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Articles 1 - 29 of 29

Full-Text Articles in Ornithology

High Prevalence Of Leucocytozoon Parasites In Nestling Northern Goshawks (Accipiter Gentilis) In The Northern Great Basin, U.S.A., Michelle I. Jeffries, Robert A. Miller, Michelle D. Laskowski, Jay D. Carlisle Sep 2015

High Prevalence Of Leucocytozoon Parasites In Nestling Northern Goshawks (Accipiter Gentilis) In The Northern Great Basin, U.S.A., Michelle I. Jeffries, Robert A. Miller, Michelle D. Laskowski, Jay D. Carlisle

Robert Miller

The Northern Goshawk (Accipiter gentilis) is currently listed as a sensitive species by the U.S.D.A. Forest Service. Previous research in our study area, the South Hills of the Minidoka Ranger District of the Sawtooth National Forest, Idaho, identified possible signs of parasite infections among the banded adult and nestling goshawks, which could influence their survival and breeding success. Therefore, we sought to quantify the prevalence and intensity of Leucocytozoon parasites among a sample of nestling goshawks in the South Hills during the 2012 breeding season. We sampled 27 nestlings from 12 nests for Leucocytozoon parasites by examining blood smears. All …


Annual Variation In Autumn Migration Phenology And Energetic Condition At A Stopover Site In The Western United States, Robert A. Miller, Jay D. Carlisle, Neil Paprocki, Gregory S. Kaltenecker, Julie A. Heath Jan 2015

Annual Variation In Autumn Migration Phenology And Energetic Condition At A Stopover Site In The Western United States, Robert A. Miller, Jay D. Carlisle, Neil Paprocki, Gregory S. Kaltenecker, Julie A. Heath

Robert Miller

Climate change is having a dramatic effect on many migratory species. Changes in climate may lead to changes in food availability or other proximate cues that affect migratory behavior. We used 13 years (2000–2012) of data on songbird banding and raptor migration counts and captures during autumn migration in the intermountain West to evaluate whether regional temperature or precipitation or hemispheric climate indices predicted autumn migratory timing and energetic condition. We examined overall trends and evaluated the effects of diet and migratory distance on phenology and conditional responses. For the 13-year study period, no temperature, precipitation, or climate index trends …


Wintering Ecology Of Adult North American Ospreys, Brian E. Washburn, Charles J. Henny, Mark S. Martell, Richard O. Bierregaard, Brian S. Dorr, Thomas J. Olexa Dec 2014

Wintering Ecology Of Adult North American Ospreys, Brian E. Washburn, Charles J. Henny, Mark S. Martell, Richard O. Bierregaard, Brian S. Dorr, Thomas J. Olexa

Brian S Dorr

North American Ospreys (Pandion haliaetus) typically migrate long distances to their wintering grounds in the tropics. Beyond the general distribution of their wintering range (i.e., the Caribbean, South America, and Central America), very little is known about the wintering ecology of these birds. We used satellite telemetry to determine the duration of wintering period, to examine the characteristics of wintering areas used by Ospreys, and to quantify space use and activity patterns of wintering Ospreys. Adult Ospreys migrated to wintering sites and exhibited high wintering site fidelity among years. Overall, Ospreys wintered on river systems (50.6%) more than on lakes …


Geographic Segregation And Evidence Of Density-Dependent Changes In Sex Ratios In An Abundant Colonial Waterbird, Brian S. Dorr, Katie C. Hanson-Dorr, Travis L. Devault, Alban Guillaumet, Scott C. Barras Dec 2014

Geographic Segregation And Evidence Of Density-Dependent Changes In Sex Ratios In An Abundant Colonial Waterbird, Brian S. Dorr, Katie C. Hanson-Dorr, Travis L. Devault, Alban Guillaumet, Scott C. Barras

Brian S Dorr

Demographic information, such as geographic segregation of sexes and sex ratio data, is needed to develop, model and evaluate conservation and management strategies for wildlife. A variety of physiological, behavioral and environmental factors can influence segregation of sexes and sex ratios, many of which originate with density- dependent processes. Departure from 50:50 sex ratios of double-crested cormorants (Phalacrocorax auritus) collected during control efforts in breeding and wintering areas across their eastern range of the USA were evaluated using using a Z-test as well as Stouffer’s weighted Z-tests. In addition, a specifically-designed randomization test was used to evaluate density-dependent effects on …


A Study Of Mexican Free-Tailed Bat Chirp Syllables: Bayesian Functional Mixed Modeling Of Nonstationary Time Series Data With Time-Dependent Spectra, Josue G. Martinez, Kirsten M. Bohn, Raymond J. Carroll, Jeffrey S. Morris Feb 2013

A Study Of Mexican Free-Tailed Bat Chirp Syllables: Bayesian Functional Mixed Modeling Of Nonstationary Time Series Data With Time-Dependent Spectra, Josue G. Martinez, Kirsten M. Bohn, Raymond J. Carroll, Jeffrey S. Morris

Jeffrey S. Morris

We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to …


Species Diversity And Abundance Of Avifauna In And Around Hombolo Wetland In Central Tanzania, Geofrey Soka, Pkt Munishi, Bernad Mgina Jan 2013

Species Diversity And Abundance Of Avifauna In And Around Hombolo Wetland In Central Tanzania, Geofrey Soka, Pkt Munishi, Bernad Mgina

Geofrey Soka

No abstract provided.


Molecular Surveillance Of Low Pathogenic Avianinfluenza Viruses In Wild Birds Across The United States:Inferences From The Hemagglutinin Gene, Antoinette J. Piaggio, Susan A. Shriner, Kaci Van Dalen, Alan B. Franklin, Theodore D. Anderson, Sergios-Orestis Kolokotronis Dec 2012

Molecular Surveillance Of Low Pathogenic Avianinfluenza Viruses In Wild Birds Across The United States:Inferences From The Hemagglutinin Gene, Antoinette J. Piaggio, Susan A. Shriner, Kaci Van Dalen, Alan B. Franklin, Theodore D. Anderson, Sergios-Orestis Kolokotronis

Alan B Franklin

A United States interagency avian influenza surveillance plan was initiated in 2006 for early detection of highly pathogenic avian influenza viruses (HPAIV) in wild birds. The plan included a variety of wild bird sampling strategies including the testing of fecal samples from aquatic areas throughout the United States from April 2006 through December 2007. Although HPAIV was not detected through this surveillance effort we were able to obtain 759 fecal samples that were positive for low pathogenic avian influenza virus (LPAIV). We used 136 DNA sequences obtained from these samples along with samples from a public influenza sequence database for …


A New Policy For Management Of Double-Crested Cormorants In The United States And An Example Of Its Implementation., Shauna L. Hanisch, Brian S. Dorr, Peter H. Butchko Jan 2011

A New Policy For Management Of Double-Crested Cormorants In The United States And An Example Of Its Implementation., Shauna L. Hanisch, Brian S. Dorr, Peter H. Butchko

Brian S Dorr

In the fall of 2003, the U.S. Fish and Wildlife Service (USFWS), in cooperation with USDA-Wildlife Services (USDA-WS), completed an Environmental Impact Statement (EIS) for the management of Double-crested Cormorants (DCCOs) in the United States. The USFWS subsequently published new regulations to implement the EIS proposed strategy. One part of the new regulations, a “public resource depredation order” (PRDO), allows state wildlife agencies, tribes, and USDA-WS to control DCCOs on a localized level to protect fish, wildlife, plants, and their habitats in 24 states. We’ll discuss this new policy and will highlight the management activities, including monitoring and evaluation efforts, …


Evaluation Of Plastic And Mylar Flagging As Repellents For Snow Geese (Chen Caerulescens), J. Russell Mason, Larry Clark Jan 1994

Evaluation Of Plastic And Mylar Flagging As Repellents For Snow Geese (Chen Caerulescens), J. Russell Mason, Larry Clark

Larry Clark

The effectiveness of white flags, black flags and Mylar streamers as visual repellents to snow geese (Chen caerulescens) was evaluated. Five farms in Cumberland and Salem counties, New Jersey served as test sites. At each farm, four 10.12 ha fields were selected randomly, and then assigned to four treatment conditions: (a) white plastic flags (one flag per 0.4 ha); (b) black plastic flags (one flag per 0.4 ha), (c) Mylar streamers (one streamer per 0.4 ha); and (d) stakes only (one stake per 0.4 ha). From 2 December 1992 to 24 March 1993, vegetation samples and goose droppings were collected …


Use Of Activated Charcoal And Other Particulate Substances As Feed Additives To Suppress Bird Feeding, J. Russell Mason, Larry Clark Jan 1994

Use Of Activated Charcoal And Other Particulate Substances As Feed Additives To Suppress Bird Feeding, J. Russell Mason, Larry Clark

Larry Clark

Osmotic strength is a function of particle number. The experiments described here were designed to test whether the consumption of a large number of small particles might induce strong osmotic effects that, in turn, could induce food avoidance learning. The experiments also evaluated whether the abrasiveness of fine particulates or their ability to act as organic adsorbants could mediate or contribute to the avoidance of adulterated diets. In experiment I. captive European starlings (Sturnus vulgaris) were given two-cup tests between plain chow and chow adulterated with activated charcoal or Anjan-activaid. a product containing large amounts of activated charcoal. Both adulterants …


Tests And Refinements Of A General Structure-Activity Model For Avian Repellents, Larry Clark, Pankaj Shah Jan 1994

Tests And Refinements Of A General Structure-Activity Model For Avian Repellents, Larry Clark, Pankaj Shah

Larry Clark

We tested the robustness of a structure-activity model for avian trigeminal chemoirritants. Fourteen benzoates and acetophenones were tested using European starlings Sturn us vulgaris as a bioassay. In general. the pre­ viously proposed model was a reasonable predictor of repellency (i.e., irritant potency). We found that the presence of a phenyl ring was critical to repel­ lency. Basicity of the molecule is the next most critical feature influencing repellency. The presence of an acidic function within the electron-withdrawing functionality seriously detracts from repellency. The presence or absence of an electron-withdrawing or -donating group may potentiate repellent effects, but its presence …


Evaluation Of A Pelleted Bait Containing Methyl Anthranilate As A Bird Repellent, J. Russell Mason, Larry Clark, Timothy Miller Jan 1993

Evaluation Of A Pelleted Bait Containing Methyl Anthranilate As A Bird Repellent, J. Russell Mason, Larry Clark, Timothy Miller

Larry Clark

No-till agriculture involves the use of granular pesticide formulations, chemically treated seeds, and pelleted baits. Some of these may accidentally kill birds. We have tested whether methyl anthranilate (MA), a known bird repellent, would eliminate consumption of a pelleted bait. In two laboratory experiments and an outdoor aviary trial, cowbirds (Molothrus ater Bodd.) were presented with pellets containing pesticide and MA, pellets containing pesticide but no MA, and carrier pellets without pesticide or MA. Consumption of any formulation was low, but the addition of MA significantly decreased bait loss in the laboratory, and prevented the disappearance of bait in the …


Interaction Between Sensory And Postingestional Repellents In Starlings: Methyl Anthranilate And Sucrose, Larry Clark, J. Russell Mason Jan 1993

Interaction Between Sensory And Postingestional Repellents In Starlings: Methyl Anthranilate And Sucrose, Larry Clark, J. Russell Mason

Larry Clark

Ingestion of concentrated sucrose solutions causes sickness in sucrase-defi­ cie_nt birds. As a result, some suggest that sucrose may represent an environmentally safe avian repellent. In the present experiments, we compared the repellency of sucrose to that of methyl anthranilate (MA), a known avian repellent. We also tested mixtures of sucrose and MA to investigate whether repellency could be enhanced, relative to sucrose or MA presentealo'!e. The results showed that the MA was strongly avoided in both drinking anf edmtnals. Conversely, only high sucrose concentrations were avoided, and only in dnnkmg tnals. No combination of MA and sucrose was as …


Odor Thresholds In Passerines, Larry Clark, K.V. Avilova, N.J. Bean Jan 1993

Odor Thresholds In Passerines, Larry Clark, K.V. Avilova, N.J. Bean

Larry Clark

Eight species of passerines were evaluated for their ability to form conditioned responses to odor stimuli. Only 5 species met training criteria and were tested for odor detection thresholds.

2. Detection thresholds were comparable to other passerines tested. Detection values were also similar to mammalian macrosmatic species, such as rats and rabbits. Thus, despite the poorly elaborated olfactory anatomy of passerines, these birds possess an adequate sense of smell.

3. Within the Passeriformes there is no correlation between olfactory acuity and relative size of the olfactory bulb. However, there is a correlation between acuity and olfactory bulb size across orders …


Information Content Of Prey Odor Plumes: What Do Foraging Leach's Storm Petrels Know?, Larry Clark, Pankaj Shah Jan 1992

Information Content Of Prey Odor Plumes: What Do Foraging Leach's Storm Petrels Know?, Larry Clark, Pankaj Shah

Larry Clark

Electrophysiological responses to odor have been recorded for concen­ trations as low as 0.01 ppm for Manx shearwaters Puffinus puffinus and Black-footed Albatrosses Diomedea nigripes, indicating that relative to most birds, procellariiforms have a keen sense of smell (Wenzel and Sieck 1972, cf.clark 1991; Clark and Smeraski 1990; Clark and Mason 1989). Such acuity is not unexpected, given the extensive development of the olfactory anatomy of these species (Bang and Wenzel 1986). Field observations indi­ cate that Procellariiformes use their sense of smell to locate food (Grubb 1972; Hutchison and Wenzel 1980; Lequette, Verheyden and Jouventin 1989). -_ However, it …


Avian Chemical Repellency: A Structure-Activity Approach And Implications, Pankaj Shah, Russell Mason, Larry Clark Jan 1992

Avian Chemical Repellency: A Structure-Activity Approach And Implications, Pankaj Shah, Russell Mason, Larry Clark

Larry Clark

Until recently, the discovery of avian sensory repellents has been empirical (MaRnn, AnAmR 'Inn l;qr\r FlR'l), Hm> !ilv!ilr, recent liltudilillil in our laboratory have shown that many avian repellents have similar perceptual and structural properties (Mason et al. 1989; Mason Clark and Shah 1991; Clark and Shah 1991; Clark, Shah and Mason 1991; Shah, Clark and Mason 1991). For example, methyl anthranilate, which has a grapy odor, is repel­ lent to birds (Kare and Pick, 1960). Ortho-aminoacetophenone has an odor and structure similar to that of methyl anthranilate, differing only in the substitution of a ketone for an ester group …


Nonlethal Repellents: The Development Of Cost-Effective, Practical Solutions To Agricultural And Industrial Problems, Russell Mason, Larry Clark Jan 1992

Nonlethal Repellents: The Development Of Cost-Effective, Practical Solutions To Agricultural And Industrial Problems, Russell Mason, Larry Clark

Larry Clark

Repellents substances and devices cause pest species to avoid otherwise attractive or palatable materials. For birds, repellents can be visual, auditory, pyrotechnic, tactile, chemosensory, physiologic, or physical. Here, we consider chemical agents only. Few substances arc registered with the U.S. Environmental Protection Agency (EPA), and thus legally available for use. This lack of available bird repellent technology reflects the small demonstrable economic impact of many agricultural bird damage problems. Accurate information about damage and market size is virtually nonexistent, and private companies are reluctant to invest resources in the unknown. To successfully commercialize new repellents, clearly lucrative markets must be …


Capsaicin Effects On Consumption Of Food By Cedar Waxwings And House Finches.­, Donald Norman, Russell Mason, Larry Clark Jan 1992

Capsaicin Effects On Consumption Of Food By Cedar Waxwings And House Finches.­, Donald Norman, Russell Mason, Larry Clark

Larry Clark

Capsaicin effects on consumption of food by Cedar Waxwings and House Finches.­ Capsaicinoids (e.g., N-vanillyl-n-nonamide. norcapsaicin, nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, homodihydrocapsaicin; Hoffman 1983) are aromatic am­ ides and the pungent principles in Capsicum peppers. Although these substances are strong chemical irritants for most mammals (e.g.. Rozin et a!. 1979), the available data suggest that they are inoffensive to some birds. For example. European Starlings (Sturn us vulgaris) and Rock Doves (Columba Iivia) are unresponsive to these compounds, even when con­ centrations greatly exceed those which mammals avoid (Szolcsanyi et al. 1986; Mason et a!.. in press).


Chemical Repellency In Birds: Relationship Between Chemical Structure And Avoidance Response, Larry Clark, Pankaj Shah, Russell Mason Jan 1991

Chemical Repellency In Birds: Relationship Between Chemical Structure And Avoidance Response, Larry Clark, Pankaj Shah, Russell Mason

Larry Clark

We examined how molecular structure of24 anthranilate and benzoic acid deriva­ tives correlated with drinking behavior in European starlings Sturnus vulgaris.The effectiveness of bird repellents was &?SOciated with basicity, the presence of an electron onating group in resonance with an electron-withdrawing carboxylic group on a phenyl ring, and a heterocyclic ring in the same pi cloud plane as the phenyl ring. Of the benzoic acid derivatives tested in this study, methyl, ethyl, dimethyl, and linalylanthranilate as well as anthranilic acid and 4-ketobenztriazine were repellent to birds. Water consumption was significantly reduced relative to control levels at concentrations as low as …


Odor Detection Thresholds In Tree Swallows And Cedar Waxwings, Larry Clark Jan 1991

Odor Detection Thresholds In Tree Swallows And Cedar Waxwings, Larry Clark

Larry Clark

No abstract provided.


Ortho-Aminoacetophenone Repellency To Birds: Similiarities To Methyl Antrhanilate, Russell Mason, Larry Clark, Pankaj Shah Jan 1991

Ortho-Aminoacetophenone Repellency To Birds: Similiarities To Methyl Antrhanilate, Russell Mason, Larry Clark, Pankaj Shah

Larry Clark

Methyl anthranilate is an effective bird repellent at concentrations 2:1.0% (g/g). Ortho-ami­ noacetophenone (OAP) has an odor similar to that of methyl anthranilate and is chemically (structurally) similar. Coincidentally, OAP is present in the scent gland secretions of mustelid species that prey on birds. For these reasons, we chose to test the bird repellency of this material and 3 isomers to European starlings (Stumus vulgaris). Ortho-aminoacetophenone was repellent at concentrations :50.01% in both choice and no-choice feeding tests. The other structural isomers (meta-, para-, alpha-) were less effective. Chemically, the results suggest that hydrogen-bonded ring structure formation and basicity predict …


Nonlethal Bird Repellents: In Search Of A General Model Relating Repellency And Chemical Structure, Larry Clark, Pankaj Shah Jan 1991

Nonlethal Bird Repellents: In Search Of A General Model Relating Repellency And Chemical Structure, Larry Clark, Pankaj Shah

Larry Clark

Identification of potential repellents through molecular modeling has implications for the devel­ opment of commerciaUy viable, ecologically sound. nonlethal bird repellents. We tested isomers (ortho, meta, para) and moieties (amino, hydroxy, methoxy) of acetophenones for their effectiveness as bird repellents to better understand the nature of repellency in birds. ChemicaUy, basicity of a substituted phenyl ring, as de&ned by the electron-donating substituent, probably is an important feature infiuencing repellency; i.e., more basic substituents result in more potent repellents. Isomeric position of the electron-donating substituent, which leads to resonance of lone pairs of electrons.• is also an important feature of repellency; …


Chemical Bird Repellents: Applicability For Deterring Use Of Waste Water, Larry Clark, Pankaj Shah Jan 1991

Chemical Bird Repellents: Applicability For Deterring Use Of Waste Water, Larry Clark, Pankaj Shah

Larry Clark

Regulatory agencies have placed increasing emphasis on agriculture and industry to protect wildlife from mortality associated with the consumption of waste water. Traditional hazjng methods to keep birds away from areas have met with marginal success. The only effective commercially available solution is .to enclose impoundments with netting. This strategy is costly and is subject to engineering constraints when large areas are to be protected. Molecular modeling techniques were used to identify chemical repellents to be added to waste water. These repellents effectively prevent birds from drinking or swimming in treated water.The most effective repellents are those containing an electron …


Prediction Of Avian Repellency From Chemical Structure: The Aversiveness Of Vanillin, Vanillyl Alcohol, And Veratryl Alcohol, Pankaj Shah, Larry Clark, Russel Mason Jan 1991

Prediction Of Avian Repellency From Chemical Structure: The Aversiveness Of Vanillin, Vanillyl Alcohol, And Veratryl Alcohol, Pankaj Shah, Larry Clark, Russel Mason

Larry Clark

The effectiveness of bird repellents is associated with the presence of an electron-withdrawing group (carbonyl or carboxyl) and an electron-donating group in resonance on a phenyl ring. The present experiments were designed to examine the relative importance of these structural features. European starlings (Sturnus vulgaris) were presented with vanillin, vanillyl alcohol, and veratryl alcohol in two-cup and one-cup feeding trials and in one-bottle drinking tests. In feeding trials, veratryl alcohol was significantly more aversive than the other two chemicals. In drinking tests. veratryl alcohol was repellent only at the highest concentration (0.5% ml/ml), and was lethal at that concentration and …


Thermal Constraints On Foraging Activity Of Adult Starlings, Larry Clark Jan 1987

Thermal Constraints On Foraging Activity Of Adult Starlings, Larry Clark

Larry Clark

The operative temperature of the environment was estimated for starlings using hollow, unheated taxidermic mounts. On average, adults foraging in full sun were characterized by shorter foraging bouts than those adults foraging in full shade. Simultaneous observations of air temperature, operative temperature, and the foraging duration of adults indicated that air temperature was a poor predictor of the maximum length of a foraging bout. The operative temperature of the environment was not correlated to the maximum and mean length of foraging bouts for temperatures below 31.5 ~ C, but was negatively related to maximum and mean foraging duration for values …


Olfactory Discrimination Of Plant Volatiles By The European Starling, Larry Clark, J Russell Mason Jan 1987

Olfactory Discrimination Of Plant Volatiles By The European Starling, Larry Clark, J Russell Mason

Larry Clark

Passerine species that re-use nest sites often incorporate fresh green vegetation into their nests, a behaviour consistent with the possibility that some birds may use chemical properties of plants to counteract the selective potential of parasites and pathogens. We tested adult starlings (Sturnus vulgaris) for their physiological capacity and behavioural ability to detect and discriminate between volatiles emitted from plant material. Multi-unit electrophysiological recordings from olfactory nerves of adults indicated that strong responses were reliably elicited by volatiles from six plant species. After pairings of plant volatiles with gastro-intestinal malaise, birds exhibited conditioned avoidance in behavioural experiments, and made all …


Use Of Nest Material As Insecticidal And Anti-Pathogenic Agents By The European Starling, Larry Clark, J Russell Mason Jan 1985

Use Of Nest Material As Insecticidal And Anti-Pathogenic Agents By The European Starling, Larry Clark, J Russell Mason

Larry Clark

Passerine birds that reuse nest sites face an increased parasite and pathogen load. They also are more likely to use fresh green vegetation during nest construction. The present results demonstrate that at least one passerine, the European Starling: (a) selects a small subset of available plant species for inclusion in nest material; and (b) chooses plants whose volatiles are more likely to inhibit arthropod hatching and bacterial growth relative to a random subset of available vegetation. The results also show that preferred plants possess greater numbers of mono- and sesqueterpenes at higher concentrations relative to a random subset of available …


Consequences Of Homeothermic Capacity Of Nestlings On Parental Care In The European Starling, Larry Clark Jan 1984

Consequences Of Homeothermic Capacity Of Nestlings On Parental Care In The European Starling, Larry Clark

Larry Clark

The homeothermic capacity of chicks varied as a function of brood size, age, and air temperature. Commitment to rooding by parents also varied as a function of brood size, age of the young brooded, and prevailing air temperature. It was experimentally determined that parents altered their brooding commitment in direct response to the achieved mean homeothermic capacity of the brood rather than energy demands of the brood per se. Because larger broods achieved a given level of homeothermic capacity earlier than smaller broods, parents spent less time brooding larger broods. This "freed" time represented an increase in potential foraging time …


Nest Site Selection By The Red-Tailed Tropicbird, Larry Clark, Robert Ricklefs, Ralph Schrieber Jan 1983

Nest Site Selection By The Red-Tailed Tropicbird, Larry Clark, Robert Ricklefs, Ralph Schrieber

Larry Clark

-Red-tailed Tropicbirds (Phaethon rubricauda) nest under shrubs in loosely associated groups on Christmas Island, Central Pacific Ocean. Aggressive interactions among adults at nest sites are high; yet, large areas of superficially similar habitat contain no tropicbird nests at all. We compared physiognomic features of nest sites with those of two sets of randomly generated "nest sites" by discriminant function analysis. Of those variables measured, the number of stems within a nest space and the amount of peripheral cover influenced the tropicbirds' choice of nest sites. Differences among localities existed. Areas where tropicbirds nested had shrubs with few stems and more …