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We reviewed morphological variation, taxonomic status, geographic distribution, ecology, and behavior of the poorly known hummingbird, the Mexican Sheartail (Doricha eliza), based on museum specimens and field studies. Although the broadly disjunct distribution of the species would suggest that two taxa are involved, morphological differences between the populations appear minor, not deserving of formal taxonomic recognition. Ecological differences between the two populations are stronger, however; modeled ecological niches are nearly nonoverlapping, and ontogenetic and behavioral differences may exist. We recommend that, given its extremely restricted distribution, the Veracruz population be considered critically endangered, whereas the Yucatan population be designated as having a restricted range and accorded near-threatened status.
RESUMEN.—Se revisaron la variación morfológica, estatus taxonómico, distribución geográfica, ecología y conducta de un taxón muy poco conocido, el colibrí tijereta mexicano (Doricha eliza), en base en estudios de campo y en museo. A pesar de que la amplia disyunción en su distribución geográfica sugiere la existencia de dos taxones diferentes, la diferenciación morfológica es mínima y no amerita reconocimiento taxonómico formal. Sin embargo, las diferencias ecológicas entre las dos poblaciones son más marcadas, con nichos ecológicos modelados que casi no se sobrelapan, y diferencias ontogenéticas y de conducta pueden existir. En general, la población de Veracruz debe ser considerada en peligro de extinción, mientras que la población de Yucatán debe ser designada de distribución restringida y con un estatus de conservación de casi amenazada.
Here I describe for the first time nests of the Chestnut-tailed Antbird (Myrmeciza hemimelaena) in Bolivia. I found two nests in the understory of tropical lowland and hill tropical forests. The nests, 25 and 28 cm above ground, were basally supported open cups with a curved Geonoma sp. palm leaf as the structural foundation, woven with pieces of brown stringy rootlets, dead leaves, and leaf exoskeletons.
We studied the relationship between group and individual display in the courtship and social system of the White-ruffed Manakin (Corapipo leucorrhoa altera) in the Atlantic slope foothills of Costa Rica. Between 20 April and 28 May 1989, we searched for display logs and conducted 358 h of observations focused on four display logs. We found logs owned by a single resident male in which activity was continuous, as well as logs and areas where displays were occasional. Six of the eight logs found in the study area were arranged in two clusters separated by about 300 m, although we also found a solitary log 200 m from the nearest active display site. The resident male was at his display site 40.7–93.7% of the time, mostly alone. Residents were visited by other males mainly before 08:00 and less frequently by females later in the day. Residents continually gave advertisement calls during the day and performed several visual displays, including an elaborate Flap-chee-wah in which the male would fly steeply upward from the display log to land explosively at high speed a few seconds later, instantly jumping while turning in the air to land facing the original landing point. Two of these displays culminated in copulations. Other common displays were a slow undulating Butterfly flight and Throat-flagging in which males slowly moved their heads, exposing the fully erected, contrasting white throat feathers. Males performed the displays alone, in the company of other males, or in the presence of females. We conclude that C. leucorrhoa displays in dispersed leks as found by other authors for C. gutturalis. Each log is owned by a single individual and the visits by other males may have a social function related to the establishment of a dominance hierarchy. We found important similarities between the two species of Corapipo and also with the genus Masius, which supports the proposed close relation between the two groups.
Although it is commonly believed that nest boxes yield artificially high estimates of nest success, few investigators have compared nesting success in nest boxes to tree cavities in the same locality during the same time period. I studied nesting success of Great Crested Flycatchers (Myiarchus crinitus) breeding in nest boxes and natural sites (i.e., old woodpecker cavities and natural tree hollows) on the same pine plantations in northern Florida. Mayfield estimates of nesting success were nearly identical between nest boxes (0.37 ± 0.05 SE, n = 32 nests) and tree cavities (0.38 ± 0.06 SE, n = 27 nests) during a 2-year period. However, nesting success was greater in nest boxes (0.53 ± 0.06 SE) than in cavities (0.33 ± 0.10 SE) during 1997 and lower in nest boxes (0.26 ± 0.07 SE) than in cavities (0.42 ± 0.09 SE) during 1998. Lower nest success in nest boxes during 1998 was due to increased predation during the incubation period. Nest predation accounted for ≥83% of all nest failures. Documented nest predators included the southern flying squirrel (Glaucomys volans) and corn snake (Elaphe guttata). Nest boxes and cavity nests did not differ significantly in any habitat variable that would influence nest concealment, nor did these variables differ significantly between years. Evidence suggests that nest predators may learn to exploit nest boxes as a prey resource, either through the development of search images or through long term spatial memory. This study demonstrates that nest boxes are not always safer sites than tree cavities and that static comparisons may give misleading results.
Forest fragmentation due to forestry management, agricultural activities, or urban development decreases habitat availability for some animals. This decline in forest area has been implicated in songbird population declines via changes in nest predation pressures. The increase of edge habitat that accompanies deforestation also may affect songbird breeding activities through changes in predation risk. This study found evidence for an interaction effect of distance from edge (1, 15, 30, and 45 m) and adjacent landscape matrix (residential or forested) on nest predation rates using an artificial nest design. In fragments bordered by other forested patches, nest predation rates were lowest 1 m from the edge and higher 15–45 m into the forest patch. When the forest fragment was embedded in a landscape matrix of residential and developed plots, predation rate was highest closest to the edge of the fragment.
We present information on nest site characteristics and breeding biology of the black-backed race of the Lesser Goldfinch (Carduelis psaltria psaltria) in montane ponderosa pine (Pinus ponderosa) woodland in the foothills of Boulder County, Colorado. We located 62 nests during summer, 1999–2001. There appeared to be strong microhabitat preferences for nest sites. Nests generally were placed toward tips of long branches in the middle of ponderosa pines. Most nests were well concealed in needle clusters in trees near forest edges and openings. Mean canopy cover at nest sites was 49%. Nests usually were oriented toward the south or east, and orientation was correlated with the aspect of the surrounding terrain. More than 70% of nests were located in small, loose colonies. Nesting success was fairly high; at least 21 nests fledged young while only 10 failed due to predation. Mayfield nest success was 73% during 2000 and 52% during 2001. Most predation events occurred after the eggs had hatched. We found only one instance of brood parasitism by the Brown-headed Cowbird (Molothrus ater). Compared to the green-backed race (C. p. hesperophila), Black-backed Lesser Goldfinches appear to breed later in the season and have smaller clutch sizes.
Previous studies of Blue-throated Hummingbirds (Lampornis clemenciae) showed that males have elaborate songs and females also sing. Here we report complex territorial systems, sexual behavior, and communicatory repertoires of both sexes. Males typically defended territories along streams throughout the reproductive season. Time budgets revealed that males allocated more time to vocalizing in territorial advertisement than in more energetically costly activities such as chases. Both observations and playback experiments indicated that two vocalizations have different roles in territorial advertisement. Strings of chips served in long distance territorial advertisement, while the lower amplitude song, more prevalent early in the season, attracted females and also repelled males from the immediate area. Agonistic interactions included long chases, some with vocalizations. During close range encounters an array of postures and sounds occurred. Females defended territories against other females during a brief period preceding egg laying. Sexual interactions were unusually intricate, consisting of a series of activities in which the female played an active role. She delivered loud calls advertising sexual readiness and performed aerial displays. Males competed with other males for access to females. We observed four presumed copulations, all preceded by a song fragment from the male. The vocal repertoire included at least 16 different sounds, all with different functions, an unusually large number for a nonoscine. Male songs were the most complex sounds. Behaviors that differed from many other hummingbirds that have been studied included strong reliance on vocal signals, lack of male aerial displays, and female advertisement of sexual readiness. These attributes may be linked to reduced sexual dichromatism and related to the species' preference for wooded riparian habitats.
I investigated the physiognomic and floristic characteristics of Swainson's Warbler (Limnothlypis swainsonii) territories at five localities within its core breeding range in Arkansas, Mississippi, Louisiana, and Florida. The warbler attained its greatest abundance (10–20 territorial males/km2) in floodplain forest characterized by small (<25 cm dbh) trees (ca 620–820 stems/ha) and understory thickets of saplings, vines, and shrubs (ca 35,000–48,000 small woody stems/ha). Territories in mature forest typically were associated with disturbance gaps. Canopy height, basal area, and floristics appear to be relatively unimportant factors in habitat selection, provided that understory requirements are met, which explains the warbler's occurrence in regenerating clearcuts as well as in relic tracts of old growth forest. Giant cane (Arundinaria gigantea), hypothesized to be an essential habitat requisite along the northern periphery of its breeding range, was sparse or absent in the prime breeding locations surveyed in this study. Selective thinning and clearcutting are viable habitat management techniques for the Swainson's Warbler.
Population trend data indicates the Henslow's Sparrow (Ammodramus henslowii) is declining. Little information is available on the status, distribution, and habitat requirements of this species during winter. We obtained winter density estimates of Henslow's Sparrows and quantified and compared habitat structure along transects occupied and unoccupied by birds in longleaf pine (Pinus palustris) forests in westcentral Louisiana. We flushed Henslow's Sparrows from 14 transects during four surveys of 48 20- × 100-m transects from January to February 1996, and 20 transects during four surveys of 46 of the same transects from December 1996 to February 1997. The range of Henslow's Sparrow densities for both survey periods combined was 0.0–13.8 birds/ha (median = 0.0, 75th percentile = 1.3, 95th percentile = 5.0). We used logistic regression to evaluate the association of vegetative structure with Henslow's Sparrow habitat use. The most parsimonious model included litter depth and herbaceous cover as habitat variables predictive of Henslow's Sparrow occurrence. The model correctly classified the occupancy status of 79% (52 of 66) of observed transects. The number of Henslow's Sparrows observed in transect surveys declined with increased number of growing seasons since the last burn, suggesting fire may influence habitat quality.
Red-eyed (Vireo olivaceus) and Blue-headed (V. solitarius) vireos have similar foraging ecologies, similar songs, and occupy similar forest habitats. Evidence suggests, however, that the typical pattern of habitat and foraging segregation in sympatric vireos may not be observed in the southern part of their range of sympatry. We tested the degree of ecological overlap in the southern Appalachians of Virginia by asking whether these species segregate via interspecific territoriality or habitat use. We quantified response to heterospecific song, territory overlap, and habitat characteristics during the breeding seasons of 1997 and 1998. Red-eyed and Blue-headed vireos responded at low frequencies (9% and 2%, respectively; years combined) to the songs of the other species. Not surprisingly, given the playback results, approximately 54% of territories examined for each species overlapped with a territory of the other species. Within territories, both vireos used structurally similar habitat. Microhabitat composition, however, differed between species. Blue-headed Vireos occurred in areas with greater abundance of white oaks (Quercus spp.), conifers, and snags, whereas Red-eyed Vireo habitat had qualitatively greater abundance of red oaks and red maples (Acer rubrum). Red-eyed and Blue-headed vireo habitat was discriminated further by the presence of striped maple (A. pensylvanicum) and black locust (Robinia pseudoacacia) in the canopy of Red-eyed Vireo habitat, whereas conifers and black birch (Betula lenta) were more common at sites where Blue-headed Vireos were observed. Shrub species composition did not differ significantly between vireo habitats. Red-eyed and Blue-headed vireos showed only subtle habitat segregation at our study site in the southern Appalachians, and we found little evidence of interspecific aggression.
Red-cockaded Woodpeckers (Picoides borealis) nest and forage in pine-dominated forests. Research indicates that substantial hardwood midstory encroachment is detrimental to Red-cockaded Woodpecker populations, although the exact mechanisms are unknown. We examined foraging behavior in relation to midstory between August 1989 and February 1990. Red-cockaded Woodpeckers foraged at greater heights in areas of taller and denser midstory in the loblolly-shortleaf pine (Pinus taeda and P. echinata, respectively) habitat, but not in longleaf pine (P. palustris) habitat with less-developed midstory vegetation than typical of loblolly-shortleaf pine habitat. In addition, Red-cockaded Woodpeckers concentrated foraging activities in or adjacent to forest stands or openings with reduced midstory vegetation. Overall, Red-cockaded Woodpeckers foraged disproportionately at heights and sites that minimized their exposure to dense midstory conditions. These results suggest that ecosystem management, preferably using prescribed fire, that reduces midstory vegetation will improve foraging habitat for Red-cockaded Woodpeckers.
Warblers are selective in what they eat, yet little is known about the dietary cues used by warblers as they decide what to eat. Semisynthetic diets may be useful for investigating how specific dietary cues, such as appearance or nutrient composition of food, influences diet preference of warblers because these dietary cues can be easily and systematically modified with semisynthetic diets. We offered Yellow-rumped Warblers (Dendroica coronata) paired choices of live waxworms (Galleria mellonella) and a waxworm mash, or waxworm mash and a semisynthetic mash. Birds strongly preferred live waxworms over waxworm mash, suggesting that natural appearance of food strongly influences diet preference of warblers when the nutrient composition of diets is similar. When birds initially were offered the two mash diets, they consistently preferred waxworm mash over semisynthetic mash within the first 15 min with food, suggesting that they were using dietary cues that provided rapid feedback as would be provided by a cue such as taste. This initial preference for waxworm mash was maintained for the first two days, but then the warblers ate similar amounts of waxworm mash and semisynthetic mash during the last two days of the experiment. The decrease in preference for waxworm mash over time probably occurred because at least some of the cues used by the birds in determining their diet preference(s) required days for reliable feedback. Thus, diet preferences of warblers apparently were influenced by dietary cues that provided immediate and delayed, postingestional feedback. These results support the use of semisynthetic diets in studies of avian diet preferences and highlight the importance of adequate acclimation time on test diets.
Almost all songbird males develop fully crystallized songs before or during their first potential breeding season, when they use these important signals during interactions that determine their social success. We describe a rare phenomenon, in which vocal maturation is delayed until the second potential breeding season, or third year of life, in Yellow-rumped Caciques (Cacicus cela vitellinus) from lowland Panama. We heard predefinitive males in their second year sing only uncrystallized song, while three definitive males known to be in their third year sang fully developed songs matching the local dialect. The unusual system of polygynous breeding colonies in caciques may account for why vocal development is delayed. We would expect to find other examples of delayed vocal maturation in polygynous, nonterritorial species, in which second-year males have little opportunity for social success.
Using museum specimens, we documented the molt cycles and molting grounds of adult Lucy's (Vermivora luciae) and Virginia's (V. virginiae) warblers. During prebasic molts, both species replace all body plumage. Prebasic primary molt takes a mean of 71 days for Lucy's Warblers, but a mean of just 42 days for Virginia's Warblers. Prebasic molt occurs exclusively on the breeding grounds. We found no evidence of a prealternate molt in Lucy's Warblers, and limited evidence of a prealternate molt in Virginia's Warblers. In both species, the seasonal change in crown color is a function of the freshly replaced gray-tipped feathers acquired during the prebasic molt being abraded during the winter, such that the basal red coloration of those same feathers is exposed during spring. These species differ from other western-breeding passerines in that they do not appear to directly exploit the late season food resources in the southwestern United States and northwestern Mexico. This difference is suggested by the lack of a shift from northern parts of their breeding range to molt in those potentially more productive regions of the southwestern monsoon region. The possibility of winter territoriality may play a role in the rapid prebasic molt exhibited by Virginia's Warblers. On the other hand, the lengthy prebasic molt of Lucy's Warblers may be explained by the use of poor nutritional resources during late summer, and/or the lack of territoriality during late summer and winter. We conclude that our data, in conjunction with data from previous studies, suggest multiple contrasting molt migration strategies among breeding passerines in western North America.
We examined differential timing of spring migration by age class for passerines banded at Long Point Bird Observatory from 1984 to 1998. Mean capture dates of after-second-year (ASY) males were earlier than second-year (SY) males for 19 of 20 species, 16 significantly so. Mean capture dates of ASY females were earlier than SY females for 11 of 12 species, 8 significantly so. There was no significant difference in the timing of migration between age classes for males of species with highly distinctive SY plumages and males of other species with more subtle plumage differences between age classes. For 12 species with adequate samples of both sexes, the mean difference in capture dates between age classes was significantly greater for males (3.5 days) than for females (2.1 days). These results suggest that differential migration by age class is widespread among passerines and that factors leading to the delayed arrival of young males also may affect females, though to a lesser extent.
We examined age and sex differences in wing loading, aspect ratio, and wing span in a sample of 208 Merlins (Falco columbarius) captured at Cedar Grove, Wisconsin, during fall migration, 1978–1993. We also examined differences in tail loading of 166 of these Merlins. Adult males had significantly greater mass and wing loading than juvenile males. Adult females differed significantly from juvenile females only in mass. Females were significantly greater than males in every measure except aspect ratio. There were no apparent age differences in tail area or flight surface loading, but females had greater values in both. Merlins show fewer age differences in aerodynamic characteristics than Sharp-shinned Hawks (Accipiter striatus), probably because of differences in how the two species pursue and capture avian prey. Merlins usually capture prey in the air, sometimes after multiple stoops and at high flight speeds. In contrast, Sharp-shinned Hawks take birds from their perch or after a brief chase, often in dense vegetation, at relatively low flight speeds. Slower flight speeds require larger control surfaces and can explain the increased age differences in wing and tail areas in Sharp-shinned Hawks.
I report on the social and breeding biology of four bee-eater species in Thailand. Little Green Bee-eaters (Merops orientalis) breed cooperatively in clusters of overlapping territories. Cooperative breeding units have one to two helpers that join the breeding pair only after incubation has begun. Nests rarely are left unguarded due to threats of predation and possible intraspecific brood parasitism. Males also guard their mates against extrapair copulations. The Blue-tailed Bee-eater (M. philippinus) breeds cooperatively and has a complex social system, with evidence suggestive of intraspecific brood parasitism and extrapair copulation. I provide evidence that the Bay-headed Bee-eater (M. leschenaulti) breeds cooperatively and report observations of noncooperative breeding at one nest in the Blue-bearded Bee-eater (Nyctyornis athertoni).
Until now, there have been no reports of extrapair parentage in Tufted Titmice (Baeolophus bicolor). During 1995–1998, we used multilocus minisatellite DNA fingerprinting to estimate paternity and degree of relatedness in eight central Ohio broods of this socially monogamous species. Our results suggest a rather low rate of extrapair fertilization in the study population; three of 34 nestlings could not be attributed to the attending male. Of the three extrapair offspring, two represented the entire brood in a nest attended by their mother and a nonparental male that appeared to be a close relative of the mother.