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I studied the relationship of nesting habitat and the spatial distribution of Red-winged Blackbird (Agelaius phoeniceus) nests with the frequency of brood parasitism by Brown-headed Cowbirds (Molothrus ater). For all nests combined, parasitism was over 18 times more frequent in the upland habitat. It is unlikely that the low frequency of parasitism in the marshes was due solely to an increase in the incidence of aggregate nesting. For aggregated nests, parasitism was over nine times more common in upland habitat than in marshes. Because Red-winged Blackbirds are known to react to and deter cowbirds when cowbirds are detected near nests, I assessed whether the ability of Red-winged Blackbirds to detect cowbirds may contribute to the low parasitism frequency observed in marshes. Red-winged Blackbirds nesting in marshes more often reacted aggressively to female cowbird mounts 1 m from a nest than those in upland habitat, indicating that cowbirds are more likely to be molested near nests in marshes. In upland habitat the frequency of parasitism of unaggregated nests was three times greater than that of aggregated nests. These results suggest that Red-winged Blackbirds can defend their nests against cowbirds and successfully prevent brood parasitism and that the effectiveness of nest defense varies with habitat and the spatial distribution of nests. This study provides the first direct evidence that hosts can sometimes prevent parasitism.
We report the presence of the Slaty-backed Nightingale-Thrush (Catharus fuscater) in Colombia's Central Cordillera, at two sites near the cities of Pereira and Manizales, at elevations of 2400–2600 m. This species is discontinuously distributed in humid montane forest in Costa Rica and Panama, and in the Andes from Colombia to Peru. In Colombia, it was previously known only from the northern end of the western Andean range, the Santa Marta and Perijá mountains, and spottily on the eastern range of the Andes. Our record fills a gap in its distribution and suggests that it may be widely distributed in all three ranges of the Colombian Andes, although its distribution may be disjunct. At Ucumarí Regional Park near Pereira, the species was found in wet second growth and the understory of 40-yr-old forest. Patterns of recaptures suggested that some individuals were sedentary residents, while others were probably temporary residents or floaters. Reproduction was concentrated in February–June, and molting in August–December. Slaty-backed Nightingale-Thrushes at Ucumarí are olive-brown instead of slaty gray, and have brown irises, not white as in other populations. The disjunct distribution of this species probably has resulted in geographic variation and differentiation.
Ornithological studies undertaken in certain sandy soil habitats of lowland northeastern Peru uncovered a previously undescribed species of Percnostola antbird. Elements of its morphology, vocalizations, and behavior indicate that it should be considered a well-differentiated species, closely related to P. rufifrons. We present a description of the new species; an analysis of how it differs from the four previously described subspecies of P. rufifrons; and a reconsideration of species limits within P. rufifrons, employing measures of morphology, vocalizations, and behavior. Under guidelines developed previously (Isler et al. 1998, 1999), vocal differences among the four subspecies (rufifrons, subcristata, minor, and jensoni) of P. rufifrons were insufficient to support considering them distinct species. However, differences in morphology among most of the four taxa were substantial, and we look forward to genetic studies of Percnostola and related groups. The localized and highly specialized habitat preferences of the new species cause grave concern for its conservation.
RESUMEN.—Estudios ornitológicos realizados en hábitats de arena blanca de las tierras bajas del nororiente peruano permitieron el descubrimiento de una nueva especie del género Percnostola. Elementos de su morfología, vocalizaciones y comportamiento claramente diferencian esta especie, y sugieren una relación cercana a P. rufifrons. Presentamos una descripción de esta nueva especie; un análisis de cómo se diferencia esta especie de las cuatro subespecies previamente descritas de P. rufifrons; y una reconsideración de los límites específicos dentro de P. rufifrons, empleando medidas de la morfología, vocalizaciones y comportamiento. Siguiendo los lineamientos desarrollados en anteriores publicaciones (Isler et al. 1998, 1999), diferencias vocales entre las cuatro subespecies previamente descritas de P. rufifrons (rufifrons, subcristata, minor y jensoni) fueron insuficientes para considerarlas especies diferentes. Sin embargo, diferencias morfológicas entre la mayoria de estos cuatro taxones fueron substanciales, por lo que es necesario esperar futuros estudios genéticos de este complejo y de otros grupos relacionados. Las preferencias de hábitat altamente localizadas y especializadas de esta nueva especie son motivo de gran preocupación por su conservación.
Ground-nesting is usual among the about fifty species of dabbling ducks (genus Anas), but a few southern hemisphere species prefer arboreal sites. One such arboreal-nesting species, the South American Speckled Teal (Anas flavirostris flavirostris), is believed to have evolved from a ground-nesting ancestor, represented today by the closely related Green-winged Teal (A. carolinensis) of North America. We studied the breeding biology and behavior of Speckled Teal in Buenos Aires province, Argentina, in an attempt to identify adaptations associated with arboreal nesting. In this region, Speckled Teal prefer to nest in cavities in the stick nests of Monk Parakeets (Myiopsitta monachus). Inter- and intraspecific competition for cavities was intense. Parakeets remained near the nest site year round, aggressively defending occupied cavities and forcing teal to compete with one another for possession of abandoned cavities. Male Speckled Teal helped their mates to obtain and hold nest sites by defending sites against other pairs. Males also accompanied broods and assisted in parental care. Although courtship occurs year round and extrapair courtship by males is common, competition for mates and the need for male assistance in acquiring nest sites limits the opportunities for polygyny in this population. Site fidelity of nesting females was very high; 19 of 22 returned the following year. The prevalence of courtship on land and inclusion of Point display in the repertoire are interpreted as behavioral adaptations associated with arboreal nesting.
I examined enemy recognition in Field Sparrows (Spizella pusilla) using models of a brood parasite (Brown-headed Cowbird, Molothrus ater), an avian nest predator (Blue Jay, Cyanocitta cristata), and a nonthreatening control (Fox Sparrow, Passerina iliaca) during two periods of the nesting cycle: the first three days of incubation and when chicks were 2–3 d old. As predicted, Field Sparrows responded more frequently to the predator model than to the control model during both periods, and gave stronger responses to the predator model (as measured by the number of “chip” calls) during the nestling period than during incubation. Field Sparrows also gave stronger responses to the cowbird model than to the control model during incubation. However, responses to the cowbird model during incubation were not stronger than the responses during the nestling period; this result does not support the hypotheses that Field Sparrows recognize cowbirds either as brood parasites or as potential nest predators. If nests were tested during the laying stage, when they are most vulnerable to parasitism (but prone to abandonment due to disturbance), it is possible that Field Sparrows would respond most aggressively to cowbirds during that period.
We documented differences in diet composition of territorial Long-billed Curlews (Numenius americanus) feeding in different locations within the Elk River Estuary, Humboldt Bay, California. We used direct observations to measure diet because curlews often handled prey for long periods (up to 4 min), which enabled us to identify prey and to estimate size. Curlews ate mainly five benthic organisms: yellow shore crabs (Hemigrapsus oregonensis), bivalves (various species), marine worms (polychaetes), ghost shrimp (Callianassa spp.), and a burrow-dwelling fish (arrow goby, Clevelandia ios). During summer, curlews on eight territories ate different proportions of bivalves, shrimp, and worms, but similar proportions of crabs, fish, and unknown prey. The proportion of prey types captured changed slightly during fall and winter. More shrimp and fish were eaten during summer than during fall and winter; more worms were eaten during winter than during summer. Despite differences in diet across some territories and seasons, energy intake rates (kcal/h) were not significantly different, but were highly variable within territories and seasons. Curlews lost worms and shrimp to gulls and other shorebirds more than expected, but lost bivalves and crabs less than expected based on capture frequency. We suggest that possible reasons for interterritorial variation in diet are temporal and spatial variation in prey availability, phenotypic differences of curlews, competition or interference, and risk of kleptoparasitism.
On Appledore Island, Maine, American Redstarts (Setophaga ruticilla) were encountered frequently during both spring and fall migration from 1990 to 1999. Males arrived earlier than females during spring, but arrival dates of males and females did not differ significantly during fall. Also, adults arrived earlier than young birds during spring, but not during fall. Recapture of banded birds at least one day after initial capture occurred more frequently during fall than spring, although mean stopover length did not differ significantly between the two seasons. Although recaptured individuals increased in mass during stopover during both seasons, mass increases were significant only during fall. However, rates of mass increase estimated by regression of condition over time of capture indicated greater mass increases during spring. Neither recapture rates, stopover lengths, nor mass changes differed significantly between males and females or between age groups within either season. These results indicate that although many American Redstarts were encountered on Appledore Island during both spring and fall migration, birds were using the site differently during the two seasons. Spring migration was more concentrated with few observed stopovers, while fall migration was protracted with increased rates of recapture. American Redstarts may have been responding differently to this site during spring and fall migration because of the proximity to breeding grounds and distance from winter grounds as well as the location of the Atlantic Ocean, which represents an ecological barrier during fall migration.
We sought to determine annual survivorship for adult male and juvenile Florida Grasshopper Sparrows (Ammodramus savannarum floridanus), a federally endangered taxon whose range is limited to central Florida. We captured, banded, and resighted 161 birds at two study sites, Avon Park Air Force Range and Three Lakes Wildlife Management Area, from 1995–1998. For the period 1995–1998, we estimated mean adult annual male survivorship with program JOLLY to be 48.2% and 53.3% at these two sites. Because sample size of banded juveniles was small, we were unable to use the JOLLY program for this age group. Therefore, we developed a new method to determine juvenile survival that incorporated known adult annual survivorship, reproductive success, and territory densities. We estimated juvenile survivorship to be 35.1%, which was 66–73% of annual adult survivorship. This survival rate was greater than the generally assumed but undocumented 25–50% survivorship rate suggested in the literature.
We investigated the relationship between habitat and landscape characteristics and the abundance and species richness of breeding birds in 12 southern Rhode Island red maple (Acer rubrum) swamps of varying size (0.5–19.2 ha). Swamp size was the most important landscape variable explaining variation in species richness for the entire bird community and for individual habitat use groups (forest interior, interior-edge, and edge species). Richness increased log linearly with size. Increased richness appeared to be due to increased habitat heterogeneity within the swamp and at the swamp edge, not a core area effect. Bird relative abundance was not predictable from swamp size. The abundance of forest interior birds was positively related to the amount of upland forest within 1–2 km of a swamp and negatively related to the regional abundance of swamp forest; the relationships between these landscape variables and the species richness of edge-related species were just the reverse. The amount of shrub foliage 2–4 m above the ground also was a positive predictor of the abundance of forest interior birds. Variation in overall bird abundance was explained by models based on peat depth and the availability of swamp forest within 1–2 km. All four of the most common forest interior species—the Veery (Catharus fuscescens), Northern Waterthrush (Seiurus noveboracensis), Black-and-white Warbler (Mniotilta varia), and Canada Warbler (Wilsonia canadensis)—occurred in swamps as small as 1 ha. This pattern suggests that overall landscape composition (i.e., total forest availability) may be more important than swamp patch size in explaining the occurrence of these area sensitive species.
The western subspecies of the Yellow-billed Cuckoo (Coccyzus americanus occidentalis) has undergone severe population declines during recent years. The current status of this subspecies has been disputed, however, because it cannot be easily separated from C. a. americanus using morphological characteristics. We sequenced most of the cytochrome b gene in five western U.S., three eastern U.S., and two Mexican Yellow-billed Cuckoos, and one Black-billed Cuckoo (C. erythropthalmus) to determine if the subspecies could be diagnosed genotypically. The haplotypes of the eastern and western subspecies differed by four fixed base changes, suggesting that they diverged approximately 205,000–465,000 yr ago. Two of these fixed differences cause amino acid coding changes. Our findings support continued separation of the two subspecies and recognition of the western subspecies as an evolutionarily significant unit.
A pair of Planalto Woodcreepers (Dendrocolaptes platyrostris) fed young in a nest cavity 6 m up in a wooded botanic garden of an old eucalyptus grove near São Paulo, Brazil, during October 1982. The pair often visited together at first, one (likely male) raising its head feathers as noted in other species of the genus. Feedings were less frequent at midday. Songs of the southeastern moist forest D. p. platyrostris were strikingly different from inland dry forest D. p. intermedius, despite intermediate specimens where the two rather distinctly colored forms come together. There are several poorly studied forms in interior dry forests, which need much more conservation effort.
We banded a Bicknell's Thrush (Catharus bicknelli) on its Vermont breeding home range and recaptured the same bird less than six months later on its winter territory in the Dominican Republic. The encounter provides a rare link between known breeding and wintering sites for a Nearctic-Neotropical migratory passerine. This individual was documented to return to its breeding site two successive summers and probably reoccupied the same territory during the winter following its initial recapture. We believe that the small breeding and wintering range of the Bicknell's Thrush, its specialized habitat requirements, and its documented site fidelity increase the species' vulnerability to habitat loss.
Wood Thrushes (Hylocichla mustelina) typically are double brooded, and triple brooding is rare, even in the southern portions of their breeding range. We discovered one instance of triple brooding by a pair of Wood Thrushes in southern Ontario near the northern edge of their continental breeding range. Each of the three nesting attempts successfully fledged young. Females may spend only a short time (less than a week) with just-fledged broods before initiating another nest; in this circumstance, the survival of young birds from the earlier brood depends on the attentiveness of males. The rearing of three broods is an uncommon event among Wood Thrushes in our study; from 1998–2000, only one of 73 color-banded females (1.3%) with early season nesting success has been triple brooded.
We studied Chestnut-sided Warblers (Dendroica pensylvanica) to determine whether there exists any relationship between plumage coloration and reproductive success in this species. We observed that males with more extensive chestnut breast coloration initiated nests significantly earlier than males with less chestnut, and had marginally larger clutch sizes as well. However, there was no significant relationship between the number of young fledged or the condition of the young and the extent of chestnut breast coloration, nor were there any significant relationships between any of these measures of reproductive success and the extent of yellow crown coloration. The extent of chestnut coloration on the breast was significantly less for males in their first breeding season, suggesting that the relationships between the extent of breast coloration and reproductive success may reflect age specific differences in these parameters.
We examined several song properties of Indigo Buntings (Passerina cyanea) breeding in open and forested habitats. Although tree density varied significantly between the two habitats, there were no significant differences in minimum frequency, maximum frequency, dominant frequency, or note-internote duration between songs from the open and forested habitats. The only marginally significant difference detected was that more males in forested habitat had songs with at least one note characterized by rapid frequency modulation than males in open habitats. The similarity in the song properties we measured may have resulted from social song learning, or may have been due to similarity of the acoustical environment surrounding the selected singing posts within both habitats.
I investigated the perch characteristics for “type I” singing (the song type used for mate attraction) by ten territorial male Golden-winged Warblers (Vermivora chrysoptera) in a mountain wetland in North Carolina. Males selected >75% of perches in the upper quarter of canopy trees. Song perches were located in trees larger and closer to forested edges and water than expected by chance. However, not all birds displayed an affinity for water, likely reflecting the uneven distribution of water across the study site. This study suggests that Golden-winged Warblers choose perches that enhance their ability to display vocally and visually to attract a mate. It also indicates that in this mountain wetland, water is an important attribute of Golden-winged Warbler territories.
An observation of opportunistic scavenging by a female Pileated Woodpecker (Dryocopus pileatus) in Missouri is reported. The bird visited a captive wolf enclosure and tore cartilage and muscle from a large fresh beef bone and consumed it immediately. The Pileated Woodpecker vigilantly observed the resident wolves during her foraging and left the enclosure at their approach. This is thought to be the first observation of a Pileated Woodpecker scavenging meat in such a fashion.
We observed interactions between a nesting pair of Pileated Woodpeckers (Dryocopus pileatus) and what appeared to be four pairs of Wood Ducks (Aix sponsa). Wood Ducks regularly approached and attempted to enter an active Pileated Woodpecker nest cavity that contained three fully feathered young Pileated Woodpeckers. The male Pileated Woodpecker often perched on a snag near their nest cavity to guard the entrance from Wood Ducks. Female Wood Ducks attempted to enter the Pileated Woodpecker nest cavity on at least 12 occasions and typically were intercepted by the male Pileated Woodpecker before they reached the lip of the nest cavity. On two occasions the male Pileated Woodpecker entered his nest cavity and forcibly evicted female Wood Ducks that had slipped into the cavity. These incidents suggest that large cavities in snags may be in high demand by Wood Ducks during the nesting season. Our observations suggest that some Pileated Woodpeckers may be able to resist attempts by Wood Ducks to usurp nest cavities during the breeding season.