Some taxa of North American birds have unknown winter ranges, because of the difficulty in tracking individuals between seasons. Stable isotopes may provide clues to help locate these nonbreeding populations. Previously, no valid records existed for the Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) from October to late April. We used stable-isotope (C, N, and H) analyses to provide estimates of where molt occurs and then searched those areas for individuals of this species. The δ¹³C and δ¹⁵N of rump feathers were consistent with the Coastal Plain Swamp Sparrow molting in more saline marshes than the nominate subspecies after the breeding season, which confirms what was already known. The values for the same isotopes from crown feathers revealed that winter molt in the Coastal Plain Swamp Sparrow probably occurred in similar coastal brackish habitats. The δD of crown feathers indicated that prebreeding molt occurred at latitudes between South Carolina and Virginia. A subsequent search of this region located 18 Coastal Plain Swamp Sparrows, all of which were found in North Carolina or southeastern Virginia. Coastal Plain Swamp Sparrows were found predominantly in brackish marshes similar to their breeding habitat. On the basis of these observations, it appears that Coastal Plain Swamp Sparrows undergo a short southerly migration to a coastal region with substantially warmer winter conditions. This study is the first to make a specific geographic prediction based on stable-isotope analysis and to test the prediction in the field.

Análisis de Isótopos Estables (C, N, H) Ayudan a Localizar la Distribución Invernal de Melospiza georgiana nigrescens

Large-scale oceanographic processes are the main drivers of seabird breeding success, but small-scale processes, though not as well understood, can also be important. We compared the success of Tufted Puffins (Fratercula cirrhata) breeding at two subcolonies only 1.5 km apart on Triangle Island, British Columbia, Canada, 2002–2005. In addition, we used stable-isotope analysis to test the hypothesis that parental foraging strategies differed between the two subcolonies, potentially underlying the variation in breeding success. Success was concordant across years at the two sites but, overall, Tufted Puffins bred more successfully at Strata Rock than at Puffin Rock. They raised chicks in all four years at Strata Rock, but in only three years at Puffin Rock; in two of those three years, Strata Rock chicks were, on average, 60 g and 100 g heavier than Puffin Rock chicks just before fledging. Discriminant analysis of carbon and nitrogen stable-isotope ratios in egg yolk and chick blood in 2004 and 2005 indicated that parental foraging differed between the two subcolonies, with both spatial (δ¹³C) and trophic-level (δ¹⁵N) differences involved. Thus, our study demonstrates the existence of foraging asymmetries in a pelagic seabird at a small spatial scale (between subcolonies), complementing patterns found at larger scales (between colonies). Moreover, the foraging asymmetries were associated with inequalities in fitness measures. We conclude that small-scale processes—in this case, systematic differences in the foraging ecology of local groups—can interact with large-scale oceanographic processes to determine seabird breeding success.

Variation sous-coloniale du succès de reproduction de Fratercula cirrhata: Association avec l'écologie de la quête alimentaire et implications

We measured the energy requirements during postnatal development of six hand-reared Common Loon (Gavia immer) chicks using continuous feeding trials and doubly labeled water. At fledging, the mean (± SE) body mass of chicks was 3,246 ± 51 g. They reached asymptotic body mass in ≈66 days and had a mean growth rate constant of 0.089 ± 0.002 day⁻¹, which was greater than growth rate constants of other, similar-sized precocial birds. Between hatch and day 66, chicks allocated 16.5% of their metabolizable energy to new tissue, lower than the average for other bird species (20%), which might be expected considering their precocial mode of development. There was a developmental change in the assimilation efficiency of food (metabolizable energy coefficient), with a mean of 0.64 ± 0.03 in chicks aged 21 days, rising to 0.83 ± 0.07 in chicks aged 35 days.

Les besoins en énergie durant la croissance chez des jeunes Gavia immer élevés en captivité

Male Lance-tailed Manakins (Chiroxiphia lanceolata) perform multi-male courtship displays for females. To characterize the behavioral repertoire and the lek spatial organization of this species, I observed lekking males on Isla Boca Brava, Chiriquí Province, Panamá. Breeding began in March and continued through June, though courtship displays were recorded as late as November. Males were active throughout the day at display areas on the dispersed lek. Display areas were spaced 102 ± 30 m apart and averaged 2,480 ± 1,060 m² in area (range: 525–4,500 m²; n = 24 display areas). The behavioral repertoire of Lance-tailed Manakins included 11 dance display elements, 7 common vocalizations, and 2 types of male-male duet songs. Duet songs and multimale dances for females were cooperative efforts by male pairs and included display elements that were never performed during courtship displays by solitary males. However, males performed both cooperative and entirely solo displays for females that ended in successful copulation, which suggests that cooperation is not obligate in this species, at least on the level of individual displays. Two sonations, or nonvocal communicative sounds, were noted during courtship displays: low-amplitude pulses of noise produced in rapid sets of 7–30 clicks during slow flight displays, and a low-frequency woosh produced at the nadir of swoop displays. The Lance-tailed Manakin display repertoire provides information useful in comparative analyses of the origin and evolution of display behavior within the manakin clade and in studies of the adaptive consequences of individual behavior within this species.

Exhibición Cooperativa y Comportamiento de Asambleas de Cortejo en Chiroxiphia lanceolata

Population dynamics of small songbirds are driven in part by fecundity and productivity (i.e., the number of young that fledge and survive the dependent stage, respectively, per adult female per year). Because of the challenges of obtaining empirical estimates for productivity or fecundity, some researchers predict fecundity using a three-factor model or more complex models such as those developed by Pease and Grzybowski (1995) or Farnsworth and Simons (2001, 2005). All these models generate a single prediction with no estimate of variability around the prediction. We developed an individual-based model that provides predictions of productivity and measurements of variability surrounding the predictions for simulated populations of Louisiana Waterthrushes (Seiurus motacilla) based on various aspects of their breeding cycle. Our empirical estimate of productivity in Louisiana Waterthrush (x̄ ± SD = 1.50 ± 1.45) was similar to that provided by our individual-based model (1.07 ± 1.24). On the basis of our model, productivity was most sensitive to and increased dramatically with increasing fledgling survival, daily nest survival, followed by nestling survival. The remaining four factors had weak, if any, effects on productivity. When compared with our individual-based model, the three-factor and Pease and Grzybowski (1995) models often produced higher predictions of fecundity, ≤2.1 additional young fledged per female. This is likely attributable to the addition of a renesting rate in our individual-based model. The Farnsworth and Simons model often produced predictions that were similar to those from our individual-based model. We believe that our individual-based model is an improvement over most existing songbird-fecundity models and can be generalized to accommodate other breeding factors, including brood parasitism and temporal variability.

¿Cuáles Componentes de la Historia de Vida Determinan la Productividad Reproductiva Individual en las Aves Canoras? Un Estudio de Caso con Seiurus motacilla

We studied habitat requirements and selection of Olrog's Gulls (Larus atlanticus) breeding at six colonies along 2,500 km of coastline in central Argentina that encompasses its entire distributional range. Colonies were located only on islands that ranged in size between 0.4 and 125.8 ha, and the islands' distance to the mainland varied from 0.12 to 16.7 km. Colonies ranged in size between 12 and 341 nests. In three of the colonies, gulls nested in subcolonies (range: 8–239 nests). They nested at relatively high densities, with a mean inter-nest distance of 0.66 ± 0.25 m. Logistic regression analysis to compare nest and random-site characteristics at each colony showed that Olrog's Gulls selected sites that were close to the high-tide line, at a lower height above sea level, far from available vegetation, and had lower vegetation cover over the nest. Olrog's Gulls showed a significant positive association with Kelp Gulls (L. dominicanus), an expanding generalist species that also nests in similar habitats. Current trends in coastal development, particularly in the Olrog's Gulls' main breeding grounds of southern Buenos Aires, indicate the urgent need for habitat-protection guidelines for this threatened species. Moreover, its breeding association with Kelp Gulls suggests a potential spatial conflict and highlights the need for increased monitoring and management actions.

Selección y Requerimientos de Hábitat Reproductivo en Larus atlanticus, una Especie Amenazada

Brood parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds”) is an important factor contributing to the endangered status of the Southwestern Willow Flycatcher (Empidonax traillii extimus, hereafter “flycatcher”). We report on factors that influence brood parasitism on the flycatcher using seven seasons of nest data (n = 491 nests) collected in riparian patches comprising cottonwood (Populus fremontii), willow (Salix spp.), and boxelder (Acer negundo) along the Gila River in southwest New Mexico. We quantified habitat and landscape characteristics that might be associated with higher levels of parasitism and assessed the correlation between those and the observed incidence of nest parasitism. Given that cowbirds associate with cattle, we were particularly interested to determine whether the distance to active summer grazing would influence the frequency of brood parasitism. We found an apparent negative trend between the distance to grazing and brood parasitism, but this trend was not statistically significant. Rather, brood parasitism was more strongly correlated with characteristics of the habitat. Specifically, nests in larger patches, and nests built near the patch edge adjacent to the river, were more susceptible to parasitism, which suggests that these areas are preferred nesting habitat for cowbirds because of a potentially greater abundance of hosts. Parasitism was significantly lower within the core of large patches, but the insulating effect was not evident in small and medium-sized patches. Higher nest height was strongly correlated with lower probability of parasitism, most notably for nests in boxelders. Nests in boxelders were less susceptible to parasitism, whereas nests in willows were more susceptible to parasitism. We discuss the results in the context of other studies. We recommend that management efforts to recover the flycatcher should focus on increasing quality habitat, and we suggest that cattle management should focus on eliminating the adverse effects of grazing on riparian health as a more feasible option than removing cattle far enough from riparian corridors so as to preclude parasitism.

Empidonax traillii extimus en un Paisaje con Pastoreo: Factores que Influyen sobre el Parasitismo de la Nidada

Inferences based on counts adjusted for detectability represent a marked improvement over unadjusted counts, which provide no information about true population density and rely on untestable and unrealistic assumptions about constant detectability for inferring differences in density over time or space. Distance sampling is a widely used method to estimate detectability and therefore density. In the standard method, we model the probability of detecting a bird as a function of distance alone. Here, we describe methods that allow us to model probability of detection as a function of additional covariates—an approach available in DISTANCE, version 5.0 (Thomas et al. 2005) but still not widely applied. The main use of these methods is to increase the reliability of density estimates made on subsets of the whole data (e.g., estimates for different habitats, treatments, periods, or species), to increase precision of density estimates or to allow inferences about the covariates themselves. We present a case study of the use of multiple covariates in an analysis of a point-transect survey of Hawaii Amakihi (Hemignathus virens).

Amélioration des estimations de densité d’oiseaux par l’utilisation de l’échantillonnage par la distance avec covariables multiples

Previous laboratory studies have shown that Red-necked Phalarope (Phalaropus lobatus), Wilson’s Phalarope (P. tricolor), Western Sandpiper (Calidris mauri), and Least Sandpiper (C. minutilla) use the surface tension of water surrounding a prey item to transport it from bill tip to mouth. Although such experimental work suggests that many species of shorebird may be capable of surface-tension feeding, no field studies have been done that examine this possibility. We studied the occurrence and interspecific variation in the performance of surface-tension transport (STT) in wild shorebirds feeding on identical prey items in shallow water. All shorebirds videotaped—Little Stint (C. minuta), Dunlin (C. alpina), Sanderling (C. alba), Curlew Sandpiper (C. ferruginea), Common Redshank (Tringa totanus), and Black-winged Stilt (Himantopus himantopus)—used STT to feed on small prey items. Individuals employing STT used one or several cycles of jaw spreading to transport the prey contained in a drop of water upward along the bill cavity, an action indicative of STT. Two distinct types of prey transport were observed: (1) use of STT in isolation by calidridine species following the description given in previous studies (i.e., an absence of other feeding mechanisms such as tongue movements, suction, or inertial transport), and (2) STT aided by inertial transport (head jerks) as seen in Common Redshank and Black-winged Stilt. Measured prey-transport variables (number of cycles, total time, and speed of transport) varied among species. The absence of significant relationships between these variables and measures of external morphology (bill length, bill length-to-width ratio, and bill length-to-depth ratio) suggests that some interspecific variations in STT performance may be attributable to differences in internal bill morphology. We show that STT is a common feeding mechanism in small or medium- sized shorebird species that feed on small prey items in shallow water. Birds using STT transported ≤3.6× faster than the theoretical value predicted by a previous model and can achieve high intake rates when foraging on high densities of available small prey items.

Ventajas de las Presas Pequeñas: Análisis de Campo del Uso de la Tensión Superficial del Agua por las Aves Playeras para Transportar las Presas

To evaluate the possibilities and limitations of using white-blood-cell (WBC) counts to characterize investment in immune-system function, we compared the prevalence and intensity of malaria infections and concentrations of WBCs in the American Robin (Turdus migratorius) in Michigan and Missouri and in the Clay- colored Robin (T. grayi) in central Panama. We ascertained infection by polymerase chain reaction (PCR) screening and quantified infection intensity and WBC concentrations by visual inspection of blood smears. Because few parasites were observed on smears, we assumed that most cases of malaria represented chronic, rather than acute, infections. Prevalence of haemosporidian infection (Panama 41%, Missouri 57%, Michigan 63%) did not differ significantly between locations. However, most infections in Panama were undetected on blood smears, whereas more than half were apparent on smears in Michigan and Missouri. Among WBCs, lymphocytes were the most abundant type, followed by heterophils; eosinophils and lymphocytes were more common in the North American sample than in Panama, and their numbers in Michigan were significantly higher in infected than in noninfected individuals. Tropical T. grayi apparently maintained infections at lower intensities but appeared to accomplish this in spite of lower abundances of immune-system cells. Furthermore, analyses of blood smears of Turdus spp. from elsewhere in the tropics revealed a wide range of prevalence, which suggests that either the regional presence of haemosporidians or the ability of hosts to control infections cannot be learned from limited samples. Additional species surveyed in Michigan and Panama revealed no consistent pattern in either infection intensity or WBC concentrations. Infection and response appear to be highly idiosyncratic. In agreement with other authors, we caution that blood parameters are difficult both to interpret and to sam- ple adequately in tests of regional or other effects.

Prevalencia de Malaria y Respuesta de Glóbulos Blancos a la Infección en un Zorzal de la Zona Tropical y Uno de la Zona Templada

Reconnecting forest patches, including those of floodplain forest, often involves the creation of long, narrow corridors that have the potential to act as ecological traps for wildlife. We examined the effect of forest width and habitat composition of the landscapes immediately around nest patches on survival and parasitism of 359 Acadian Flycatcher (Empidonax virescens) nests in the Cache River Bioreserve in southern Illinois. Nests were distributed among 19 floodplain forest corridors along a small river system that is being restored and reconnected along its original floodplain. The corridors spanned a range of widths (80–3,170 m) and varied with the presence or absence of natural water-related habitats (beaver ponds, backwater swamps, and creeks). Although nest success varied slightly between stages of the breeding cycle, confidence intervals overlapped, which suggests constant nest success throughout the breeding cycle. Nest survival was relatively high by regional standards but did not vary significantly with any of the landscape variables measured. Contrary to predictions, probabilities of brood parasitism decreased with increasing proportions of anthropogenic habitats surrounding nests. Probabilities of brood parasitism also decreased, but only slightly, as the breeding season progressed. Finally, Acadian Flycatcher nests were located significantly more often near natural (forest-water interface) edges than expected at random. Narrow corridors such as those along floodplain restoration projects do not necessarily create ecological traps for all forest species. Acadian Flycathcers, however, are one of the only forest-nesting Neotropical migrants that nest in narrow corridors and, therefore, may be less vulnerable to negative effects of fragmentation.

Éxito de Nidificación de Empidonax virescens en Corredores de Bosque de Planicies Inundables

We examined the relationship between mass late in the first summer and survival and return to the natal breeding colony for 12 cohorts (1986-1997) of female Black Brant (Branta bernicla nigricans). We used Cormack-Jolly-Seber methods and the program MARK to analyze capture-recapture data. Models included two kinds of residuals from regressions of mass on days after peak of hatch when goslings were measured; one based on the entire sample (12 cohorts) and the other based only on individuals in the same cohort. Some models contained date of peak of hatch (a group covariate related to lateness of nesting in that year) and mean cohort residual mass. Finally, models allowed survival to vary among cohorts. The best model of encounter probability included an effect of residual mass on encounter probability and allowed encounter probability to vary among age classes and across years. All competitive models contained an effect of one of the estimates of residual mass; relatively larger goslings survived their first year at higher rates. Goslings in cohorts from later years in the analysis tended to have lower first-year survival, after controlling for residual mass, which reflected the generally smaller mean masses for these cohorts but was potentially also a result of population-density effects additional to those on growth. Variation among cohorts in mean mass accounted for 56% of variation among cohorts in first-year survival. Encounter probabilities, which were correlated with breeding probability, increased with relative mass, which suggests that larger goslings not only survived at higher rates but also bred at higher rates. Although our findings support the well-established linkage between gosling mass and fitness, they suggest that additional environmental factors also influence first-year survival.

Supervivencia y Ventajas Reproductivas de los Pichones de Mayor Tamaño de Branta bernicla nigricans: Variación entre y dentro de las Cohortes

We describe a postcranial skeleton of a stem-group tody (Aves: Alcediniformes: Todidae) from the early Oligocene of Germany. The fossil is tentatively assigned to Palaeotodus itardiensis Mourer-Chauviré, 1985, which previously was known only from a few incomplete bones from the early Oligocene of France. It is the most substantial fossil record of a Paleogene stem-group tody described so far and shows many previously unknown skeletal details. The specimen confirms the occurrence of Todidae, which are today restricted to the Caribbean Greater Antilles, in the Paleogene of Europe. The biogeographical significance of these finds depends on the phylogenetic relationships between Todidae and other alcediniform birds. If Todidae are not the sister taxon of Momotidae (motmots) as suggested by a recent phylogenetic analysis of molecular data, occurrence of stem-group Todidae in the Old World fossil record actually follows from the currently assumed Old World origin of alcediniform birds.

Ein Todi (Alcediniformes: Todidae) aus dem unteren Oligozän Deutschlands

The Central Valley of California is an important breeding area for Mallards (Anas platyrhynchos), but estimating recruitment rates for this population has been hampered by lack of data on duckling survival. To gain a better understanding of factors affecting brood and duckling survival, we radiomarked 56 brood hens and 112 ducklings (two per brood) on two actively managed wetland complexes in the San Joaquin Valley during 1996-1997. Total brood mortality was extensive, affecting 27 of 53 broods (51%). Survival of individual ducklings from hatching until 30 days of age was 24.8% (95% confidence interval: 0.178–0.335), with most mortality resulting from predation during the first 12 days of life. Survival differed between years and study areas but was unaffected by hatching date. Broods preferred reverse-cycle seasonal wetlands to more permanent wetlands throughout their first 30 days of life, and ducklings also had higher 2- to 30-day survival probabilities in reverse-cycle wetlands (x̄ ± SE = 0.755 ± 0.095) than in semipermanent-permanent wetlands (0.189 ± 0.056) or moist-soil units (0.173 ± 0.067). We recommend that waterfowl managers in the Central Valley provide reverse-cycle seasonal wetlands during the broodrearing period to enhance survival of locally breeding Mallards.

Supervivencia y Uso de Hábitat por Nidadas de Anas platyrhynchos en el Valle de San Joaquín, California

We tested the monophyly and determined the phylogenetic relationships of the seven genera (Laniisoma, Laniocera, Iodopleura, Pachyramphus, Schiffornis, Tityra, and Xenopsaris) and 27 of the 31 recognized species of the subfamily Tityrinae using complete gene sequence data from the mitochondrial gene NADH dehydrogenase subunit 2. Monophyly of all seven genera was recovered using both weighted parsimony and Bayesian methods. Intergeneric relationships were nearly identical between the two methods and are largely in concordance with previous studies. Both analyses recovered two basal clades within the Tityrinae: one clade contained Schiffornis, Laniocera, and Laniisoma; the other clade consisted of Iodopleura, Tityra, Xenopsaris, and Pachyramphus. All genera in the Tityrinae that contained multiple species were monophyletic and are concordant with current taxonomy. We present the first phylogeny for Pachyramphus and suggest that Platypsaris is not valid. Character mapping of morphological, nest-construction, and breeding-system data on our phylogeny suggest conservative evolution of most characters. We recommend elevating the Tityrinae to family level.

Sistemática y Evolución de los Tityrinae (Passeriformes: Tyrannoidea)

In alternate plumage, the White-throated Sparrow (Zonotrichia albicollis) is polymorphic, such that individuals exhibit a median crown stripe that is either white or tan in color. This plumage polymorphism is believed to be caused by a chromosomal inversion and predicts many aspects of an individual’s aggressive and parental behavior, which makes this species an interesting and valuable subject for the study of the genetic basis of social behavior. Although the plumage polymorphism is well described, in practice the determination of morph for individual birds is not perfectly straightforward. Whereas morph can be assessed relatively easily in alternate plumage, birds in basic plumage tend to show coloration characteristic of both morphs. During the winter and fall, therefore, plumage morph cannot be determined with 100% accuracy by visual inspection alone. Here, we describe a genotyping assay that reliably predicts morph in alternate plumage. DNA from one drop of blood is amplified by PCR, digested and run on an agarose gel. The resulting banding patterns are used to distinguish white-striped from tan-striped birds with 100% accuracy. This method is fast and economical compared with karyotyping, is far less subjective than assessment of morph by plumage characteristics, and can be performed using any kind of sample from which DNA can be extracted.

Un test génotypique pour déterminer la forme du plumage chez Zonotrichia albicollis

In response to evidence of sexual segregation at foraging grounds as well as male-biased band recoveries, we investigated the ontogeny of the female- biased adult sex ratio in the Waved Albatross (Phoebastria irrorata), an IUCN “critically endangered species” essentially endemic to Isla Española, Galapagos, Ecuador. Using a molecular technique to determine the sex of chicks and adults and known fate analysis of chicks during rearing, we found no evidence of a sex-ratio bias at hatching or fledging in three consecutive years with variable reproductive success. Although male chicks were significantly larger than females at fledging, survival to fledging of a large sample of male and female chicks did not differ. The sex ratio among a cohort of young adults at approximately the age of first breeding (eight years) also did not differ significantly from parity. Differential adult mortality, including male-biased mortality in fisheries, is the most probable cause of a female- biased population sex ratio, and is at least partially responsible for an apparent reduction in the number of breeding pairs of this species.

El Albatros Phoebastria irrorata, una Especie con Dimorfismo Sexual, Presenta una Mayor Proporción de Hembras Luego del Cuidado Parental

Hermit Warblers (Dendroica occidentalis) and Townsend’s Warblers (D. townsendi) meet and hybridize in three replicate zones in Washington and Oregon. Using male specimens, we show that the ratio of hybrid to parental phenotypes varies systematically across these three zones: there were 60.4% hybrids among 96 males from the Olympic zone, 43.3% hybrids among 411 males from the Washington Cascade zone, and 27.8% hybrids among 209 males from the Oregon Cascade zone. We found no evidence of habitat or climatic factors driving these systematic differences in hybrid frequencies, and we argue that they are related to differences among these zones in the immigration of pure parentals and time since contact. Building on earlier hypotheses about massive movement of the coastal zones (Rohwer and Wood 1998), we can infer that the Olympic and Washington Cascade zones are old and of similar age. The Washington Cascade zone, but not the Olympic zone, receives Townsend’s immigrants from the Rocky Mountains through the Okanogan high- lands, as shown by the linkage analyses in Rohwer et al. (2001). This immigration apparently accounts for the lower frequency of hybrids in the Washington Cascades. The Washington Cascade and Oregon Cascade zones are both situated adjacent to forest corridors that connect them to the Rocky Mountains to the east, so both of these zones should receive Townsend’s immigrants from the east (linkage analyses have yet to be done for the Oregon Cascades because the mitochondrial DNA haplo- types for these specimens have not been determined). The Washington Cascade zone, however, is old, whereas the Oregon Cascade zone appears to have been established only recently in response to anthropogenic habitat changes, which accounts for its low frequency of hybrids. We are unaware of any other replicate set of hybrid zones where differences in time since contact and dispersal have been related to variation in hybrid frequencies.

El Tiempo Transcurrido desde el Contacto y el Flujo Genético Podrían Explicar la Variación en la Frecuencia de los Híbridos entre Tres Zonas de Hibridación entre Dendroica townsendi y D. occidentalis (Parulidae)

Studies of source-sink dynamics are often prompted by concerns about negative population trends. Estimates of population trajectories are usually based on assumptions about survival rates and empirical measures of fecundity. Most models ignore the influence of the rates of renesting and multiple brooding. We used the Ovenbird (Seiurus aurocapilla) as a model Neotropical migratory songbird species to investigate the relative effects of annual female survival and components of annual fecundity on population growth rates. We applied productivity data from a three- year field study and data from Hann (1937) to several models of annual fecundity to examine the sensitivity of lambda to variations in annual female survival and the likelihood of renesting and double-brooding. Our simulations illustrate the importance of incorporating estimates of annual survival and rates of additional breeding attempts in songbird population models because population growth rates are quite sensitive to variations in these parameters. Lambda is especially sensitive to survival estimates and changes with them at the same order of magnitude. Whenever feasible, female survival and probabilities of additional breeding attempts should be estimated by direct methods. The indirect methods used in our study (annual female survival estimated from the age ratio of breeding females, and rates of renesting and double- brooding determined from the timing of reproduction) probably underestimated these parameters.

Modelado del Crecimiento Poblacional de Seiurus aurocapilla en el Sur de los Apalaches

Double sampling involves combining information from inexpensive rapid counts with intensive complete counts to provide an efficient population estimate. This technique is a valuable approach for calibrating population indices based on incomplete counts and improving the precision of monitoring studies. Data collected through a double-sampling protocol can be analyzed with either a ratio or a regression estimator. The ratio estimator is recommended when the relationship of the actual count to the rapid count is a straight line through origin, which may not be valid when surveying populations that have a small number of individuals per site and a low detection probability. In such situations, the regression estimator may be more appropriate. I investigated the properties of these two different estimators through a simulation study and tabulated sample sizes to control bias of the population average and standard error. Further, I used the results to evaluate when double sampling is a cost-effective design and how to design surveys that meet precision requirements. The design process is illustrated with the Spring Eastern Waterfowl Survey, which shows that double sampling is not always appropriate.

Directives pour l’utilisation de l’échantillonnage double dans le suivi des populations d’oiseaux

Pointed wingtips and low wing-loading are believed to reduce the amount of energy used during migratory flight. If this is true, individuals with pointed wingtips or consistently low wing-loading should be able to migrate faster than conspecifics and may arrive on the breeding grounds and at stopover sites earlier. To test this hypothesis, I captured 97 Swainson's Thrushes (Catharus ustulatus; hereafter “thrushes”) during May in three consecutive field seasons, 2003-2005, at a stopover site in central Illinois. I used molecular techniques to sex 47 of these thrushes and created a discriminant function analysis using wing, tarsometatarsus, and tail lengths that predicted sex with 80.9% accuracy (P < 0.001). I applied this function to the remaining 50 thrushes so that I could control for any sexual dimorphism in morphology and arrival timing, and then examined seasonal trends in sex and morphology. Male thrushes arrived earlier at my stopover site than females (P < 0.001). After controlling for sex, thrushes with more pointed wingtips (P = 0.002) and lower wing-loading (P = 0.044) arrived earlier than thrushes with more rounded wingtips and higher wing-loading. The general linear model with sex, wingtip pointedness, and wing-loading explained nearly one-third of the variation in arrival date (P < 0.001, r² = 0.281, n = 90). Pointed wingtips and lower wing-loading may help migratory birds cover distance more quickly and arrive at the breeding grounds sooner; alternatively, thrushes with more pointed wingtips and lower wing-loading may have departed from the wintering grounds earlier. If wing shape and size affect rate of migration, these variables may be important determinants of individual quality in migratory passerines.

El Sexo, la Forma de las Puntas de las Alas y la Carga Alar Predicen la Fecha de Arribo de Catharus ustulatus a un Sitio de Escala Migratoria

We report seasonal residency and local annual survival rates of migratory Semipalmated Sandpipers (Calidris pusilla) at the Cabo Rojo salt flats, Puerto Rico. Residency rate (daily probability of remaining on the flats) was 0.991 ± 0.001 (x̄ ± SE), yielding a mean length of stay of 110 days. This finding supports the inclusion of the Caribbean as part of the species' winter range. Average estimated percentage of fat was low but increased throughout the season, which suggests that birds replenish some spent fat reserves and strive for energetic maintenance. Local annual survival rate was 0.62 ± 0.04, within the range of values reported for breeding populations at Manitoba and Alaska (0.53–0.76). The similarity was not unexpected because estimates were obtained annually but at opposite sites of their annual migratory movements. Birds captured at the salt flats appeared to be a mix of birds from various parts of the breeding range, judging from morphology (culmen's coefficient of variation = 9.1, n = 106). This suggested that origin (breeding area) of birds and their proportion in the data should be ascertained and accounted for in analyses to glean the full conservation implications of winter-based annual survival estimates. Those data are needed to unravel the possibility that individuals of distinct populations are affected by differential mortality factors across different migratory routes. Mean length of stay strongly suggested that habitat quality at the salt flats was high. Rainfall and tidal flow combine to increase food availability during fall. The salt flats dry up gradually toward late January, at the onset of the dry season. Semipalmated Sandpipers may move west to other Greater Antilles or south to sites such as coastal Surinam until the onset of spring migration. They are not an oversummering species at the salt flats. Conservation efforts in the Caribbean region require understanding the dynamics of this species throughout winter to protect essential habitat.

Tasas de Supervivencia Anual Local y de Residencia Estacional de Calidris pusilla en Puerto Rico

From 1996 to 2001, researchers at 10 Appalachian study sites collected radiotracking data sufficient to delineate 1,054 seasonal home ranges of Ruffed Grouse (Bonasa umbellus; hereafter “grouse”). Using information-theoretic model selection and paired comparison of home ranges from individual grouse, we evaluated individual, local, and landscape factors hypothesized to affect grouse home-range size. Females and juvenile males occupied home ranges that averaged >2× larger than those of adult males, and home ranges of females averaged 2.6× larger during successful breeding seasons than during years of reproductive failure. Clearcuts and forest roads are considered high-quality covers, and both were more prevalent in smaller home ranges. Several factors operating at a regional and landscape scale were also important. Previous studies have reported that southern grouse use relatively large home ranges, and we observed a continuous decline in home-range size with increasing latitude across the 710-km range spanned by our study sites. Home-range size of males, particularly juvenile males, was positively related to an index of population density. Given the species' “dispersed lekking” mating system, we interpret this as evidence of competition for preferred display sites. As has been reported for other game birds, all sex and age classes of grouse used smaller home ranges following closure of sites to hunting. Grouse inhabiting oak-hickory forests used larger home ranges than conspecifics in mixed mesophytic forests, and other factors interacted with forest type. In oak-hickory forests, female home-range size was inversely related to use of mesic bottomlands, which support important forage plants, and home ranges of adult grouse increased 2.5× following poor hard-mast crops. By contrast, home ranges of grouse inhabiting mixed mesophytic forests were unrelated to use of bottomlands, and the influence of hard mast was reduced. This is in line with the view that in Appalachian oak-hickory forests, grouse are under strong nutritional constraint. However, this constraint is reduced in mixed mesophytic forests, likely because of the presence of high-quality alternative foods (e.g., cherry [Prunus spp.] and birch [Betula spp.]).

Facteurs associés à une variation de la taille du domaine vital de Bonasa umbellus dans les Appalaches

Four thrush species are sympatric in the central Appalachians: Veery (Catharus fuscescens), Hermit Thrush (C. guttatus), Wood Thrush (Hylocichla mustelina), and American Robin (Turdus migratorius). The four species often nest near one another, which suggests that habitat partitioning may have developed to minimize past interspecific competition. Our objectives were to determine which specific characteristics of nesting habitat were partitioned among the species and to evaluate the relationship of these characteristics to nest survival. We monitored nests and sampled habitat variables at three spatial scales: nest substrate, nest site, and territory. A multivariate analysis of variance indicated a difference (P < 0.01) in the nest sites of all species and in each pairwise species contrast. An analysis of variance and Fisher’s exact tests detected differences (P < 0.05) among species in 21 of 36 variables measured. Classification tree analysis correctly classified nests by species at a rate better than would be expected at random. Habitat partitioning among the four thrush species occurred at all three scales sampled, with the most important partitioning variables being nest height, distance-to-edge, sapling density, and elevation. Mayfield logistic regression found a positive relationship (P < 0.05) between decreasing nest height and American Robin nest survival. Overall, nest survival was similar among the four thrush species examined, and most of the variables that we measured were unrelated to survival.

Partition de l’habitat de quatre espèces sympatriques de grives à trois échelles spatiales dans une forêt aménagée de la Virginie-Occidentale

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists’ Union.

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists’ Union.

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists’ Union.

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists’ Union.