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Bachman's Sparrows (Aimophila aestivalis) occupy fire-dependent, longleaf pine (Pinus palustris) ecosystems of the southeastern United States. Their populations have declined, due, in part, to fire suppression and degradation of longleaf pine forests. Populations decline when longleaf stands go more than 3 years without fire. The influence of fire on breeding productivity, however, is poorly understood because territories are large and it is difficult to find the well-hidden nests of this ground-nesting sparrow. In an earlier study, densities of Bachman's Sparrows were similar across pine stands burned 1 to 3 years previously, but declined significantly by the 4th year since burning. To assess whether the decline in density might be associated with a decline in breeding success, in 2001 we used a reproductive index to estimate breeding productivity of 70 territorial males, and from 1999 to 2001 we monitored 28 nests. We examined the influence of (1) season (growing versus dormant) when last burned and (2) years since burning on breeding productivity of Bachman's Sparrows in longleaf pine stands in the Conecuh National Forest, Alabama. Reproductive indices were greater (Z = 1.99, P = 0.047) during the first 3 years after burning (mean = 3.8, SE = 0.4, n = 10) than they were 4 years after burning (mean = 2.0, SE = 0.5, n = 3), similar to the pattern of change in Bachman's Sparrow density. We found no effect of burn season on the breeding productivity index (Z = 0.075, P = 0.94). The parallel patterns of declining density and lower breeding success suggest that Bachman's Sparrow density may be positively correlated with habitat quality. We conclude that burning longleaf pine forests on a 2–3 year rotation will best maintain populations of Bachman's Sparrows.
Using radiotelemetry, we studied variation in home-range size of the Bachman's Sparrow (Aimophila aestivalis) at the Savannah River Site (SRS), South Carolina, during the 1995 breeding season. At SRS, sparrows occurred primarily in two habitats: mature pine habitats managed for Red-cockaded Woodpecker (Picoides borealis) and pine plantations 1 to 6 years of age. The mean 95% minimum convex polygon home-range size for males and females combined (n = 14) was 2.95 ha ± 0.57 SE, across all habitats. Mean home-range size for males in mature pine stands (4.79 ha ± 0.27, n = 4) was significantly larger than that in 4-year-old (3.00 ha ± 0.31, n = 3) and 2-year-old stands (1.46 ha ± 0.31, n = 3). Home-range sizes of paired males and females (n = 4 pairs) were similar within habitat type; mean distances between consecutive locations differed by habitat type and sex. We hypothesize that a gradient in food resources drives home-range dynamics.
The Cerulean Warbler (Dendroica cerulea) is a Nearctic-Neotropical migratory bird species that has declined significantly over the long-term. Poor reproductive success may be an important factor contributing to the observed decline, but reproductive output has been measured for very few breeding populations. From 2003 to 2005, I intensively monitored 22–23 breeding territories/year in each of two large forest habitats in southwestern Michigan: oak- (Quercus spp.) hickory (Carya spp.) (2003: Barry State Game Area) and black locust- (Robinia pseudoacacia) black cherry (Prunus serotina) (2004–2005: Fort Custer U.S. Army Michigan National Guard Reservation). I also gathered descriptive data on nonsong vocalizations and age of territorial males. I describe four distinctive call notes, by sex, including the social and environmental contexts in which they were used. Using two independent methods of aging, there was a strong preponderance of after-second-year males at both study sites. Only 9 (n = 7 nests), 12 (n = 14), and 30 (n = 25) fledglings were produced during the 2003, 2004, and 2005 breeding seasons, respectively. Nest heights were the highest recorded for this species (mean = 19–20 m). During the same period, male reproductive success was 0.30, 0.32, and 0.80 male fledglings/breeding male and 0.60, 0.63, and 1.58 fledglings/breeding pair. Productivity estimates, not thought to be self-sustaining, were even lower than those of a well-studied Cerulean Warbler population in southern Ontario. Thus, reproductive output was low in two geographic regions—representing three different forest types—in the northern portions of the Cerulean Warbler's breeding range. The preponderance of after-second-year males at the Michigan study sites and in southern Ontario suggests a need for regional models of Cerulean Warbler population dynamics.
We evaluated the effect of shorebird predation on invertebrates at a wetland complex along the Illinois River, west-central Illinois, during spring migration. Using a new exclosure experiment design adapted to the shifting nature of foraging microhabitat of interior wetlands, we found that shorebird predation did not significantly deplete total invertebrate density or total biomass in open (no exclosure) versus exclosure treatments. Chironomids and oligochaetes were the most common invertebrates occurring in substrate samples. The density of oligochaetes was lower in open treatments, though the degree of difference varied both spatially and temporally. Shorebird density was positively correlated with the amount of invertebrate biomass removed from the substrate during the late-May sampling period. Our results suggest that shorebirds use an opportunistic foraging strategy and consume the most abundant invertebrate prey. The dynamic hydrology at our study site likely played a role in preventing invertebrate depletion by continually exposing new foraging areas and prey.
The aggregation of nonbreeding insectivorous songbirds into multispecies feeding flocks during migration and on their wintering grounds is a well-known and important aspect of their ecology. The establishment of multispecies feeding flocks on the temperate breeding grounds of North American Neotropical migrants, however, remains poorly known or understood. To address this gap, we investigated the composition and timing of flocking behavior among several species occurring in the southern boreal mixed-wood forest of western Canada. Of 67 species observed in 216 flocks, the most abundant were Tennessee Warbler (Vermivora peregrina) and several resident species: Black-capped Chickadee (Poecile atricapillus), Red-breasted Nuthatch (Sitta canadensis), and Boreal Chickadee (Poecile hudsonica). Consistent with previous work on Eurasian boreal species, residents appeared to play a pivotal role in flock occurrence and cohesion. Flocking tended to begin in late June, and flock sizes increased throughout the summer. This suggests that unsuccessful breeders, early breeders, and early migrants are the first to join flocks, whereas later-nesting species may delay joining flocks until after their young fledge. We also investigated the propensity of several species to display flocking behavior in areas with and without a superabundant food source—the spruce budworm (Choristoneura fumiferana). These data provided some support for the hypothesis that flocking facilitates foraging, as species tended to flock in areas where food abundance was lower.
We investigated the relationships between egg nutrient constituents and fresh egg mass in Bufflehead (Bucephala albeola) and Barrow's Goldeneye (B. islandica). We found consistently positive relationships between egg mass and yolk, albumen, lipid, mineral, and water (absolute amounts); however, the proportions of nutrient components to fresh mass were highly variable in the eggs of both species (allometric relationships). In Bufflehead eggs, all components except mineral exhibited negative allometry with fresh egg mass. In Barrow's Goldeneye eggs, only mineral exhibited negative allometry, whereas yolk, lipid, and water all exhibited positive allometry with fresh egg mass. Overall, larger eggs of both species contained greater absolute amounts of nutrients; therefore, larger eggs were of better quality than smaller eggs. Nutrient content, however, was more highly correlated with mass in Barrow's Goldeneye eggs than in Bufflehead eggs. We propose that this may be due to the source of egg nutrients: because of their smaller body size, Buffleheads typically rely more on exogenous nutrients than Barrow's Goldeneyes.
We estimated apparent annual survival and recapture probabilities for adult Black-headed Grosbeaks (Pheucticus melanocephalus) and Spotted Towhees (Pipilo maculatus) at four sites along the Sacramento River, California. To calculate our estimates, we used capture-recapture mist-net data collected over two time periods at four study sites: from 1993 to 1995 at Flynn, Ohm, and Sul Norte, and from 1995 to 2000 at Ohm and Phelan Island. Our primary objective was to determine whether there were site-specific differences in adult survival and recapture probabilities for each species. Such differences are rarely investigated, yet, if present, suggest site-specific differences in habitat quality, with important implications for source/sink dynamics. We found site-specific variation in Black-headed Grosbeak survival within both the 1993–1995 dataset (Flynn = 0.797 ± 0.496, Ohm = 0.158 ± 0.191, Sul Norte = 0.773 ± 0.131) and the 1995–2000 dataset (Ohm = 0.088 ± 0.090, Phelan Island = 0.664 ± 0.111). For Spotted Towhees (1993–1995 data), the most supported model assumed constant survival across sites (0.602 ± 0.240), but there was some support for site variation in survival, as well (Flynn = 0.653 ± 0.365, Ohm = 0.214 ± 0.253, Sul Norte = 0.632 ± 0.258). These results clearly suggest site variation for Black-headed Grosbeaks, and weak evidence of site variation for Spotted Towhees. For both species, the general pattern was low survival at Ohm, suggesting low-quality habitat there and/or reduced site fidelity. The magnitude of site-to-site variation in survival observed in the Black-headed Grosbeak, and suggested for Spotted Towhee, has strong implications for determining source versus sink population status. To determine source versus sink status, we conclude that investigators must not only take into account site variation in reproductive success, but also consider site-specific estimation of adult survival.
Hatching-year (HY) and presumed HY Flammulated Owls (Otus flammeolus) were captured during a period of pre-migratory activity in central New Mexico from 2000 to 2003. Mass gains were evident through the pre-migratory period. Fat deposition was an important component of these mass gains; muscle growth appeared to contribute to a lesser degree. Fat scores and pectoral-muscle scores were positively related to body mass and to each other, and, from first to last capture, most recaptured owls showed increases in body mass that were accompanied by fat deposition and growth in pectoral muscles. These data add to a growing body of research indicating that pre-migration increases in fat and muscle mass may be interdependent, but the magnitude of increased muscle mass may be too small to be detected at certain scales.
Island species, particularly endemics, tend to have lower genetic diversity than their continental counterparts. The low genetic variability of endemic species and small populations has a direct impact on the evolutionary potential of those organisms to cope with changing environments. We studied the genetic population structure and morphological differentiation among island populations of the Galapagos Dove (Zenaida galapagoensis). Doves were sampled from five islands: Santa Fe, Santiago, Genovesa, Española, and Santa Cruz. Five microsatellite markers were used to determine genetic diversity, population structure, gene flow, and effective population sizes. FST and RST values did not differ among populations; in general, populations with greater geographical separation were not more genetically distinct than those closer to one another, and estimated gene flow was high. There were no significant differences in allelic richness and gene diversity among populations. Although there was extensive morphological overlap among individuals from different island populations for both males and females, we found significant differences in overall body size only between populations on Santa Fe and Santa Cruz (males and females) and between Española and Santa Fe (males only). Significant differences in body size between populations undergoing high rates of gene flow indicate that differentiation may be due to either phenotypic plasticity or ecotypic differentiation. Based on the results of previously conducted disease surveys, we discuss the conservation implications for the Galapagos Dove and other endemics of the archipelago; we also discuss the possible effects of wind currents on gene flow.
American (Fulica americana) and Caribbean (F. caribaea) coots nested colonially at brackish Southgate Pond, St. Croix, United States Virgin Islands (USVI), following a 50-year rainfall event in mid-November 2003. Breeding occurred during three time periods: seven pairs bred from 6 December to 2 January (early), seven from 17 January to 15 February (middle), and eight from 26 April to 19 May (late) (range of clutch initiation dates = 165 days). Hatching success was high (65.3%), but overall reproductive success was low (27%) owing to poor brood survival. Coots built all but 2 of 22 nests at the water line in sturdy crotches of small, live white mangroves (Laguncularia racemosa); two late nests were built on remnant stubs of dead white mangroves after water levels had sharply declined. Early pairs nested in manglars (islets of one or more mangroves without solid land) farther away from shore and in deeper water than middle or late pairs (65.6 versus 42.1 and 29.0 cm, respectively). Southgate Pond remains the preferred breeding site for coots on St. Croix and the USVI. Coots have also recently nested on St. Croix at seven semi-permanent or permanent, man-made, freshwater ponds where they have probably been overlooked, as coots respond rapidly to changes in water levels at semi-permanent or permanent wetlands. Predominance of non-assortative pairing at Southgate Pond suggests that American and Caribbean coots are morphs of one species.
We conducted mist netting each October from 1994 to 2004 on Guana Island, British Virgin Islands, and recorded bird sightings to develop a more complete inventory of the island's resident and migrant species. During our study, we recorded four new species for the British Virgin Islands: Magnolia Warbler (Dendroica magnolia; 1996), Golden-winged Warbler (Vermivora chrysoptera; 1997), Swainson's Thrush (Catharus ustulatus; 2000), and Red-necked Phalarope (Phalaropus lobatus; 2004). Blackpoll Warbler (Dendroica striata) was the most frequently captured Neotropical migrant landbird, despite only being first detected in the region in 1989. Captures and detections of other Neotropical migrant landbirds suggest that many species may be more common in the region than previously believed, or, as speculated by other researchers, that migrant routes may be shifting eastward due to habitat degradation on western Caribbean islands. We also used recapture data to establish longevity records of resident species, including Caribbean Elaenia (Elaenia martinica; ≥7 years), Bananaquit (Coereba flaveola; 7 years), Black-faced Grassquit (Tiaris bicolor; ≥9 years), and Zenaida Dove (Zenaida aurita; 5 years). Longevities of other resident species were similar to, or slightly less than, those reported elsewhere.
We studied the breeding biology of the Panamanian subspecies of the Yellow-crowned Parrot, Amazona ochrocephala panamensis, during 1997–1999 in the province of Chiriquí, Panama, to provide basic information regarding the breeding behavior and reproductive success of these parrots in their natural habitat. We recorded parrot behaviors throughout the reproductive period, monitored nest success, and characterized occupied and non-occupied tree cavities. All breeding attempts involved a male-female pair. Clutch size ranged from 2 to 4 eggs, which were incubated only by the female, beginning when the first egg was laid. Incubation averaged 25 days and the eggs hatched asynchronously. During the incubation period, females remained inside the nest for long periods of time, though they often departed from the nest area during early mornings and late afternoons, presumably to forage; during this period, males were not observed entering the nest, though they often remained nearby. During the nestling period, males contributed significantly to feeding the offspring. Pairs nested in trees that were in good or fair condition, and did not favor cavities in any one tree species. As found in many other field studies of parrots, breeding success was low. Only 10% (1997–1998) and 14% (1998–1999) of the nests survived poaching and natural predation. Because nest poaching was the primary cause of breeding failure and poses a serious threat to population viability, we also present data on poaching techniques and the local trade of nestling parrots. Overall, the pool of breeding adults is likely made up of aging individuals that are not being replaced, setting the stage for a rapid population decline.
We studied Thick-billed Parrot (Rhynchopsitta pachyrhyncha) nest-site density and social nesting behavior from 1998 to 2001 in Madera, Chihuahua, Mexico. The species formed high-density nesting clusters; 45 nesting attempts (30%) involved nesting pairs sharing nest trees, with a maximum of three nesting pairs per tree. The majority of nest trees were live or dead quaking aspens (Populus tremuloides). Clusters contained a mean of 11.5 breeding pairs (5 nests/ha). The highly social nesting behavior of Thick-billed Parrots may have important implications for management and conservation of their breeding habitat.
Nazca Booby (Sula granti) broods in the Galapagos Islands showed 0% extra-pair fertilization, based on multilocus band-sharing values. The 95% CI of this estimate for all chicks was 0–0.098, and for all broods it was 0–0.139. These are the first data on extra-pair paternity to be reported for a member of the family Sulidae.
Nest-site selection behaviors have rarely been described for songbirds. Furthermore, male involvement in nest-site selection is generally assumed to be minimal among most species, especially those predominantly exhibiting female nest building. This assumption has held true for the federally endangered Golden-cheeked Warbler (Dendroica chrysoparia), a breeding resident of central Texas. We observed Golden-cheeked Warbler males and females searching for nest sites together on three separate occasions, 2001– 2003. Although rare, such observations add to our knowledge of the life history of songbirds.
During the 2003–2004 and 2004– 2005 nesting seasons, we studied parental behavior at seven Magellanic Woodpecker (Campephilus magellanicus) nests in Argentine Patagonia. Food items delivered to nestlings included wood-boring larvae (57.6%), arachnids (13.1%), and vertebrates (4.6%, including a bat, lizards, and avian eggs and nestlings). Less frequent items were adult insects, caterpillars, and pupae. Small, unidentified invertebrate prey made up 19.8% of the observations. Males delivered most of the large prey (wood-boring larvae and vertebrates; 61.7%), while females brought most of the small prey (arachnids and small, unidentified invertebrates; 79.6%), suggesting differences in foraging strategies between sexes. This is the first published account of Magellanic Woodpeckers provisioning nestlings with vertebrates. The frequency of Magellanic Woodpecker predation on vertebrates outside of the breeding seasons is unknown.
We present the first report of reverse mounting in the Bearded Vulture (Gypaetus barbatus). The reverse mounting, which occurred in the Pyrenees of northeastern Spain, took place between the female and the alpha male in a polyandrous trio. The function of reverse mountings is discussed in relation to the previously reported high frequency of male-male mountings in this raptor species.
The vocalizations of galliform species are typically sexually dimorphic in that only the males crow. I observed crowing by a female California Quail (Callipepla californica), a galliform species that ranges along the Pacific coast of North America. I recorded the female crowing during a period of the breeding season when many other females were paired. The female's crow was similar in frequency to a typical male crow, though it was slightly shorter in duration. I discuss possible mechanisms and conditions that could result in female crowing.
While evaluating reproductive parameters in Rio Grande Wild Turkeys (Meleagris gallopavo intermedia) in the Edwards Plateau region of Texas, we observed a case of poult adoption and abandonment of an active nest. In wild turkeys, adoption of poults has been described previously, but during our observation the hen also abandoned her nest at a late stage of incubation. Most research discussing adoption in gallinaceous birds has focused on brood abandonment after hatch. Although poult adoption in conjunction with nest abandonment is probably rare, our observations indicate that it can occur, at least in Rio Grande Wild Turkeys.
We describe predation of a Green-crowned Brilliant (Heliodoxa jacula) by a Blue-crowned Motmot (Momotus momota) in southern Costa Rica. We did not witness the capture of the hummingbird, but did observe the motmot swallow the prey whole. Although the diet of the Blue-crowned Motmot is highly variable and can include birds, this is the first report of predation on an adult hummingbird.