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D.C. Hahn

Publications and source records attributed to D.C. Hahn.

17 recordsLinked to original sources
USGS2009

A simplified method for extracting androgens from avian egg yolks

Female birds deposit significant amounts of steroid hormones into the yolks of their eggs. Studies have demonstrated that these hormones, particularly androgens, affect nestling growth and development. In order to measure androgen concentrations in avian egg yolks, most authors follow the extraction methods outlined by Schwabl (1993. Proc. Nat. Acad. Sci. USA 90:11446-11450). We describe a simplified method for extracting androgens from avian egg yolks. Our method, which has been validated through recovery and linearity experiments, consists of a single ethanol precipitation that produces substantially higher recoveries than those reported by Schwabl.

Zoo Biology↗
USGS2007

Comparison of immune responses of brown-headed cowbird and related blackbirds to West Nile and other mosquito-borne encephalitis viruses

The rapid geographic spread of West Nile virus (family Flaviviridae , genus Flavivirus , WNV) across the United States has stimulated interest in comparative host infection studies to delineate competent avian hosts critical for viral amplification. We compared the host competence of four taxonomically related blackbird species (Icteridae) after experimental infection with WNV and with two endemic, mosquito-borne encephalitis viruses, western equine encephalomyelitis virus (family Togaviridae , genus Alphavirus , WEEV), and St, Louis encephalitis virus (family Flaviviridae , genus Flavivirus , SLEV). We predicted differences in disease resistance among the blackbird species based on differences in life history, because they differ in geographic range and life history traits that include mating and breeding systems. Differences were observed among the response of these hosts to all three viruses, Red-winged Blackbirds were more susceptible to SLEV than Brewer's Blackbirds, whereas Brewer's Blackbirds were more susceptible to WEEV than Red-winged Blackbirds. In response to WNV infection, cowbirds showed the lowest mean viremias, cleared their infections faster, and showed lower antibody levels than concurrently infected species. Brown-headed Cowbirds also exhibited significantly lower viremia responses after infection with SLEV and WEEV as well as coinfection with WEEV and WNV than concurrently infected icterids. We concluded that cowbirds may be more resistant to infection to both native and introduced viruses because they experience heightened exposure to a variety of pathogens of parenting birds during the course of their parasitic life style.

Journal of Wildlife Diseases↗
USGS2006

Passive West Nile virus antibody transfer from maternal Eastern Screech-Owls (Megascops asio) to progeny

Transovarial antibody transfer in owls has not been demonstrated for West Nile virus (WNV). We sampled chicks from captive adult WNV-antibody-positive Eastern Screech-Owls (Megascops asio) to evaluate the prevalence of transovarial maternal antibody transfer, as well as titers and duration of maternal antibodies. Twenty-four owlets aged 1 to 27 days old circulated detectable antibodies with neutralizing antibody titers ranging from 20 to 1600 (median 1:40). Demonstrating that WNV antibodies are passively transferred transovarially is important for accurate interpretation of serologic data from young birds.

Avian Diseases↗
USGS2006

Parasitic Cowbirds have increased immunity to West Nile and other mosquitoborne encephalitis viruses

The rapid geographic spread of West Nile Virus [WNV, Flaviviridae, Flavivirus] across the United States has stimulated interest in comparative host infection studies of avian species to delineate competent reservoir hosts critical for viral amplification. Striking taxonomic differences in avian susceptibility have been noted, offering the opportunity to strategically select species on the basis of life history traits to examine aspects of pathogen virulence or host immunity. We hypothesized that avian brood parasites would show increased resistance to pathogens compared to related taxa, because they have been exposed in their evolutionary history to a wide array of infectious organisms from their different parenting species. The Brown-headed Cowbird (Molothrus ater) is a generalist brood parasite that parasitizes 200+ North American species. Elevated exposure to other species? parasites may have created an unusual degree of pathogen resistance. We compared the relative susceptibility of adult cowbirds to three closely-related non-parasitic species, Red-winged blackbirds, Tricolored blackbirds and Brewer?s blackbirds, to invading NY99 strain of WNV that is highly virulent for many passeriform birds. Previously we had experimentally infected these species with two North American mosquitoborne encephalitis viruses, western equine encephalomyelitis virus [WEEV, Togaviridae, Alphavirus] and St. Louis encephalitis virus [SLEV, Flaviviridae, Flavivirus]. Our results showed that cowbirds exhibited significantly lower viremia responses against all three viruses as well as after co-infection with both WEEV and WNV than did the three related, non-parasitic species. These data supported our hypothesis and indicated that cowbirds were more resistant to infection to both native and introduced viruses.

Book chapter↗
USGS2005

Auditory brainstem responses in the Eastern Screech Owl: An estimate of auditory thresholds

The auditory brainstem response (ABR), a measure of neural synchrony, was used to estimate auditory sensitivity in the eastern screech owl (Megascops asio). The typical screech owl ABR waveform showed two to three prominent peaks occurring within 5 ms of stimulus onset. As sound pressure levels increased, the ABR peak amplitude increased and latency decreased. With an increasing stimulus presentation rate, ABR peak amplitude decreased and latency increased. Generally, changes in the ABR waveform to stimulus intensity and repetition rate are consistent with the pattern found in several avian families. The ABR audiogram shows that screech owls hear best between 1.5 and 6.4 kHz with the most acute sensitivity between 4?5.7 kHz. The shape of the average screech owl ABR audiogram is similar to the shape of the behaviorally measured audiogram of the barn owl, except at the highest frequencies. Our data also show differences in overall auditory sensitivity between the color morphs of screech owls.

Journal of the Acoustical Society of America↗
USGS2002

Parasitism at the landscape scale: Cowbirds prefer forests

Landscape-scale examination of parasitism patterns of Brown-headed Cowbirds ( Molothrus ater ) revealed heterogeneous parasitism rates across the mosaic of a forest and associated old-field communities. In a two year study in Dutchess County, New York, we found a significantly higher parasitism rate in the forest-interior community ( n = 301 nests; 17 species) than on the species in the adjacent and nearby old field and edge ( n = 328 nests; 15 species; 32.3% versus 6.5%; p < 0.0001). Cowbirds invaded a mature 1300-ha forest stand even when their traditional host species were available in adjacent old-field and edge habitats. The forest and old-field study areas were located in a 38,000-ha township with 55% forest cover and contained numerous agriculture, dairy, and horse farms that provided favorable habitat for cowbirds. Within-forest examination of parasitism patterns revealed four aspects of cowbird parasitism that contrasted with patterns described in other regions: (1) parasitism was concentrated significantly more often on ground- and low-nesting (nests ≤ 1 m) forest species than on medium- and high-nesting species (nests> 1 m; 35.01% versus 29.93%; p = 0.0393); (2) parasitism was not significantly greater on Neotropical migrant species than on short-distance migrants and residents; (3) the parasitism rate was not higher in nests close to edges; and (4) the parasitism level was low on certain forest species (such as Wood Thrush) that have experienced high parasitism levels in the Midwest. From a management perspective these data suggest that cowbirds exhibit regional differences in host and habitat use; the target host community of a particular cowbird population is unpredictable at the landscape scale; and a landscape scale should be used in designing cowbird studies to accurately assess local population dynamics.

New York↗
USGS2002

Contrasting determinants of abundance in ancestral and colonized ranges of an invasive brood parasite

Avian species distributions are typically regarded as constrained by spatially extensive variables such as climate, habitat, spatial patchiness, and microhabitat attributes. We hypothesized that the distribution of a brood parasite depends as strongly on host distribution patterns as on biophysical factors and examined this hypothesis with respect to the national distribution of the Brown-headed Cowbird (Molothrus ater). We applied a classification and regression (CART) analysis to data from the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC) and derived hierarchically organized statistical models of the influence of climate and weather, cropping and land use, and host abundance and distribution on the distribution of the Brown-headed Cowbird within the conterminous United States. The model accounted for 47.2% of the variation in cowbird incidence, and host abundance was the top predictor with an R2 of 18.9%. The other predictors identified by the model (crops 15.7%, weather and climate 14.3%, and region 9.6%) fit the ecological profile of this cowbird. We showed that host abundance was independent of these environmental predictors of cowbird distribution. At the regional scale host abundance played a very strong role in determining cowbird abundance in the cowbird?s colonized range east and west of their ancestral range in the Great Plains (26.6%). Crops were not a major predictor for cowbirds in their ancestral range, although they are the most important predictive factor (33%) for the grassland passerines that are the cowbird?s ancestral hosts. Consequently our findings suggest that the distribution of hosts does indeed take precedence over habitat attributes in shaping the cowbird?s distribution at a national scale, within an envelope of constraint set by biophysical factors.

Book chapter↗
USGS2000

Use of lice to identify cowbird hosts

The host specificity of avian lice ( Phthiraptera ) may be utilized by biologists to investigate the brood parasitism patterns of Brown-headed Cowbirds ( Molothrus ater ). As nestlings, brood parasites have a unique opportunity to encounter lice that are typically host specific. Lice are permanent hemimetabolic ectoparasites, a group found strictly on the body of the host, and they are transferred almost exclusively by bodily contact between hosts during care of young and at copulation. We investigated whether cowbird nestlings become infested with avian lice from their host parents and carry these lice away when they fledge, in effect bearing ectoparasite indicators of the species that raised them. The technique of examining the lice on cowbird fledglings to identify their foster parents would be much less costly than hiring a team of experts to determine parasitism patterns in the conventional way by finding hundreds of songbird nests. We examined 244 cowbird fledglings and found that they carried a rich fauna of lice representing 11 species and six genera, almost the entire spectrum of louse genera known to occur on passerines. We also examined 320 songbirds from 30 species, all known hosts of the Brown-headed Cowbird. As a group the host birds bore a diversity of louse species comparable to that on the fledgling cowbirds: 13 species of lice from seven genera. In contrast, most individual passerine host species yielded only 1 or 2 louse species, significantly fewer than the cowbird fledglings (p < 0.0001). Of 44 fledgling cowbirds carrying lice, 11 were linked to their probable avian foster parents via louse indicators, and these are the Wood Thrush and Red-winged Blackbird. Eighteen additional fledglings were linked to one of two possible foster parents. We concluded that cowbird fledglings do carry away host lice and this survey technique provides a partial assessment of local community parasitism patterns. The incomplete state of passerine louse taxonomy requires anyone using this technique to de-louse both cowbird fledglings and local host species in order to have a reference collection of lice. Lice from cowbird fledglings can be identified by a skilled taxonomist and linked to particular host species, and the principal difficulty is the scarcity of skilled avian louse taxonomists. We also found an unusually rich louse fauna on 219 adult cowbirds, which supports the interpretation that lack of opportunity due to physical isolation has been the fundamental factor in the host specificity of lice observed in certain avian orders.

The Auk↗
USGS1999

[Book review] Cowbirds and Other Brood Parasites by Catherine Ortega. Tucson, Arizona: University of Arizona Press (1998). The Avian Brood Parasites: Deception at the Nest by Paul A. Johnsgard. New York: Oxford University Press (1997) Parasitic Birds and their Hosts: Studies in Coevolution edited by S.I. Rothstein & S.K. Robinson. New York: Oxford University Press (1998)

We are in a golden age for the study of brood parasitism, judging from both the quantity and quality of recent scientific publications on cuckoos, cowbirds and parasitic finches by investigators working in Europe, the Americas, Africa and Asia. As Johnsgard (1997) remarks in his preface, the evolutionary, ecological, and behavioural questions posed by obligate brood parasites are among the most intriguing contemporary ornithological topics. Rothstein & Robinson (1998) explain that brood parasites make ideal subjects for testing the generality of models for the evolution of social and mating behaviour, foraging behaviour, spatial distribution, and vocal development, because the strategy of providing no parental care removes constraints imposed on other birds. Since Aristotle, people have been fascinated by brood parasites, but only in the past two decades has the number of investigators working on this topic reached a critical mass and created momentum that promises many breakthroughs. New studies are being completed so rapidly that a general book is inevitably out of date on some topics by the time it is published. A complete library on brood parasitism should add two recent volumes (Morrison et al. 1999; Smith et al., in press).to the three reviewed here.

Animal Behaviour↗
USGS1999

Low abundance of microsatellite repeats in the genome of the brown-headed cowbird (Molothrus ater)

A cosmid library made from brown-headed cowbird ( Molothrus ater ) DNA was examined for representation of 17 distinct microsatellite motifs including all possible mono-, di-, and trinucleotide microsatellites, and the tetranucleotide repeat (GATA) n . The overall density of microsatellites within cowbird DNA was found to be one repeat per 89 kb and the frequency of the most abundant motif, (AGC) n , was once every 382 kb. The abundance of microsatellites within the cowbird genome is estimated to be reduced approximately 15-fold compared to humans. The reduced frequency of microsatellites seen in this study is consistent with previous observations indicating reduced numbers of microsatellites and other interspersed repeats in avian DNA. In addition to providing new information concerning the abundance of microsatellites within an avian genome, these results provide useful insights for selecting cloning strategies that might be used in the development of locus-specific microsatellite markers for avian studies.

Journal of Heredity↗
USGS1999

A spatial and genetic analysis of Cowbird host selection

Our study of brood parasitism patterns in forest communities revealed the egg-laying frequency and host selection patterns of female cowbirds. By integrating molecular genetics and spatial data, we have the first published estimate on cowbird laying rates in field studies. The 29 females in the study laid only 1-5 eggs each, much lower than previous estimates from captive cowbirds and extrapolations from ovarian development in capture/recapture studies that had suggested that as many as 40 eggs could be laid per individual cowbird. Cowbird females also were shown for the first time to lay significantly more eggs within the home range areas they established rather than outside the home range. No patterns were uncovered for individual females preferentially parasitizing particular host species

Book chapter↗
USGS1999

Introduction

Explore the source record for details and available documents.

Book chapter↗
USGS1995

DNA fingerprint similarity between female and juvenile brown-headed cowbirds trapped together

This DNA fingerprinting study investigates whether females of the brood parasite brown-headed cowbird, Molothrus ater, associate with their own juvenile offspring at feeding sites more often than would be expected by chance. Cowbirds lay their eggs in the nests of a variety of host species and, as far as is known, leave them to the care of foster parents. Using baited walk-in funnel traps, 36 adult female-juvenile pairs (or trios) of cowbirds were trapped. Blood samples were collected from these individuals to conduct DNA fingerprinting analyses, calculate similarity indices, and to compare S-values for the 11 comparisons of juveniles and the females with which they were caught with S-values of random pairings of juveniles and the females in adjacent gel lanes with which they were not caught. Overall band-sharing was significantly higher for the individuals trapped together than for the random pairings. These associations between juvenile cowbirds and their mothers could occur as a result of female cowbirds monitoring the development of their young in the nests where they have laid. Alternatively, nestling cowbirds in the nest could become familiar visually and locally with a female parent that is frequently in their territory and could follow her when she departs for feeding grounds. In either case these data suggest that adult cowbirds associate with juveniles, in some cases their own offspring, and that offspring may learn to function as cowbirds in part from this association.

Animal Behaviour↗
USGS1995

[Book review] The Eastern Screech Owl: Life History, Ecology and Behavior in the Suburbs and Countryside, by Frederick Gehlback

Review of: Eastern Screech Owl: Life History, Ecology, and Behavior in the Suburbs and Countryside. Frederick R. Gehlbach. Issue 16; Issue 2008 of W. L. Moody Jr. Natural History Series. Texas A&M University Press; 1st edition (November 1994). ISBN: 0890966095. For ornithologists and ecologists alike, Fred Gehlbach's book promises to hold both interest and information value as a comprehensive study of the eastern screech owl (Otus asio hasbroucki). Gehlbach was intrigued with screech owls as a boy and encouraged as an undergraduate by William Hamilton, who underscored that in-depth studies of familiar backyard species can be as fascinating as those in exotic sites. Correspondence with another owl-aficionado, the late H. N. Southern, inspired the author's long-term study of screech owls in a woodland landscape in central Texas and led him to provide nest boxes to enhance his access and sample size. This book is based on observations over a 25-year period-beginning in 1967, with intensive study during an 11-year period (1976-1987) in Texas south of Waco, where Gehlbach teaches at Baylor University. The study represents observations on 659 screech owls, covering several generations of birds and entire lives of many individuals. Gehlbach compares screech owl nesting behavior in a rural versus suburban setting and includes chapters on food supplies and predation tactics; egg-laying, incubation, and parental behavior; vocalizations; and population structure and flux. He discusses why screech owls are widespread across the eastern half of North America and why they succeed among people in suburban environments, where they adapt as easily to mailboxes and porch columns as to natural tree cavities. The book mixes two approaches: on the one hand the dense style of a technical book in which the professional biologist can find information on many aspects of screech owl behavior, life history, and population, including tables, figures, summary statistics, results of statistical comparisons, and experimental tests of hypotheses. On the other hand, each chapter begins with and includes vivid visual images, personal experiences, and thoughtful reflections to draw in the general reader, bridging the interesting topic to the technical details and making the information accessible to a wider audience. The reader is impressed with Dr. Gehlbach's love of his subject, his devotion to long-term study, and his care in presenting the work to his fellow ornithologists, ecologists, and all those interested in wildlife and conservation. It will be a useful reference because of its wealth of information on all aspects of screech owl life history. It is well documented and, in addition to its 10 chapters, includes 10 appendices with information on types of food supplies, bird species that mob screech owls, a daily chronology of nestling development, and a selection of edited field notes to provide background for each chapter. The book is thoroughly referenced and indexed. The Eastern Screech Owl will be read with interest by those with an interest in long-term, in-depth studies and those who love charming stories about remarkable birds with strong personalities and interesting behavior.

Wildlife Review↗
USGS1977

Effects of tide cycles on habitat selection and habitat partitioning by migrating shorebirds

We studied assemblages of feeding shorebirds in three intertidal habitats on the coast of New Jersey during August to document how species segregate spatially both among and within habitats and to determine the effects of tidal cycles on these patterns. The habitats were a sandy beach facing the ocean proper (outer beach), a sandy beach on the mainland side of a barrier island (inner beach), and a small mudflat adjacent to a Spartina alterniflora salt marsh. We were able to identify several microhabitats on the outer beach and mudflat. Most species fed in more than one habitat, but only two, Charadrius semipalmatus and Calidris canutus , used all three habitats regularly. Within habitats, most species exhibited strong preferences for the wettest areas, but we found differences among species in degrees of preference. The least amount of partitioning occurred on the inner beach, where birds crowded into a small zone near the water's edge and had frequent agonistic encounters suggesting intense competition. Shorebird feeding activity was partly a function of tide time: each habitat had a characteristic temporal pattern of use by shorebirds related to tide time rather than diel time; within habitats, we found species-characteristic feeding activity rhythms that were also a function of tide time. Feeding by most species peaked during the first 2 hours after low tide on the outer beach and mudflat. The results are discussed in terms of feeding strategies and interspecific competition.

The Auk↗