Agricultural management, particularly haying, can cause synchronous nest failure of ground-nesting songbirds. As a consequence, these birds may subsequently renest and choose a new social mate (divorce). This study (1) quantified within-year and between-year divorce rates of grassland songbirds, and (2) determined if divorce rates differed after haying or predation-caused nest failure, and if so, whether divorce influenced reproductive success. From 2002 to 2017, we monitored 121 Bobolink (Dolichonyx oryzivorus) pairs and 436 Savannah Sparrow (Passerculus sandwichensis) pairs in an agricultural region of Vermont, USA. Within-year and between-year divorce rates were 0–84.9% for Bobolinks and 17–69.1% for Savannah Sparrows. Between years, Bobolinks, but not Savannah Sparrows, were more likely to divorce after nest failure, but haying did not influence divorce rates. Within years, Savannah Sparrows were more likely to divorce after nest failure, but as with Bobolinks, divorce rates in Savannah Sparrows were not different between nests that failed due to haying or predation. Across all Savannah Sparrow renests, divorce had no influence on the number of young fledged per female. However, between years, female Bobolinks that divorced fledged more young in their first attempt while those that did not divorce fledged more young in their second attempt. This study showed that pairing decisions were not differentially affected by cause of nest failure. Further, we identified no reproductive benefit to divorce. Our results indicate no adaptive benefit and potentially a significant reproductive cost to divorce, and that these effects vary between species.

House Sparrow (Passer domesticus) populations declined across much of their global range in the late 20th century. Most research examining this decline is conducted in the species' native European range, but Europe encompasses a small portion of the species' current distribution. House Sparrow population trends in the United States and Canada, and the potential mechanisms driving these trends, remain relatively unexplored. We use 21 years of data from Project FeederWatch, a large-scale citizen science project, to investigate House Sparrow population trends in North America. We found winter flocks in urbanized areas were larger than flocks in rural areas, with widespread spatial heterogeneity in local population trends. Despite greater abundance in developed areas, House Sparrow populations declined in developed areas from 1995 to 2016 while remaining stable in rural areas. House Sparrow population declines coincide with an increase in populations and expansion of the winter distributions of Accipiter hawks, which are known predators of House Sparrows. However, we do not find a direct connection between the presence of Accipiter hawks at count sites and House Sparrow population declines in winter. These results expand our knowledge of widespread House Sparrow declines to North America and provide context for continuing research on House Sparrow declines in the introduced range.

Cities are constant-expanding novel ecosystems that present multiple pressures for birds, but they can offer opportunities for generalist taxa with traits that ease their establishment. The Crested Oropendola (Psarocolius decumanus) is a Neotropical blackbird that nests colonially in different environments, from mature lowland forest edges to cultivated clearings, including other human-altered ecosystems. Here, we aim to characterize Crested Oropendola colonies in Caracas, Venezuela, a city where these birds have become more common in recent years. During 3 years (2016–2018), we recorded the number of complete nests per colony and tested for differences in colony size based on site characteristics and urban features. Additionally, we did multivariate ordinations (NMDS) to detect associations between such features and colony size, as well as spatial autocorrelation tests for size and change in the number of nests across years. By 2018, we recorded 45 colonies with 317 nests in Caracas (mean = 7), the largest quantity of oropendola colonies found in any locality until now. We report for the first time evidence of solitary nesting behavior and show that colonies placed in multiple trees were fairly common (29%). Colony size was not related to most nesting site features, with the exception of presence of nearby roads. Colonies close to roads showed significantly larger sizes than colonies far from them, potentially due to their isolation from predators. The mean distance between colonies was 1.1 km and we detected a slight negative spatial autocorrelation in nest change among neighboring colonies. We pinpoint differences in colony size and nesting patterns among Psarocolius species, likely related to different degrees of polygyny. Finally, we discuss the potential relationship of coloniality and isolated nesting sites, among other factors, in facilitating the establishment of this species in the city. The Crested Oropendola population in Caracas offers an opportunity to investigate reproductive and social aspects of the species and the evolution of colonial icterids.

Breeding Common Terns (Sterna hirundo) have been studied extensively in North America and Europe, but little is known of the small, isolated populations south of the main continental ranges. We conducted a 69 year study of Common Terns in the Bermuda archipelago (in the western North Atlantic Ocean at ∼32°N) to document their phenology, distribution, numbers, and breeding biology. Common Terns arrive at Bermuda in March and start to nest about 10 April, 2–3 weeks earlier than any other population of the species studied to date. Unlike the colonially nesting mainland populations, Bermudian Common Terns nest singly or in very small groups on many small islets and artificial nest sites (n = 50 sites) scattered throughout the archipelago. The population included 15–36 pairs in the 1970s and 1980s, but declined by about 50% following each of 3 major hurricanes in 1987, 2003, and 2010, and is now critically endangered. Since the 2003 hurricane, the population has included many (up to 7) female–female pairs laying infertile eggs. In contrast, the mean clutch size of male–female pairs was 3.01, with mean productivity >2.2 fledglings/pair over the 69 year period, the highest values reported for the species anywhere in its range; in at least 10 cases, pairs raised 4 chicks to fledging. The Bermudian population of Common Terns is intensively managed but remains critically endangered, and its recent shift to nesting on small rafts and buoys about 3 m in diameter poses new challenges for management.

Predation is typically the primary cause of nest failure for songbirds, even within unfragmented forested landscapes. In recent years, video cameras have been used to study causes and patterns of nest failure in a variety of habitats and regions. However, surprisingly few video camera studies have been performed in forests of northeastern North America. Over 5 years, we monitored Veery (Catharus fuscescens) nesting success in a mature forest landscape in northeastern Pennsylvania and used video cameras at a subset of nests to identify the predator assemblage and to describe relevant patterns of predation. Overall, we located 289 nests and recorded 67 of these nests with video cameras. Annual nest survival rates varied substantially across years (0.17–0.44) with this variation driven primarily by the dominant source of nest mortality: predation. Video cameras recorded 40 predation events by 12 predator species. Mammals (7 species), birds (4 species), and snakes (1 species) accounted for 75%, 20%, and 2.5% of predation events recorded, respectively. Predation events occurred during the day more often than expected by chance. Logistic exposure analyses indicated that both camera presence and nest age affected nest survival by influencing predation rates, but date did not. The diverse predator community observed depredating Veery nests led to low nesting success in some years, but also demonstrated that causes of nest failure vary by year and cannot be attributed to any single predator species or group. A greater apparent predation rate at nests with cameras likely resulted from a more frequent visitation rate to these nests by researchers compared to those without cameras and suggests a potential bias with artificially decreased nest survival estimates in years in which cameras were used.

Interactions between hummingbirds and potentially dangerous or aggressive insects at shared food sources may result in interference competition and risk-avoidance behaviors. To examine the potential interplay between perceived risk and interference competition, we observed the vigilance behaviors of Ruby-throated Hummingbirds (Archilochus colubris) foraging at artificial feeders with and without visual obstruction in the presence and absence of 3 species of wasp (Hymenoptera: Vespidae: Vespinae). Hummingbirds withdrew their bills from the visually obstructed feeder more rapidly than when feeding with a clear view of the surroundings. Wasps caused hummingbirds to spend a greater proportion of their visit vigilant, an effect positively correlated with the number of wasps at the feeding station. Aggressive competitive interactions at feeders were asymmetric. Hummingbirds avoided feeders with wasps and switched between available feeders more often and were never observed pursuing wasps away from the feeder. Instead, hummingbirds were chased by wasps or avoided foraging from feeders when wasps were present. Changes in hummingbird vigilance patterns in response to wasp aggression match those of other avian species whose antipredator vigilance patterns have been thoroughly examined. Thus, although interference competition inevitably occurs, vigilance patterns suggest that hummingbirds do perceive wasps as a potential threat and not solely as competitors.

Urbanization alters ecological systems, disturbance regimes, food webs, and a variety of other processes that can influence local flora and fauna. In birds, most studies have focused on behavioral or demographic responses to altered conditions; however, the physiological mechanisms associated with these responses have been understudied. We have previously documented shifts in foraging behavior because of the availability of human-provided food; we sought to see if this was driven by or associated with a change in field metabolic rates. We measured field metabolic rates (FMR), a measure of daily energy expenditure (DEE), of Florida Scrub-Jays (Aphelocoma coerulescens) in 2 habitats using doubly labeled water (DLW). One population of jays lived in wildland habitat, the other in a suburban area where the habitat was badly degraded. During the breeding season FMR of suburban males exceeded that of wildland males by over 100%. Female FMR did not differ between sites but increased following incubation. In the wildlands, FMRs of females were barely lower than those of males, but in the suburban landscape, female FMRs were much lower than in males. For both sexes in the wildlands, FMRs were about 3.5× basal rates of metabolism (BMR) during breeding; in the suburbs female FMR exceeded BMR by 4× but did not differ from that of wildland females. Suburban male FMRs exceeded BMR by 7.1×. During the nonbreeding seasons of fall and winter, FMR did not differ between habitats, ranging from 1.7× to 2.1× BMR, thus it is the breeding season that separated wildland and suburban jays energetically. In both habitats, a low water economy index (mL/kJ) and low water fluxes indicated that these jays are well adapted to their xeric habitat, but their FMRs distinguished them from desert birds. The very high energetic cost associated with breeding for suburban males may help explain why in the metapopulation of Florida Scrub-Jays, suburban jay populations are sinks. This study underscores the value of physiology in the conservation of listed species.

This study presents breeding phenology, fledgling production, and nest success for the Black Swift (Cypseloides niger) over a 22 year period at the Box Canyon colony, Ouray, Colorado, USA. Data were collected annually from 1996 to 2017 by direct observation from arrival of the birds at the nesting colony until all adults and fledglings departed. We documented dates of first arrival, laying, incubation onset, hatching, and fledging, and determined the intervals from arrival to laying, laying to incubation, length of incubation, and length of the nestling period in each year. Breeding events followed each other closely and showed little chronological change throughout the study. We identified a negative trend in the number of nest attempts and fledged Black Swift chicks over time but found no relationship between these 2 trends and the environmental factors of summer temperature, summer precipitation, or tourist visitation. The Mayfield estimate of nest success for all nest attempts was 77.5%. There was unexplained annual variation in nest success, but the trend in nest success remained static, with no correlation between nest success and temperature, precipitation, or tourist visitation. This study represents the largest dataset and longest-duration investigation into the breeding phenology and nest success of the Black Swift.

Seabird colony attendance during their breeding seasons is driven by reproductive obligations of incubation and chick rearing, resulting in relatively predictable attendance patterns near breeding sites. Less is understood about patterns and function of activity ashore at colony sites outside the breeding season. We attempted to quantify year-round activity of crevice-nesting Crested Auklets (Aethia cristatella) at Gareloi Island, Alaska, a site with some of their largest colonies. In June and July 2013 and 2014, 94 Crested Auklets (92 adults and 2 subadults) were fitted with uniquely coded 1.0 g VHF radio-tags (0.6% of body mass) at 2 inland study plots in the southeast colony. Radio receiver–loggers remotely detected and recorded individuals present on the nearby colony site surface 24 h/d from date of tagging through autumn, winter, spring, and summer 2013–2015. Notably, we found Crested Auklets present in all months of the year, with half of our radio-tagged auklets (n = 47, 29 females, 10 males, 8 unknown sex) detected inland at the colony site during nonbreeding months (Sep–Mar). Visit duration for these individuals comprised about 0.4% of their total annual colony site activity; this is the first evidence of year-round Crested Auklet colony attendance that may be unique to Gareloi. Other findings included extreme individual variability and intersexual differences in colony attendance frequency, differences in attendance between breeding and nonbreeding birds, a lapse in surface activity prior to laying in May, and frequent nocturnal activity on the colony surface. Enhanced circannual patterns of Crested Auklet colony attendance at this island may relate to defense of nesting site and other social advantages, permitted by a nearby highly productive sea area with year-round foraging opportunities.

Species-specific vocalizations can act as a reproductive isolating mechanism between closely related populations. We analyzed vocal differences between 2 hybridizing species of sex-role reversed polyandrous shorebirds, the Northern Jacana (Jacana spinosa) and Wattled Jacana (J. jacana). We found that Northern Jacana calls have higher fundamental frequency and peak frequency than Wattled Jacana calls. We also compared calls between females and males, as both jacana species are sex-role reversed and females compete for male mates. Males produce calls with a higher fundamental and peak frequency and shorter notes than females. These results suggest that vocal differences between Northern and Wattled jacanas have the potential to act as a behavioral mediator of interspecific interactions, and that sex differences in vocalizations may relate to sex-role reversal in territorial defense and mate attraction.

I report on the nesting ecology of the Northern Pygmy-Owl (Glaucidium gnoma) in northwestern Oregon based on 71 breeding attempts, including observations at 66 nest cavities during 12 years of study (2007–2013, 2016–2020). I focus on the annual shift in the start of laying and in productivity (clutch size) in relation to prey composition. For all years combined, the start of laying spanned 2 months (27 Mar–30 May). The mean annual start of laying varied across consecutive years by nearly 3 weeks (19.0 ± 6.5 d); mean productivity at nests varied annually by 23% (1.2 ± 0.5 eggs). Observed clutch size was most frequently 5 or 6 eggs (5.6 ± 0.9, range 4–8 eggs, n = 47), but most clutches in early-nesting years were 6 or 7 eggs, and 4 or 5 eggs in late-nesting years. The mean incubation and nestling periods were 29.4 ± 1.1 d and 26.4 ± 1.2 d, respectively. Pygmy-owls fledged a mean of 5.1 ± 1.1 young at 58 successful nests and 4.2 ± 2.2 for all breeding attempts. Vertebrate prey composition varied annually and seasonally. Pygmy-owls took mammalian prey more often early in the breeding season (66% of vertebrate prey) and in early-nesting years (65%); avian prey were more frequently taken late in the breeding season (66%) and in late-nesting years (66%). Pygmy-owls nested disproportionately in coniferous trees (χ² = 67.48, P < 0.001, df = 1, n = 66); nests in western redcedars (Thuja plicata) fledged 1.5 more owlets and failed less often (5% failed) than nests in other tree species (22% failed). Observations at this largest ever collection of Northern Pygmy-Owl nests reveal a commitment by these small owls (1) to produce young annually, even when they had to overcome obstacles such as mate procurement, mate loss, and nest depredation, and (2) to use mammalian prey to increase productivity in some years.

Floodplain forests of large rivers in the midwestern United States are naturally fragmented by sloughs, backwaters, wetlands, and shrub carr. On the highly altered Upper Mississippi River (UMR), resource managers want to protect and manage floodplain forests to benefit forest “interior” bird species. To discover bird relations with interior and edge floodplain forest, we characterized bird assemblages during spring migration and breeding season in 3 forest types: habitat in the interior of forest areas > 100 m from an edge, edges associated with interior areas, and other areas of forest not associated with an interior area (random sites) on the UMR between Hastings and Red Wing, Minnesota. The random sites represent the majority of UMR floodplain forest area because only a small percentage of forest occurs >100 m from edge. Estimated habitat characteristics did not differ among interior, edge, and random sites. Bird relative abundance, species richness, diversity, assemblage composition, and detections of all but one species (in spring) did not differ among interior, edge, and random sites during both seasons. Our results suggest a homogeneous bird assemblage across UMR floodplain forest in the study area during spring migration and the breeding season, and that individual forest bird species do not seem to be more abundant in interior or edge areas as we defined them.

Many species of seabirds and waterfowl are predominantly colonial breeders, suggesting that colonial breeding is beneficial in some way. For Arctic nesting geese, colonial breeding may be an adaptive approach to minimize the risk of nest failure through predator swamping. Yet evidence for predator swamping is inconclusive. Species in low-lying coastal zones may have to manage tradeoffs between historical (e.g., predation) and increased frequency of other threats (e.g., coastal flooding associated with storm events). As the climate continues to change, coastal obligates will be subject to rising sea levels and an increase in extreme weather events, which could exacerbate the tradeoff between flooding and predation risk. We studied the effect of nest density on nest success in the colonial nesting Black Brant (Branta bernicla nigricans) on the Tutakoke River Colony in western Alaska and explored how density effects change during years of heavy Arctic fox (Alopex lagopus) predation and coastal flooding associated with storm events. We classified the colony as containing 2 strata that differed in elevation and vegetation, and were separated by the Tutakoke River. The stratum north of the Tutakoke River was 0.25 m lower in elevation and subject to periodic tidal flooding, while the southern stratum never flooded. Nest density positively affected brant nest success in years with high levels of fox predation. Nest success was greatest at the highest density during Normal years (low levels of fox predation and no flooding; northern stratum nest success 0.81 ± 0.01, southern stratum nest success 0.81 ± 0.01) and lowest in areas of low density during Fox years (northern stratum nest success 0.38 ± 0.01, southern stratum nest success 0.31 ± 0.01). Nest success was routinely higher during Normal years at all densities compared to Flood and Fox years. Our results support the hypothesis that colonial nesting, at least in tundra habitats, may have developed as a defense mechanism to swamp mammalian predators.

Eared Grebes (Podiceps nigricollis) are colonial-nesting waterbirds that use waterbodies along Great Salt Lake (GSL), Utah, during the breeding season. We examined the habitat characteristics of nesting colonies established by Eared Grebes, including water depth, invertebrate biomass density, vegetation species, vegetation cover, waterbody area, distance to shore, distance to nearest emergent vegetation, and distance to GSL. Samples and measurements were taken during the summer of 2018 from inside Eared Grebe nesting colonies, outside colonies but within the same waterbody, and unused waterbodies that did not contain colonies. We compared colonies sites to non-colonies sites that were within the same waterbody using logistic regression to build models and found no differences between them, suggesting that space for a colony is not lacking within a colony waterbody. Colony waterbodies differed from unused waterbodies (those not containing a colony) in having deeper water and higher percent cover of submerged aquatic vegetation. Results from Eared Grebe colonies around GSL were compared to colonies found in a literature review. Water depth in colonies around GSL were shallower than colonies located elsewhere. All of the colonies in this study were established on mats of submerged aquatic vegetation as opposed to colonies in other studies that were built on emergent vegetation. Wildlife biologists around GSL can manage for nesting Eared Grebes by maintaining a water depth (35–55 cm) that is conducive for submerged aquatic vegetation growth and high invertebrate densities. Climate change models predict that the American Southwest, which is already arid, will become drier in the future. When combined with increasing diversions of water for human uses, the waterbodies where Eared Grebes currently locate their colonies may become entirely dry or too shallow in the future to sustain them.

Landbirds are especially vulnerable during migration as they move through novel habitats and encounter enhanced predation risk, unpredictable food resources, enhanced competition, and inclement weather. Further, numerous studies suggest exotic vegetation species have the potential to alter habitat quality, in turn affecting the fitness of migratory birds. The purpose of this study was to evaluate fitness correlates associated with fall migrant use of shrubland habitat dominated by nonnative honeysuckle (Lonicera spp.) in northeastern Pennsylvania. Additionally, we looked for differences in stopover ecology between demographic cohorts (age, and in the case of Common Yellowthroat [Geothlypis trichas], both age and sex). We used estimates of mass change as our primary fitness indicator, assuming that evidence of positive mass change reflects fat deposition and hence indicates quality habitat. Our results suggest that of 7 species, 1 gained mass, 5 neither gained nor lost mass, and 1 lost mass. Further, while we found little evidence of age or sex differences in migratory timing, we did find evidence that older birds gained mass at a higher rate than younger in 2 species and that, while male Common Yellowthroats maintained mass while using our site, females lost mass. We conclude that our exotic-dominated shrubland habitat does not provide high-quality stopover habitat for most species.

Apart from obligate and facultative brood parasitism in birds, mixed-species clutches and broods are uncommon. Competition among birds for limited nest sites can result in antagonistic interactions leading to nest usurpation. When one species evicts and takes over the nest of another it can, on rare occasions, result in a clutch containing eggs of both species. Here I report an instance of Carolina Chickadees (Poecile carolinensis) usurping a Prothonotary Warbler (Protonotaria citrea) nest that resulted in the first documented instance of chickadees fledging a brood containing both chickadee and warbler nestlings. During a nest box study in southern Illinois during 1994–2006, this was the only nesting attempt (n = 6,076) where there was interspecific nest usurpation. In this case, a female chickadee contributed to building the nest cup in the box and laid eggs on 3 of the same days as the female warbler. The chickadee pair usurped the nest from the warblers, and ultimately fledged a mixed brood containing 3 chickadees and 3 warblers. The displaced adult warblers nested in a nearby nest box where they fledged 3 warbler nestlings, subsequently reused the original usurped nest box for an attempt at a second brood after the chickadees' brood fledged, and fledged 5 more warbler nestlings from it. This was not a case of facultative brood parasitism because the warblers were first to start building a nest in the box, only to have the chickadees contribute to nest building before evicting the warblers after there were 3 eggs of each species in the nest. The potential for the Neotropical migrant warbler nestlings/fledglings to mis-imprint on the resident chickadees that raised them likely diminished the warblers' ability to successfully survive their first year of life and/or subsequently mate with other Prothonotary Warblers. The rarity of nest usurpation in this bottomland forest study system suggests that cavities that serve as nest sites are not limiting.

We tracked 47 Wood Thrushes (Hylocichla mustelina) using radio telemetry over 2 breeding seasons in Virginia, USA. Here we present 2 noteworthy observations from this effort. First, we recorded one adult male with synchronous tail replacement in postbreeding molt during tracking from the early breeding season until the fall migration. Synchronous tail molt is seldom documented in Passeriformes and may have consequences for behavior and habitat use during this period of reduced mobility. Second, we recorded a widower male providing parental care by feeding young for nearly the entire nestling period. These observations highlight both the vulnerability of the Wood Thrush immediately following the breeding season and its potential reproductive resilience in the case of mate loss.

The timing of migratory passage for sexes and ages of birds is difficult to document because migration is spread out over time and space. We compared sex and age ratios from 10 species of birds that were banded in Wisconsin during fall migration to a sample of autumn window-killed birds from Chicago, Illinois. We assumed that these specimens were a random sample of the migrating population because dates of passage in Wisconsin either predate or were coincident with specimens recovered in Chicago. More juveniles than adults collided with windows, which is expected because of the higher number of juveniles in the fall migratory population. For Connecticut Warbler (Oporornis agilis), Dark-eyed Junco (Junco hyemalis), Ovenbird (Seiurus aurocapilla), and White-throated Sparrow (Zonotrichia albicollis), statistically fewer adults collided with windows than expected. It is possible that adults of these species, who have made at least 2 prior successful migratory journeys, might have experienced some degree of learning to avoid windows. For specimen data, ratios of males to females were approximately equal, except for Swamp Sparrow (Melospiza georgiana; 1:0.82). However, banders were unable to determine sex for a high percentage of each species, ranging from 98.5% undetermined sex for Hermit Thrush (Catharus guttatus) to 48% for Common Yellowthroat (Geothlypis trichas). Taken at face value, banding records for Common Yellowthroat, Dark-eyed Junco, and White-throated Sparrow indicated a much higher percentage of males, whereas for Song Sparrow (Melospiza melodia), females were much more common; 6 species showed no apparent difference in sex ratio between the banding and window samples. In species for which banders declined to identify an individual's sex for a high percentage of birds, we questioned whether the identification of sex in the remaining small percentage was accurate. Thus, we considered the alternative possibility that the specimen data were in fact the most appropriate null hypothesis, and if so, it would suggest that banders have misidentified sexes consistently in 4 species, and ages in 7 species.

Brood parasites reduce the reproductive success of many bird species by laying eggs in their nests. Hosts that reject parasitic eggs (“rejecters”) avoid most costs of brood parasitism altogether by physically ejecting eggs from nests or abandoning parasitized nesting attempts. Species that accept parasitic eggs once these are laid (“accepters”) may reduce or eliminate costs by aggressively responding to brood parasites at their nests to prevent parasitism from taking place. Accordingly, accepters should recognize brood parasites and nest predators as different nest threats with different levels of aggression, whereas rejecters may not. We exposed active Eastern Phoebe (Sayornis phoebe, an accepter host) and American Robin (Turdus migratorius, a rejecter host) nests to models of a female brood parasitic Brown-headed Cowbird (Molothrus ater), an eastern chipmunk (Tamias striatus, nest predator), and a European Starling (Sturnus vulgaris, nonthreatening control) during the incubation stage. Phoebes alarm-called equally toward the nest predator and brood parasite models, but attacked the nest predator model more than the brood parasite model. Robins, in contrast, alarm-called toward and attacked all 3 models equally. Interpreting these results is challenging due to experimental design elements, specifically small sample sizes and restricting the experiment to the incubation stage. Nonetheless, our experiment contributes to the paucity of comparative studies on accepter versus rejecter nest defense behavior in response to both nest parasites versus predators, and adds a new tested accepter species to the literature.

Ground-nesting birds typically maintain a nest free of foreign materials but occasionally are known to incubate a foreign object, often in the presence of other eggs. In May 2012, we discovered a Common Nighthawk (Chordeiles minor) incubating a turkey oak (Quercus cerris) acorn along with 2 eggs within a mesic flatwoods forest in Clay County, Florida, USA. Herein, we report this observation and include 3 possible hypotheses for this behavior.

The clutch size of the American Kestrel (Falco sparverius) has been well studied across a range of latitudes and habitats and typically is 4 or 5 eggs. Neither polygyny nor brood parasitism has been reported for the species. I report here 3 instances of supernormal clutches, of 8 or 9 eggs, documented in kestrel nest boxes in north-central Florida and discuss 4 possible explanations for these observations. In 2 nests only 1 egg hatched, and in 1 nest none of the eggs hatched. Although I was unable to make a conclusive finding about the cause for supernormal clutches, it is likely that they were laid by more than 1 female, either cooperatively or non-cooperatively.

Understanding how ducks use breeding habitat can help managers ensure conservation efforts are focused on the types, locations, and connectivity of habitat species require. Recent technological advancements have provided high temporal and spatial resolution on animal movements, revealing unexpected patterns in movement and habitat use. As part of a larger study, we attached a GPS-GSM backpack transmitter to a second-year female Mallard (Anas platyrhynchos) captured in a decoy trap on 28 April 2018 in Alberta, Canada's boreal forest. Following marking, we qualitatively inferred from the duck's movement path that she made at least one nesting attempt; however, we were unable to confirm a nest location. Approximately 30 d after marking, the duck made a long-distance (>200 km) movement west-southwest into the boreal transition zone and then proceeded to make another long-distance movement southeast (>450 km) into the prairie potholes region, where we suspected she made at least one more nesting attempt in early July based on clustered GPS data. After spending just over 30 d in a localized prairie potholes region (all points within ∼1 km radius), she began moving north in early August and by the end of the month had returned to within 4 km of where she was originally marked, and to the same boreal wetland where she first attempted to nest. Overall, the female Mallard traveled >1,000 km within the breeding period and used habitats in 2 disparate biomes for presumed nesting, the prairie potholes and the boreal forest. Herein we provide additional details about our observation and propose some hypotheses to explain the phenomenon.

The Honduran Emerald (Amazilia luciae) is an endangered hummingbird, endemic to dry forest communities of Honduras. Limited information exists regarding the species' breeding ecology. In 2015, we sampled vegetation surrounding Honduran Emerald nests and an equal number of randomly selected available locations within dry forest fragments in the Agalta Valley, Honduras. We compared Honduran Emerald occupied nest sites and available nest sites through a multivariate analysis, paired t-tests, and Wilcoxon signed rank tests. We found that nest plant height at nest sites was lower than those random plants at available sites. Additionally, we identified 4 other vegetation characteristics that warrant inclusion in future research: nest plant stem diameter, shrub–sapling density, Opuntia hondurensis density, and cacti height from multiple species. Finally, we propose that future research should study the influence of fine- and site-level vegetation on Honduran Emerald nesting success.

During migration, transient birds usually find themselves stopping in unfamiliar habitats in order to rest and refuel before resuming migratory flight. Here we document the first case, to our knowledge, of a Tennessee Warbler (Leiothlypis peregrina) entrapped in a spiderweb. The warbler's tarsus became caught in the mooring thread of a golden silk orb-weaver (Trichonephila clavipes) web and the bird was unable to free itself, resulting in death. While the role of spiderweb-related mortalities is likely minimal, they may represent a type of additive mortality that has been largely unconsidered during migration. Given the spatiotemporal overlap in the prevalence of spiderwebs and movement of migratory birds, researchers should document and report such anecdotal observations to determine the role spiders may play in mortality events during migration.

Cooper's Hawks (Accipiter cooperii) typically lay 3–5 eggs per clutch, rarely 6 eggs, and there are 2 accounts of 7-egg clutches and 1 record of a maximum 8-egg clutch for the species. Brood sizes of 3–5 young are common and the previous maximum brood count is 6 young. However, in 2019, we found an urban nest in Stevens Point, Wisconsin, with 7 eggs that resulted in a record high of 7 fledglings. We genetically confirmed that the attending male sired all the offspring and the attending female laid all 7 eggs. Larger body size of the tending adults may have been a factor in the exceptional reproduction reported here.

Nest predation is the dominant cause of nest failure in the tropics. However, our knowledge about tropical nest predator identity and community structure is still quite limited. On 9 January 2019, we video-recorded an Olive Sunbird (Cyanomitra olivacea) removing and flying off with an egg from an African Paradise Flycatcher (Terpsiphone viridis) nest in the East Usambara Mountains, Tanzania. This observation is surprising because the Olive Sunbird is a specialized nectarivore. Nectar, however, is a poor source of nitrogen and cannot meet the protein requirements for nectarivores. We hypothesize that bird eggs are a potential source of protein for selected long-billed sunbird species—species that can grasp and handle small bird eggs. Our observation of nest predation by an Olive Sunbird adds a heretofore unknown behavior to nectarivores in general and to sunbirds specifically.

Hosts of brood parasitic Brown-headed Cowbirds (Molothrus ater) have acquired a suite of behavioral responses against them, including egg rejection and nest defense. Several cavity-nesting species have been shown to exhibit egg rejection, including the Mountain Bluebird (Sialia currucoides). Previous work reported egg rejection rates as low as 20%, under the assumption that they may instead be relying heavily on aggressive interactions to defend their nests from parasitism. In the present study, we evaluated the egg rejection and aggression behaviors of a population of Mountain Bluebirds in western Montana. Results indicate a higher rate of rejection than previously documented, with model cowbird eggs rejected in over 40% of trials (n = 37), compared with 5% rejection of mimetic eggs. In contrast, we found little aggressive response by Mountain Bluebirds toward both an adult cowbird model and a nonthreatening American Goldfinch (Carduelis tristis) model. Aggression patterns were consistent between sexes, with the most common behaviors including sitting and watching from within 5 m and flying past the models (n = 21). Hovering above the model was observed on a few occasions, and physical contact by bluebirds happened on only 3 occasions toward the goldfinch model. In summary, Mountain Bluebirds in western Montana showed relatively high rates of cowbird egg rejection but little aggressive response toward adult heterospecific nest intruders.

The American Three-toed Woodpecker (Picoides dorsalis) is a relatively poorly known species due to its remote northern distribution, the low density of its populations, and its cryptic behavior. In this article, we report the observation of an 11-year-old individual, nearly 2 times older than the previous record for the species. This longevity is similar to values reported for the closely related Eurasian Three-toed Woodpecker (P. tridactylus). We report on the observation of a male that was captured, aged, color-banded, and photographed in 2010, and photographed again when it was resighted in 2019. This finding has potential implications for the modeling of population viability and the possibility of extinction debt in marginal habitat.

Deaths at the nest caused by hailstorms are rarely reported in birds and are usually revealed based on ex post monitoring. As a result, it is often difficult to draw inferences on the behavioral responses of individuals to hailstorms. In this note, I report the death of a female Lesser Whitethroat (Sylvia curruca) at its nest during the laying stage during a severe hail event in Poland. I inspected the nest soon after the storm and found traces that allowed me to reconstruct the nesting female's behavior. This observation contributes to the infrequent documentation that hailstorms may have lethal effects on shrubland birds, considered to be relatively resistant to hail-related mortality. It also shows evidence of partial incubation (nest attendance before clutch completion) during an extreme weather event. Finally, the female Lesser Whitethroat of this report lost all of her rectrices and other feathers that were found intact and spread out in the nest. Although feather loss due to hail trauma cannot be ruled out, the most likely explanation was their ejection (known as fright molt), possibly triggered by hail-associated stress. Should this be confirmed, this would be the first case of fright molt associated with a hailstorm reported in wild birds. My report adds further insights into bird responses to increasingly extreme meteorological events.

We document the first recorded instance of a fish depredating a hatchling bird while in the nest. Some coastal marsh-nesting avian species, such as the Seaside Sparrow (Ammospiza maritima), experience tradeoffs between the threat of nest predation and nest flooding. Nesting too low may result in nest flooding during the twice-daily high tides and increasing nest height increases the risk of nest predation. However, not much is known about how nest height affects exposure to different predators. We observed a mummichog (Fundulus heteroclitus) enter a Seaside Sparrow nest during a nest flooding event and depredate a hatchling. This observation expands our understanding of the predator–prey relationships experienced by coastal marsh-nesting birds, and the potential detriments of intensifying sea level rise on their nesting success.