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Eggs that are abnormally small are called runt eggs, and they occur in clutches across a wide variety of bird species. We surveyed waterfowl researchers to determine the natural frequency of occurrence of runt eggs in wild nesting ducks, geese, and swans. Of 551,632 eggs examined, 215 were runts, yielding a frequency of 0.039%. They occurred at about four times this frequency (0.156% in 21,832 eggs) in a museum oological collection. Runt eggs were not significantly more common within any taxonomic group among wild waterfowl, and their occurrence was not related to the mean clutch size of a species or to whether waterfowl exhibited regular conspecific nest parasitism. Cavity-nesting waterfowl had lower incidences of runt eggs than ground-nesting species. Our results represent the largest examination of the occurrence of this size anomaly in eggs of wild birds, and are consistent with the hypothesis that runt eggs result from a temporary impairment of the reproductive tract. This may explain why runt eggs occur in all bird species studied.
I examined the size of small mammal prey taken by White-tailed Kites (Elanus leucurus) in the Americas from data obtained in the literature and unpublished material from southern Brazil. Mean weight of adult small mammal prey in the kite's diet ranged between 19.5 and 64.2 g. Mammalian prey taken weighed between 2 and 53% of the kite's body weight. Although the White-tailed Kite is a small mammal specialist, in relation to the size of prey taken, this raptor can be considered a generalist hunter.
Stopover areas are vital for the successful migration of many species of shorebirds, as they, in part, allow individuals to deposit large quantities of fat needed to fuel their northward and southward journeys. While much research has focused on bird migration, few studies closely examine the environmental characteristics of specific stopover areas. For our study, we conducted prey availability surveys and documented shorebird habitat use during northward summer migration for three historically important stopover areas along the Connecticut Long Island Sound coastline in 2000. Coastal Connecticut provides important habitat not only for shorebirds migrating from northern Canada to South America, but also for resident breeding shorebirds (e.g., oystercatchers, plovers, and sandpipers). Our prey availability surveys indicate that all three stopover sites were characterized by some combination of polychaete worms, crustaceans, and mollusks. Polychaete worms of the family Neredidae were the most common prey item at two of the three sites. In addition, the site frequented by the greatest densities of shorebirds also had the greatest density of nereid worms and the greatest diversity of invertebrates. In terms of habitat use, our results indicate that foraging densities tended to be highest on intertidal habitats that were sheltered from coastal wave action and where densities of benthic (burrowing) and epifaunal (surface-dwelling) prey tended to be high. However, some shorebird species, including one breeding resident, the American Oystercatcher (Haematopus palliatus) and one migrant, the Ruddy Turnstone (Arenaria interpres), both of special management concern, favored foraging on beach-front habitats. In contrast to foraging habitat preferences, shorebirds roosting at high tidal phases showed strong preferences for beach habitats fronting the Long Island Sound. The use of beach-front habitats for both foraging and roosting poses a challenging situation for beach managers.
Nest-dwelling parasites are known to have detrimental consequences for many birds, and thus it may be desirable for management practices to remove these parasites. In addition, manipulation of parasite loads is often necessary for studying host-parasite evolution. While there are various methods that are effective at reducing parasite loads in nests, many of them have shortcomings because they require specialized equipment, are time consuming, or involve toxic substances that may be dangerous to both birds and researchers. I evaluated the efficacy of simple-to-use, non-toxic diatomaceous earth (DE) at reducing ectoparasite loads in nests of Tree Swallows (Tachycineta bicolor) over two field seasons. Diatomaceous earth significantly reduced population sizes of bird fleas (Ceratophyllus idius) and various species of blow flies (Protocalliphora spp.) in both years. Diatomaceous earth appeared to be more effective at reducing the numbers of fleas, possibly because fleas have smaller body size and so are more easily desiccated by the abrasive action of DE. Although DE was effective against both fleas and blow flies, it did not completely rid nests of either type of parasite.
Lagopus leucurus saxatilis, a subspecies of White-tailed Ptarmigan endemic to Vancouver Island, is listed as vulnerable by the British Columbia Conservation Data Centre, but little is known about its population status or trends. The only previous journal paper concerning this subspecies was published in 1939. Data on distribution, gathered using historical records and public survey (166 records) in combination with our field studies, indicated that this ptarmigan subspecies currently inhabits most, if not all, available habitat on Vancouver Island, and the range has not contracted over the past 25 yr.
I assessed nest-site characteristics of two cavity-excavating species, the Acorn Woodpecker (Melanerpes formicivorus) and Northern Flicker (Colaptes auratus), and two secondary cavity-nesting species, the Flammulated Owl (Otus flammeolus) and Western Bluebird (Sialia mexicana). These species were common in mixed coniferous-deciduous forests within my New Mexico study areas. I predicted that nests of the woodpecker species could be differentiated by cavity size and that the excavator species of nest cavities used by secondary cavity-nesters could be predicted with this model. Flickers excavated nest cavities that were larger and surrounded by denser forest than Acorn Woodpecker nests, and three characteristics of cavity size alone differentiated 84% of woodpecker nest sites. Acorn Woodpeckers nested in live Gambel oak (Quercus gambelii) most frequently and Northern Flickers in ponderosa pine (Pinus ponderosa) snags, and these differences may be attributed to the excavation ability of each species. The secondary cavity-nesters did not show a preference for trees of different condition (i.e., alive or dead). A multivariate regression model predicted that Flammulated Owls and Western Bluebirds should nest in cavities excavated by both woodpeckers, but owls showed a preference for Northern Flicker cavities and bluebirds for Acorn Woodpecker cavities. Owl nest cavities were larger and surrounded by denser forest than bluebird nest cavities, similar to the differences observed between woodpecker nest sites. I suggest that these differences can be partially attributed to body size as well as ecological similarities between the primary and secondary cavity-nesters. Western Bluebirds showed a preference for cavities facing south and east, and this may have been due to thermal advantages.
We studied the prey base, foraging behavior, and energetics of Snowy Egrets (Egretta thula) and Great Egrets (Ardea alba) in the Arthur Kill region of New York–New Jersey during the 2002 breeding season. Prey density increased 10-fold, from 0.12 to 12.0 items/m2 between May and August, with the greatest increase occurring in young-of-the-year mummichogs (Fundulus heteroclitus). Despite increases in prey biomass, birds had higher foraging success in May (47%) than in August (28%). This decrease may have been the result of predator confusion and/or foraging inexperience by newly fledged birds. As a result, birds experienced a net gain of 227.0 W in May and 52.5 W in August. Striking at prey was more costly for Great Egrets (4.15 J, 4.88 W/strike) than for Snowy Egrets (0.34 J, 0.30 W/strike). Pursuing prey by walking and running was relatively inexpensive; Snowy Egrets and Great Egrets spent 0.04 W and 0.06 W, respectively. Snowy Egrets averaged 0.13 m/s while foraging, while Great Egrets moved at a third of that speed (0.04 m/s), supporting the notion that Snowy Egrets could disturb prey that then become more accessible to Great Egrets. Snowy Egrets moved faster in August than in May, but Great Egrets maintained or slowed their foraging speed. Sixty-six percent of the variation in Great Egret energy intake was accounted for by four variables (date, steps, obtuse turns, and attacks from other birds), while 39% of the variation in Snowy Egret energy intake was accounted for by three variables (date, tide, and obtuse turns). Snowy Egrets may sample more foraging locations than Great Egrets, the latter species choosing locations where other birds have already found prey.
The blood stress protein response can be used to evaluate physiological or environmental stress in individuals and populations. It is important that sample conservation and transport are correct to avoid confounding effects on protein analyses. We show that Great Tit (Parus major) blood samples can be centrifuged and frozen any time within eight hours of collection, as during this period there are no significant changes in stress protein HSP70 and HSP60 levels. These findings simplify future research on the stress protein response in wild birds because samples can be safely kept in a cool box for a relatively long time.
To investigate the potential expression of territorial behavior of Burrowing Owls (Athene cunicularia) in southwestern Idaho, we used a playback protocol to determine if Burrowing Owls actively defended their nesting site from conspecifics, and if so, to determine the extent of their territorial boundaries. Eighty-eight percent of male Burrowing Owls responded to the broadcast of conspecific primary calls. All responsive males uttered primary calls, and many owls approached the broadcast speaker, exhibited white-and-tall stances, and bobbed. Females responded less frequently than males, but one female whose mate was presumably dead exhibited an intense response to the playback trial. There were no differences in number of primary calls uttered, number of white-and-tall stances performed, or number of bobs of focal males among three broadcast distances: (0 m, 50 m, and 100 m) from the active nest burrows. However, focal owls approached the broadcast speaker more closely at broadcast distances of 0 m and 50 m than at 100 m. These findings suggest that owls actively defended their nesting site from conspecifics and that they defended an area larger than that immediately surrounding the nest burrow. Although they continued to vocalize at distances of at least 100 m, they did not physically approach an intruder at this distance as frequently as at shorter distances. Therefore, Burrowing Owls appear to defend a territory that encompasses some, but not all, of the foraging area used during nesting.
Food supplementation can be an important experimental technique in studies of avian reproductive ecology, energetics, and parental care. We developed a method of food supplementation suitable for ground-foraging insectivorous passerines and tested it on Ovenbird (Seiurus aurocapilla) and Wood Thrushes (Hylocichla mustelina). We provided mealworms at feeding stations made of plastic transparency film covered with a thin layer of green moss. Feeding stations were placed on the ground or on logs or boulders in the vicinity of nests. Direct and indirect evidence suggested that 92% of breeding Ovenbirds and 79% of breeding Wood Thrushes used supplemental food. The impact of non-target consumers was not significant: they were observed eating mealworms at approximately one-third of our food-supplemented nests. However, diurnal non-target consumers were only detected on a single occasion for each species, and nocturnal consumers fed on small amounts of mealworms left after daytime feeding experiments. This method proved very effective for Ovenbirds and Wood Thrushes, and it may be applicable to other ground-foraging insectivorous passerines.
From 1994–1996 we investigated effects of Brown-headed Cowbird (Molothrus ater) parasitism on Black-throated Sparrow (Amphispiza bilineata) nesting success in the Verde Valley of central Arizona. Of 56 Black-throated Sparrow nests, 52% were parasitized. Black-throated Sparrows appear to respond to natural parasitism by accepting the cowbird egg, deserting the nest, or burying the cowbird egg. Removal and damage of host eggs by female cowbirds effectively reduced clutch size from an average of 3.4 to 1.9 eggs. Because of this reduced clutch size, Black-throated Sparrow reproductive success was significantly lower in parasitized nests (0.2 young fledged/ nest) as compared to nonparasitized nests (1.6 young fledged/nest). When comparing cowbird parasitism between two habitat types, we found significantly higher parasitism frequencies in crucifixion-thorn (Canotia holacantha) versus creosote-bush (Larrea divaricata) habitat. We argue that this difference in parasitism is due to the greater number of tall perches (e.g., shrubs >4 m) available in crucifixion-thorn habitat, providing vantage points for female cowbirds to better find Black-throated Sparrow nests.