We re-evaluate the plausibility that five species of birds that breed in late summer in northwestern Mexico are migratory double breeders that first bred earlier in the same season to the north. We use data aggregated from scientific collections to generate abundance indices that adjust counts of specimens in collections by collecting effort, which we measure as the number of passerines collected in the same region and time period as the species of interest. Our abundance indices generally show displaced phenologies, such that presumed double breeders arrive and breed early in the north, then later in northwestern Mexico. We also compare breeding records for these regions, but these records could not be corrected for effort. Our phenologies suggest that the breeding populations of the Yellow-billed Cuckoo (Coccyzus americanus) from the western U.S. and northwestern Mexico may be derived from birds that bred earlier in eastern North America. Similarly, Orchard Orioles (Icterus spurius) breeding in late summer in northwestern Mexico and on the Mexican plateau may be derived from birds that attempted to breed earlier in North America. Our abundance indices and other new data suggest migratory double breeding is less likely in the Hooded Oriole (I. cucullatus) and probably not occurring in the Yellow-breasted Chat (Icteria virens) and Cassin's Vireo (Vireo cassinii).

Vegetation structure is important in structuring avian communities. In the sagebrush biome, where continued habitat loss is thought to threaten shrusteppe-obligate birds, both remotely sensed and field-acquired measures of big sagebrush (Artemisia tridentata) cover have proven valuable in understanding avian abundance. Differences in structure between the exotic annual cheatgrass (Bromus tectorum) and native bunchgrasses are also expected to be important. We used abundance from 318 point-count locations, coupled with field vegetation measurements and a detailed vegetation map, to model abundance of four shrub- and four grassland-associated avian species in southeastern Washington. Specifically, we ask whether species' abundances in bunchgrass and cheatgrass differ and whether mapped categories of cover adequately explain species' abundances or whether finegrained, field-measured differences in vegetation are also important in explaining abundance. We found that the abundance of shrub associates did not differ in sagebrush with a cheatgrass vs. bunchgrass understory, but grassland associates tended to use bunchgrass more than cheatgrass grasslands (Horned Lark, Eremophila alpestris; Grasshopper Sparrow, Ammodramus savannarum), or, in one case, cheatgrass more than bunchgrass (Long-billed Curlew, Numenius americanus). In the comparison of map- and field-based models, mapped cover types alone were sufficient for predicting abundance of five species studied, but models containing field-measured sagebrush cover outperformed models based on maps only for three species, the Sage Sparrow (Amphispiza belli) ( ), Horned Lark (-), and Grasshopper Sparrow (-). We conclude that cover-type maps that consider understory composition and sagebrush density can predict avian distribution and abundance in the sagebrush biome efficiently.

The species composition of the Chilean avifauna is well-defined taxonomically but is not well known ecologically. We sampled avian communities at a biosphere reserve in coastal north-central Chile in three seasons over six years (18 surveys total) and characterized them in terms of community structure and composition. The avifauna (S = 56 species) was dominated by insectivores (S = 20), carnivores (S = 14), and granivores (S = 13), with lesser contributions by omnivores (S = 5), nectarivores (S = 2), folivores (S = 1), and one vagrant piscivore. The fauna varied greatly between summer and winter, and in most years the breeding season also was distinct. Eighteen species constituted a core group of residents observed in nearly all surveys, but at least 15 species were nomadic or migratory. Our site supported more insectivorous species in winter but more granivores and omnivores in the breeding season, although this observation may be confounded by species' detectability. The structure of the set of species was nested temporally, but this was not clearly caused by seasonal influx supplementing a core fauna of residents. Ordination clearly segregated all three seasons, except for one survey that was explained by very dry conditions in that year. Further research will quantify productivity and demographic responses to long-term climatic variation to compare avian and mammalian patterns with respect to extrinsically generated pulses in resources (e.g., El Niño/Southern Oscillation).

Food quality and physiological capacities and limitations in recognizing and processing food are among the factors influencing the choices of desert birds in feeding. Seed-eating birds of the central Monte desert generally select grass seeds rather than forb seeds. We studied some of the mechanisms underlying seed-selection patterns in seed-eating birds of the Monte desert, analyzing nutrients and secondary compounds of the 15 most abundant seeds in the soil and their relationship with the diet of six species of seed-eating birds. Grass seeds contained more starch and less total phenols than did forb seeds and were free from alkaloids. The diet of the most graminivorous birds was correlated with seeds' starch concentration, while generalists' diet was correlated with seed abundance. To assess the plausible mechanisms underlying birds' selection of seed, we experimented with three species differing in the breadth of their diet: a generalist, the Rufous-collared Sparrow (Zonotrichia capensis), and two graminivores, the Many-colored Chaco-Finch (Saltatricula multicolor) and Common Diuca-Finch (Diuca. diuca). We postulated that the level of starch and the presence of phenolic compounds and alkaloids influence food preference. Results suggest that most graminivorous birds prefer high-starch diets and avoid diets with phenols and alkaloids. In contrast, the generalist foraged regardless of starch content, and its food intake was reduced only by some of the phenols and alkaloids tested. Seed chemistry may explain some important features of seed selection by birds in the Monte desert.

Eighteen species of Amazonian birds have been considered river-island obligates in northeastern Peru, but some of these species have been detected recently at mainland sites along the Amazon River. We document the presence of supposed river-island obligate birds at riparian sites on the mainland and characterize these birds' habitat use on the islands and the mainland on the basis of point counts at five island sites, five riparian mainland sites, and five upland mainland sites. We regularly encountered seven species of supposed river-island obligates on the islands and four of them, including the Ash-breasted Antbird (Myrmoborus lugubris), Black-and-white Antbird (Myrmochanes hemileucus), Castelnau's Antshrike (Thamnophilus cryptoleucus), and Fuscous Flycatcher (Cnemotriccus fuscatus), also occurred regularly at the riparian mainland sites, but none occurred at the upland mainland sites. These four species are primarily birds of early-successional scrub or forest, but they also used agricultural habitats on both the islands and the mainland. The presence of these species on the mainland may have been overlooked by previous researchers, who may neglect human-dominated habitats during avifaunal surveys, or these species may have only recently colonized the mainland in response to an increase in the amount of small-scale agricultural plots in the region. Supposed river-island obligate birds are, in fact, habitat specialists, and can occur on the mainland if appropriate natural or anthropogenic habitat exists there. Human-dominated tropical landscapes may provide habitat suitable for disturbance-adapted bird species and should not be overlooked during avifaunal surveys.

To identify factors potentially limiting the abundance of ducks at the northern latitude of Lake Ontario, we investigated whether the lipid levels and foraging behavior of sea ducks wintering there were best explained by endogenous or exogenous mechanisms. We used an information-theoretic approach to evaluate if date (14 December–15 March; endogenous mechanism), percentage ice cover of Lake Ontario (long-term exogenous mechanism), short-term ambient temperature (exogenous mechanism), or some combination of these factors best explained variation in lipid reserves and foraging effort of the Bufflehead (Bucephala albeola), Common Goldeneye (B. clangula), and Long-tailed Duck (Clangula hyemalis). In the Long-tailed Duck, date explained lipid declines best, whereas in the Bufflehead and Common Goldeneye lipid reserves varied negatively with percentage ice cover. Conditions at our study site appeared to necessitate foraging because all species foraged, on average, ≥69% of daylight hours, and they increased foraging through the winter and when temperatures decreased. We calculated the number of days until lipid reserves should reach zero (i.e., fasting potential). Fasting potential differed in December, when Buffleheads (11 fasting days) had proportionately more lipid than did Common Goldeneyes (8 days) and Long-tailed Ducks (5 days). By March, the fasting potentials of the three species were similar (4 days), suggesting their survival strategies during similar winter conditions differed. Spatial and temporal modeling of temperature and ice cover with sea duck abundance at Lake Ontario and other Great Lakes may clarify factors that limit sea duck use of the region during winter.

Understanding selection of breeding habitat is critical to conserving and restoring habitats for the Greater Sage-Grouse (Centrocercus urophasianus), particularly in xeric landscapes (≤25 cm annual precipitation). We monitored radio-marked female sage-grouse in south-central Wyoming in 2008 and 2009 to assess microhabitat use during nesting and brood rearing. For each model we grouped variables into three hypothesis sets on the basis of the weight of support from previous research (a priori information). We used binary logistic regression to compare habitat used by grouse to that at random locations and used an information-theoretic approach to identify the best-supported models. Selection of microhabitat for nests was more positively correlated with mountain big sagebrush (Artemisia tridentata vaseyana) than with Wyoming big sagebrush (A. t. wyomingensis) and negatively correlated with cheatgrass. Nesting hens also selected microhabitats with greater litter cover. Microhabitat for brood-rearing had more perennial grass and sagebrush cover than did random locations. Microhabitat variables most supported in the literature, such as forb cover and perennial grass cover, accounted for only 8% and 16% of the pure variation in our models for early and late brood rearing, respectively. Our findings suggest sage-grouse inhabiting xeric sagebrush habitats rely on sagebrush cover and grass structure for nesting as well as brood-rearing and that at the microhabitat scale these structural characteristics may be more important than forb availability. Therefore, in xeric sagebrush, practices designed to increase forb production by markedly reducing sagebrush cover, as a means to increase sage-grouse productivity, may not be justified.

Birds' choices concerning nest attendance are influenced by state-dependent and environmental variables including food availability and predation pressure. Parents of altricial young with biparental care face a dilemma: they can choose to guard their nestlings against predation with their physical presence at the nest and ensure the fledging of at least one chick, or they can choose to leave the young unguarded so they can forage for more food, increasing provisioning rates and the probability of fledging more young. In group-nesting birds, parents may be able to dilute the risk of nest predation while leaving the nest to forage if they leave the nest unguarded when there are many other unguarded nests in the colony. The complexity of the parental decision to leave a nest unguarded is highlighted by variation in the chicks' age, within a nest and within the colony, and by differences in effects on nest success and nest fecundity. Our results suggest that the incremental fitness advantage of reducing predation risk by continuing to guard the nest is eventually outweighed by opportunities to reduce nestlings' risk of starvation. The effect is likely to reduce fledgling production within a colony when less food is available, which reinforces the importance of healthy and productive wetland ecosystems in maintaining viable populations of the Great Egret.

The Yellow Rail (Coturnicops noveboracencis) is among the most enigmatic and least studied North American birds. Nesting exclusively in marshes and wetlands, it breeds largely east of the Rocky Mountains in the northern United States and Canada, but there is an isolated population in southern Oregon once believed extirpated. The degree of connectivity of the Oregon population with the main population is unknown. We used mitochondrial DNA sequences (mtDNA) and six microsatellite loci to characterize the Yellow Rail's genetic structure and diversity patterns in six areas. Our mtDNA-based analyses of genetic structure identified significant population differentiation, but pairwise comparison of regions identified no clear geographic trends. In contrast, microsatellites suggested subtle genetic structure differentiating the Oregon population from those in the five regions sampled in the Yellow Rail's main breeding range. The genetic diversity of the Oregon population was also the lowest of the six regions sampled, and Oregon was one of three regions that demonstrated evidence of recent population bottlenecks. Factors that produced population reductions may include loss of wetlands to development and agricultural conversion, drought, and wildfire. At this time, we are unable to determine if the high percentage (50%) of populations having experienced bottlenecks is representative of the Yellow Rail's entire range. Further genetic data from additional breeding populations will be required for this issue to be addressed.

Species distribution modeling is valuable for assessing rare or elusive species and in landscapes where accessibility is limited, such as agricultural lands. While birds' local habitat associations are often well known, knowledge of broad-scale relationships and the spatial patterns of environmental factors is generally lacking. In this study, we develop and validate a predictive habitat model for the King Rail (Rallus elegans) in the rice-growing region of southwestern Louisiana and identify important areas for this elusive bird. In a previous localized study we found it to be associated with canopy cover and ditches/streams around the perimeter of rice fields. Here, we used a geographic information system (GIS) to extrapolate these habitat associations to the region (>940 000 ha). We determined the proportion of rice fields within a 5-km radius and quantified canopy cover and ditches within a 1-km radius. In repeated call-back surveys from 2007 to 2009 we recorded King Rails at 44 of 155 locations. On this basis, accounting for imperfect detection, we modeled King Rail occurrence. The validation results showed the model had good predictive ability, and in 17% of the area the predicted probability of occurrence was high. Accounting for imperfect detection resulted in an increased probability of occurrence. Most importantly, the spatial pattern revealed the threat of encroaching woody vegetation and the vulnerability of rail habitat to hurricanes and further land-use changes. Our study illustrates that field research can be extrapolated to GIS-based spatial models, which can identify key spatial patterns in a species' distribution.

Studies examining the effects of human disturbance on avian parental behavior and reproductive success are fundamental to bird conservation. However, many such studies fail to also consider the influence of natural threats, a variable environment, and parental roles. Our work examines interactive relationships of cyclical (time of day, tide, temperature, seasonality) and stochastic (natural/human disturbance) processes with incubation patterns (attendance, bout lengths, recess rates) of the Black Oystercatcher (Haematopus bachmani), a shorebird of conservation concern. We used 24-hr-per-day video monitoring of 13 molecularly sexed breeding pairs to systematically examine incubation, revealing previously undocumented information that may inform conservation practices for the genus. Seven of 22 video-monitored nests failed, primarily from egg depredation by nocturnal mammals. Analyses of 3177 hr of video footage indicated a near doubling of incubation-bout lengths at night, corresponding to the increased risk of nighttime egg predation. Females had higher overall nest attendance (54% vs. 42%) and longer mean incubation bouts than did males (88 min vs. 73 min). Uninterrupted incubation bouts were over twice as long as bouts interrupted by disturbance. Incubating males departed nests substantially more frequently because of nest-area disturbances than did females in one but not both years of our study. Our findings suggest that the sexes incubate in different but complementary patterns, facilitating efficient egg care in a dynamic environment with several nest threats. We emphasize the importance of considering natural influences when human threats to shorebird reproductive behavior and success are evaluated.

During its fall migration stopover on mudflats in the upper Bay of Fundy, Canada, the Semipalmated Sandpiper (Calidris pusilla) is thought to feed primarily on the amphipod Corophium volutator (mudshrimp). Semipalmated Sandpipers typically use a peck-probe foraging strategy and, until recently, there had been little evidence of variability or opportunism in their foraging habits during this stopover. From 2006 to 2008 we recorded data on the sandpipers' foraging behavior and food availability at three commonly used mudflats. Behavior and food availability varied considerably at one site in one year. In 2006 at Grande Anse, where mudshrimp densities were exceptionally low and ostracod densities very high, the peck-probe strategy was almost completely abandoned for “skimming,” a foraging behavior novel in this species. Because of similarities between skimming and grazing, used by Western Sandpipers (Calidris mauri) to consume biofilm, we hypothesized that birds switched to skimming to feed on biofilm. However, chlorophyll a concentration in the top 2–3 mm of sediment, an index of biofilm abundance, was not a good predictor of proportion of time spent skimming. Instead, skimming had a strong, positive relationship with ostracod density, suggesting that the sandpipers skimmed opportunistically to feed on ostracods rather than to target biofilm. Thus Semipalmated Sandpipers are capable of adapting to changes at traditional staging areas by using novel foraging mechanisms, apparently to forage opportunistically on alternative prey. If staging habitats continue to change, alternative foods and foraging modes may become increasingly important to the success of this species' migration.

The Least Tern (Sternula antillarum) has undergone large population declines over the last century as a result of direct and indirect anthropogenic factors. The genetic implications of these declines are unknown. We used historical museum specimens (pre-1960) and contemporary (2001–2005) samples to examine range-wide phylogeographic patterns and investigate potential loss in the species' genetic variation. We obtained sequences (522 bp) of the mitochondrial gene for NADH dehydrogenase subunit 6 (ND6) from 268 individuals from across the species' range. Phylogeographic analysis revealed no association with geography or traditional subspecies designations. However, we detected potential reductions in genetic diversity in contemporary samples from California and the Atlantic coast Least Tern from that in historical samples, suggesting that current genetic diversity in Least Tern populations is lower than in their pre-1960 counterparts. Our results offer unique insights into changes in the Least Tern's genetic diversity over the past century and highlight the importance and utility of museum specimens in studies of conservation genetics.

We examined wetland selection by the Black Tern (Chlidonias niger), a species that breeds primarily in the prairie pothole region, has experienced population declines, and is difficult to manage because of low site fidelity. To characterize its selection of wetlands in this region, we surveyed 589 wetlands throughout North and South Dakota. We documented breeding at 5% and foraging at 17% of wetlands. We created predictive habitat models with a machine-learning algorithm, Random Forests, to explore the relative role of local wetland characteristics and those of the surrounding landscape and to evaluate which characteristics were important to predicting breeding versus foraging. We also examined area-dependent wetland selection while addressing the passive sampling bias by replacing occurrence of terns in the models with an index of density. Local wetland variables were more important than landscape variables in predictions of occurrence of breeding and foraging. Wetland size was more important to prediction of foraging than of breeding locations, while floating matted vegetation was more important to prediction of breeding than of foraging locations. The amount of seasonal wetland in the landscape was the only landscape variable important to prediction of both foraging and breeding. Models based on a density index indicated that wetland selection by foraging terns may be more area dependent than that by breeding terns. Our study provides some of the first evidence for differential breeding and foraging wetland selection by Black Terns and for a more limited role of landscape effects and area sensitivity than has been previously shown.

Despite the importance of the post-fledging period in avian population dynamics, little is known about habitat use during this life stage. We examined habitat selection by radio-tracked juvenile Slender-billed Parakeets (Enicognathus leptorhynchus) at multiple spatial scales in a fragmented agricultural landscape of southern Chile. Using home ranges versus study area (home-range selection) and locations versus combined home range (habitat-type selection), we based spatial analyses of habitat selection on the population level. Slender-billed Parakeets made similar habitat choices across the hierarchical levels examined, except for riparian and native second-growth forests, which they avoided at the level of overall home-range selection but used in proportion to availability at the level of habitat-type selection. Farmland and pastures with high densities of scattered mature trees were the only habitats positively selected at multiple spatial scales, adding to the increasing amount of literature highlighting the value of such trees for native fauna in highly modified areas. These trees appeared to be important for the birds during the post-fledging period as sites for feeding, perching, and roosting and to facilitate movement through open agricultural landscapes.

Woodpeckers are particularly susceptible to habitat changes resulting from forest management because of their reliance on trees and snags for nesting and foraging. However, the influence of habitat variables on the reproductive success of woodpeckers has received less attention than it has in other avian taxonomic groups. We estimated nest-survival rates for the White-headed Woodpecker (Picoides albolarvatus), Hairy Woodpecker (P. villosus), and Northern Flicker (Colaptes auratus) in managed ponderosa pine (Pinus ponderosa) forests along the eastern slope of the Cascade Range in Washington, 2005–2010. Using a model-selection framework, we found that the most supported models included terms for a quadratic effect of date and habitat type for the Hairy Woodpecker, a negative effect of percent shrub cover for the White-headed Woodpecker, and a negative linear effect of date and habitat type, a negative linear effect of snag density, and a positive linear effect of tree density for the flicker. Survival rates over the entire cycle (laying incubation nestling stages) were 0.51 in unburned stands and 0.41 in burned stands for the Hairy Woodpecker, 0.70 for the White-headed Woodpecker, and 0.41 in unburned stands and 0.80 in burned stands for the flicker. In both habitats of our study survival rates of Hairy Woodpecker nests are lower than those reported in other studies, while those of White-headed Woodpecker nests are comparable to those reported in other areas of that species' range.

We studied the responses of the Brown Creeper (Certhia americana) to forest edges in the southern Sierra Nevada, California. We censused birds and monitored nests in four forest types over an elevational gradient. We identified habitat patches homogeneous in terms of forest type, seral stage, and canopy cover and rated edges between adjoining patches as soft, moderate, or hard on the basis of relative differences in the suitability of adjacent patches. Brown Creepers were more abundant in sites with less high-contrast edge and more medium- and high-quality habitat. They avoided soft and moderate edges when selecting nest sites. Successful nests were in large-diameter trees and snags in forest with lower canopy closure and farther from moderate and hard edges than were unsuccessful nests. Clear negative responses to edge in terms of abundance, nest location, and nest survival were surprising because previous work has suggested that edge effects and the processes underlying them may differ in western coniferous forests because of their natural heterogeneity and because past forest management in the region resulted in fairly soft edges. The strength of the response was somewhat tied to the severity of the edge, although creepers avoided even soft edges. Hard edges were relatively rare and resulted primarily from natural discontinuities. Our results suggest that Brown Creepers should benefit from forest management that retains mature forest with minimal discontinuities, regardless of their source. Results also suggest that differences in relative habitat quality rather than differences in vegetation were responsible for observed patterns.

We studied the effect of botfly (Philornis seguyi) parasitism on survival and growth of House Wren (Troglodytes aedon) nestlings. We investigated whether nestling survival was related to (1) the intensity of botfly infestation, (2) age of the nestling at the time it was parasitized, and (3) the order in which a chick hatched within a brood. The prevalence of botfly parasitism was 25%; the mean intensity and age at parasitism were 12.8 larvae per nestling and 3.9 days, respectively. Nestling survival was 42% lower in infested than in noninfested broods. Nestling survival was negatively associated with the mean intensity of parasitism of the brood and positively associated with the age of the nestling at the time it was parasitized. Within infested broods, nestling survival was higher in chicks hatched first than in chicks hatched last. Infested nestlings that survived until fledging grew at lower rates and remained in the nest longer than did nestlings in noninfested broods. Our results reveal that P. seguyi has lethal and sublethal effects on House Wren nestlings and that the intensity of parasitism, age of nestlings at the time they are infested, and sequence of hatching are important factors that influence the survival of parasitized nestlings.

It has been hypothesized that incubation begins before laying is completed because it controls bacterial growth on eggshells and infection of eggs. If so, early incubation should be associated with decreased abundance of bacteria on eggshells. There is no detailed information on incubation during daytime or nighttime during laying and its association with bird eggshells' bacterial loads. We used temperature sensors placed in contact with eggs and connected to data-loggers to measure early incubation by females of the Pied Flycatcher, Ficedula hypoleuca, a hole-nesting passerine, beginning with laying of the third egg (day 3). Incubation usually began with laying of the fourth egg (day 4), the modal clutch size in our population being six. We sampled heterotrophic bacteria on eggshells from the whole clutch soon after it was completed. We used colony-forming units counted on trypticase soy agar to estimate bacterial loads. Clutches incubated more intensively during daytime on day 4 and also during nighttime on days 3–5 had fewer bacteria on eggshells than clutches incubated less. The temperature of the air around the eggs seemed not the key explanatory variable for the eggshell's bacterial loads, suggesting that mechanisms other than thermal changes associated with incubation may be more relevant to control of bacterial proliferation. Ours is the first study showing a correlation between increased incubation on the day incubation begins during laying and a reduction in bacteria on the eggshells of wild birds. It supports the hypothesis that early incubation is an antimicrobial defense of the clutch.

Recent research has shown repeatable individual variability in temperament traits. We tested the hypotheses that individual Bobolinks (Dolichonyx oryzivorus) vary consistently in their response to predators, a temperament trait, and that this individual variation is associated with breeding-site selection. Specifically, we tested whether measures of behavioral response to human approaches are associated with either patch area or patch openness and thus to area sensitivity. We made two to seven sequential approaches to Bobolinks in 2009 and 2010, measuring starting distance, flight-initiation distance, and the distance from the observers to where the birds landed. We analyzed the data with repeatability estimates and linear mixed modeling. Flight-initiation distance was repeatable when starting distance was controlled for, but distance to landing was not after starting distance and flight-initiation distance were controlled for. We found no strong effect of area or openness on either flight-initiation distance or distance to landing. We conclude that this measure of response to predators shows individual variation, but this variation does not explain patterns of settlement among habitat patches. Because flight-initiation distance is often used to identify distances at which human behavior disrupts wildlife, we estimate its mean (21.8 m) and the distance at which 75%, 95%, and 99% of the Bobolinks flushed (28, 40, and 59 m, respectively).

Brood parasitism by the Brown-headed Cowbird (Molothrus ater) can substantially affect host species' reproductive success. The “host-activity” hypothesis suggests that parasites eavesdrop on conspicuous behaviors to locate and parasitize hosts, and several studies of cowbird hosts support this hypothesis. In contrast, a recent study of the Least Bell's Vireo (Vireo bellii pusillus) reported a negative association between the host's vocalization rate near the nest and brood parasitism. This contradictory pattern is intriguing because Bell's Vireo is a common cowbird host and vocalizes near and on its nests. We tested a key assumption of the host-activity hypothesis in a different subspecies (V. b. arizonae) to determine whether the contradictory pattern reported in V. b. pusillus is an anomaly or could be generalized to other subspecies. Unparasitized vireos vocalized more frequently than parasitized birds, confirming that the pattern in Bell's Vireos is the opposite of that reported for other cowbird hosts. Nesting stage played a role: unparasitized birds vocalized more than parasitized birds only during the nest-building and incubation stages. Given that vocalization rate and other behaviors change through the breeding season, future tests of the host-activity hypothesis should control for nesting stage. Moreover, future efforts to identify the underlying cause for the association between vocalization rate and probability of parasitism should consider the possibility of reciprocal causal relationships between them. We propose five additional hypotheses to explain why in Bell's Vireo the pattern between these two traits is opposite of what has been reported in other birds.

The Montserrat Oriole (Icterus oberi) is a critically endangered species, confined to a small range in the hill forests of the volcanic island of Montserrat in the eastern Caribbean. From 1998 to 2005 we studied its breeding biology and survival of adults, finding that the Montserrat Oriole has a smaller clutch, more extended parental care, and higher adult survival than do orioles nesting in the North Temperate Zone. Adults' probabilities of survival varied by year from 0.60 to 0.76 but were similar for both sexes. Average clutch size was 2.6 eggs (± 0.04 SE), and post-fledging parental care was 40 ± 5 days. We found nest success of 29% (n = 275 nests), and 87% of nest failures were due to predation by either introduced rats (Rattus sp.) or the native Pearly-eyed Thrasher (Margarops fuscatus). Most pairs initiated several nesting attempts after both failed and successful first broods, leading to an overall annual productivity of 1.2 fledged chicks per pair. Despite being able to raise up to three broods per season, the Montserrat Oriole's annual productivity was lower than that of its temperate-zone congeners, and we recommend that conservation management focus on enhancing nesting success via rat control.