Douglas A. Bell

Comparing Clines on Molecular and Phenotypic Traits in Hybrid Zones: A Window on Tension Zone Models

Abstract The study of zones of secondary contact provides insight into the maintenance of reproductive isolation. Tension zone theory supplies powerful tools for assessing how dispersal and selection shape hybrid zones. We present a multimodal analysis of phenotypic clines in conjunction with clines at molecular markers in a hybrid zone between Larus glaucescens and Larus occidentalis. We developed a new method to analyze simultaneously clines of quantitative traits and molecular data. Low linkage disequilibrium and the lack of coincidence between clines at six microsatellites, a mitochondrial DNA region, and two phenotypic traits indicated introgression. However, the hypothesis of neutral diffusion was rejected based on evidence that all of the clines were concordant and narrower than expected for neutral clines, indicating some indirect selection. The analysis of phenotypic variance gave evidence of restricted phenotypic introgression and together with the bimodal distribution of phenotypes suggested that disruptive selection is acting across the hybrid zone, especially on the coloration of bare parts. Multimodal analysis of phenotypic clines also highlighted a shift between the peak of intermediates and the cline center, left behind by hybrid zone motion. High-resolution analysis of phenotypes distribution thus proved useful for detecting hybrid zone movement even without temporal data.

A Metapopulation Model of the Peregrine Falcon in California: Viability and Management Strategies

We modeled the Peregrine Falcon (Falco peregrinus anatum) population in California to determine its viability under different management strategies by modifying Lefkovitch stage class matrix models to include the introduction of captive-reared birds and the dynamics of two subpopulations linked by migration. The model projections using published parameter values indicated that the population would not sustain itself without supplemental introductions. Sensitivity analysis suggested that enhancing adult survivorship is more effective than enhancing fledging success to achieve a viable population. The model with connected subpopulations predicted fewer pairs than did nonspatial models and indicated that concentrating management efforts on the healthier, high-density population in northern California, rather than on the poorly performing population in central and southern California, would yield the largest overall population sizes. Fits of the model to yearly population data from 1980-1989 accurately predicted the size of the southern subpopulation, but slightly underestimated the size of the northern subpopulation, by six pairs. The model fit well when we excluded birds on newly discovered sites that possibly were active in previous years. Increasing northern adult survivorship to predict northern population sizes adequately led to a viable population exhibiting a source-sink relationship between subpopulations. Our results provide insight into the critical data to collect and the most successful strategies to execute in a management program, and give further indication of the importance of spatial structure to the dynamics of populations.

Novel Scavenger Removal Trials Increase Wind Turbine—Caused Avian Fatality Estimates

Abstract For comparing impacts of bird and bat collisions with wind turbines, investigators estimate fatalities/megawatt (MW) of rated capacity/year, based on periodic carcass searches and trials used to estimate carcasses not found due to scavenger removal and searcher error. However, scavenger trials typically place ≥10 carcasses at once within small areas already supplying scavengers with carcasses deposited by wind turbines, so scavengers may be unable to process and remove all placed carcasses. To avoid scavenger swamping, which might bias fatality estimates low, we placed only 1–5 bird carcasses at a time amongst 52 wind turbines in our 249.7-ha study area, each carcass monitored by a motion-activated camera. Scavengers removed 50 of 63 carcasses, averaging 4.45 days to the first scavenging event. By 15 days, which corresponded with most of our search intervals, scavengers removed 0% and 67% of large-bodied raptors placed in winter and summer, respectively, and 15% and 71% of small birds placed in winter and summer, respectively. By 15 days, scavengers removed 42% of large raptors as compared to 15% removed in conventional trials, and scavengers removed 62% of small birds as compared to 52% removed in conventional trials. Based on our methodology, we estimated mean annual fatalities caused by 21.9 MW of wind turbines in Vasco Caves Regional Preserve (within Altamont Pass Wind Resource Area, California, USA) were 13 red-tailed hawks (Buteo jamaicensis), 12 barn owls (Tyto alba), 18 burrowing owls (Athene cunicularia), 48 total raptors, and 99 total birds. Compared to fatality rates estimated from conventional scavenger trials, our estimates were nearly 3 times higher for red-tailed hawk and barn owl, 68% higher for all raptors, and 67% higher for all birds. We also found that deaths/gigawatt-hour of power generation declined quickly with increasing capacity factor among wind turbines, indicating collision hazard increased with greater intermittency in turbine operations. Fatality monitoring at wind turbines might improve by using scavenger removal trials free of scavenger swamping and by relating fatality rates to power output data in addition to rated capacity (i.e., turbine size). The resulting greater precision in mortality estimates will assist wildlife managers to assess wind farm impacts and to more accurately measure the effects of mitigation measures implemented to lessen those impacts.

Genetic differentiation, geographic variation and hybridization in gulls of the Larus glaucescens-occidentalis complex

Survey of morphometric, colorimetric, and allozymic variation in the Glaucous-winged Gull (Larus glaucescens), the Western Gull (L. occidentalis) and their hybrids is based on 706 specimens taken from 33 colony areas located throughout the breeding range of both species. Whereas most morphometric characters overlap between taxa, colorimetric characters exhibited significant intraspecific and interspecific clinal variation. Canonical discriminant function analysis of colorimetric characters clearly separated pure and hybrid morphotypes and confirmed the intermediacy of character expression in hybrids. Plumage melanism of the mantle and primary tips are among the best discriminators of hybrids. Twenty-five of 32 presumptive genetic loci were polymorphic. Although there were no fixed differences between taxa, gene frequencies exhibited significant heterogeneity across geography. Despite moderately high gene flow (Nm = 2.8 individuals per generation), populations of the L. glaucescens-occidentalis complex are not panmictic, and the hybrid zone forms a partial barrier to gene flow. Hybrids are genetically more similar to L. glaucescens than to L. occidentalis. The hybrid zone extends from Juan de Fuca Strait, Washington, south to Coos Bay, Oregon. A broad zone of introgression extends from the Queen Charlotte Islands in British Columbia south to Coos Bay, Oregon. The hybrid zone appears to have expanded in recent years, yet its midpoint near Grays Harbor, Washington, has remained stable. Hybridization appears to be responsible for skewed introgression and elevated genic diversity in L. glaucescens. The fact that L. glaucescens shows high levels of introgression while maintaining its genetic identity lends support to the hypothesis that hybridization in birds may serve as a mechanism for increasing or restoring genetic diversity in forms that are adapted to local environments.

Hybridization and Reproductive Performance in Gulls of the Larus glaucescens-occidentalis Complex

The Glaucous-winged Gull (Larus glaucescens) and the Western Gull (L. occidentalis occidentalis) hybridize along the Pacific Coast from Cape Flattery, Washington, south through central Oregon. A hybrid index, based on plumage and soft part colors, was used to study the distribution of morphotypes (e.g., pure and hybrid birds), mating patterns and reproductive performance at eight sympatric and two allopatric colonies. Mate choice appears to be weakly positive-assortative. In 1989 in the hybrid zone, L. o. occidentalis experienced significantly greater reproductive performance, measured as clutch size and egg volume difference, than either L. glaucescens or mixed pairs containing at least one hybrid individual. Although the hybrid zone has expanded somewhat in recent times, the midpoint of the zone and the relative proportion of morphotypes has remained stable. The hybrid zone is situated on a marine-ecotone. Within the hybrid zone, relative reproductive performance of L. o. occidentalis and hybrids may shift between years, whereas L. glaucescens may experience poor reproductive performance in all years. The selection-hybridization balance hypothesis may best explain the L. glaucescens-occidentalis hybrid zone.

Assessing predictions of population viability analysis: Peregrine Falcon populations in California

Population viability analysis (PVA) has been an important tool for evaluating species extinction risk and alternative management strategies, but there is little information on how well PVA predicts population trajectories following changes in management actions. We tested previously published predictions from a stage-structured PVA of Peregrine Falcons (Falco peregrinus) in California, USA (Wootton and Bell 1992), against population trajectories following the 1992 termination of statewide, active management (population supplementation of captive-reared young). In the absence of extensive post-management monitoring, we developed surrogate estimates of breeding population size by calibrating several citizen science data sets (Christmas Bird Count, CBC; and North American Breeding Bird Survey, BBS) to intensive population surveys taken primarily during the active management period. CBC abundance data standardized by observer effort exhibited a strong relationship to intensive survey data (r2 = 0.971), indicated significantly reduced annual population growth rates after management was terminated (λ = 0.023 ± 0.013 SE) than when supplementation occurred (λ = 0.089 ± 0.023 SE), and demonstrated an increasing population as predicted by the PVA. The population trajectory fell within the 95% CI of stochastic simulations of the model either with or without density dependence and assuming either measurement error or process error, but models with process error were most strongly supported by the data. These results indicate that PVA can quantitatively anticipate population trajectories following changes in management, highlight the importance of post-management monitoring of species of concern, and illustrate the benefits of using management changes as large-scale experiments to more rigorously test PVA.

Hybridization among Arctic white-headed gulls (Larus spp.) obscures the genetic legacy of the Pleistocene

We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes (Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites (FST= 0.129), introns (ΦST= 0.185), and mtDNA control region (ΦST= 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger τ estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed.

Foraging by Swainson's Hawks in a Vineyard-Dominated Landscape

ABSTRACT We studied habitat use for foraging by Swainsons Hawks (Buteo swainsoni) within a complex agricultural crop matrix in Californias Central Valley to ascertain if vineyards were used for foraging. Central Valley vineyard agriculture has increased recently, especially in areas supporting the highest regional numbers of Swainsons Hawks. There is concern that increased vineyard coverage may reduce the amount of foraging habitat available for Swainsons Hawks, because vineyards have been considered poor foraging habitat for this species, due to the height and density of the vines. In 2002 and 2003, we conducted road surveys to record observations of foraging Swainsons Hawks in relation to agricultural habitats. Using chi-square tests and 95% CIs, we assessed habitat selection for foraging Swainsons Hawks and determined whether habitat use varied throughout the breeding season. Swainsons Hawks used 10 unique habitat types for foraging during the breeding season. Swainsons Hawks used vineyards less than expected and irrigated hay and dryland grain habitats more than expected, with some variation in habitat use as the season progressed. The variety of habitats that Swainsons Hawks used for foraging in our study area suggests that maintenance of large heterogeneous areas of agricultural habitats that include crops such as alfalfa, as well as large tracts of grazed grasslands, should be one of the priorities for conservation of this species in this region.

Relationships of some mannikins and waxbills in the estrildidae

There is disagreement as to the number of genera comprising the mannikins (Lonchurinae). Some authors recognize two to five of the following genera:Lonchura, Euodice, Padda, Spermestes andOdontospiza. Other authors have merged the last four taxa into the enlarged genusLonchura. We bring together data from downy plumes (neossoptiles), nestling palate markings, begging vocalizations, agonistic behaviour, courtship postures and starch gel electrophoresis of allozymes to solve these taxonomic problems. PAUP analysis of the combined data set indicates thatSpermestes andOdontospiza belong to a monophyletic clade separate fromEuodice, Padda andLonchura. We propose mergingOdontospiza withSpermestes, which suggests an African radiation of the group, and placing the generaPadda andEuodice in withLonchura, which represents a mostly Australasian radiation. The genusAmadina has been treated by some as a mannikin (Lonchurinae) and by others as a waxbill (Estrildinae). Our data indicate thatAmadina should be assigned to the estrildines rather than the lonchurines.Amadinas relatively large, mannikin-like conical bill is a result of convergence, probably reflecting selection pressure on bill shape associated with diet specializations. Die eigentliche Zahl an Gattungen innerhalb der Nonnen (Lonchurinae) ist umstritten. Einige Autoren erkennen zwei bis fünf von den folgenden Gruppen an:Lonchura, Euodice, Padda, Spermestes, undOdontospiza. Letztere vier Gruppen sind von anderen Autoren in eine vergrößerteLonchura-Gattung vereinigt worden. Um diese taxonomischen Probleme zu lösen, präsentieren wir Daten an neossoptilen Daunenfedern, Rachenzeichnungen, Bettellautäußerungen, agonistischen Verhaltensweisen, Balzverhalten und Stärkegel-Elektrophorese von Proteinen. Eine PAUP (phylogenetische) Analyse aller Daten ergibt folgendes:Spermestes undOdontospiza gehören einer monophyletischen Clade an. Gleiches gilt für die GattungenEuodice, Padda undLonchura. Demzufolge schlagen wir vor, daßOdontospiza der GattungSpermestes, undPadda undEuodice der GattungLonchura, zugeordnet werden sollen. Damit stellt sichSpermestes als eine afrikanische, undLonchura als eine hauptsächlich australasiatische Radiation vor. Die GattungAmadina wird von einigen Autoren den Nonnen (Lonchurinae), von anderen den Eigentlichen Prachtfinken (Estrildinae) zugeordnet. Unsere Daten zeigen, daßAmadina den Estrildiden und nicht den Lonchurinen angehört. Der große kegelförmige, nonnenähnliche Schnabel vonAmadina ist aufgrund nahrungsbedingtem Selektionsdruck wohl durch Konvergenz zustande gekommen.

Genetic Evidence for Global Dispersal in the Peregrine Falcon (Falco peregrinus) and Affinity with the Taita Falcon (Falco fasciinucha)

Abstract We analyzed variation in cytochrome b mitochondrial DNA sequences in 11 subspecies of the Peregrine Falcon (Falco peregrinus), three samples of the Taita Falcon (F. fasciinucha) from Africa, and several other Falco and outgroup species, to assess haplotype diversity in the Peregrine Falcon on a worldwide basis. We identified 16 haplotypes from 31 Peregrine Falcon samples, of which 11 were unique and 5 were shared among two or more subspecies. There was neither concordance between cytochrome b variation and taxonomic designation at the subspecies level, nor any phylogeographic pattern in the genetic data. The Taita Falcon was nested within the Peregrine Falcon clade. Percent sequence divergence between the Taita Falcon and the Peregrine Falcon (0.4–1.2%) overlapped that among subspecies of the Peregrine Falcon (0.0–1.0%), suggesting very close genetic affinity between the two species. We hypothesize that historical and recent dispersal, combined with rapid morphological evolution, contributed to the lack of concordance between variation in cytochrome b mitochondrial DNA sequences and phylogeography in the Peregrine Falcon. EVIDENCIA GENÉTICA DE DISPERSIÓN GLOBAL DE FALCO PEREGRINUS Y SU AFINIDAD CON FALCO FASCIINUCHA Analizamos la variación en el citocromo b de secuencias de ADN mitocondrial en 11 subespecies de Falco peregrinus, en tres muestras de F. fasciinucha de África y en otros Falco y especies fuera del grupo para determinar la diversidad de haplotipos en F. peregrinus a escala mundial. Identificamos 16 haplotipos en 31 muestras de F. peregrinus, de las cuales 11 fueron únicas y 5 estuvieron compartidas entre dos o más subespecies. No hubo concordancia entre la variación del citocromo b y la designación taxonómica a nivel de subespecie, ni en el patrón filogeográfico en los datos genéticos. F. fasciinucha estuvo anidado dentro del clado de F. peregrinus. La divergencia porcentual de secuencia entre F. peregrinus y F. fasciinucha (0.4–1.2%) se superpuso con la de subespecies de F. peregrinus (0.0–1.0%), sugiriendo una afinidad genética muy cercana entre las dos especies. Hipotetizamos que la dispersión histórica y reciente, combinada con una evolución morfológica rápida, contribuyó a la falta de concordancia entre la variación en el citocromo b de secuencias de ADN mitocondrial y la filogeografía en F. peregrinus.