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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.

The Dark-eyed Junco (Junco hyemalis) is one of the most abundant birds in North America and exhibits versatility in its selection of nest sites. Although typically ground-nesting birds, juncos also nest occasionally in trees, on buildings, and in natural recesses such as rock crevices. To our knowledge, juncos have never been reported nesting in a fully enclosed nest box specifically provided for songbirds. We report the first record of nest box adoption by Dark-eyed Juncos, supported by photographic evidence. A nest box containing a nest attended by a pair of Dark-eyed Juncos was monitored in 2016 in western Washington, USA, and reported to the Cornell Lab of Ornithology's NestWatch program, a national citizen-science program wherein volunteers submit data on wild nesting birds. The nest in question hatched successfully, and three nestlings fledged from the box. Cavity nesting in New World sparrows appears to be very rare, and we found only four additional observations of juncos utilizing natura...

Increasing populations of Hooded Mergansers (Lophodytes cucullatus) (Heusmann et. al 2000) may be out-competing Wood Ducks (Aix sponsa) for nest boxes on some sites in Massachusetts. Hooded Mergansers' use increased from ≤2% of boxes in 1979 to 25% by 2013, while Wood Ducks' use increased from an average of 22% in 1979 to a peak of 65% by the mid-1990s and has since declined to 57%. We estimate that Hooded Mergansers may be important nest competitors on 13 of 51 study sites.

Destruction of conspecific and heterospecific eggs and nestlings occurs in several species of passerines. Two main hypotheses have been proposed to explain the adaptiveness of this behavior: as a mechanism to avoid competition or to gain access to reproductive opportunities. In Colombia, Southern House Wrens (Troglodytes aedon musculus) broke eggs and/or killed nestlings of Spectacled Parrotlets (Forpus conspicillatus, 24 cases), Apical Flycatcher (Myiarchis apicalis, one case) and of other House Wrens (four cases). Wrens attacked parrotlet nests in three contexts: 1) wrens took over and used a parrotlet nestbox within their territory, 2) wrens with an active nest attacked a neighboring parrotlet nest, or 3) the attacker was unknown but was inferred to be a wren. Wrens also attacked trial nests with natural and artificial wren eggs that were placed near active wren nests. These observations suggest that infanticidal behavior by wrens at this locality may be driven by competition for nest sites. I...

Nest reuse is a common phenomenon in many passerine and non-passerine birds species. Although interspecific nest reuse has been reported in many African species, it is rare in passerines that nest in open, cup-shaped nests. Here, I report on interspecific nest reuse in larks (Alaudidae), specifically of a pair of Chestnut-backed Sparrow-larks Eremopterix leucotis using a nest previously occupied by Pink-billed Larks Spizocorys conirostris. It is possible that the Chestnut-backed Sparrow-larks selected a nest site in an area where predation seemed low as there were other successful nests or nests with nestlings in the near vicinity. The interspecific nest reuse reported here suggests opportunistic occupation of a previously used nest while at the same time saving the pair some energy during a period of peak activity and high energetic demands.

Native bird diversity is compromised in urban areas partially because of the lack of available habitat for some species. As urbanization continues to increase, it is important to understand the behavioral dynamics of bird species located in cities. The Black-capped Chickadee (Poecile atricapillus), as a generalist species, offers an opportunity to investigate how common native birds use urban areas that lack natural habitat features while additionally competing with non-native, invasive species (e.g., House Sparrows, Passer domesticus). Our objectives were to determine nest box use and nesting success rate of Black-capped Chickadees and House Sparrows using artificial nest boxes in natural habitats located in an urban area, specifically a recently restored 5.66- ha area of pond sedge surrounded by oak (Quercus spp.) savannah located south of Lincoln Park Zoo in Chicago, Illinois, USA. Artificial nest cavities with 3 cm diameter entrance holes, intended to exclude House Sparrows, were installed on...

Indirect predator cues have been shown to enhance perceived nest predation risk in both open-cup and cavity-nesting birds. We hypothesized that scent from the raccoon (Procyon lotor) inside nest boxes, supplemented with raccoon hair as a visual cue on the outside of the box, would enhance perceived risk to the European Starling (Sturnus vulgaris), resulting in reduced use of treated nest boxes and negative effects on reproduction. The starling is recognized, outside its native range, as a competitor with indigenous cavity nesters and a pest species, and efforts to deter its nesting have generally been unsuccessful. Our objectives were to examine nest initiation, clutch development, and hatching success by starlings relative to 4 nest box treatments. Starlings selected from nest boxes treated with a novel visual cue at the entry hole, predator scent inside the nest box and supplemented with a predator visual cue at the entry hole, the predator visual cue, or a novel odor inside the box and supplemented with the novel visual cue at the entry hole (n = 120 boxes; n = 30 per treatment). Starlings established nest bowls in 65% of nest boxes (novel visual cue = 21 boxes, predator scent/predator visual cue = 19 boxes, predator visual cue = 17 boxes, novel odor/novel visual cue = 21 boxes); clutches (≥1 egg) were laid in 80 boxes, but 2 boxes contained a single egg with no nest. We observed no effects of treatment on likelihood of starlings laying a clutch, date of first egg, clutch size, or hatchling number. We conclude that raccoon scent inside nest boxes, supplemented by raccoon hair as a visual cue, failed to enhance perceived risk to starlings such that nesting was deterred. We suggest that direct or indirect experience with nest predation attempts (which enhance perceived risk) and the starling's plasticity in antipredator responses are key hurdles in development of an efficacious nesting deterrent. Therefore, we encourage the evaluation of direct predation risk via use of predator effigies on or in nest boxes, as well as in foraging areas proximate to nest boxes.

Interspecific nest usurpation, a relatively common nesting strategy, is the act of one bird species taking over the nesting site of another species. Although used by secondary cavity-nesters, nest usurpation has never been reported for the Tufted Titmouse (Baeolophus bicolor). In this paper, we document a mixed brood successfully reared by Tufted Titmice after usurpation of an Eastern Bluebird (Sialia sialis) nest in northeastern Arkansas during the 2019 breeding season. We monitored the focal nest box every 3–4 d from the first sign of nest building on 23 March 2019 until chick fledging by 12 May 2019. The Tufted Titmice took over the nest at the time the Eastern Bluebird had laid its fourth egg in the nest. By the end of the nesting period, the Tufted Titmice fledged 2 of their own chicks and 3 Eastern Bluebird chicks. Such successful rearing of non-conspecific nestlings is rare and we discuss factors that may have allowed it.

Construction of nests containing multiple layers or “stories” has been observed in a number of passerine species. These atypical nest structures are frequently a response to brood parasitism, wherein the host female will bury the parasite’s egg under a new layer of nesting material. They may also occur as a result of either intra- or interspecific competition for limited nest sites, with one individual usurping another’s nest and adding new material on top. However, such structures have not previously been documented in the Cerulean Warbler (Setophaga cerulea), a Neotropical migrant species that breeds in the eastern U.S. and Canada. Here, we report our observations of an unusual “double-decker” nest that was constructed in 2014 in Brown County, southern Indiana. A female Cerulean Warbler first built a typical nest, and several days later we discovered a second visibly distinct nest superimposed on top of the original one. Subsequent retrieval and inspection of the two-story nest revealed no buri...

Interspecific competition among secondary cavity nesters can involve physical conflicts between individuals, which may lead to serious injuries or death. Here we report a case of aggression by a pair of Chilean Swallows (Tachycineta meyeni) towards a nestling of the Thorn-tailed Rayadito (Aphrastura spinicauda) in the sub-Antarctic forests of Chile. This aggression caused the displacement of the breeding rayaditos from an occupied nest box and it appears, nestling mortality. Since levels of aggression among cavity nesters depend on the synchrony of their breeding phenologies, further research is needed to study the prevalence of nest usurpation by Chilean Swallows and its relation to the degree of breeding synchrony with other cavity nesters inhabiting the sub-Antarctic forests.

Laughing Falcons (Herpetotheres cachinnans) are common, medium-sized falconids that occur throughout the Neotropical region and marginally in the Nearctic American continent. There is little data on their breeding biology with the only information available based on scattered records. Here, we report data on 11 nests of H. cachinnans from the Pantanal, Brazil, including four in nest-boxes, between 2007–2008. The breeding season occurred between July–December, which is in accordance with the few records for this region. Records of two eggs or nestlings were found in 28% (n = 3) of nests, while the remaining 72% (n = 8) had one egg or nestling. The eggs were rounded and buff with brown markings or dark brown or purplish brown with darker markings. The hatchlings, even when a few days old, are pale buff overall in plumage with the distinctive black mask, typical of the adults. An undescribed vocalization of the nestling was recorded, which is similar to an uncommon vocal type emitted by the adul...

In California, oak woodlands are being converted into vineyards, resulting in a loss of songbird nesting sites. Although many vineyards contain wooded riparian habitat, no previous research has examined the avian species composition in oak-vineyard landscapes. We compared the avian communities associated with vineyard, edge, and riparian habitats and examined to what degree the riparian habitat in vineyard landscapes continues to support birds associated with native oak woodland habitat that spanned the region before agricultural intensification. We further tested whether the presence of nest boxes in vineyard and riparian areas altered avian species composition in the landscape. Mist nets were used to survey the avian community in vineyard, edge, and riparian habitat at four sites during the breeding season. Permutational ANOVAs, using presence-absence data from captures, identified habitat, study sites, and time over the breeding season as highly significant main effects that explained differen...

Interspecific feeding is an uncommon yet widespread phenomenon where an individual of one species feeds the young of another. There are numerous hypotheses to explain why this behavior might occur, but in most cases the observer can only speculate on the cause because they lack information on the nesting histories of the species involved. We observed a color-banded male Eastern Bluebird (Sialia sialis) feed 10-day-old Tree Swallow (Tachycineta bicolor) nestlings in a paired nest box 29 times during a 3 h nest observation. The male bluebird had previously fledged young from the box where the Tree Swallows were currently nesting and currently was nesting in the paired box, suggesting that the probable cause for this reproductive error was both the close proximity of the box and an attachment to the box where he had previously raised young. This observation suggests that instead of identifying the young by call, the male was using a place-based decision rule when he responded to the calls from the box where he had previously nested. Pairing nest boxes, a common practice used to reduce competition for nest boxes between bluebirds and Tree Swallows, may inadvertently increase the probability of interspecific feeding as a result of location-based decision rules for feeding and care of young.

Japanese weasels (Mustela itatsi) artificially introduced to Miyake-jima Island, a peripheral island of Japan, in the early 1980s increased predation on bird nests. We investigated the breeding biology of Japanese Bush Warblers (Horornis diphone) before and after the weasel introduction. Nest height was higher after than before the introduction, while clutch size did not differ significantly between the periods. These results suggest that introduced carnivores affect not only nest predation but also the nest site selection of birds.

We compared House Wren (Troglodytes aedon) nests in nest boxes with either small (28 mm) or large (38 mm) entrance holes. Spring clutch size did not differ between wrens using boxes with large and small holes. Nests in boxes with large holes had a significantly taller ‘berm’ of sticks between the box entrance and the nest cup than did nests in boxes with small holes. This was true even when the same wren pairs were given boxes with different-size holes for spring and summer nests. We compared the difficulty of touching the eggs when we removed the frontplate of the nest box as an alternative measure of nest vulnerability to predators and brood parasites. There was a significant association between hole size and accessibility: boxes without the protection of a small entrance hole were far more likely to be categorized as ‘inaccessible.’ We found a similar relationship between berm height and nest architecture: nests with tall berms were generally less accessible than were nests with shorter berms....

I investigated the relationship between the probability of nest predation and nest-site characteristics: (1) nest height above ground, (2) number of branches attached to a nest, and (3) number of thorny branches around the nest for a population of Bull-headed Shrikes (Lanius bucephalus) breeding in Japan. Thirty-eight nests were located during 2008 and 2009 of which 16 were lost to predation, 14 were successful in fledging young, four were abandoned, two were parasitized, and two may have been partially depredated, although the actual reason is unclear. Neither nest height nor the number of thorny branches was correlated with breeding success. However, the number of branches was negatively correlated with probability of nest predation. The primary predators were believed to be birds, based on physical evidence at depredated nests. A high density of branches around nests of Bull-headed Shrikes may ensure they are not easily discovered and depredated by predators.

I monitored the breeding biology of House Sparrows (Passer domesticus) in a suburban colony in Cook County, Illinois, USA. I found a significant statistical correlation between clutch size and the base area of the nest box (r = 0.592, P < 0.0029) with mean clutch size varying from 4.49 eggs (in a ‘small’ nest box, 112 cm2 basal area) to 4.77 eggs (in a ‘large’ nest box, 221 cm2 basal area). Other measures of breeding success (hatching and fledging success, mean egg mass, and nestling condition) had no statistically significant relationship with nest-box size. Measures of nest site preferences, as suggested by earlier date of first egg of season or by greater number of broods per season, also show no statistically significant correlation with nest-box size.

I observed 514 nest-box departures of 12 different individual Eastern Screech-Owls (Megascops asio), both males and females, at dusk in Falmouth, Massachusetts over a period of 12 years and compared their departure times to local sunset. Mean (± SD) delay after sunset was 21 ± 12 min, identical for males and females, but longer than those reported for more southerly locations. Females departed significantly earlier on overcast evenings. Females advanced their departure times during the nestling period by as much as 2.6 min/day, on average, over a 25-day period. The observed differences in departure delays among populations in Texas, the Washington, D.C. area, and Massachusetts may be an expression of differences in behavior among subspecies of M. asio.

We used time-lapse video cameras and track plates to identify nest predators of Red-faced Warblers (Cardellina rubrifrons) and Yellow-eyed Juncos (Junco phaeonotus) in high-elevation (> 2,300 m) forests of the Santa Catalina Mountains in southeastern Arizona. Mammals, especially gray fox (Urocyon cinereoargenteus) and cliff chipmunk (Tamias dorsalis), were the principal nest predators of Red-faced Warblers and Yellow-eyed Juncos within our study system, accounting for 89% of all nest depredations. Our study is one of the first to use video cameras at real nests to document the prevalence of nest predators in montane forest ecosystems. Additional research is needed to learn if mammals are the dominant nest predators in other montane environments.

We describe the nest and eggs of two Philippine endemic passerines, the Rusty-faced Babbler (Robsonius rabori) and the Blue-breasted Blue Flycatcher (Cyornis herioti). We also describe a novel type of nest and nest placement for the Short-crested Monarch (Hypothymis helenae), and provide the first description of the eggs of this species. We discuss similarities among eggs and nests of these species with their relatives, and the need for more information regarding natural history and breeding habits for the Philippine avifauna.

We studied use of nest boxes by Great Tits (Parus major) in rural village gardens in a semi-arid area. Great Tits occupied 46.6% of the nest boxes, and used nest boxes within higher tree densities and with more tree species in the vicinity. Breeding success was greater in nest boxes with higher plant density, more plant species, and greater height of trees in the vicinity of the nest. The presence of children or dogs (Canis lupus familiaris) near nest boxes did not affect breeding parameters. Syrian Woodpeckers (Dendrocopos syriacus) enlarged 38.0% of nest box entrances during the first year. House Sparrows (Passer domesticus) occupied 41.0% of the nest boxes with enlarged holes and none of those with normal holes. Great Tits occupied both types, but significantly fewer pairs breeding in nest boxes with enlarged holes succeeded in fledging at least one young, probably due to their eviction by the larger House Sparrows.

We found the first documented wild nest of a Coral-billed Ground Cuckoo (Carpococcyx renauldi) at Khao Yai National Park, Thailand in June 2007. The large stick nest was monitored for 24 days including 1095 hrs of video footage; it contained two eggs and was in dense vegetation 4.85 m above the ground. Nest attentiveness of adults was almost constant with both birds taking turns to incubate or brood. Food delivered to nestlings included lizards, nestlings, a snake, frogs, earthworms, and other invertebrates. Nest defense was observed against several known nest predators but the nest ultimately failed due to predation by a pig-tailed macaque (Macaca nemistrina). These observations provide insight into the breeding ecology of the only two congeners, C. viridis and C. radiceus, for which little is known of their ecology and both are endangered.

We studied orientation-dependent differences in nest box microclimate and American Kestrel (Falco sparverius) reproductive parameters in Idaho, USA. Unoccupied nest boxes facing west were ,0.6u C cooler than boxes that faced south or east and had ,20% lower relative humidity levels than boxes facing all other cardinal directions. Clutches in occupied boxes that faced southwest had a proportionately lower chance of hatching success (12 of 21 nests were successful), defined as having at least one egg hatch, than boxes that faced northwest (9 of 9 nests) or southeast (9 of 12 nests). The possible link between orientation-dependent differences in microclimate and hatching success, and the question of whether American Kestrels may select for orientation adaptively requires further investigation. Received 25 September 2008. Accepted 3 June 2009.

We present the first detailed information on egg laying, egg temperature (Tegg), and development of attentiveness and incubation in Western Bluebirds (Sialia mexicana). We used miniature infrared CCD video cameras to record egg laying at three nest boxes and validate attentiveness measurements derived from Tegg in seven other nests. Females entered the nest box on egg-laying days between 0522 and 1037 hrs PST and laid an egg on average 11.4 6 4.3 min later (n 5 11). Warm weather early in egg laying often elevated Tegg above physiological zero (27u C), despite low parental attendance. Females often began roosting in the nest box 2-3 nights before clutch completion, and most birds began steady night-time incubation with the penultimate egg. Attentiveness, mean Tegg, and number of minutes Tegg exceeded 27u C reached their highest values 1 day or night after clutch completion. Western Bluebirds exhibit gradual onset to incubation that is attributable to vagaries of weather and varying patterns of parental attentiveness. Received 8 September 2008. Accepted 10 February 2009.

Common Goldeneyes (Bucephala clangula) and Hooded Mergansers (Lophodytes cucullatus) are common cavity-nesting ducks but the importance of fast-flowing rivers as suitable nesting habitat may have been overlooked. We monitored the use of >90 nest boxes installed along a boreal forest river over a 5-year period. A high nest box occupancy rate was reached in the second year (40%) and was maintained thereafter (48 to 55%). On average, 35 nest boxes were occupied by goldeneyes and 11 by mergansers each year. Laying date was similar between the two species but merganser nests hatched slightly later. Both species had similar clutch sizes but merganser nests contained more eggs than goldeneye nests when heterospecific parasitic eggs were included. On average, 16% of goldeneye nests were parasitized by mergansers, and 49% of merganser nests were parasitized by goldeneyes. Density of suitable natural cavities in the area was relatively low suggesting the high occupancy rate of nest boxes may be a response ...

We examined nest defense behavior of the Carolina Wren (Thryothorus ludovicianus) in response to avian intruders at the nest. Freeze-dried mounts of a brood parasite (female Brown-headed Cowbird [Molothrus ater]), nest predator (Blue Jay [Cyanocitta cristata]), and a control (Swainson's Thrush [Catharus ustulatus]) were presented at wren nests to examine if wrens were able to distinguish among these threats. The primary nest defense behavior of Carolina Wrens was alarm calls. Wrens spent more time alarm calling to the Blue Jay model than the control and Brown-headed Cowbird models suggesting cowbirds were not recognized as threats to the nest. Wrens were less likely to respond during laying stage trials, probably due to a lack of nest visitations at this time. Intensity of alarm calls did not increase from the laying to nestling stage for any of the models presented. Carolina Wrens are both socially and genetically monogamous, and males should invest heavily in care of young due to their high con...

We describe an adoption event by a female Eastern Bluebird (Sialia sialis) and suggest a mechanism by which adoption could be adaptive. The foster female adopted three young and we were able to quantify two measures of parental care (nestling provisioning and nest defense). The foster female successfully reproduced with the father of the young in the same location later in the breeding season. The adopting female may be increasing her fitness by gaining future reproduction with a fertile mate at a productive nest box through parental care for young that are not related.

The Banded Ground-cuckoo (Neomorphus radiolosus) is a rare and endangered bird species whose basic biology is poorly known. We provide the first information on nesting biology for the species. We documented two nesting attempts in the Mache-Chindul Ecological Reserve, Esmeraldas Province, northwest Ecuador. Both the first nest, active in March and April 2005, and the second nest, active in May 2005, were in primary rain forest. Both nests were ∼5 m above ground in small understory trees (Melastomataceae). A pair of adult Banded Ground-cuckoos attended the first nest and contributed equally to incubation, brooding, and provisioning of a single nestling. The nestling spent 20 days in the nest from hatching to fledging and was fed a wide range of both invertebrates (primarily grasshoppers) and vertebrates (mainly small frogs). The chick fledged successfully. The second nest, also attended by a pair of adults, failed during incubation. We relate our findings to what is known of other ground-cuckoo sp...

Tree Swallows (Tachycineta bicolor) show one of the highest levels of extra-pair mating among bird species, yet extra-pair copulations are rarely observed. Despite the suggestion that extra-pair copulations could be taking place away from nest sites, very little is known about movement patterns of individual Tree Swallows during the pre-laying and laying periods. We used radio telemetry to track movement patterns of four female Tree Swallows at dawn and dusk during the pre-laying and laying periods. Our tracking results indicate that individual females differed in their movement patterns: some remained close to their nest site on multiple nights while others were rarely detected near their nest box at night. Despite differences in movement patterns, all four females that we tracked produced extra-pair offspring for which we were unable to identify extra-pair sires, even after sampling the majority of males breeding within our nest-box grids. Despite the small sample size, our results confirmed ex...

Loss of oak woodlands to vineyard development in California is a growing concern to conservationists. Analyzing breeding performance of birds that nest in and around vineyards versus those that nest in nearby native habitat can provide information on the suitability of vineyard environments to birds. We placed predator-protected nest boxes in vineyard and oak-savannah habitats and monitored nest-box occupancy, nesting success, and life history characteristics of Western Bluebirds (Sialia mexicana) that used the boxes. Western Bluebirds were common occupants in both habitats, occupying >50% of available nest boxes. Analysis using program MARK revealed that nest survival was not associated with habitat type; however, clutch size was greater and nests were initiated earlier in vineyard than in oak-savannah habitat. Our results suggest that when naturally occurring nest sites are limiting, vineyards could be converted to good breeding habitat for Western Bluebirds with the addition of nest boxes. Nes...

We describe the first known instance of Black-billed Magpies (Pica hudsonia) nesting in a fully enclosed, pre-formed cavity. Magpies built an undomed nest of sticks in a nest box designed for Wood Ducks (Aix sponsa) near Olds, Alberta, Canada, in 2008. All nesting material was removed from the box after an apparently successful nesting attempt. Magpies built a new nest in the box and fledged at least four young in 2009. These observations indicate that cavity nesting is a distinct, novel behavioral trait that can arise in this species. We describe several potential costs of cavity nesting in this species, which may explain in part why this trait has not become established in any of the many studied magpie populations around the world.

I describe an Eastern Screech-owl (Megascops asio) hatching three Wood Duck (Aix sponsa) eggs in a suburban nest box. Wood Duck(s) removed all five eggs of a completed screech-owl clutch, the earliest of which had already been incubated for at least 19 days, and laid three eggs in their place. The female screech-owl hatched the Wood Duck eggs, preened the ducklings, and attempted to feed them until they exited the nest box within 48 hrs of hatching.

The Rota White-eye (Zosterops rotensis) is an endangered species endemic to the island of Rota in western Micronesia. We monitored eight nests from 2003 to 2005, four of which produced at least one fledgling. Clutch size was two in each of five nests that were counted; the average number of fledglings from successful nests was 1.5 (n = 4). We filmed six nests and captured two nest predation events on video. A Mariana Crow (Corvus kubaryi), which is also an endangered species, was filmed taking nestlings from one white-eye nest. Another nest containing eggs was depredated by a rat (Rattus spp.); however, this may have occurred after the nest was abandoned due to the presence of the camera.

On 21 May 2003, we discovered a completed Blue Grosbeak (Passerina caerulea) nest in an Eastern Bluebird (Sialia sialis) nest box. On 28 May, the nest contained four whitish-tan eggs with light-brown, streaky and spotty markings, an unusual color pattern for Blue Grosbeak eggs. Species' identification was confirmed by capturing the breeding female in the nest box, and confirmed again later with identification of the chicks as Blue Grosbeaks. To our knowledge, this is the first published account of cavity nesting, artificial or otherwise, for this species.