Sara R. Morris

Comparison of geometric morphometric outline methods in the discrimination of age-related differences in feather shape

BackgroundGeometric morphometric methods of capturing information about curves or outlines of organismal structures may be used in conjunction with canonical variates analysis (CVA) to assign specimens to groups or populations based on their shapes. This methodological paper examines approaches to optimizing the classification of specimens based on their outlines. This study examines the performance of four approaches to the mathematical representation of outlines and two different approaches to curve measurement as applied to a collection of feather outlines. A new approach to the dimension reduction necessary to carry out a CVA on this type of outline data with modest sample sizes is also presented, and its performance is compared to two other approaches to dimension reduction.ResultsTwo semi-landmark-based methods, bending energy alignment and perpendicular projection, are shown to produce roughly equal rates of classification, as do elliptical Fourier methods and the extended eigenshape method of outline measurement. Rates of classification were not highly dependent on the number of points used to represent a curve or the manner in which those points were acquired. The new approach to dimensionality reduction, which utilizes a variable number of principal component (PC) axes, produced higher cross-validation assignment rates than either the standard approach of using a fixed number of PC axes or a partial least squares method.ConclusionClassification of specimens based on feather shape was not highly dependent of the details of the method used to capture shape information. The choice of dimensionality reduction approach was more of a factor, and the cross validation rate of assignment may be optimized using the variable number of PC axes method presented herein.

A ten-year study of the stopover patterns of migratory passerines during fall migration on Appledore Island, Maine

This study examined the autumnal stopover patterns of migratory passerines on Appledore Island, Maine, from 1983 to 1992. We recaptured 13.4% of migratory passerines at least one day after initial capture with species averages ranging from 2.8% in Eastern Wood-Peewee (Contopus virens) to 33.5% in Philadelphia Vireos (Vireo philadelphicus). Most observed stopovers were less than four days. Young birds were more prevalent than adults in all species studied. Among Red-eyed Vireos (Vireo olivaceus), Black-and-white Warblers (Mniotilta varia), and Northern Waterthrushes (Seiurus noveboracensis) young birds were more likely to be recaptured than adults. Young Northern Waterthrushes had significantly longer stopovers than adults. No difference in recaptures was detected between the sexes in any species studied. Most of the birds captured were lean (fat class 0 or 0.5) at initial capture. In several species, young birds were significantly leaner both in terms offat class and mass than adults. Most species studied experienced significant increases in fat class and mass during stopovers. We did not find significant differences in mass or fat increases between age groups or between the sexes in any species studied. Cape May Warblers (Dendroica tigrina), Black-and-white Warbiers, and American Redstarts (Setophaga ruticilla) did not exhibit any differences in recaptures, stopover lengths, or mass increases among years. Northern Waterthrushes exhibited significant differences in recaptures and Red-eyed Vireos exhibited differences in recaptures and mass increases among years during this study.

COMPARISON OF SPRING AND FALL MIGRATION OF AMERICAN REDSTARTS ON APPLEDORE ISLAND, MAINE

Abstract 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.

SPRING MIGRATION AND STOPOVER ECOLOGY OF COMMON YELLOWTHROATS ON APPLEDORE ISLAND, MAINE

Abstract Although Common Yellowthroats (Geothlypis trichas) are Nearctic-Neotropical migrants that are common breeders across the United States and Canada, very little has been published about the migration and stopover ecology of this species. We used spring migration banding records of Common Yellowthroats from 1992–2001 on Appledore Island, Maine, to investigate potential sexual and age-related differences in migration timing and stopover ecology of this species. Arrival dates of males were significantly earlier than arrival dates of females during spring, with mean male arrival five days earlier than female arrival. Also, after-second-year (ASY) birds arrived significantly earlier than second-year (SY) birds within each sex. Males also were significantly heavier than females upon arrival on Appledore. During spring migration, 5.0% of males and 4.2% of females were recaptured at least one day after initial capture, resulting in a mean stopover length of approximately three days for both sexes. We found no significant difference in the mean minimum stopover length nor the rate of mass change between the sexes based on recaptured individuals. Furthermore, we found no significant differences in stopover ecology between age groups within either sex. Both sexes significantly increased mass during stopover, both as calculated from recaptured individuals and as estimated by regression of condition (mass × 100/wing chord) over time. Results of this study confirmed differential migration among Common Yellowthroats, which is consistent with previous studies of passerine migration ecology. Lack of differences in stopover ecology between the sexes or between age groups suggests that earlier arrival of males than females and of ASY birds than SY birds may be due to an earlier onset of migration rather than increased migration speed.

Strain Diversity of Borrelia burgdorferi in Ticks Dispersed in North America by Migratory Birds

ABSTRACT: The role of migratory birds in the dispersal of Ixodes scapularis ticks in the northeastern U.S. is well established and is presumed to be a major factor in the expansion of the geographic risk for Lyme disease. Population genetic studies of B. burgdorferi sensu stricto, the agent of Lyme disease in this region, consistently reveal the local presence of as many as 15 distinct strain types as designated by major groups of the ospC surface lipoprotein. Recent evidence suggests such strain diversity is adaptive to the diverse vertebrate hosts that maintain enzootic infection. How this strain diversity is established in emergent areas is unknown. To determine whether similar strain diversity is present in ticks imported by birds, we examined B. burgdorferi strains in I. scapularis ticks removed from migrants at an isolated island site. Tick mid-guts were cultured and isolates underwent DNA amplification with primers targeting ospC. Amplicons were separated by gel electrophoresis and sequenced. One hundred thirty-seven nymphal ticks obtained from 68 birds resulted in 24 isolates of B. burgdorferi representing eight ospC major groups. Bird-derived ticks contain diverse strain types of B. burgdorferi, including strain types associated with invasive Lyme disease. Birds and the ticks that feed on them may introduce a diversity of strains of the agent of Lyme disease to emergent areas.

MULTIPLE-DAY CONSTANCY AS AN ALTERNATIVE TO POOLING FOR ESTIMATING MARK-RECAPTURE STOPOVER LENGTH IN NEARCTIC-NEOTROPICAL MIGRANT LANDBIRDS

Abstract Capture-mark-recapture models require estimation of parameters that may be either constant or time-dependent. Open-population models have been adapted for use in estimating stopover duration of migratory songbirds. However, with data collected over an extended period or with relatively few recaptures, small sample sizes may preclude use of fully time-dependent models. Pooling is commonly used to reduce the number of parameters estimated in time-dependent models. In pooling, all captures and recaptures during a specified interval are treated as a single capture event, which results in a loss of information about recaptures within the interval. Additionally, pooling of banding data of migratory songbirds appears to bias stopover-length estimates upwards. An alternative to pooling is use of multiple-day-constancy models. Advantages of this approach include maintenance of all recapture data, simultaneous Akaike’s Information Criterion-based comparison of models using different constancy intervals, and unbiased stopover estimates. Constancia de Múltiples Días como una Alternativa a la Combinación de Datos de Captura-Recaptura para Estimar la Duración de las Paradas de Aves Migrantes Neárticas-Neotropicales Terrestres

UTILITY OF OPEN POPULATION MODELS: LIMITATIONS POSED BY PARAMETER ESTIMABILITY IN THE STUDY OF MIGRATORY STOPOVER

Abstract Open population models using capture-mark-recapture (CMR) data have a wide range of uses in ecological and evolutionary contexts, including modeling of stopover duration by migratory passerines. In using CMR approaches in novel contexts there is a need to determine the conditions under which open population models may be employed effectively. Our goal was to determine whether there was a simple a priori mechanism of determining the conditions under which CMR models could be used effectively in the study of avian stopover ecology. Using banding data (n = 188 capture histories), we examined the challenges of using CMR-based models due to parameter inestimability, adequacy of descriptive power (Goodness-of-Fit, GOF), and parameter uncertainty. These issues become more apparent in studies with limited observations in a capture history, as is often the case in studies of avian stopover duration. Limited sample size and sampling intensity require an approach to reducing the number of fitted parameters in the model. Parameter estimability posed the greatest restriction on the utility of open population models, with high parameter uncertainty posing a lesser challenge. Results from our study also indicate the need for >10 observations per estimated parameter (approximately 3 birds captured or recaptured per day) to provide a reasonable chance of successfully estimating all model parameters.

Density of Ixodes scapularis ticks on Monhegan Island after complete deer removal: A question of avian importation?

ABSTRACT: Questing adult blacklegged tick (Ixodes scapularis Say) abundance declined markedly three years after the 1999 removal of white-tailed deer (Odocoileus virginianus Zimmermann) from Monhegan Island, ME. Since 2000, subadult ticks have not been found on Norway rats (Rattus norvegicus Berkenhout); questing nymphs have not been found since 2002. This suggested I. scapularis was reintroduced annually via bird importation of subadult ticks, but unable to complete its two-year life cycle on the island due to lack of deer. To investigate this, we used uncertainly analysis to estimate 1) questing adult ticks/ha that would result from avian importation of nymphs, and 2) questing adult ticks/ha on Monhegan Island, using bird capture and tick burden data from Appledore Island, ME, flagged tick data from Monhegan Island, and ten uncertain parameters. During the deer-fed period (1990–2001), estimated tick density on Monhegan Island was 18 times greater than that of imported ticks. During the post-deer-fed period (2002–2008), Monhegan Island tick density was equivalent to imported tick density. This supported the premise that all I. scapularis ticks on Monhegan Island have been bird-derived since 2002.

Migrant Songbird Species Distribution and Habitat Use During Stopover on Two Islands in the Gulf of Maine

Abstract We compared the distribution of migrant bird species between two islands in the Gulf of Maine to examine if differences in habitat resulted in differences in avian species composition and relative abundance during stopover. Ninety-one species were captured on both islands and those species captured on only one island were either breeding species or rare visitors to the islands. Differences in bird species distribution between islands were species-specific and consistent among sampling periods for nearly all species. Twelve species were captured more frequently on Star Island and 11 species more frequently on Appledore Island. Stopover species distribution appeared to be related to habitat structure, vegetation, diet, and habitat area. Scrub-shrub/open habitat breeding species and forest breeding species were not evenly distributed between islands. Island use was most closely associated with breeding habitat. All but two of the eight species that breed in scrub-shrub or open habitat were captured more frequently on Star Island. Ten of the species more common on Appledore Island breed in forested habitat. Nine of the 11 species more common on Appledore Island are area-sensitive in breeding areas, suggesting potential area sensitivity during migration. Differential habitat use indicates a large number of stopover sites in a wide variety of habitats are necessary to meet migration needs of passerine species.

Patterns of testosterone in three Nearctic-Neotropical migratory songbirds during spring passage.

Preparation for breeding may overlap extensively with vernal migration in long-distance migratory songbirds. Testosterone plays a central role in mediating this transition into breeding condition by facilitating changes to physiology and behavior. While changes in testosterone levels are well studied in captive migrants, these changes are less well known in free-living birds. We examined testosterone levels in free-living Nearctic-Neotropical migrants of three species during their vernal migration. Testosterone levels increased during the migratory period in males of all three species but significantly so in only two. Testosterone levels in females remained the same throughout their migration. Our results support the extensive overlap between vernal migration and breeding preparation in male songbirds. The pattern of testosterone changes during vernal migration is far from clear in females.