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Entanglement and mortality of Palila (Loxioides bailleui), an endangered Hawaiian honeycreeper, occurred when birds were radio-tagged with transmitters equipped with a long, limp, solder-tipped antenna. Birds were found suspended in trees by their transmitter antenna on eight occasions. Although these birds eventually freed themselves or were freed by us, at least one bird died afterwards. For radio telemetry studies of small passerine species we recommend avoiding transmitters equipped with an antenna that is bulbous at the tip, >16 cm in length, limp, and shiny.
Obligate brood parasitic birds may improve their reproductive success if they cause the failure of nests that they had not parasitized, because many host species renest soon after failed nesting attempts and replacement nests may be available for future parasitism. Presently there is conflicting evidence on a key correlate of this parasite-predator hypothesis, namely whether parasitized nests survive at higher rates than non-parasitized nests. Using data collected by volunteers for the Cornell Nest Record Program and by examining nest survival in a northeastern population of Song Sparrows (Melospiza melodia) where parasitism by Brown-headed Cowbirds (Molothrus ater) was common, I found that parasitized sparrow nests in the nestcard sample were more likely to survive at the early stages of the nesting cycle than non-parasitized nests. In addition, while overall reproductive success in the focal study population did not differ significantly between parasitized and non-parasitized hosts, non-parasitized nests were significantly more likely to fail due to predation prior to hatching than non-parasitized nests. Whether the correlation between the presence of parasitic eggs and decreased predation occurs due to cowbirds causing the failure of non-parasitized nests or, alternatively, preference for safe host nests and/or the protection of parasitized nests by parasitic females, will require direct observations and experimental manipulations.
We trapped Sharp-shinned Hawks (Accipiter striatus) during fall migration, using House Sparrows (Passer domesticus), European Starlings (Sturnus vulgaris), and Ringed Turtle Doves (Streptopelia risoria) as lures. Adults and males initiated attacks on sparrows more frequently than juveniles and females. Adult females initiated attacks on starlings and doves more often than adult males, but there was no such difference between the sexes in juveniles. Females actually struck all three species of lure more frequently than males, and juvenile females struck lures more frequently than adult females. There was no age difference in the incidence of strikes by males. Larger (longer-winged) juvenile males and females attacked starlings more often than smaller juveniles, but there were no size differences in strikes on prey in any age and sex group of hawks, suggesting that sexual dimorphism in size is not a result of selection for differences in prey size. Females struck disproportionately larger lures than males, presumably because they are less efficient at capturing smaller prey. Juveniles attacked doves as frequently as starlings, and there was little age difference in the incidence of strikes, suggesting that inexperience in judging the size of prey is an inadequate explanation for the many attacks that fail to result in strikes.
Nest building by House Wrens (Troglodytes aedon) has been described as occurring in two stages. Males arrive on territories before females and begin the first stage by building a stick foundation in a suitable cavity. In the second stage, females build a soft cup-like structure into the stick base. However, descriptive data from over 300 h of observation of House Wren nest construction in New York demonstrate that female House Wrens actually carry significantly more sticks to nest cavities than do males. Because females perform a behavior previously attributed to males, these data refocus the question of the function of sticks in House Wren nests.
Survey stations to measure Marbled Murrelet (Brachyramphus marmoratus) activity in low-elevation forest are often preferentially placed on stream channels because they provide wide visibility and the greatest chances of visually detecting birds and thus behaviors possibly associated with nesting. Detections of birds flying along stream channels to access nesting habitat farther inland will inflate estimates of activity associated with the adjacent forest. We compared numbers and types of murrelet detections between 12 paired stations within 100 m of each other on streambeds and in similar habitat in adjacent forest during 8 Jun–10 Jul. 1997 in Clayoquot Sound, British Columbia. Circling and below-canopy flight, thought to be indicative of nesting, were observed at all streambed survey stations and at less than half of paired forest stations. Numbers of such “occupied” detections were six times greater at streambed than forest sites. Size of opening at survey stations accounted for much of the difference in detection rates between forest and streambed stations, but numbers of total, visual, and occupied detections, specifically those of circling birds, were lower at forest than streambed stations even after the effect of opening size had been considered. Correlations between opening size and numbers of detections at streambed but not at forest locations, also indicated that differences between streambed and forest stations were not solely a function of opening size. Observations at one pair of stations where murrelets were using a flight corridor over the forest station indicated that a corridor effect may not be confined to streambed locations. Results indicated that placement of survey stations on stream channels is appropriate if the goal is to determine murrelet presence or the occurrence of occupied detections in an area. However, if a comparison of murrelet activity between habitat types is the objective, then forest stations with comparable opening sizes may be needed to provide unbiased results.
Loss of wetlands to agriculture and development negatively impacts waterfowl. Greentree reservoirs are forested tracts that are purposefully flooded to increase hunting opportunities for sportsman and to provide shelter for waterfowl such as Mallards (Anas platyrhynchos). These human-made wetlands can also make natural foods such as acorns and invertebrates available to Mallards. Food habits analysis conducted in 1959 indicated acorns composed 24% of the volume of diets of Mallards collected from a variety of habitats including agricultural fields, naturally flooded bottomland forests, and greentree reservoirs in Arkansas. However, changes that may have occurred in food use by Mallards in bottomland hardwood habitats in Arkansas since last examined are unclear. We examined foods used by Mallards in greentree reservoirs from November 1990 to February 1991 in southeastern Arkansas. Seventeen species of plants and 21 families/orders of animals occurred in the diet of Mallards. Mallards consumed 65% plant matter, primarily seeds of narrowleaf foresteria (Foresteria angustifolia), Nuttall oak (Quercus nuttallii), Pennsylvania smartweed (Polygonum pensylvanicum), and rice (Oryza sativa). Invertebrate taxa, constituting 6% or more of the sample by both volume and mass, included the orders Coleoptera, Diptera, and Isopoda. Diets of Mallards present in greentree reservoirs in our study indicate Mallards still use natural foods, though agricultural seeds were in close proximity to natural foods.
We describe sexual dichromatism in the plumage of juvenile Brown-headed Cowbirds (Molothrus ater obscurus) collected in Ventura County, California in 1991. The dichromatism was based on two colorimetric features. The first was the contrast between the greater underwing coverts and the remiges, with males having darker coverts, and therefore greater contrast between their underwing coverts and remiges. The second was the color and extent of pale feather edges on the underside of the distal portion of the carpometacarpal joint, with males having wider, slightly darker feather edging. Five observers were used to test the reliability of these characters in a sample of museum wings from cowbirds of known sex. They were 88–94% accurate at determining the sex of 33 juvenile cowbirds (17 males, 16 females) using these two colorimetric characters. This technique was slightly more reliable than wing chord (84.8% accurate) and tarsometatarsus (also 84.8% accurate) measurements in differentiating the sex of our sample individuals.
For six years we examined the reproductive biology of Common Moorhens (Gallinula chloropus) nesting in an impounded cattail (Typha spp.) marsh in South Carolina, USA. The egg-laying period averaged 78 days. Most (52%) of 82 nests were started in May. The moorhens appeared to be single-brooded. Mean clutch size was 6.55, the same as that reported from field studies in Britain, but significantly smaller than that calculated from South Carolina oology data. Common Moorhens occasionally built their nests on those of Boat-tailed Grackles (Quiscalus major), and in one instance a moorhen laid an egg in a grackle nest. About 18% of moorhen nests were parasitized by other moorhens, which usually added one or two eggs. Over four years, we estimated that 68% of 54 moorhen nests produced at least one fledgling, an estimate close to that reported by researchers in Britain. Most nest mortality probably was caused by snakes, because large mammals and avian predators rarely were noted in the study area. The relatively high reproductive success of Common Moorhens appears to be related to the species' use of extensive stands of cattails growing in a sheltered area with controlled water levels. The moorhens also may benefit from the presence of American alligators (Alligator mississippiensis), which discourage large mammals, and from Boat-tailed Grackles, which mob avian predators.
Data collected in a 40-ha reedbed of southern France were used to compare the efficiency and limitation of mist-net and point-count techniques in estimating the composition and structure of a bird assemblage dominated by the Bearded Tit (Panurus biarmicus), the Moustached Warbler (Acrocephalus melanopogon), and the Reed Warbler (Acrocephalus scirpaceus). Null model analyses were used to determine the effect of spatial variability on estimates of species richness and relative abundance with the two sampling techniques. A 50-m net line operated during 5 h or two 50-m radius point counts of 10 min conducted 6 wk apart provided a similar estimation of species composition and relative abundance. While a sampling effort of 10 net lines or 13 point counts would permit the detection of a 25% difference in the relative abundance of most species (whether over time or among sites), the analyses on community structure suggest that 26 net lines or 13 point counts are necessary to sample adequately the structure of the bird assemblage (proportion of individuals from each species) in the 40-ha reedbed. This minimum sampling effort, however, is strongly influenced by the variance in number of individuals sampled, which differed among bird species. For instance, removal of highly mobile species such as the Bearded Tit, reduced by half the minimum sampling effort. To provide a reliable estimate of species richness and relative abundance, point counts must be based on both visual and auditory cues (30% of the birds sampled were silent), and be carried out at different periods to cover the early breeding season of any abundant species. While point counts are less demanding in the field, manipulation of netted birds permits the documentation of various aspects of their biology, which compensated for the increased time and effort needed.
We examined nest sites of Red-tailed Tropicbirds (Phaethon rubricauda) on Rose Island of the Rose Atoll National Wildlife Refuge, American Samoa, to determine habitat features important for nest-site selection of this species. We quantified habitat characteristics at 27 nest sites and at 27 random sites during September 1991. All nests were located under beach heliotrope (Messerschmidia argentea) shrubs or pisonia (Pisonia grandis) trees. Nest sites were placed farther under the nest shrub, had more stems in the nest space, and greater percent shade cover than random sites. Nest sites averaged 24.9 m from their nearest neighbor, ≥20 m greater than has been reported elsewhere for this colonial species. We suggest that an overpopulation of Polynesian rats (Rattus exelans) may have influenced nest-site selection by Red-tailed Tropicbirds on Rose Island.
From 1995–1998 we studied the breeding ecology of Yellow Rails (Coturnicops noveboracensis) in southcentral Oregon. We found 34 Yellow Rail nests; 26 had either hatched or failed when found, and eight were active (seven of these hatched). These nests were the first found in Oregon in 65 years and further substantiate recent findings that a small, disjunct population of breeding Yellow Rails persists west of the Rocky Mountains. Nests hatched between 8 June and 9 August with a mean clutch size of eight eggs (SD = 1.1). We measured vegetation in 1-m2 plots around each nest. Total live vegetation cover averaged 48.7% ± 10.9, and Carex simulata dominated at 26.1% ± 12.3. Other vegetative species characterizing Yellow Rail nest sites were: C. utriculata, C. vesicaria, Eleocharis palustris, Juncus balticus, and J. nevadensis. Dead or senescent vegetation from the previous year provided 49.7% cover. Water depths at active nests were 0.5–5.0 cm. A canopy of senescent vegetation or a dome of live vegetation was present above every nest, often concealing the nests from view.
Despite the Hermit Thrush's wide distribution and exceptional singing ability, its vocal behavior is poorly known. In recorded samples from Arizona and New England, we show that males have repertoires of 6 to 12 discrete song types. Those types can be presented in highly regular sequences, but the order varies among males, perhaps depending on context or motivation. Arizona and New England songs differed in several frequency and temporal features, such as the duration and frequency of the introductory whistle and the remainder of the song, suggesting regional differences in Hermit Thrush songs. How these geographic differences in song are influenced by song development and dispersal should be a focus of future research.
Community-level indices of reproductive success are useful for measuring or monitoring demographic effects of habitat alteration on birds. We present a time-efficient method to estimate the relative reproductive activity of the forest songbird community. A recording of mobbing calls of Black-capped Chickadees (Poecile atricapillus) was broadcast at pre-selected stations during the breeding season. These calls attracted individuals of many bird species present in the vicinity, allowing visual detection of reproductive activity (e.g., adults carrying food or presumed pairs). In mature deciduous forests of northern New Brunswick, 50 bird species responded to the playbacks. Playbacks significantly increased the probability of visual observations of birds compared to silent observations conducted before broadcasting mobbing calls. In coniferous forests of central Québec, playbacks attracted 24 species and also provided a significantly greater opportunity to make visual observations of individual birds. In New Brunswick, mobbing playbacks facilitated more observations of reproductive evidence relative to point counts. Observation periods were brief and a 306-ha plot (1.75 × 1.75 km, 64 points spaced 250 m apart) could be surveyed by foot in less than 32 observer-hours. The proportion of individuals of a given species showing evidence of reproductive activity was used as an index of reproductive success. Black-throated Blue Warblers (Dendroica caerulescens) and Ovenbirds (Seiurus aurocapillus) had a reproductive index consistent with their true nesting success as derived from intensive nest monitoring on the same plots.
Researchers often use nasal saddles or discs to identify individuals in studies of waterfowl ecology, but previous studies showed that these markers may have detrimental effects on reproductive behavior and success of Ruddy Ducks (Oxyura jamaicensis). To our knowledge, a non-intrusive, external marker that is easy to observe does not exist for breeding Ruddy Ducks. We evaluated effects of a modified nasal marker on behavior of female Ruddy Ducks during pre-laying, laying, and brood rearing. There was no evidence that nasal markers had an adverse influence on nesting patterns of pre-laying and laying females. During brood rearing, however, nasal-marked individuals spent more time scratching their bills and less time alert than unmarked controls. Although bill scratching was more frequent, nasal markers did not appear to influence overall reproductive behavior during nesting and or brood rearing, but we do not know whether reduced vigilance behavior affected survival of young during brood rearing. This nasal marker is a relatively non-intrusive and visible alternative for studying the short-term reproductive ecology of female Ruddy Ducks and possibly other Oxyurinae or anatids not commonly studied because of unique nasal morphologies (i.e., partially divided nasal septa and small nasal openings) which make them difficult to mark. Additionally, this marker may have application for species wintering in colder regions where nasal markers are at risk of icing. Nevertheless, we strongly suggest that researchers evaluate possible effects of these markers as part and parcel of future studies.
Demographic data are presented from an 8-yr study of a marked population of the Dusky Antbird (Cercomacra tyrannina), a sedentary neotropical passerine with year-long territories and pairbonds. Dusky Antbirds had an annual survival rate of 82%, and the survivorship curve was linear. Sexes did not differ in survival. The probability of reproducing successfully, based on the number of pairs accompanied by independent young the following dry season, was only 8% and no territory produced more than one successful nest, if any. In one year (1997) reproduction was significantly better (25%) than the other years, perhaps associated with lowered predation during an extremely dry wet season. We suggest that for Dusky Antbirds, a species with no extra-pair mating behavior, a long adult lifespan appears to be the primary means to increase lifetime reproductive success.
We analyzed 2426 records of recoveries of banded House Wrens (Troglodytes aedon) to identify wintering sites of individuals coming from different parts of this species' broad North American breeding range. Records suggest that most birds breeding approximately east of the Appalachian Mountains (n = 6) winter in the far southeastern United States, especially Florida. In contrast, birds breeding west of the Appalachian Mountains (n = 23) into the eastern Great Plains may winter anywhere from South Carolina and Florida west into Texas. It also appears that individuals from the same breeding populations winter in different sites. The few recoveries (n = 4) of birds from breeding sites on the western Great Plains indicate that at least some individuals from this region travel not due south but rather southeast during migration and winter in the eastern half of the southern U.S. No long-distance recoveries have been made of birds from breeding in or west of the Rocky Mountains.
We report on the use of alternate drumming sites by male Ruffed Grouse (Bonasa umbellus) during 1976–1997 within activity centers in a managed and an unmanaged forest in central Pennsylvania. Density of drumming males ranged from 1.6–12.5 males/km2 in the managed forest and from 1.7–7.6 males/km2 in the unmanaged forest. The proportion of males that used alternate drumming sites within activity centers ranged from 2% to 44% and was positively correlated with drumming male density. The number of alternate sites used within activity centers also increased with density; males used up to five alternate sites during a high-density year. Distances between alternate drumming sites and primary sites were not correlated with density but were greater on the unmanaged forest. The spatial orientation of multiple alternate sites relative to the primary site within each activity center suggested the use of alternate sites was a directional response. The actual direction of the response was not consistent among activity centers in the study area indicating it was not a result of prevailing abiotic factors such as wind, climate, or geomorphology. Similarly, the placement of alternate drumming sites was not directed toward nearest neighboring males. We discuss potential causes of the behavior, its adaptive significance, and implications to commonly used survey techniques for Ruffed Grouse populations.
We studied the effects of brood parasitism by Brown-headed Cowbirds (Molothrus ater) and predators on the reproductive biology of Yellow Warblers (Dendroica petechia) in La Plata County, Colorado, 1992–1996. Overall, 36.4% of Yellow Warbler nests (n = 66) were parasitized by Brown-headed Cowbirds. Although parasitized and nonparasitized nests were equally likely to fledge at least one warbler, in nonparasitized nests, warblers had larger clutches, hatched more young, and tended to fledge more young. Frequency of parasitism was not influenced by nest height and, on a weekly basis, was not correlated with number of warbler nests initiated. Overall, 39.1% of Yellow Warbler nests were lost to predators, but complete predation was not affected by nest height. On a weekly basis, percent complete predation of warbler nests increased with number of active nests. No significant relationship existed between frequency of complete predation and frequency of parasitism in Yellow Warbler nests.
From May through July 1997 and 1998, I quantified nest tree and cavity characteristics of 32 Red-breasted Sapsucker (Sphyrapicus ruber) nests in the high-elevation coastal forests of northern Vancouver Island, British Columbia. Nests were located in western white pine (Pinus monticola), hemlock (Tsuga sp.), and Douglas-fir (Pseudotsuga menziesii) snags. Nest trees were significantly taller and had a greater DBH than random snags. Nest height was positively correlated with tree height. All nests were in dead trees. The orientation of nest cavity entrances did not differ from random orientations. When choosing nest sites, Red-breasted Sapsuckers are likely balancing predation risk (decreasing at higher nest heights) and adequate nest space and insulation (greater with increasing diameter at lower nest heights).
Not accounting for collar loss when using observations of collared geese to estimate survival can result in an underestimation of the survival rates and a loss of precision. As part of a study of goose populations in the Western Canadian Arctic, we determined collar retention rates for “small” Canada Geese (mainly Branta canadensis parvipes) and Greater White-fronted Geese (Anser albifrons) that had been collared in one year and recaptured in a subsequent year. We recaptured 5.3% (133/2504) of the Canada Geese and 7.3% (373/5098) of the Greater White-fronted Geese that we collared. Annual retention rates for thin (0.08 cm), double-wrapped collars placed on Canada Geese were low for males (0.650 ± 0.052 SE) but significantly higher for females (0.826 ± 0.044). Retention rates of thick (0.16 cm), single-wrapped collars placed on Greater White-fronted Geese were high for males (0.982 ± 0.007) and even higher for females (1.000 ± 0). Retention rates did not vary with collar age, but our study probably did not continue long enough, or have large enough samples, to adequately assess this. Retention rates for Canada Goose collars depended on manufacturer, with rates as low as 0.282 ± 0.111 for males and 0.566 ± 0.114 for females for collars produced by one supplier. Our data suggest that collar loss was a significant problem for Canada Geese, but not for Greater White-fronted Geese. We recommend that other researchers using observations of collared individuals to calculate survival should also assess if estimates need to be adjusted because of collar loss.
Molting adult Steller's Eiders (Polysticta stelleri) were banded at Izembek Lagoon (1961–1998) and Nelson Lagoon (1995–1997) along the lower Alaska Peninsula to determine breeding distribution and movements. Of 52,985 Steller's Eiders banded, 347 were recovered. The overall low recovery rate may not be indicative of harvest levels but may be due to low reporting rates of bands. Almost all recoveries during summer were from Russia and recovery rates did not differ between sexes. We found no evidence that Steller's Eiders molting in specific locations were more likely to be recovered in specific geographic locations in Russia. Our recoveries suggest that Steller's Eiders molting along the Alaska Peninsula were from Russian breeding sites and from remnant breeding populations in Alaska.