oil spill of 2010. Blood samples were analyzed for stable isotope ratios of carbon, nitrogen and sulfur as proxies for habitat use and diet in order to expand our understanding of the trophic position of wintering loons. The δ¹³C and δ ³⁴S values indicated that these Common Loons feed in coastal estuarine habitats. Trophic position was estimated indirectly by comparing loon stable isotope ratios with those of Brown Pelicans (Pelecanus occidentalis), a known piscivore, sampled concurrently in 2014. The isotopic signatures of the two species were not significantly different; this is consistent with the hypothesis that both species foraged primarily in coastal estuarine habitats and mainly as piscivores. No significant differences were found between subadult and adult Common Loons with respect to isotopic signatures, suggesting similar habitat usage and diet. Adults weighed more and were in better body condition than subadults. Stable isotope composition and body condition were not significantly related. Using a parallel data set of polycyclic aromatic hydrocarbons (PAH, an indicator or oil contamination) in the blood of the same loons, there was no significant relationship between PAH contamination and stable isotopic composition. Therefore, PAH-contamination could not be linked to a distinctive foraging habitat or diet.

Mixed-species foraging aggregations of waterbirds result from foraging and anti-predator behaviors, and understanding the dynamics of these aggregations is useful in planning the conservation of waterbirds species and understanding their ecological functions within the ecosystem. This paper describes the dynamics in composition and structure of mixed-species foraging aggregations during the wet and dry seasons in the lagoon system of Las Salinas, Ciénaga de Zapata, Cuba. We surveyed these aggregations monthly from 2009 to 2017. Aggregation structure was analysed through relative abundance per guild, percentage of presence, and participation weight and participation rate. Forty-two mixed-species foraging aggregations of waterbirds were observed throughout the study, with greater species richness (n = 12 species, confidence interval: 10–13) and number of individuals (n = 800 individuals, confidence interval: 565–1,055) in the wet season. During the dry season, the most prominent species in aggregation formation were Snowy Egrets (Egretta thula), American White Ibises (Eudocimus albus) and Roseate Spoonbills (Platalea ajaja), which have been identified as nuclear species in other studies. In the wet season, American White Pelicans (Pelecanus erythrorhynchos) appeared to be the nuclear species within aggregations, something that had not previously been described in mixed-species aggregations of waterbirds. Confirming these nuclear species at Las Salinas is an important next step, given that conservation efforts focused on nuclear species might benefit the maintenance and function of the entire assembly.

The daily nest-survival rates of Red-billed Tropicbirds (Phaethon aethereus) were estimated over six breeding seasons on St. Eustatius in the Caribbean. We analyzed 338 nesting attempts between 2013 and 2020. The daily survival rate (DSR) of tropicbird nests was modeled as a function of nest initiation date, sea surface temperature (SST), elevation, vegetation in front of the nest, and year. Yearly nest survival rates (± SE) of the best fitting models ranged from 0.21 ± 0.06–0.74 ± 0.13 (n = 338 nests). DSR of the most parsimonious models averaged 0.39 ± 0.04 during the incubation period, 0.83 ± 0.05 during the chick-rearing period, and 0.30 ± 0.04 during the nesting period (incubation through fledging) when data were pooled across all years. Models with linear and quadratic trends of nest initiation date combined with SST and elevation received strong support in the incubation and nesting periods. Nests initiated in peak nesting season, when SSTs were lower, had higher DSR estimates than nests initiated early or late in the season. Compared to studies of the same species from Saba and the Gulf of California, survival probability on St. Eustatius was lower during the incubation stage but higher during the chick-rearing period. Similar to populations in the Gulf of California, tropicbird reproduction differed and laying date varied among years, and survival was influenced by SST. Our results are consistent with a study on White-tailed Tropicbirds (Phaethon lepturus) in Bermuda which found that survival was affected by temporal factors rather than physical site characteristics. Our study contributes to a better understanding of the factors that influence Red-billed Tropicbird survival on a small Caribbean island.

Coastal marshes of Lake St. Clair, in southwest Ontario, CAN and Lake Erie, in northwest Ohio, USA are important migratory staging locations for waterfowl despite experiencing substantial wetland losses. Waterfowl habitat management at these locations focuses on providing food resources for Mallards (Anas platyrhynchos), a highly sought game species. We examined direct recovery rates of Mallards banded prior to the 2014, 2015, and 2016 hunting seasons as a measure of harvest mortality. We compared harvest mortality between the two locations, among years, among four sex and age cohorts, and as a function of body condition. We found that banding location for juvenile Mallards was an important variable predicting harvest mortality. The probability of being a direct recovery was 126% greater for juvenile females and 70% greater for juvenile males banded at Lake St. Clair compared to those banded in northwest Ohio. Average body condition was slightly less for juvenile male Mallards banded in northwest Ohio during 2016 compared to those banded in 2015 or those banded in LSC in 2014 or 2015. We did not detect any other significant differences related to body condition and location or location-year with respect to direct recovery rates. We hypothesize that harvest mortality of juvenile Mallards could be related to differences in harvest regulations, bird abundances, or hunter density between the two study sites, all of which may have different implications for those interested in managing Mallard populations in the lower Great Lakes region.

Colonies of Herring (Larus argentatus) and/or Ring-billed Gulls (L. delawarensis) on Lake Ontario and the upper St. Lawrence River were searched annually, 1981–2018, for nesting Great Black-backed Gulls (L. marinus). Great Black-backed Gulls nested at nine sites where both Herring and Ring-billed Gulls nested, at seven sites with only Herring Gulls, and at one site where they nested solitarily. Nests per site ranged from 1–21 on Lake Ontario and 1–5 on the St. Lawrence River. On Lake Ontario, nest numbers increased from six nests in 1981 to 51 nests in 2001 (+ 11.3%/yr), then declined to zero nests in 2008, where they have remained ever since. The decline in nesting Great Black-backed Gulls was due primarily to mortality from Type E botulism that affected that species to a greater degree than other gull species, probably because of their superior ability to dominate and scavenge toxin-laden carrion. Temporal changes in routes and efficiency of botulinum toxin transfer likely explain why Great Black-back Gulls were initially able to colonize Lake Ontario, but have undergone extirpation in recent times. Our results illustrate how changes in disease prevalence in the Great Lakes can degrade environmental quality to the extent that some species simply cannot persist.

Aggression between adult Common Loons (Gavia immer) occurs frequently during the breeding season. In the past, it was suspected that most instances of intraspecific aggression took place between adult males. However, recent reports from the field suggest that female adult loons also participate in these battles. Postmortem investigation has shown that the damage incurred during these battles can range from incidental to fatal injuries. Sternal punctures are the most lasting evidence of this trauma and can serve as long-term records. Nearly half (46%, n = 268/574) of the loons received at Tufts Wildlife Clinic for postmortem from 2007 to 2015 were found to have sternal punctures. We conducted a focused analysis of the sternal punctures of 102 of these adult loons (49 female and 53 male) and found no significant difference in the number, distribution, or severity of sternal punctures between male and female loons. This suggests that the frequency and intensity of aggressive physical contests are remarkably similar between sexes and that there is no gender difference in the severity of these battles. Female Common Loons participate in lethal combats as often as their male counterparts. These findings provide an opportunity to better understand and study the biological or behavioral drivers of this aggression that is prevalent among both male and female Common Loons.

Many birds migrate at night, but little is known about whether they base nocturnal settlement decisions on visual or acoustic cues. Studies of conspecific attraction have found that songbirds and seabirds are attracted by day to call playback or decoy models, and birds will also settle preferentially in certain environments based on the presence of vegetation or water bodies. Remotely activated broadcasts and Autonomous Recording Units were applied to study whether Soras (Porzana carolina), common nocturnally migrating rails in central Illinois, could be enticed to settle in farm field habitats. At three study areas (farms) we used cues to attempt to attract Soras, with our experimental design consisting of Sora vocalizations, small ponds (Sora habitat), both cues, and no cues. Neither conspecific playback, visual pond cues, nor their combination significantly influenced Sora settlement. However, there were significant differences between farms in Sora calls recorded. One study area, Franklin Farm, had the most Sora detections during the study period, consistent with its high-quality habitat status as a Nature Conservancy restored wetland. As nocturnal calls were detected at every farm sampled, these results may assist wetland managers in promoting Sora settlement in critical breeding habitats in Illinois and beyond.

In most birds, parental incubation of eggs is necessary for embryo development and survival. Using a combination of weekly nest visits, temperature dataloggers, infrared video cameras, and GPS tracking of hens, we documented several instances of duck eggs hatching after being abandoned by the incubating female. Of 2826 Mallard (Anas platyrhynchos) and Gadwall (Mareca strepera) nests monitored 2015–2019 in Suisun Marsh, California, 48 (1.7%) were abandoned during late incubation (≥ 20 days). Of these, we identified six (12.5%) where at least one egg hatched 2–9 days after abandonment. In all six cases, eggshell membranes were found in the nest (indicating hatch), and ducklings were observed at three nests. Abandoned nests were unattended for an average of 5.9 days before eggs hatched; during this time, mean nest temperatures (23.6°C–29.0°C) were substantially lower than before nest abandonment (31.7°C–36.4°C). We estimated that abandonment resulted in a 9% longer time period between clutch completion and hatch (0–4 days longer) and a lower rate of egg hatching success (36%). Our results provide evidence that some older embryos (≥ 20 days) in mild climates can survive without parental incubation for several days and continue to develop (at a reduced rate) to the point of successfully hatching.

We initiated a telemetry study on the Saddle-billed Stork (Ephippiorhynchus senegalensis) in western Zambia in 2019 to address knowledge gaps about spatial ecology. As the first such field study on the species, we encountered multiple challenges in attempting to capture free-ranging storks, including limitations in manpower and trapping techniques. In three field trips, we captured and deployed transmitters on only three storks. All transmitters have since failed, and the longest one transmitted data was for only five months, during which we recorded a dispersal event into Angola and back to its natal area. Our work has painstakingly demonstrated that field techniques are not always transferable between species and study systems, and that initiating work on an unstudied species has unforeseen difficulties.

Little is known of rail migration ecology, consequently limiting efforts to effectively conserve rail populations. Therefore, we investigated changes in the migratory arrival/departure dates for Virginia Rails (Rallus limicola), King Rails (Rallus elegans) and Sora (Porzana carolina) north of Ocean Springs, Mississippi. Using citizen science data collected over the last 25 years, we inspected summarized data for patterns of primary arrival and departure windows indicated by first or last observations of each species at the lagoons, respectively, alongside 10^th/90^th quantiles that controlled for outliers (i.e., early arrivals, late departures). Regression models found no differences in spring migration departures for any species. In fall migration we found a difference only in Virginia Rail arrivals, which became later over time. King Rail arrived in autumn first in mid-September (September 22^nd) followed by Sora (October 5^th) and Virginia Rails (October 21^st). In spring migration, Virginia Rails departed first (March 19^th), then King Rails (March 24^th), and Sora (April 20^th). Trends for King Rails may have been skewed by some individuals having non-migratory behavior. Despite limitations, citizen science efforts were useful for an initial investigation of rail migration ecology, and future applications could be used to identify and assess factors affecting migration timing (e.g., climate change, habitat availability, weather shifts).

Roseate Terns (Sterna dougallii) frequently lay single eggs and desert them without incubating them. In a multi-year study, single deserted eggs comprised 4.2% of all clutches and 2.7% of all eggs. Laying dates and masses of single deserted eggs resembled those of first-laid eggs of female-male pairs and multi-female associations, but their masses differed from those of second-laid eggs of female-male pairs. An egg-transfer experiment showed that most single deserted eggs were fertile and that chicks hatched from them were viable when raised by female-male pairs. I hypothesize that single deserted eggs result from females laying their first eggs before the pair has settled on the location of a nest site. Fostering of single deserted eggs could be used to increase chick production in small colonies.

The diet of the Imperial Shag (Phalacrocorax atriceps) at Vintter Lake, Patagonia, Argentina, was investigated through analysis of 157 regurgitate pellets collected during the summer seasons of 2008–2010 and 2016–2017. The native fish Galaxias platei was the main prey throughout the study period, accompanied only by a few gastropod species (2010) and coleopterans (2009 and 2016). Our results markedly differ from those previously reported for Imperial shags breeding at Vintter Lake and other sites. The results are discussed in relation to the population decline observed in shags at Vintter Lake throughout the study period.