Coastal Louisiana—and its Mississippi River Delta, in particular—provides large and diverse habitats for many types of birds in North America and beyond. The Mississippi River and its distributaries have shaped Louisiana's unique coast, which includes extensive marsh and marsh islands, sandy barrier headlands and sandy islands, and isolated patches of maritime forest on natural levees, cheniers, and canal spoil banks. Louisiana thus supports large populations of many obligate marsh bird species as well as marine bird species that require islands for breeding sites. Here, we have collated available data and attempt to estimate the breeding population sizes of 17 bird species in coastal Louisiana. We then summarize the importance of the Louisiana coast for these bird species in the contexts of regional, national, and global bird populations. These preliminary estimates indicate that Louisiana's coast supports a high percentage of regional, national, and, in some cases, global populations of several coastal bird species. For example, we estimate that 73% of the United States population of Sandwich Tern (Thalasseus sandvicensis) breeds in Louisiana, and comparable estimates range from 24 to 55% for Mottled Duck (Anas fulvigula), Clapper Rail (Rallus crepitans), Tricolored Heron (Egretta tricolor), Wilson's Plover (Charadrius wilsonia), Royal Tern (Thalasseus maximus), Black Skimmer (Rynchops niger), and Seaside Sparrow (Ammodramus maritimus). Because most of these other bird species are distributed across state, regional, and national jurisdictions, management of birds and bird habitats in Louisiana has wide-reaching implications for the conservation of these shared natural resources. In this light, this paper is intended to be a resource for managers of avian resources in North America and beyond.

Exurban development (i.e., low-density residential housing) comprises at least 25% of the contiguous United States and disturbs the natural landscape, typically impairing habitat for forest interior songbirds and creating habitat for urban-adapted species. However, it is poorly known how exurban development affects shrubland birds, which require disturbance to create habitat (i.e., early successional vegetation). Therefore, our objective was to explore landscape patterns associated with shrubland bird occupancy in a forested region undergoing extensive exurban development. To address this objective, we conducted point counts across a natural–exurban gradient in Macon County, North Carolina, USA, and measured 8 land-cover covariates within 200 m and 1,000 m of survey sites. The covariates were percent canopy cover (CANOPY), contagion (CONTAG), percent of the landscape (PLAND) that was developed (DEV), elevation (ELEV), PLAND forest (FOREST), forest edge density (ED_DF), Simpson's landscape diversity index (SIDI), and PLAND shrub (SHRUB). We modeled occupancy for 12 shrubland species using a hierarchical occupancy model that accounts for falsepositive detections. We fit a global model that incorporated all non-collinear covariates and used stochastic search variable selection to determine which covariates showed a relationship with occupancy. The most frequently selected covariate was CANOPY (8 species), followed by ELEV (5 species), DEV (4 species), SIDI (3 species), and CONTAG (2 species). CANOPY and DEV were negatively associated with occupancy. SIDI and CONTAG are both metrics of landscape heterogeneity; heterogeneity was positively associated with occupancy. Additionally, of the study species, generalists showed the highest occupancy rates, while specialists showed the lowest occupancy rates. We suggest that the associations between occupancy and canopy cover and landscape heterogeneity are logical because natural disturbance, in addition to creating early successional habitat, decreases canopy cover and increases landscape heterogeneity. Furthermore, we suggest that exurban development can drive these patterns, but, given the negative (or neutral) relationship between DEV and shrubland bird occupancy, we hypothesize that exurban development as a form of disturbance does not generate early successional habitat. We conclude that exurban development will benefit only a small subset of urban-adapted shrubland species without creating habitat for most shrubland birds, despite exerting considerable disturbance to forested landscapes.

Large numbers of Semipalmated Sandpipers (Calidris pusilla) use the Bay of Fundy, Canada, as a stopover site during their southbound migration from breeding to wintering grounds. The species exhibits a geographic cline in bill length on the breeding grounds (larger in east). Based on a previous analysis of morphometric traits that detected a small temporal decline in bill length, it has been suggested that observed declines in the Semipalmated Sandpiper population staging in the Bay of Fundy were driven by a disproportionate loss from the eastern breeding population. New data collected in the Bay of Fundy has made it possible to reassess this suggestion. We compared new bill length data from the Bay of Fundy (2009–2014) to historical data (1981–1989, 1997–2007) to examine temporal changes in bill length at this stopover site. We also examined count data at a major roost site from 1981 to 2014 to assess temporal changes in migratory passage. Variation in median passage date is explained best by a combination of year and Arctic climate data. Birds are now migrating through the region later in the season; median passage date has advanced approximately 5 d from 1980s values. Our analyses suggest that while there was a small decline in bill length between the 1980s and early 2000s, it has since reversed and bills are now comparable to historical values. Given this reversal in mean bill length, coupled with population estimates that are still low relative to historical values, there is now little evidence to support the hypothesis that the decline between the 1980s and today in birds passing through the Bay of Fundy is linked to disproportionate losses of eastern breeders. We therefore suggest that population declines may be distributed more broadly across the breeding range of birds that use the Bay of Fundy as a stopover site.

We report on the breeding biology of the Sabota Lark (Calendulauda sabota), a widespread and common but poorly known species. We present the results of data collected at 57 nests over 2 breeding seasons (2011–2013). Breeding coincided with the peak of the wet season in the study area and the breeding season appeared to be shorter in the study area compared to the rest of the species' range. Only females were observed constructing nests and laying and incubating started before the nest was completed, a strategy to reduce the overall nesting time. Nest quality varied considerably, including in the presence or absence of a dome and an apron. The mean clutch size was 2.5 ± 0.5 with incubation commencing upon clutch completion, performed by the female only and lasting 12.3 ± 0.5 d. Mean nest attendance during incubation was 74% and there was a steady increase in the duration of incubation on-bouts with progression of the incubation period. The mean nestling period lasted 11.7 d with both parents delivering food and both sexes performing brooding duties, a seemingly unique feature in the mirafrid clade of larks. There was evidence of subtle sex-specific roles during the nestling period with females primarily being responsible for brooding and males mainly provisioning. Breeding success using Mayfield's estimator was 33% with predation being the main cause of nest failure. Given the relatively poor breeding success, replacement broods were common but repeat-brooding attempts in a single season were rare with only 2 records during the course of this study. Although many of the reproductive features of Sabota Lark were similar to those of other larks, there were some differences and some apparently unique features that contribute to our knowledge of the Alaudidae.

The White-fronted Woodpecker (Melanerpes cactorum) drills wells in living branches and trunks of trees and shrubs to feed on sap flows, providing an energy-rich food resource for other bird species diverse in ecological attributes and taxonomic affinities. The aim of this study was to explore the avian assemblage that consumes sap from sap wells drilled by the White-fronted Woodpecker in 4 regions of Argentina distributed along an aridity gradient (precipitation and temperature), reaching from humid forest of the Chaco in the north to scrublands and open forest of the Monte in the south. We classified sap-feeding species according to the importance of nectar in their diet (specialist, facultative, or occasional nectarivores) and their efficiency in assimilation of sucrose (the main sugar in sap). We also compared the proportion of observed sap-feeding species with diversity of potential sap-feeding birds along the geographical aridity gradient. Forty-six bird species were recorded feeding at sap wells drilled by the White-fronted Woodpecker. Proportion of sap-feeding species was similar along the aridity gradient, and the type of diet and sucrase activity were not associated with the geographical aridity gradient. However, the proportion of occasional nectarivores with a low rate of sucrose assimilation was higher in Arid Monte (the most arid region) than in regions of lower aridity. Sap-feeding species could supplement their diets with sap, in varying degrees, during periods of scarcity of food resources, and White-fronted Woodpeckers through their sap wells could contribute to the persistence of this assemblage of sap-feeding bird species. Nevertheless, sap consumption by sapfeeding birds depends ultimately on the physiological and behavioral characteristics of each species.

The present study aimed to evaluate the breeding biology of Rusty-collared Seedeater (Sporophila collaris) from the grasslands in southern Brazil. Data from 52 nests were collected during the 2015–2016 breeding season. Breeding started in mid-September with a peak in early December and extended to early April, a period of ∼203 d, which is clearly longer than the period recorded for Argentine populations. Only females built the nests, which were open cups. The nests were built in herbaceous and shrubby plants at an average height of 116.3 ± 40.6 cm; 85% were located above the ground and 15% over water. The most common clutch size was 2 eggs (n = 12 nests), followed by 3 eggs (n = 7 nests), with egglaying occurring on consecutive days. Only the female is in charge of incubation, spending an average of 12.8 ± 0.7 d on this activity. The average on-bout was 20.9 ± 15.92 min and the average off-bout was 12.23 ± 8.62 min. The hatching rate was 81% and the fertility rate was 90%. Both parents took care of the nestlings. Visiting frequency to the nest differed between the sexes (female = 5.67 visits/h, n = 170 visits; male = 1.83 visits/h, n = 55 visits; z = 2.80, P = 0.005). The nestlings remained in the nest for an average 11.1 ± 0.78 d. The apparent success was 25% and the nest success estimation varied from 13% (Mayfield method) to 29% (MARK).

Birds select critical resources to meet needs that vary in response to spatial, temporal, and individual variation. As an example, perch or roost sites may be at locations that provide protection from predators, mobbing, or inclement weather. Applied to large, soaring predators, this theory suggests that they may select perch and roost sites near food resources or at sites where environmental updrafts develop. To test these theories, we characterized selection of nonflight locations throughout the annual cycle for Golden Eagles (Aquila chrysaetos) in eastern North America. We determined factors associated with selection of perching (daytime) and roosting (nighttime) sites by eagles by comparing land cover and topographic characteristics of GPS telemetry locations for eagles (used) with random (available) locations. We separately assessed selection for perch and roost sites during each of 4 seasons (winter, summer, and spring and fall migration). Golden Eagles showed different selection patterns for perching by season and age. Throughout the year, eagles selected perch sites on steep slopes. The direction these slopes faced differed among seasons, with eagles selecting south-facing slopes in summer and east-facing slopes during migration. Adults showed greater preferences for broadleaf forests in summer and for ridges in fall. Patterns of perch-site use were consistent with selection for sites that provide thermal protection and access to thermal updrafts. We found few patterns of selection for roosting sites. Our analysis provides insight into decision-making by a longdistance migrant across its annual cycle and throughout its geographic range, and thus into how resource selection changes seasonally.

Bald Eagles (Haliaeetus leucocephalus) and Common Loons (Gavia immer) have been the subject of intensive recovery efforts over 4 decades in New Hampshire. In the last 2 decades, eagles have increased from 1 to 40 territorial pairs, and loons have increased from 208 to 284 territorial pairs. Eagle predation of loons and loon eggs has been documented in a limited but increasing number of cases. We looked for evidence that this predation has begun to limit loon productivity or provoke territorial shifts to avoid predation during the initial period of Bald Eagle population recovery (1998–2013). Using 16 yr of breeding census data, we found support for the prediction that eagle nest proximity may be contributing to >3% of observed loon nest failures. Our findings indicate that eagles may already be exerting a measurable predation pressure. However, at current eagle densities, this pressure does not explain observed local declines in loon abundance. Our counterfactual analysis identified subsets of the data (e.g., loon nest sites on islands) where eagle nest density had the strongest negative association with loon productivity; it may be a useful tool for similar ecological models.

For bird species in which plumage characteristics are associated with social dominance, the analysis of status badges may reveal habitat preferences. We analyzed the extent of male Chestnut-sided Warbler (Setophaga pensylvanica) chestnut-colored plumage in relation to age and body size to determine whether badge size was a potential indicator of resource-holding potential. We then modeled badge size in relation to habitat variables including habitat patch size, patch shape, and microhabitat characteristics in 101 different silvicultural openings in western Massachusetts during 2014 and 2015. Overall, older and larger Chestnut-sided Warblers had larger badges. Badge size showed a strong positive relationship with patch area. Notably, our findings reveal a greater sensitivity to area than was apparent from a different study's analysis of abundance at the same study site during the same time period. Badge size was positively related to patch shape complexity—an environmental variable not previously identified as important for this species by other studies. Our findings indicate that remote assessments of avian status badges may serve as reliable indicators of habitat preferences and suggest that this approach has the potential to reveal responses to gradients in habitat not reflected by abundance.

The Brown Parrotbill (Cholornis unicolor) is endemic to the central and eastern Himalayas and occurs in alpine bamboo thickets at an altitude of 1,980–3,600 m. Fieldwork was conducted in the Gaoligongshan National Nature Reserve and cameras were used to record reproductive behaviors. Duration of incubation, nestling provisioning, and other parental care behaviors were extracted from the videos, and measurements of the nest, eggs, and nestlings were taken in the field. One nest with a clutch of 3 eggs was found 2.1 m above the ground in a bamboo thicket in May, thus extending the documented breeding season. Two of the three eggs hatched and both nestlings fledged. Both the male and the female incubated the eggs and brooded and provisioned the nestlings. The incubation period lasted for at least 13 d and the nestling period was 15 d. As incubation progressed, incubation-bout duration decreased and recess frequency increased. During the nestling period, the frequency of parental provisioning increased as the nestlings matured. Our observations provide the first description of the nest, nestlings, and incubation behavior of Brown Parrotbill. Alpine bamboo thickets are assumed to be an important breeding habitat for Brown Parrotbills, as this is typical for at least 6 parrotbill species.

The American Robin (Turdus migratorius) is one of the most widespread, common bird species in North America; yet, very little is known about its migratory connectivity, migration timing, and migratory routes. Using archival GPS tags, we tracked the movements of 7 individual robins from 3 breeding populations in the United States. Four robins captured in Denali National Park and Preserve, Alaska, overwintered in Texas, Nebraska, Oklahoma, and Montana, up to 4,500 km from the capture location. One robin captured in Amherst, Massachusetts, overwintered in South Carolina 1,210 km from the capture location, whereas 2 robins captured in Washington, D.C., spent the entire year within 6 km of their original capture location. Understanding the annual cycle and differences in migration strategies for a species that exhibits large regional variation in movement has the potential to provide novel insights into how conspecific populations respond to current and future heterogeneity in climate and habitat. The regionspecific patterns presented here suggest robins could serve as sentinels of environmental change at a continental scale.

Improved knowledge of movements of the Interior population of Band-tailed Pigeons (Patagioenas fasciata) is needed to inform management decisions. We investigated daily and seasonal movements of adult Bandtailed Pigeons marked with satellite transmitters in 2015–2016. Band-tailed Pigeons were marked at 3 geographically separate locations in Silver City, Weed, and Los Alamos, New Mexico, USA. Thirteen of 15 satellite transmitters provided sufficient data to estimate daily and seasonal movements. Mean daily movements ranged from 1.8 km to 17.8 km for individual Band-tailed Pigeons. Minimum distance moved between consecutive locations was less than detectable given accuracy of PTT transmitters, while the maximum distance moved between locations was 553.7 km. Seven of the 13 Band-tailed Pigeons made seasonal movements (>200 km) from their respective capture sites. Five Band-tailed Pigeons captured in southern New Mexico traveled south into northern Mexico whereas 2 Band-tailed Pigeons captured in northern New Mexico migrated to southern New Mexico for the nonbreeding season. Our results are the first to provide detailed movement information between breeding season and nonbreeding season sites for adult Band-tailed Pigeons captured in New Mexico. This data will allow a greater understanding of daily and seasonal movements of Band-tailed Pigeons from New Mexico and will aid in more targeted, collaborative conservation and management.

Female song is more widespread than previously assumed, and is adaptive in many species; however, it may also be an aberrant, nonfunctional, behavior in others. We document novel vocalizations, including female song, from 2 paired female Cerulean Warblers (Setophaga cerulea) recorded in southern Indiana, USA, in June 2017. This is the first documentation of female song in this species. When assessed spectrographically, one female's vocalizations were similar to the typical zeet call of this species, but with appreciable differences in duration, composition, and frequency bandwidth. The other female's vocalizations, which we define as a song, had large frequency modulations as well as harmonics. The females' vocalizations resembled neither each other's nor the typical song of an adult male Cerulean Warbler. Unlike most other instances of infrequent female song in temperate-breeding passerines, these vocalizations only occurred during the incubation and nestling stages, rather than during mate acquisition. Based on their context, they appeared to function in intersexual communication with the male mate. We discuss potential explanations, both adaptive and nonfunctional, and urge researchers of this species to pay particular attention to the vocalizations of females in their study populations.

The ability to recognize other individuals (e.g., mates, neighbors, and offspring) is crucial to process relationships between group members in social species. For bird species with limited use of visual information, like species living in colonies or dense environments, the acoustic channel provides a long-distance and fast means to effectively convey identity-related information. The Rook (Corvus frugilegus) is a monogamous species, and one of the most social corvids, living in highly cohesive groups within colonies of hundreds to thousands of individuals. However, despite being a highly vocal species, only a few studies have focused on its acoustic communication skills, investigating mostly its vocal repertoire and kin recognition in fledglings. Among the vocal repertoire of the Rook, the “caw” is the most common sound type. It is emitted independently in various contexts and is often considered as a “presenting” vocalization, serving to introduce the identity of the emitter bird to the assembly. In this study, we investigated the potential individual signature of the caw. To do so, we recorded the caws of 5 semi-captive male Rooks and conducted acoustic analyses on both the frequency and time domains. A discriminant function and a potential for individuality coding analyses revealed the existence of a clear individual signature (mean of 75% correct classification, SD 10), which was mainly supported by the caw duration and distribution of energy in the low-frequency part of the spectrum. We discuss the potential variability of individuality coding across behavioral contexts and social affinities that needs further work.

Nectar from plants is a particularly important food source for a number of bird families. Here, 4 observations of nectar foraging by family groups of Little Ravens (Corvus mellori), a species only recently recorded as consuming nectar, are described. There are few details of nectarivory in the major reviews of the Corvidae, but this behavior has been recorded for 11 of the approximately 45 species of Corvus worldwide and is summarized here.

Non-kin infanticide is the killing of unrelated young by a conspecific adult, and occurs infrequently in some bird species. We observed a case of non-kin infanticide committed by a male Japanese Marsh Warbler (Locustella pryeri) in 2008. The sudden disappearance of a nesting male from his territory made the neighboring male expand his original territory to the vacant area where the unrelated nestlings were being reared by a female in the nest. The male found the nest and attacked the unrelated nestlings. We inferred that the infanticide sequence was done as food resource competition and/or sexually selected infanticide.

Behavioral innovations are likely to contribute to the persistence of native species in developed areas. Innovativeness has been well-studied in birds, and the frequency with which they innovate is related to their relative brain size. However, the mechanisms by which behavioral innovations emerge and spread remain poorly known. Two major mechanisms are thought to play a fundamental role: the independent appearance of the same innovation in different individuals and innovation diffusion by social learning. Here, we describe observations of multiple Blue-faced Honeyeaters (Entomyzon cyanotis) collecting sugar packets, a technical innovation that had not been published in that species. We also demonstrate that this behavior emerged in 2 developed areas separated by 1,200 km, with multiple individuals engaging in the behavior within one of the sites, such that both independent innovation and social diffusion are likely to have occurred. Using brain size data on 62 species of the Meliphagidae family, we then discuss the likely importance of relative brain size in determining innovativeness in this family, and suggest that anatomical specialization such as the curvature of beaks used in nectar foraging could constrain the emergence of new behaviors in some large-brained species.

For decades, researchers have attempted to understand why some avian species expend energy building nests that are not explicitly used for breeding (i.e., dummy nests). Most work has focused on whether dummy nests serve as indicators of male fitness or as decoys for confusing nest predators. Anecdotal observations suggest that dummy nests may also be used as temporary shelters for adults and fledglings, but the frequency with which this occurs is unknown. While trapping Cistothorus palustris griseus (Worthington's Marsh Wren) nestlings as part of a larger study in the saltmarshes of northeast Florida, we observed newly fledged young using dummy nests on 8 of 45 occasions (18%) during which one or more nestlings were absent from the natal nest. It is likely that the actual frequency of dummy nest use by fledglings is greater than what we observed because our efforts to locate fledglings were infrequent and opportunistic, and because depredation may account for a significant proportion of the occasions when no fledglings were found. Dummy nests may play a larger role in post-fledging survival than previously thought and warrant further investigation.

Red-shouldered Hawks (Buteo lineatus) feed primarily on mammals, amphibians, and reptiles, but invertebrates also comprise a significant portion of the diet. The majority of invertebrates consumed are insects and crustaceans, with the latter represented to date only by crayfish. In 2016, we observed a Red-shouldered Hawk attack and dismember another crustacean, the ghost crab (Ocypode quadrata), on a coastal beach in South Carolina, USA. Actual consumption of the crab by the hawk was not observed but is probable. Consumption of ghost crabs by Red-shouldered Hawks is not unexpected, as these crustaceans are abundant within their range, active when hawks are foraging, and occur in open habitats (beaches and dunes) where they are more vulnerable to avian predators. To our knowledge, this is the first report of a Red-shouldered Hawk attacking and presumably consuming any species of crab and the first report of probable ghost crab predation by a raptor in North America.

The first confirmed nesting location of the Hawaiian population of the Band-rumped Storm-Petrel (Oceanodroma castro), an endangered seabird, was recently discovered on Hawai‘i island after decades of searching. Following the discovery, we analyzed nest site preferences of the Band-rumped Storm-Petrel at this site using a paired design. Band-rumped Storm-Petrels preferred deeper crevices compared with those available within 100 m of the nest sites. Physical and environmental characteristics of Hawaiian Bandrumped Storm-Petrel nest sites may aid conservation efforts including on-the-ground searches, removal of invasive mammalian predators, identification of potential translocation sites, and habitat restoration for this endangered species.

The House Sparrow (Passer domesticus) and the brown anole (Anolis sagrei) are both invasive species in South Florida where they have occurred in sympatry for nearly 100 years. While the opportunistic feeding style of the House Sparrow is likely a large contributor to its success as an invader, there have been no reported incidents of House Sparrows consuming vertebrate prey. Here we report the first predation of a vertebrate prey (A. sagrei) by House Sparrows, suggesting an evolutionary shift in dietary preference following novel invasive species interactions.

Despite the American Kestrel (Falco sparverius) being one of the most commonly occurring and one of the most thoroughly studied raptors in North America, it has only been documented consuming wild carrion one time in the literature. Here, we document at least one American Kestrel feeding on the carcass of a domesticated turkey (Meleagris gallopavo) near Boise, Idaho. Each day for 5 consecutive days in January/ February 2018, we observed at least one unbanded female kestrel feeding on the turkey carcass for approximately 15 min per visit. American Kestrels have a diverse diet, but feed primarily on small rodents, insects, and other small prey, and demonstrate preferences for more active prey. Results reported here provide documentation for a rare feeding strategy in American Kestrels.

The Mottled Duck (Anas fulvigula) is a range-restricted species endemic to the western Gulf Coast states and peninsular Florida. As a year-round resident, it relies on coastal marsh and nearby upland habitat during the breeding season. All previous breeding research on Mottled Ducks has observed them nesting in upland habitat such as prairie, rice fields, pastures, levees, dredge-spoil islands, or dry marsh. Here, we report on the first documented cases of overwater nesting for this species. We located 2 transmitter-marked Mottled Ducks nesting in freshwater marsh on an elevated platform constructed of cutgrass, with a water depth >10 cm surrounding the nest. Existing conservation and management plans for nesting Mottled Ducks emphasize protection of upland habitat, but our results suggest that broadening the scope of habitat types assumed to be suitable for nesting Mottled Ducks may be warranted.

Apart from some species that reuse their nests regularly, the reuse of open nests is an uncommon phenomenon in the majority of species, especially the passerines. The interspecific reuse of open nests has rarely been described. Here I examine a case of such reuse in thrushes, specifically the reuse of a Fieldfare's (Turdus pilaris) nest by a Song Thrush (Turdus philomelos). A total of 14 Song Thrush nests with eggs were found in an orchard; more than half of these clutches were unsuccessful. Breeding success in the Song Thrush in the orchard was 29% for first clutches/broods and 60% for second clutches/broods. Eleven Fieldfare nests contained clutches: 87% of them were unsuccessful. Breeding success was as low as 14% in the case of first clutches/ broods, and no second clutches/broods were successful. Having reviewed the hypotheses relating to nest reuse, I consider that this case was not brought about by a lack of suitable nesting sites. It was, however, advantageous in that the time and costs of building a new nest were much reduced, given that the nesting territory was of high quality, and that the nesting season is short and breeding success low.

Because nest site competition among cavity-nesting birds is often intense, the practice of pairing nest boxes has been promoted as a way to reduce nest-site competition and allow for the relatively peaceful coexistence of a dominant and a subordinate species within an area. Although apparently effective for promoting the coexistence of Tree Swallows (Tachycineta bicolor) and Eastern Bluebirds (Sialia sialis), it is unknown whether this practice might be effective for other competing species pairs. We conducted an experiment to test whether providing paired identical boxes would promote the adjacent breeding of Eastern Bluebirds and 2 smaller/subordinate cavity nesters: the Carolina Chickadee (Poecile carolinensis) and the Brown-headed Nuthatch (Sitta pusilla). Our box pairs were of 2 types. Our Big/Small pairs consisted of one box with a bluebird-sized (38 mm) entrance hole and another with a 26 mm hole (too small for a bluebird but appropriate for a nuthatch or chickadee). Our other pairs (Big/Big) consisted of 2 boxes with identical 38 mm holes. Boxes within pairs were 10 m apart. If bluebirds are intolerant of subordinate cavity nesters breeding nearby, we would expect to find similar (and low) occupancy by nuthatches and chickadees in box pairs of either type containing bluebirds. If, however, bluebirds simply defend their own nest cavity, we would expect to find similar (and high) occupancy by nuthatches and chickadees in box pairs of either type containing bluebirds. Finally, if bluebirds guard all usable nest boxes in a small area, we would expect to find high occupation of Big/Small box pairs by nuthatches and chickadees and low occupation by these species of Big/ Big box pairs. We found that bluebirds excluded both nuthatches and chickadees from adjacent big-hole boxes but not from adjacent small-hole boxes, indicating that pairing identical boxes does not promote coexistence of bluebirds and these smaller species. Smaller, less competitive species require nest boxes that exclude larger and more competitive species.