Possible Use of Wading Birds as Beaters by Snail Kites, Boat-Tailed Grackles, and Limpkins

Foraging in single- or mixed-species flocks is common among many bird species, and the advantages of being in these flocks have been the focus of several investigations (reviewed by Moynihan 1962, Bertram 1978). It has been hypothesized that birds occurring in mixed-species flocks gain advantages from (1) reduced predation risk (e.g., Moynihan 1962, Morse 1970), (2) increased foraging efficiency (e.g., Moynihan 1962, Morse 1970), or (3) social learning (e.g., Ward and Zahavi 1973). Here, we report the anomalous occurrence of flocks consisting of species not typically found in the types of aggregations we describe and suggest the possible function of these aggregations with respect to these hypotheses

Demography and movements of Snail kites in Florida

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The Proportion of Snail Kites Attempting to Breed and the Number of Breeding Attempts per Year in Florida

During the breeding season of 1995 we monitored the proportion of adult and subadult Snail Kites (Rostrhamus sociabilis) attempting to breed and the number of breeding attempts using radio telemetry. Our sample consisted of 23 adults (14 females, 9 males) and 9 subadults for which we had data over the entire breeding season. All adults attempted to breed at least once with an observed average of 1.4 (± 0.6 SD) breeding attempts per individual. In contrast, only 3 (33%) of the subadults attempted to breed. Of the adults, 15 (65%) made one breeding attempt, 7 (30%) made two breeding attempts,and 1 (4%) attempted three times. Only one bird (4%) successfully raised two broods. Our data are consistent with previous reports that \u3e1 breeding attempt by Snail Kites in Florida is common during some years, although our estimate for 1995 was lower han previously reported estimates. A combination of our estimation procedures, definitions of a breeding attempt, and annual variability of this parameter probably account for the disparity between our data and previous reports

An investigation of polymorphisms in the 17q11.2-12 CC chemokine gene cluster for association with multiple sclerosis in Australians

BACKGROUND: Multiple sclerosis (MS) is a disorder of the central nervous system (CNS) characterised by inflammation and neuronal degeneration. It is believed to result from the complex interaction of a number of genes, each with modest effect. Chemokines are vital to the migration of cells to sites of inflammation, including the CNS, and many are implicated in MS pathogenesis. Most of the CC chemokine genes are encoded in a cluster on chromosome 17q11.2-12, which has been identified in a number of genome wide screens as being potentially associated with MS. METHODS: We conducted a two-stage analysis to investigate the chemokine gene cluster for association with MS. After sequencing the chemokine genes in several DNA pools to identify common polymorphisms, 12 candidate single-nucleotide polymorphisms (SNPs) were genotyped in a cohort of Australian MS trio families. RESULTS: Marginally significant (uncorrected) transmission distortion was identified for four of the SNPs after stratification for several factors. We also identified marginally significant (uncorrected) transmission distortion for haplotypes encompassing the CCL2 and CCL11 genes, using two independent cohorts, which was consistent with recent reports from another group. CONCLUSION: Our results implicate several chemokines as possibly being associated with MS susceptibility, and given that chemokines and their receptors are suitable targets for therapeutic agents, further investigation is warranted in this region

Snail Kite Nest Success and Water Levels : A Reply to Beissinger and Snyder

Beissinger and Snyder present a commentary on our recent paper on spatial and temporal variability in nest success of Snail Kites (Rostrhamus sociabilis) in Florida (Dreitz et al. 2001). Beissinger and Snyder reanalyze a subset of data presented in our original paper to show that water levels have a significant influence on nest success. To make their argument, the authors conduct separate analyses for 5 of the original 11 wetlands; including only those having the most data. We agree with Beissinger and Snyder that water levels can affect nest success in some areas or years, as we stated in Dreitz et al. (2001). However, the purpose of our original paper was to examine the influences of nest success over broad spatial and temporal scales. When viewed in this context, using a meta-analysis, water levels alone explain only a small amount of the observed variation in nest success. One of the advantages of using a meta-analysis is that it uses all of the available data to provide an indication of the overall magnitude of an effect, which can easily be misinterpreted when viewed in a narrower context of individual study sites. We discuss the management implication of these alternative perspectives on water levels in light of their effect on habitat quality and persistence

Spatial and Temporal Variability in Nest Success of Snail Kites in Florida : A Meta-Analysis

Nesting success of Snail Kites (Rostrhamus sociabilis) in Florida is highly variable among years and locations, and hydrology is the most frequently reported explanatory factor. We conducted a meta-analysis to evaluate the extent of spatial and temporal variability in nesting success, and explicitly tested for the effects of annual minimum water levels. Data were obtained from six independent studies spanning 22 years and 11 wetlands. Our results indicated there was substantial spatial and temporal variability in nest success and that annual minimum water level, either as a categorical or continuous response, was not a significant source of this variation. Our results do not imply that low water levels do not influence nest success. Rather, they indicate that the number of nests affected by low water conditions was quite low

Annual Survival of Snail Kites in Florida: Radio Telemetry versus Capture-Resighting Data

We estimated annual survival of Snail Kites (Rostrhamus sociabilis) in Florida using the Kaplan-Meier estimator with data from 271 radio-tagged birds over a three-year period and capture-recapture (resighting) models with data from 1,319 banded birds over a six-year period. We tested the hypothesis that survival differed among three age classes using both data sources. We tested additional hypotheses about spatial and temporal variation using a combination of data from radio telemetry and single- and multistrata capture-recapture models. Results from these data sets were similar in their indications of the sources of variation in survival, but they differed in some parameter estimates. Both data sources indicated that survival was higher for adults than for juveniles, but they did not support delineation of a subadult age class. Our data also indicated that survival differed among years and regions for juveniles but not for adults. Estimates of juvenile survival using radio telemetry data were higher than estimates using capture-recapture models for two of three years (1992 and 1993). Ancillary evidence based on censored birds indicated that some mortality of radio-tagged juveniles went undetected during those years, resulting in biased estimates. Thus, we have greater confidence in our estimates of juvenile survival using capture-recapture models. Precision of estimates reflected the number of parameters estimated and was surprisingly similar between radio telemetry and single-stratum capture-recapture models, given the substantial differences in sample sizes. Not having to estimate resighting probability likely offsets, to some degree, the smaller sample sizes from our radio telemetry data. Precision of capture-recapture models was lower using multistrata models where region-specific parameters were estimated than using single-stratum models, where spatial variation in parameters was not taken into account

Model predictions of wave overwash extent into the marginal ice zone

A model of the extent of wave driven overwash into fields of sea ice floes is proposed. The extent model builds on previous work modelling wave overwash of a single floe by regular waves by including irregular incoming waves and random floe fields. The model is validated against a laboratory experiment. It is then used to study the extent of wave overwash into marginal ice zones consisting of pancake and fragmented floe fields. The effects of wave conditions and floe geometry on predicted extents are investigated. Finally, the model is used to predict the wave overwash extent for the conditions observed during a winter (July) 2017 Antarctic voyage in which the sea surface was monitored by a stereo-camera system

A re-analysis of the influence of reproduction on the following year's breeding population of little egrets in the Camargue, S. France

Dans un article précédent (Hafner et al., 1994), nous avions conclu à un effet positif de la production en jeunes de l'année N-1 sur l'effectif reproducteur d'Aigrettes garzettes à l'année N en Camargue. L'analyse de cinq années de données supplémentaires nous permet de rectifier nos conclusions quant au rôle du recrutement. Il apparaît que les effectifs reproducteurs, tout en étant corrélés à ceux de l'année précédente, ne présentent pas une relation positive avec la taille moyenne des nichées de l'année N-1. D'autres facteurs tels que l'immigration seraient nécessaires pour expliquer les effectifs reproducteurs et méritent une investigation plus approfondie