We measured fresh body mass, total body fat, and fat-free dry mass (FFDM) of three species of Arctic-nesting calidrid sandpipers (Baird's Sandpiper [Calidris bairdii], hereafter “BASA”; Semipalmated Sandpiper [C. pusilla], hereafter “SESA”; and White-rumped Sandpiper [C. fuscicollis], hereafter “WRSA”) during spring stopovers in the Prairie Pothole Region (PPR) of North Dakota, and evaluated the contribution of stored fat to (1) energy requirements for migration to their Arctic-breeding grounds and (2) nutrient needs for reproduction. All spring migrant WRSA (n = 124) and BASA (n = 111), and all but 2 of 99 SESA we collected were ≥2 years old. Male and female BASA migrated through North Dakota concurrently, male SESA averaged earlier than females, and WRSA males preceded females. Fat indices (ratio of fat to FFDM) of male and female SESA and WRSA averaged approximately twice those of male and female BASA. Total body fat of male and female BASA increased with date in spring 1980, but not in 1981; slopes were similar for both sexes each year. Male and female SESA arrived lean in 1980 and 1981, and total body fat increased with date in both years, with similar slopes for all combinations of sex and year. Male and female WRSA arrived lean in 1980–1981 and 1981, respectively, and total body fat increased with date, whereas females arrived with fat reserves already acquired in 1980. Interspecific and sex differences in migration schedules probably contributed to variation in fat storage patterns by affecting maintenance energy costs and food availability. Estimated flight ranges of BASA suggest that few could have met their energy needs for migration to the breeding grounds exclusively from fat stored by the time of departure from North Dakota. Estimated flight ranges of SESA and WRSA, along with fresh body masses of both species when live-trapped on or near their breeding grounds in northern Canada, suggest that major parts of both populations stored adequate fat by departure from temperate mid-continental North America to meet their energy requirements for migration and part of their nutrient needs for reproduction.

Dinámica de la Grasa en Chorlos que Nidifican en el Ártico durante la Primavera en el Área Continental Central de América del Norte

A new species of Hawaiian finch is described from two fossil maxillae recovered from Holocene lacustrine sediments in Makauwahi Cave, island of Kaua‘i. The new species is assigned to Loxioides on the basis of characters defined in a previous study of drepanidine phylogeny. The maxilla of the new species resembles that of L. bailleui (the only other member of the genus) in its distinctly foreshortened shape, but differs in size and several qualitative characters. The species was sympatric with Loxioides cf. bailleui during the Holocene on Kaua‘i. Like L. bailleui, it may have been a resource specialist feeding mainly on leguminous pods. The radio-carbon chronology of the Makauwahi site indicates that the species became extinct in the late Holocene and, more tentatively, that it may have survived well beyond the time when humans first discovered and colonized Kaua‘i.

Una Nueva Especie de Pinzón de Hawaii (Drepanidini: Loxioides) de la Cueva Makauwahi, Kaua‘i

Point-transect sampling is widely used for monitoring trends in abundance of songbirds. It is conceptualized as a “snapshot” method in which birds are “frozen” at a single location. With conventional methods, an observer records birds detected from a point for several minutes, during which birds may move around. This generates upward bias in the density estimate. I compared this conventional approach with two other approaches: in one, the observer records locations of detected birds at a snapshot moment; in the other, distances to detected cues (songbursts), rather than birds, are recorded. I implemented all three approaches, together with line-transect sampling and territory mapping in a survey of four bird species. The conventional method gave a biased estimate of density for one species. The snapshot method was found to be the most efficient of the point-sampling methods. Line-transect sampling proved more efficient than the point-sampling methods for all four species. This is likely to be generally true, provided that terrain and habitat allow easy use of a design with random transect lines. I concluded that the snapshot method is more appropriate than the conventional timed-count method for surveying songbirds. Although precision was rather poor with the cue-based method (partly because too few resources were devoted to cue rate estimation), it may be particularly useful for some single-species surveys. In addition, it is the only valid method for estimating abundance from surveys in which acoustic equipment is used to detect birds.

Muestreos en Transectos Puntuales para Aves Canoras: Metodologías Robustas

We assessed seed preference in four species of sparrows that are common to the central Monte desert of Argentina. Our hypotheses are that (1) sparrows always prefer grass over forb seeds and (2) different species of sparrows show the same preferences when consuming seeds. We presented seeds from eight species of plants (four grasses and four forbs) in both choice and nonchoice experiments. In general, sparrow species preferred grass over forb seeds, though one of them (Rufous-collared Sparrow [Zonotrichia capensis]) included one forb species (Parthenium hysterophorus) among its preferred seed items. Among grass seeds, sparrows avoided or showed less preference for the tiny seeds of Sporobolus cryptandrus, which suggests that seed weight may affect seed choice among grasses. Avoidance of most forb species, by contrast, could not be associated with seed size, probably because of the presence of unpalatable or toxic compounds in forb seeds. Experimental evidence suggests that the main feeding pressure of sparrows is clearly directed to grass seeds, which coincides with reported information on bird diet. Results support assertions that sparrows can cause a negative effect on the composition and abundance of grass seeds in the soil seed-bank, a necessary condition for birds in playing a significant role on grass population dynamics in the central Monte desert of Argentina.

Preferencias por Semillas de los Emberízidos del Desierto del Monte, Argentina: Implicancias para la Interacción Semillas-granívoros

We used a multiscale approach to examine use of riparian forests by Acadian Flycatchers (Empidonax virescens) at three distinct scales: microsite (nest or territory), local stand (3-ha patch of forest), and landscape (1-km-radius area). We examined the extent to which understory arthropod biomass, vegetation structure, and breeding productivity affected habitat use by Acadian Flycatchers across 36 mature riparian forests along an urbanization gradient in central Ohio, 2001–2002. Using an information-theoretic approach, we found that although vegetation structure and understory arthropod biomass were associated with nest and territory location at small spatial scales, they failed to explain habitat use across stands. Instead, percentage of urban cover in the landscape best explained variation in the abundance of Acadian Flycatchers among stands. In fact, Acadian Flycatchers were >3× more abundant in the most rural (≤1% urban) riparian forests than in the more urban (≥10% urban) riparian forests. Nest survival and productivity also declined as urban development increased within the landscape. We suggest that increased nest predation in urban riparian forests, coupled with either reduced productivity or site fidelity or both, may be an underlying mechanism of landscape-scale patterns. Results suggest that explicit consideration of multiple spatial scales, and especially landscape matrix composition, is critical for understanding habitat use.

Uso del Hábitat Dependiente de la Escala por parte de Empidonax virescens en el Centro de Ohio

The sperm of the Eurasian Bullfinch (Pyrrhula pyrrhula) differs markedly in gross morphology from that of all other passerines examined to date. In other passerines, the sperm head is pointed and helical, and the midpiece comprises a mitochondrial helix extending along the flagellum; whereas in the Eurasian Bullfinch, the sperm acrosome is rounded, not helical, and the midpiece is extremely short. In a pairwise study, using principal component analysis (PCA), we combined quantitative and qualitative sperm morphology traits and conducted a phylogenetic correlation to compare the sperm morphology of Eurasian Bullfinch and Beavan's Bullfinch (P. erythaca) with nine other pairs of congeneric passerines. The analysis revealed that Eurasian Bullfinch was a dramatic outlier in sperm morphology and that Eurasian and Beavan's bullfinches are more different than any other pair of species. Excluding Eurasian Bullfinch from the analysis showed that most variation in sperm morphology in the other species was attributable to phylogeny. The Eurasian Bullfinch also has extremely small testes for its body size, which indicates that sperm competition is infrequent in this species; we discuss the possibility that relaxed selection, via lack of sperm competition, may have contributed to the species' unusual sperm morphology.

Morfología Espermática Inusual en Pyrrhula pyrrhula

We evaluated the relationship between salinity and Bald Eagle (Haliaeetus leucocephalus) population parameters using 26 years of survey data for the lower Chesapeake Bay. Tidal tributaries within the study area were stratified according to the Chesapeake Bay Program's segmentation scheme, and segments with the same salinity classification were considered spatial replicates. Salinity categories included tidal fresh, oligohaline, mesohaline, and polyhaline. Four parameters— colonization rate, nesting density, projected carrying capacity, and productivity— were derived from nesting data within each shoreline segment and compared across the salinity gradient. The study-wide Bald Eagle population is exhibiting exponential growth, with an average doubling time of 7.9 years. All population parameters showed significant directional variation with salinity. Average population doubling time for tidal fresh reaches was <6 years, compared with >16 years for polyhaline areas. Current Bald Eagle nesting density is negatively related to salinity and varies by a factor of 4 across the gradient. Comparison of current densities with projected carrying capacity suggests that these differences will be stable or increasing as the geographic areas approach equilibrium densities. We suggest that fisheries within lower saline reaches, including spring spawning runs of anadromous Clupeidae (shad and herring), are the most likely explanation for salinity effects. Observed distribution patterns suggest that lands along low-salinity waters are the core of the Bald Eagle nesting population within the lower Chesapeake Bay and should be the focus of long-term programs designed to benefit nesting eagles.

Salinidad y Parámetros Poblacionales de Haliaeetus leucocephalus en la Bahia de Chesapeake

We investigated effects of ecological and physiological factors on brood patch area and prolactin levels in free-ranging Lesser Snow Geese (Chen caerulescens caerulescens; hereafter “Snow Geese”) and Ross's Geese (C. rossii). On the basis of the body-size hypothesis, we predicted that the relationships between prolactin levels, brood patch area, and body condition would be stronger in Ross's Geese than in the larger Snow Geese. We found that brood patch area was positively related to clutch volume and inversely related to prolactin levels in Ross's Geese, but not in Snow Geese. Nest size, nest habitat, and first egg date did not affect brood patch area in either species. Prolactin levels increased as incubation progressed in female Snow Geese, but this relationship was not significant in Ross's Geese. Prolactin levels and body condition (as indexed by size-adjusted body mass) were inversely related in Ross's Geese, but not in Snow Geese. Our findings are consistent with the prediction that relationships between prolactin levels, brood patch area, and body condition are relatively stronger in Ross's Geese, because they mobilize endogenous reserves at faster rates than Snow Geese.

Factores Ecológicos y Fisiológicos que Afectan el Área del Parche de Incubación y los Niveles de Prolactina en Gansos Nidificantes del Ártico

In the coevolutionary “arms race” between Common Cuckoos (Cuculus canorus) and their hosts, several adaptations and counter-adaptations have evolved. Here, we investigated natural parasitism and host sensitivity to egg rejection in Marsh Warblers (Acrocephalus palustris) in Bulgaria. The level of Common Cuckoo parasitism was high (28%), and average mimicry of Common Cuckoo eggs was good. Experimental parasitism with four egg-types that showed various degrees of mimicry of the host eggs revealed a generally high rejection rate of foreign eggs (37.5–100%). In addition, naturally laid Common Cuckoo eggs were rejected at a moderate rate (50%). The Marsh Warbler's ability to reject foreign eggs was strongly dependent on the degree of mimicry of the parasite egg but apparently not on differences in size between host and foreign eggs. Furthermore, intraclutch variation in host egg appearance was not related to the probability of egg rejection. The Marsh Warbler's highly developed egg-recognition ability and the good mimicry of Common Cuckoo eggs suggests that this poorly known host-parasite arms race has reached an advanced stage. The present study provides new insight into variables that are important for egg rejection in a heavily parasitized host population.

Rechazo de Huevos en Nidos de Acrocephalus palustris Fuertemente Parasitados por Cuculus canorus

Tracking seasonal movements of songbirds is a key step in understanding the annual cycle of migrants. To better understand autumn migration of wood warblers, I analyzed stable-hydrogen isotope ratios of feathers collected from three species captured during stopover at the Bosque del Apache National Wildlife Refuge, New Mexico. To assess the form and strength of the relationship between timing of migration and breeding origins, I regressed stable-hydrogen isotope ratios of feathers against date of capture. These analyses indicated that Orange-crowned Warblers (Vermivora celata) and Common Yellowthroats (Geothlypis trichas) breeding in the southern portion of these species' ranges precede their northern conspecifics in autumn migration. By contrast, Yellow Warblers (Dendroica petechia) from northern breeding sites arrived before more southerly breeding conspecifics. This pattern is similar to that reported previously in Wilson's Warbler (Wilsonia pusilla). These findings suggest that, among wood warblers, (1) timing of autumn migration is often strongly related to breeding location and (2) interspecific variation in the direction of this relationship is large. The direction and strength of these patterns have implications for our understanding of inter- and intraspecific geographic variation in the life histories of migrants.

Evidencia de Isótopos Estables Conecta la Geografía de Nidificación con el Momento de la Migración en Especies de Parulidae

Point counts are often used to provide information on abundance of songbirds. If data from point counts are to be compared in space or time, however, any bias in the estimate should be consistent and linearly related to the true abundance. Several studies have suggested that this assumption may be violated for songbirds. Here, we used double sampling to test whether point counts are linearly related to true abundance, as estimated from spot mapping, for 12 songbird species in the boreal mixed-wood forest of northern Alberta, Canada. We found that total abundance of birds across several point-count stations was positively correlated with the number of territories and confirmed that point counts were linearly related to spot-mapping abundance for the species tested. However, large sampling errors masked this relationship at the scale of a single point-count station (100-m fixed-radius plot). Double-sampling models that accounted for differences in abundance between spot-mapping grids using random effects improved prediction for most species. We found no year effect on detectability. Maximum abundance over point-count rounds was a more sensitive index of abundance than mean abundance and tended to produce better-fitting models. Point-count abundance was more closely related to true abundance in species with relatively small territories, or those with large spatial or temporal variation in density. Our results further suggest that point-count abundance may be proportional to the total length of territorial boundaries in the plot rather than the total fraction of territories in the plot. Our analysis suggests that point counts provide a reasonable index of abundance, even though individual point-count stations are not consistently effective in estimating the density of territorial individuals.

Est-ce que les Points D'Écoute de Passereaux Boréaux Constituent une Méthode Fiable pour L'Obtention D'Estimateurs D'Abondance Plus Avancés?

The evolution of avian migration continues to be an intriguing research subject, even though relationships between migration and factors such as seasonality clearly exist. The question remains whether these relationships are evident within phylogenies containing both sedentary and migratory taxa. We explore the evolution of migration in the family Motacillidae by evaluating existing hypotheses for the evolution of migration in a comparative, phylogenetic framework at the interspecific level. Many hypotheses to explain the evolution of avian migration—such as the “evolutionary precursor” hypothesis (Levey and Stiles 1992, Chesser and Levey 1998) and the “stepping-stone” hypothesis (Cox 1968, 1985)—are based on New World migratory systems. The central components of these hypotheses should apply across biogeographic realms (i.e. the Old World), given that seasonality and habitat regimes are similar in the New and Old worlds. Using a molecular phylogeny containing most species in the Motacillidae, we investigated the potential interactions of seasonality and ecology with migratory and sedentary behavior. Our results suggest that habitat and migration are not correlated in the manner predicted by the evolutionary precursor hypothesis, but they also suggest the importance of increasing seasonality in explaining the patterns of the evolution of migration, an expected but previously unexamined evolutionary relationship. While understanding the limitations of applying generalizations to a complex evolutionary system such as migration, we have delineated here a broad methodology for testing hypotheses about the evolution of migration within a phylogenetic context.

Pruebas Filogenéticas de Hipótesis sobre la Evolución de la Migración: Un Estudio de Caso en la Familia Motacillidae

Understanding reproductive and survival consequences of space use is of general interest to ecologists and vital to successful conservation planning. Hypothesized effects of home-range habitat composition and female attributes on these vital rates have not been adequately evaluated in breeding female Mallards (Anas platyrhynchos). Thus, we investigated reproductive and survival consequences of home-range variability and individual characteristics for 126 female Mallards studied on 12 study areas in the Canadian prairie parklands, 1995–1998. We used nine variables to discriminate between three reproductive categories (females that did not nest, nested but failed, or nested successfully) and two survival categories (killed by predator and survived the nesting season). Discriminant function analysis separated females that nested successfully from those that did not, with successful females having higher percentages of wood-shrub and planted grass habitat within their home ranges, a lower percentage of seasonal and semipermanent wetlands, smaller home-range sizes, and a higher percentage of wetlands at the study-area scale. We also distinguished females that did not nest from failed nesters; females that did not nest were younger and smaller and had larger home-range sizes, with a higher percentage of seasonal and semipermanent wetlands. Females that were killed did not differ from nesting-season survivors of either individual or home-range characteristics.

Características del Rango de Hogar, Edad, Tamaño Corporal y Desempeño Reproductivo de las Hembras en Anas platyrhynchos

The nests of some birds are built exclusively by males and then displayed to females. In such species, one expects females to choose those nests that provide maximum safety to themselves and their offspring. What attributes of a nest should females use in making these choices? Here, I examine the correlates of nesting success in the Baya Weaver (Ploceus philippinus), a species in which males provide nests and little else. In particular, I examine which of two suites of nest attributes best predicts nesting success: nest location (which reflects male competitive ability) or nest architecture (which reflects male building skill). Because whether a nest has successfully fledged young is sometimes uncertain, I supplement generalized linear model analyses with survival analyses, which can incorporate ambiguity in nest fate. Together, these analyses reveal that nests built in thorny trees and woven with fine fiber have high success. Nesting success also increases with nest height and with thickness of the supporting branch. Overall, nest location is a slightly better predictor of success than nest architecture; this is consistent with previous findings that female choice of nests is influenced more by location than by architecture.

¿Qué Hace a un Nido un Buen Nido? Beneficios de la Selección de Nidos para las Hembras en Ploceus philippinus

The phylogeny of kingfishers was reconstructed by comparing mitochondrial and nuclear DNA sequences representing 38 ingroup species. Analysis of the combined data and the nuclear data alone recovered the Alcedininae as the basal lineage in the family. This basal arrangement, and support for many relationships within the three subfamilies, allows discussion of biogeographic issues. The Australian region and Pacific islands display the highest diversity of kingfishers, but this diversity is not a reflection of a long history in the region. Rather, high diversity and endemism in the Australian region is inferred to result from relatively recent radiations from southern Asia. The most parsimonious explanation for the origin of New World taxa is two dispersal events from the Old World. Within the large Halcyon radiation, the phylogeny is well resolved and allows evaluation of generic assignments. The phylogeny supports splitting Todiramphus from Halcyon. Todiramphus and Syma are sister taxa, as are Halcyon and Pelargopsis. Thus, merging or retaining those genera is a more subjective decision. Although not fully resolved, relationships within the alcedinines indicate that Ceyx and Alcedo, as currently delimited, are not natural groups.

Phylogénie Moléculaire des Alcedinidae avec un Aperçu de l'Histoire Biogéographique Ancienne

Natal dispersal in vagile species such as songbirds can shape a population's range and structure. Although effective conservation practices depend on knowledge of the scale and frequency of natal dispersal, these issues remain poorly understood because of methodological gaps. In this exploratory study, we assessed whether element signatures within natal feathers might be used to identify the geographic birth site of first-year breeders. We used two related techniques, inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma with optical emission spectrometry (ICP-AES), to quantify element levels in natal feather samples from 7 species at 27 sites across the eastern United States. The techniques differed in the manner in which elements were quantified and in their detection limits. Our goal was to determine whether element analyses of feathers could discriminate (1) different species within a site and (2) different sites within a species. Additionally, because spatial autocorrelation of element levels is needed for element analysis to be an effective tool in assessing natal dispersal, we also evaluated the spatial autocorrelation of ICP-AES samples at 18 sites across the eastern United States.

Both ICP-MS and ICP-AES analyses separated species within a site with fairly high accuracy, though the discriminating elements varied with site. However, within a species, natal feather locations were not identified with high accuracy on the basis of feather elements. We were not able to determine whether there is spatial correlation among individual elements or a principal component analysis (PCA) score that described the elemental makeup of a feather. A kriging model was fit to the semivariogram of PCA scores to produce a base-map of element signatures across the eastern United States. This map was ineffective at predicting feather-element values at sample sites. Whether elemental analyses can identify natal dispersal distances requires further study. We suggest that future studies evaluate elements with ICP-MS methodologies on a single, box-nesting species that is sampled more intensively at smaller geographic scale, or on species that occur in very discrete populations. Additionally, this methodology should be evaluated in concert with stable-isotope analyses of feathers and, potentially, genetic analyses.

Suivre la Dispersion chez les Oiseaux: Évaluer le Potentiel de Marqueurs Élémentaires

We examined the effects of environmental and ecological factors associated with seasonal fecundity on spatial and temporal patterns of productivity in Sagebrush Brewer's Sparrow (Spizella breweri breweri) in British Columbia, the northwestern edge of its breeding range. This study is the first examination of seasonal fecundity in this species. Seasonal fecundity of females varied from 1998 to 2000. It was highest in 2000, when nest predation was lowest and number of clutches per female was intermediate, and lowest in 1998, when nest predation and number of clutches per female were the highest and warm El Niño conditions led to early breeding. Potential fecundity gains from early breeding were diminished by the interaction of shifting predation rates and variable effects of weather at different elevations. Early breeding in 1998 proved an advantage only at the low-elevation site, because an early spring storm destroyed 43% and 20% of first nests at two high-elevation sites. High seasonal fecundity varied between the sites, such that the best site in 1998 became the least productive in 1999 and vice versa. The overriding factor driving spatiotemporal variation was shifting rates of nest predation, though the elevation-related storm effects and variation in number of clutches were partly responsible. To maintain high productivity for Sagebrush Brewer's Sparrow at the northern edge of its range, where conditions are unpredictable and where there is no consistently best or worst site in terms of productivity, managers must protect sites from habitat loss or alteration across a range of elevations and conditions.

Fécondité Saisonnière de Spizella Breweri Breweri à la Limite Nord de Son Aire de Reproduction

Early arrival at breeding sites can influence reproductive success through enhanced access to critical resources such as nest sites or mates. One hypothesis explaining protandry, or male-first arrival at breeding sites, proposes that males arrive earlier to increase their extrapair copulation (EPC) opportunities, which may, in turn, enhance males' reproductive success through extrapair fertilizations (EPFs) (“mate opportunity hypothesis”). Extrapair behavior is unexpected in long-lived birds, in which the male is expected to abandon a brood of uncertain paternity, because his probability of future reproduction is high. A previous study of the Waved Albatross (Phoebastria irrorata), a long-lived, socially monogamous seabird, showed evidence of EPFs in 4 of 16 (25%) families. Here, we combined behavioral observations of copulations with additional molecular genetic evidence of EPFs in Waved Albatross families to investigate the fitness consequences of protandry under the mate opportunity hypothesis. During three breeding seasons, we documented 3,661 attempted copulations between birds of known identity; >60% of copulations that involved at least one breeding bird were classified as EPCs. Protandry was pronounced in all three study years: 76.3–96.6% of males arrived before (typically, 6–10 days before) their social mates. Early arrival was associated with increased opportunities for copulations: individual EPC frequencies were higher for breeding males than for breeding females, and males that arrived earlier than their social mates engaged in the most EPCs. Extrapair fertilizations were also regular in our study population; social fathers were excluded as the genetic sire in 14–21% of families. Egg laying dates of EPFs tended to be earlier in the season than those of within-pair fertilizations (WPFs). However, earlier arrival by a male did not translate into a higher probability of siring either within-pair or extrapair offspring, nor did cuckolding males have enhanced reproductive success. Although the fitness consequences of early arrival remain unclear, these findings suggest alternative advantages of early arrival for male Waved Albatrosses.

La Hipótesis de Oportunidad de Apareamiento y Paternidad Extra-pareja en Phoebastria irrorata

Partial migration is often considered a transitory stage between migration and residency, and whether partial migrants take weather conditions into account during migration is largely unknown. To assess whether partial migrants differ from regular migrants in their responses to weather, we compared the migratory intensity of a partial migrant, the Blue Tit (Cyanistes caeruleus), with more regular migrants in relation to weather at a migratory passage site in southern Sweden (Falsterbo) during the years 1993–2002. The regular migrants in the study were Linnet (Carduelis cannabina), Common Chaffinch (Fringilla coelebs), Brambling (F. montifringilla), and European Robin (Erithacus rubecula). The Blue Tit differed from the regular migrants mainly in showing a striking negative correlation between migratory activity and cloud cover. Also, weather had the highest explanatory power for migratory intensity in the Blue Tit. This suggests that the Blue Tit is more sensitive to weather conditions on migration than the regular migrants and that it preferably awaits days with wholly or partly clear skies before migrating past Falsterbo. As a consequence, Blue Tits usually restrict their migratory flights to the safest occasions, with relatively calm weather, good visibility, and all orientation cues (solar as well as magnetic) available.

¿Difieren los Migrantes Parciales y Regulares en sus Respuestas al Clima?

The “immunocompetence handicap” hypothesis predicts that reproductive hormones, in particular testosterone (T), are immunosuppressive and consequently increase susceptibility to diseases and parasite infections, but this prediction has not been evaluated in free-living birds and the factors mediating the immunosuppressive influence of T remain poorly known. To address these issues, we administered supplemental T via implants to free-ranging adult male Dark-eyed Juncos (Junco hyemalis) and characterized the effects of this treatment on infection with the two most prevalent hematozoan parasites in this species, Leucocytozoon fringillinarum and Trypanosoma avium. Males caught at the beginning of their breeding season (May) received T-filled, empty (control), or no Silastic capsules, and were recaptured five weeks later. Capsule implantation had, by itself, no effect on parasite infections, body mass, or size of an androgen-dependent secondary sexual characteristic, the cloacal protuberance. Testosterone treatment maintained physiologically high plasma levels of the steroid for the duration of the study, thus preventing the seasonal decline in these levels that occurred in control males. As predicted by the immunocompetence handicap hypothesis, the hormone treatment increased blood L. fringillinarum abundance. This increase was specific, in that implanted T did not affect (1) either the prevalence or the incidence of L. fringillinarum, (2) body mass, or (3) size of the cloacal protuberance. Trypanosoma avium prevalence was not influenced by T treatment either, but it increased between May and June, which suggests that it is regulated by factors other than the activity of the reproductive system. These findings provide the first demonstration in free-ranging birds that experimentally elevated physiological T levels increase hematozoan infection.

El Tratamiento de Testosterona en Machos Silvestres de Junco hyemalis Exacerba la Infección de Hemoparásitos

Variation in plasma metabolite profiles can provide information on physiological state and relative rates of mass change in free-living birds caught only once, and this technique could be used to compare rates of mass change (fattening) among populations or sites in relation to habitat quality. We compared plasma metabolite levels, as an index of relative refueling rates, in migratory Arctic-nesting Western Sandpipers (Calidris mauri), on a landscape scale at as many as nine sites over two years and during three different migratory stages within the Georgia Basin-Puget Sound region of British Columbia and Washington. There was significant intersite variation in plasma triglyceride levels in both years, but only for the northward migration. By contrast, there was little evidence of intrasite variability (i.e. metabolite profiles of birds using the same site were consistent between years and migratory stages), though we documented intrasite variation resulting from birds' use of different microhabitats at the same site. Plasma glycerol levels did not vary systematically among sites, though they varied among years; on average, birds had higher glycerol levels during northward migration than during southward migration. For the northward migration only, there was a positive relationship between plasma triglyceride levels and total macrofaunal prey abundance among sites. Birds using smaller sites with a lower index of mudflat exposure (mean number of kilometer-hours of mudflat exposed in a 24-h period, reflecting the opportunity to forage at each site) tended to have lower triglyceride levels.

Fisiología a Escala de Paisaje: Diferencias entre Sitios en las Tasas de Reabastecimiento Indicadas por Análisis de Metabolitos del Plasma en Chorlos Migratorios Silvestres

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.