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We describe for the first time the nest and eggs of the Tepui (Brown-breasted) Antpitta (Myrmothera simplex). Nest structure and eggs are very similar to those described for M. simplex's extant sister species, the Thrush-like Antpitta (M. campanisona), and nests of this genus are similar to those described for other members of the ground antbirds (Formicariidae).
Canyon Towhees (Pipilo fuscus) normally nest in trees, shrubs, and cacti. I found a nest on the ground under an octagonal road sign in Santa Fe County, New Mexico, on 14 May 2001. No young were fledged, but the eggs were incubated for ≥10 days. Additional records of Canyon Towhee nests in a building and an enclosed trailer are indicative of a plasticity in their nest site selection process that led to use of this unusual nest site.
Pileated Woodpeckers (Dryocopus pileatus) cause damage to Red-cockaded Woodpecker (Picoides borealis) cavity trees in the form of cavity enlargement or other excavations on the surface of the pine tree. However, it is not known whether Pileated Woodpeckers excavate more frequently on Red-cockaded Woodpecker cavity trees than on noncavity trees or how stand structure is related to the frequency of Pileated Woodpecker excavation. Also, it is unclear whether the cavity itself provides the stimulus to Pileated Woodpeckers to excavate or whether the presence of Red-cockaded Woodpeckers and their activities are attracting them. We surveyed all of the Red-cockaded Woodpecker cavity trees (n = 202) and 110 control trees in the loblolly (Pinus taeda)-shortleaf (P. echinata) pine habitat on the Angelina National Forest for recent Pileated Woodpecker excavation and found that approximately 7.4% of all cavity trees were damaged while no control trees showed any evidence of Pileated Woodpecker damage. The rate of Pileated Woodpecker excavation was negatively associated with hardwood midstory height and density. Pileated Woodpeckers appeared to focus most of their excavations on Red-cockaded Woodpeckers cavity entrances. We suggest that Pileated Woodpeckers may be attracted to Red-cockaded Woodpecker cavity trees, especially the cavity, and that midstory removal used to improve Red-cockaded Woodpecker habitat may increase the incidence of damage to the cavity trees by Pileated Woodpeckers in the current fragmented landscape.
We studied the nesting ecology of Least Bitterns (Ixobrychus exilis) during 1999 and 2000 within an 8,000-ha wetland complex in western New York. We used radio telemetry to track 33 adult Least Bitterns to locate nests and determine movement patterns, and 12 chicks to determine postfledging movements. Least Bittern Mayfield nest success rates were 43.8% (n = 38) in 1999 and 52.5% (n = 35) in 2000, and they renested and had double broods. Mean home range of adults was 9.7 ha (n = 33), but varied (range = 1.8–35.7 ha) depending upon whether birds used one or two areas during the breeding season. The mean movement of chicks from their nests was 13.4 m between capture and 23 days posthatching (n = 11), and 29.4 m when 24–27 days old (n = 4). Mean age at first flight was about 29 days old (n = 4). Vegetational structure and composition and marsh size appear to be important factors to consider when managing for Least Bittern populations.
We quantified home range size and habitat selection of seven female Northern Saw-whet Owls (Aegolius acadicus) on Assateague Island, Maryland, during the winters of 1996 and 1997. Home range size (95% fixed kernel) was 103.5 ha (± 50.3 SE). Home range size increased with time spent radio tracking as biweekly home ranges were smaller than those calculated for longer time periods. Home ranges often overlapped in time and space and in one instance the home range for one owl was completely within that of another owl. Northern Saw-whet Owls used primarily pine woods and shrub swamp habitats, with pine woods used more often than any other habitat type and significantly more than expected based on habitat availability.
To assess the relationship between marsh area and relative abundance of tidal marsh bird species, we surveyed birds on 86 circular plots in 40 salt and brackish tidal marshes in Connecticut. We measured marsh area in two ways: the amount of contiguous marsh vegetation not interrupted by broad barriers (>500 m of open water or >50 m of upland habitat) and by narrow barriers (>30 m of open water or >10 m upland). We determined the relationship between marsh area and the relative abundance of particular species (mean number of individuals per survey plot) with linear or logistic regression. When the broad barrier definition was used, we found that all three species of short grass meadow specialists, Willets (Catoptrophorus semipalmatus), Seaside Sparrows (Ammodramus maritimus), and Saltmarsh Sharp-tailed Sparrows (A. caudacutus), were less abundant or absent in survey plots in smaller marshes. The Seaside Sparrow and Willet also showed a significant tendency to be less frequent in smaller marshes when the narrow barrier definition was used. In contrast, species that used a wider range of wetland types, as in the Virginia Rail (Rallus limicola), Marsh Wren (Cistothorus palustris), and Swamp Sparrow (Melospiza georgiana), were equally frequent on plots in marshes of different areas. Our results are consistent with the hypothesis that fragmentation of marsh systems with artificial habitat causes a decline in the density of short grass meadow specialists in the remaining patches of appropriate habitat.
The effects of Red-cockaded Woodpecker (Picoides borealis) management on nontarget birds is not widely known. Intensive management for pine specialists such as the Red-cockaded Woodpecker may negatively impact both Nearctic-Neotropical and Temperate Zone migrants associated with hardwood vegetation. To evaluate possible positive and negative associations, we surveyed avian communities from 1995–1997 using point counts within managed Red-cockaded Woodpecker cavity tree clusters and mature forest control sites in longleaf pine (Pinus palustris) and loblolly (P. taeda)-shortleaf (P. echinata) pine habitats. In general, sites managed for Red-cockaded Woodpeckers supported more diverse and numerous bird populations than mature forest control sites. During the breeding season in loblolly-shortleaf and longleaf pine habitats, respectively, species richness was 47% and 23% greater, avian abundance was 57% and 65% greater, and bird species diversity was 25% and 21% greater within managed Red-cockaded Woodpecker cluster sites than within control sites. During winter, species richness and avian abundance each were 52% higher within managed Red-cockaded Woodpecker cluster sites than control sites in loblolly-shortleaf pine habitat.
Concern has been raised that the viability of Bicknell's Thrush (Catharus bicknelli) populations is precarious due, in part, to threats to its breeding habitat. Qualitative descriptions of habitat use have suggested that the species breeds primarily in dense, high elevation forests of northeastern North America. However, there is little quantitative information on habitat use patterns, which impedes formulation of effective conservation plans. To address this knowledge gap, we characterized the habitat of 42 sites occupied by Bicknell's Thrushes and 19 unoccupied sites on two mountains in the Estrie region, Quebec. Occupied sites were dominated by balsam fir (Abies balsamea) growing at high density, whereas unoccupied sites had a larger component of hardwoods at lower density. We found significant differences in vegetation composition and habitat structure between occupied and unoccupied sites for each mountain separately, and the two combined, though the particular variables distinguishing the two site types varied between the two mountains likely because of differences in management history. Our results show that the structure of occupied habitats may differ among sites even within a single region. However, it was evident that dense balsam fir-dominated habitats were used selectively by Bicknell's Thrushes at both study sites, and that the maintenance of such habitats should be a conservation priority in the Estrie region.
We examined foraging behavior and microhabitat use of four passerine bird species inhabiting an old growth coastal woodland in Buenos Aires Province, Argentina. Based on foraging maneuvers, we identified two groups: (1) nonaerial foragers formed by Tropical Parulas (Parula pitiayumi) and Masked Gnatcatchers (Polioptila dumicola) that hopped on branches and twigs while searching and gleaning prey from the nearby foliage, and (2) aerial foragers formed by White-crested Tyrannulets (Serpophaga subcristata) and Small-billed Elaenias (Elaenia parvirostris) that searched for and detected prey while perched, and captured it from foliage or in the air. Nonaerial foragers found prey primarily in the canopy while aerial foragers captured prey at all heights in the woodland. Tree species selection was similar among the four species. All bird species disproportionately foraged in Scutia buxifolia and avoided the use of Ligustrum lucidum trees. Our results indicate that these bird species differed in microhabitat selection in old growth coastal woodland, and that nonaerial foragers were more sensitive to foliage architecture and foliage height distribution than aerial foragers. These results illustrate the importance of woodland logging to bird densities, and provide basic information for effective management.
RESUMEN.—Nosotros estudiamos el comportamiento de alimentación y el uso de microhábitats de cuatro especies passeriformes que habitan bosques costeros maduros de la Provincia de Buenos Aires, Argentina. Considerando las maniobras de alimentación encontramos dos grupos: (1) las recolectoras, formado por Pitiayumí (Parula pitiayumi) y Tacuarita Azul (Polioptila dumicola), las cuales saltando por las ramas y ramitas buscan y recolectan presas desde el follaje cercano, y (2) las cazadoras por revoloteo, formado por Piojito Común (Serpophaga subcristata) y Fiofío Pico Corto (Elaenia parvirostris), que buscan y detectan presas desde una percha y, usando tácticas aéreas, capturan las presas desde el follaje o en el aire. Las especies recolectoras capturan sus presas principalmente en el dosel del bosque, mientras que las cazadoras por revoloteo se alimentan en todas las alturas. El uso de las especies arbóreas del bosque fue similar para las cuatro especies de aves. Todas seleccionaron alimentarse en árboles de Scutia buxifolia y evitaron usar los de Ligustrum lucidum. En general, las especies de aves difieren en su selección de los microhábitats en el bosque costero maduro; las especies recolectoras fueron más afectadas por la arquitectura del follaje y la abundancia de cobertura en altura que las especies cazadoras por revoloteo. Los resultados obtenidos ayudan a comprender los efectos del talado del bosque sobre la densidad de aves, y proveen información básica para su efectivo manejo.
Foraging site selection by birds may be related to foraging efficiency, food availability and abundance, and predation risk. We identified selectively used foraging habitat within home ranges of 29 adult radio-tagged Northern Flickers (Colaptes auratus) in British Columbia during the nestling period. We compared habitat characteristics of flicker foraging locations to randomly selected locations in their home range using discriminant function analysis. Foraging plots were located in grassland and were characterized by a lack of tall vegetation, a large percentage of bare ground, and a high density of small anthills. Foraging plots had five times more anthills than random plots. Foraging plots also were closer to trees and forest edges than random plots. The random plots had significantly more medium and tall vegetation than foraging plots, and litter (dead grass) was the most abundant type of cover. Mortality of adult flickers attributed to avian predation while foraging was 14% during 1999 and 3% during 2000. The sparse ground cover of foraging plots likely increased access to food, whereas foraging near trees likely decreased avian predation. The marked selectivity of foraging areas by flickers suggests that foraging ability could be negatively affected by land use practices that alter the structure of ground cover.
Using constant effort (1993–1996) and playback mist netting with color banding (1996–1999), we estimated annual survival rates of Ovenbirds (Seiurus aurocapillus) and American Redstarts (Setophaga ruticilla) at four sites in the boreal forest of central Saskatchewan. For both species, the model that best described our data included a residency index that differentiated individuals caught more than once within the breeding season of initial capture (residents) from individuals caught only once (transients). Transients had considerably lower recapture rates than residents. The residency index was a more effective means of addressing violations of the homogeneity of capture assumption inherent in Cormack-Jolly-Seber models than a two-stage or age-structured model. We detected no significant differences in survival or recapture rate of male Ovenbirds between constant effort and playback mist netting techniques, although our estimate of annual survival for male Ovenbirds captured using playback (0.62 ± 0.06 SE) was higher than when we used constant effort netting (0.44 ± 0.13 SE). We observed no significant differences in survival between male (n = 99) and female (n = 113) American Redstarts or between second-year (n = 50) and after-second-year (n = 49) American Redstart males (overall survival = 0.55 ± 0.09 SE). For Ovenbirds, the model that best fit the data incorporated sex specific differences in survival with females (n = 76) having lower survival (0.21 ± 0.09 SE) than males (n = 197, 0.60 ± 0.12 SE). Without accounting for the presence of transient birds in our models, our estimates of survival would have been unrealistically low. Residency indices based on the number of times an individual was captured within a season seem to provide an effective means to account for transients.
I estimated hourly mass change at stopover sites for 14 species of migrant passerines from 15 sites across southern Canada by analyzing size-corrected mass of birds at first capture as a function of time of day of handling. Mean mass gains were 0.40% of lean body mass/h during spring and 0.53% during fall. Mass gain estimates varied significantly with season, site, and species, and were negatively related to condition of birds in the early morning. However, standard errors were large, such that few individual estimates were significantly different. Several sites with consistently low rates of mass gain had characteristics that probably reduced local food supply. Swainson's Thrushes (Catharus ustulatus) also had consistently low rates of mass gain. I estimated the time required to accumulate sufficient mass to fuel a 10-h migratory flight, and found that the majority of estimated mass gains were sufficient for birds to refuel during <1 week of stopover in southern Canada. At mean rates of mass gain from this study, migrants in southern Canada could potentially refuel completely during 2–3 days in both seasons, but true periods are likely somewhat longer. Analysis of mass change along migration routes (instead of across them, as in this study) is needed to detect whether there are differences among species in timing and location of maximum fuel deposition, as has been found in Europe.
We examined molting, plumage abrasion, and seasonal color changes of Lawrence's Goldfinch, Carduelis lawrencei, to determine to what extent the reported brightening of male colors at the approach of the breeding season results from plumage renewal. Lawrence's Goldfinch has only one molt per year, a complete postbreeding prebasic molt. Color changes during spring result entirely from plumage abrasion and fading, not from a prealternate molt as previously was thought. The yellow breast feathers of the males, but not the females, are unusually resistant to wear, so that the yellow on the breast appears to expand and brighten, as less durable surrounding gray feathers abrade. This may be due to a one-third greater thickness of the rachillae of the yellow barbs in males, so that instead of the rachillae progressively losing yellow-pigmented material, the brown pigmented barbules break off, leaving intact the rest of the barb with only yellow pigment. In contrast, the yellow breast feathers of females abrade progressively at the tips of the rachillae. Females change dorsal coloration little, but males develop a yellowish area on the center of the back, which results when the olive to brown tips overlapping adjacent feathers wear off and uncover yellow proximal portions of neighboring feathers. We point out the need to examine plumage microscopically when studying molting and plumage changes so as not to reach false conclusions about the causes of the changes.
We studied variation in the carotenoid color of flight feathers of hybrid Northern Flickers (Colaptes auratus) and its correlation with reproductive performance and survival. Color scores provided by a digital camera revealed in 218 individuals a continuous spectrum from yellow to red. Males tended to be slightly redder than females. Within individuals, an analysis of color change with age revealed that males, but not females, became redder with age. Except for yearling females, body condition did not improve with age, suggesting that color is not linked to body condition measured during incubation. We did not detect any correlations between feather color and measures of reproductive performance, such as clutch size, hatching success, or fledging success, or return rate to the study area. In a hybrid population where intraspecific variation in color is controlled partly by genes, hue or brightness may not be a useful signal of individual quality, contrary to other studies of birds. About 25% of flickers had one or more tail feathers that differed from the rest of the plumage. In each case, the “odd” feathers were paler or yellower in color and may have been caused by diet or stress when the feathers were lost and regrown during winter. Such odd colors support the hypothesis that red carotenoid pigments are costly to maintain under stressful conditions.
During a study of Northern Flickers (Colaptes auratus) nesting in central British Columbia, I discovered a polyandrous female attending two nests 447 m apart. The phenology at the two nests was staggered so that the female took incubation shifts and fed nestlings at both trees. Hatching success was typical but the female appeared to divide her provisioning effort between the broods. At one nest, only about 20% of visits were by the female, compared to a typical rate of 50%. Polyandrous mating benefited the female, who fledged all six nestlings in one brood and all seven in the other. The mean number of fledglings for monogamous females in this population was 5.9. Two other cases of polyandry possibly related to human disturbance are discussed. These results suggest exceptions to the idea that, in Picidae, the full contribution of both genders during incubation and brood rearing is required to fledge young.
We studied Mallards (Anas platyrhynchos) nesting in artificial nesting structures in northeastern North Dakota and compared clutch size between landscapes where proportion of cropland was either high (mean = 68.9%, cropland landscapes) or low (mean = 30.2%, grassland landscapes). Mallard clutch size was significantly related to nest initiation date and landscape composition. Mean clutch size, controlled for nest initiation date, was 1.24 ± 0.33 SE eggs smaller on cropland landscapes than on grassland landscapes. Generality of this pattern across space, time, and type of nesting sites is unknown, as is causation. Demographic importance of variation in clutch size may be influenced by covariation with other demographic variables, such as nest success and abundance of breeding pairs, which also are negatively correlated with landscape proportion of cropland. We suggest that researchers examine relationships between clutch size and landscape composition in both structure-nesting and ground-nesting Mallards, in other geographic areas, and in other duck species.
We document the first reported observation of helping at the nest of a Henslow's Sparrow (Ammodramus henslowii). Video surveillance recorded two unbanded adults (a presumed male and female) and one banded adult male feeding chicks. No intraspecific aggression among the adults was observed.
We report an instance of interspecific adoption of Black-winged Stilt (Himantopus himantopus) chicks by Common Terns (Sterna hirundo), two species that nest in similar habitats but differ substantially in their behavior and diets. This is the first report of adoption between these two species.
Here I report a feeding innovation by Shiny Cowbirds (Molothrus bonariensis) in which the birds feed on the nectar of flax (Phormium tenax) flowers. Flax frequently is cultivated in Mar del Plata City, Buenos Aires Province, Argentina, as an ornamental plant, and the Shiny Cowbird is common there. The length of the cowbird's bill is similar to that of the flax flower tube, which permits the cowbird to access the nectar. Further, the panicle stem of the flax is sufficiently rigid for perching, and the short distance between the stem and the flower enables a perched cowbird to reach the flower. At this site, flax nectar probably is utilized in a sustainable manner, as the flowers apparently are not harmed. Future investigations should examine whether or not the observed behavior is restricted to this particular population and if it is not, determine the spatial and temporal extent to which it occurs.
The breeding range of the Bay-breasted Warbler (Dendroica castanea) is thought to include only the northernmost portions of six northeastern and northcentral states in the United States. During a 10-year banding study of Kirtland's Warblers (Dendroica kirtlandii) in northern Lower Michigan, we caught 44 Bay-breasted Warblers outside of their reported migration dates during 9 of the 10 years. Two birds captured in 1997 were in breeding condition; one possessed a cloacal protuberance and the other a full brood patch. We also captured two hatching year birds with fleshy rictal flanges in 1997. We suggest that these records indicate a long term presence of Bay-breasted Warblers on breeding grounds considerably farther south than previously recorded.