Many species of marsh birds (e.g. rails and bitterns) are believed to be declining in North America, yet we lack an effective monitoring program to estimate their population trends. Broadcast of prerecorded calls to elicit vocalizations is a commonly used method in surveys of marsh birds, but whether gains in detection and index precision outweigh the drawbacks of call-broadcast is unclear. To evaluate the effectiveness of call-broadcast surveys, we pooled marsh-bird survey data from 8,047 point-count surveys contributed by 11 cooperators and compared numbers of birds detected and variation in numbers detected between call-broadcast and passive surveys. For most rails (particularly Virginia Rails [Rallus limicola]), call-broadcast surveys were effective at increasing the detection probability (e.g. average number of Virginia Rails detected per occupied point was 1.25 for call-broadcast surveys and 0.17 for passive surveys). The proportion of points at which no birds were detected was high for all species (range 74–99%) and was slightly lower on call-broadcast surveys as compared with passive surveys. Coefficient of variation (CV) among replicate surveys was higher for passive surveys, particularly for rails (average CV in number of birds detected per point was 209% for passive surveys and 189% for call-broadcast surveys). On the basis of those results, we recommend a marsh-bird monitoring protocol that includes an initial passive period followed by a period of call-broadcast to provide survey data that incorporate the benefits while avoiding the drawbacks of call-broadcast. We also recommend separating both the passive and the call-broadcast periods into 1-min subsegments that will allow estimates of components of detection probability within the monitoring effort.

Efectividad de Censos que Reproducen Vocalizaciones Pregrabadas para Monitorear Aves de Pantano

Decreased nest success and elevated levels of nest predation have been linked to changes in landscape configuration and increased edge. However, our current understanding of the mechanics of nest predation is limited. Using radiotelemetry and artificial nest experiments, we studied the ranging and nest-predation behavior of the Steller's Jay (Cyanocitta stelleri) in the managed forests of western Washington. Steller's Jays used a variety of forest seral stages, 95% of foraging observations occurred within 50 m of edges, and home range did not appear to be influenced by breeding success. Predation on artificial nests was elevated in high-use areas of home ranges, which suggests that Steller's Jays find nests incidentally while foraging for primary prey (insects). Steller's Jays did not appear to use a specialized search strategy to find nests, though they had a search image for nests and were capable of performing area-restricted searching for other food items (peanuts). To assess the risk of nest predation by Steller's Jays, it may be useful for managers to survey areas of concern for Steller's Jays and their foods. By equating relative abundance of Steller's Jays with nest predation risk, managers can then map predation risk onto the landscape of concern at the scale of the management unit.

¿Es la Depredación de Nidos por Cyanocitta stelleri Incidental o es el Resultado de una Estrategia de Búsqueda Especializada?

Since early in its taxonomic history, placement of the Socorro Wren (Thryomanes sissonii) has been an object of contention. Of particular interest is its current placement in the genus Thryomanes, which makes that genus ditypic and leads to an odd biogeographic scenario for the Socorro Wren's colonization of Socorro Island. We assessed its phylogenetic position by analyzing 516 base pairs of mitochondrial DNA sequences from the ND2 gene of this species and 14 additional wren taxa. Contrary to its present placement, the Socorro Wren is nested phylogenetically within the House Wren species complex, being placed as sister to the clade Troglodytes aedon T. musculus. The current hypothesis (i.e. sister to Thryomanes bewickii) is strongly invalidated by our analysis. Our analyses indicate that the most appropriate taxonomic classification for the Socorro Wren is Troglodytes sissonii.

Posición Filogenética y Ubicación Genérica de Thryomanes sissonii

Although many studies have revealed differences in patterns of extrapair paternity between species and between populations of the same species, possible differences in female extrapair behavior within populations have received far less attention. Here, we propose and test the hypothesis that females of the highly polygynous Red Bishop (Euplectes orix) follow two different extrapair strategies, with benefits of extrapair copulations depending on the quality of their social mate (”conditional-extrapair-strategy hypothesis”). In particular, we propose that females mated to low-quality males enhance the genetic quality of their offspring by performing extrapair copulations with males of higher quality than their social mate (in accordance with the good-genes hypothesis), whereas females mated to high-quality males perform extrapair copulations as insurance against temporary infertility of their social mate caused by sperm depletion due to frequent copulations (in accordance with the fertility-insurance hypothesis). Several predictions derived from our hypothesis, regarding differences in frequency and distribution of both unhatched eggs and extrapair young between high-quality and low-quality males, are tested and shown to be supported. Most importantly, hatching failures occurred more often in territories of high-quality males than in those of low-quality males, and the proportion of unhatched eggs within the territory was positively correlated to breeding synchrony for high-quality males only. Those results suggest that sperm depletion is a risk for females mated to high-quality males with many mating opportunities. The fact that broods of high-quality males without unhatched eggs had a significantly higher proportion of extrapair young than broods of high-quality males with unhatched eggs is consistent with the hypothesis that females mated to high-quality males were successful in performing EPCs as insurance against temporary infertility of their social mates. Furthermore, genetic fathers of extrapair young hatched in territories of low-quality males were found to be of higher quality than the corresponding social fathers, whereas no difference in quality was found between genetic and social fathers of extrapair young hatched in territories of high-quality males. Although we cannot exclude the possibility that the observed pattern was a result of females mating randomly from within the available pool of extrapair males, it is in accordance with our prediction that females mated to low-quality males perform extrapair copulations with males of higher quality than their social mate to enhance offspring fitness. Overall, the data presented here suggest that females within our study colony adjusted their extrapair behavior to the quality of their social mate, even if we cannot entirely rule out alternative explanations for some of the results obtained. Thus, the study provides support for the conditional-extrapair-strategy hypothesis, which states that within populations, females may follow different extrapair strategies to gain different benefits.

Fertilizaciones Extra-pareja en Euplectes orix: ¿Siguen las Hembras Estrategias Extra-pareja Condicionales?

Protandry, the earlier arrival of males than of females on breeding areas, occurs in many taxa, including many migratory birds. Numerous hypotheses have been generated to explain protandry. Using bird-banding records, I show that protogyny, the earlier migration of females, frequently occurs in the autumn, though it is less universal and less dramatic than spring protandry. In one species, it occurs in both hatch-year and adult birds. When (1) spring and autumn, (2) departures and arrivals, and (3) breeding and wintering ground conditions are considered, hypotheses generated only to explain spring protandry can be more thoroughly evaluated. Using that approach, the most parsimonious explanation of differential migration between the sexes explains earlier male arrival in spring and later male departure in autumn through either (1) indirect selection operating on intrasexual male competition for territories or (2) direct selection operating on intersexual relations requiring males to be present on breeding territories when females are present. In autumn-protogynous species, males may ”play chicken,” balancing the benefits of remaining longer than females and protecting territories for subsequent years against the costs of remaining in the north under deteriorating conditions and delaying the acquisition of a good winter territory.

Protogynie et migration automnale: Est-ce que les mâles ”jouent les dégonflés”?

The importance of repertoire size to mate choice by female songbirds has been widely debated but has not been addressed in Brown-headed Cowbirds (Molothrus ater; hereafter ”cowbirds”), despite extensive work on this species' songs. Male cowbirds cycle through repertoires of 2–8 perched song (PS) types in rapid sequences immediately prior to and during copulation, which suggests that repertoire size or content is important in mating contexts. Because male mating success in one well-studied cowbird population is correlated with large PS repertoires, we predicted that repertoire size is a cue in female mate choice. To test that prediction, we played three repetitions of conspecific songs in rapid succession to estradiol-primed female cowbirds (M. a. obscurus), to simulate the rapid song sequences that accompany naturally occurring matings. Females were presented with three different PS types, three repetitions of the same type, and heterospecific control songs of the same duration as the conspecific playbacks. Females gave longer copulation solicitation displays to three different PS types than to three repetitions of a single PS type, regardless of whether the playback songs were local or foreign. This is one of the few experimental studies on songbirds to show greater female responsiveness to a song repertoire presented so as to mimic singing in a natural mating context, and the first to present such a result for cowbirds. We conclude that presentation of multiple PS types is more sexually stimulating to females than a single type, because females prefer larger repertoires or singing patterns with a higher frequency of song-type switching.

Preferencias Sexuales de Hembras de Molothrus ater por Repertorios de Canto de Percha

Hybridization is pivotal in framing ideas about species concepts and has the potential to produce novel genotypes that may serve as starting points for new evolutionary trajectories. Presently, Nelson’s Sharp-tailed Sparrows (Ammodramus nelsoni subvirgatus) and Saltmarsh Sharp-tailed Sparrows (A. caudacutus caudacutus) are in contact in salt marshes of Maine, New Hampshire, and northern Massachusetts. These two species hybridize, but the extent and direction of introgression has not been determined. We assessed morphological and genetic variation of 123 sharp-tailed sparrows from 5 salt marshes in New England. We used six morphological variables, including a plumage-scoring index, and five mic-rosatellite primers to assess the extent of introgression and to determine whether there was concordance between phenotypic and genotypic variation. We identified apparent hybrids and each of the two sharp-tailed sparrow species using a plumagescoring index. In general, we found that hybrids were more similar morphologically and genetically to Saltmarsh Sharp-tailed Sparrows. The alleles of hybrids were 62% Saltmarsh and 38% Nelson’s Sharp-tailed Sparrows, supporting the asymmetrical hybridization hypothesis.

Concordancia entre Marcadores Morfológicos y Moleculares al Evaluar la Hibridación entre Ammodramus nelsoni subvirgatus y A. caudacutus caudacutus en Nueva Inglaterra

Vocal alarm calls are important to the vigilance and likely the organization of mixed-species flocks, but community-wide studies of alarm calling in flocks are lacking. We investigated which species alarm-call, and the characteristics of their calls, in a large flock system of a Sri Lankan rainforest. We recorded naturally elicited alarm calls during several attacks by Accipiter hawks and while following flocks for 10 h. We then artificially elicited alarms by throwing a stick to the side of the flock, in a total of 70 trials at 30 flock sites. The Orange-billed Babbler (Turdoides rufescens) was the most frequent caller to both the artificial and natural stimuli, followed by the Greater Racket-tailed Drongo (Dicrurus paradiseus). Several other species also called, and multiple species often called to the same stimulus (in 23 trials, and in all of the hawk attacks). The species differed in their rapidity of response and in their sensitivity to different natural stimuli. Calls of the gregarious babbler usually provided a first, unreliable warning of an incoming threat, whereas later calls of other species emphasized the seriousness of the threat. We suggest that birds in mixed-species flocks may be particularly aware of aerial predators for two reasons: (1) a “numbers effect,” whereby nongregarious species are more aware of predators when surrounded by large numbers of other species; and (2) an “information effect,” whereby species differ in the information available in their alarm calls, leading to an accumulation of information in a mixed-species flock.

Llamadas de Alarma en Bandadas Mixtas de Aves en Sri Lanka

We present a phylogenetic hypothesis for 40 species in the bird family Paridae, based on comparisons of nucleotide sequences of the mitochondrial cytochrome-b gene. Parids, including tits and chickadees, are an older group than their morphological stereotypy suggests. The longest cytochrome-b distances between species reach 12% in uncorrected divergence. With the exception of one thrasher-like terrestrial tit species of the Tibetan plateau (Pseudopodoces humilis), morphological and ecological stasis have prevailed since the initial parid radiation in the Old World during the mid-Tertiary.

All trees support monophyly of the family Paridae, which includes Parus (sensu lato) and the monotypic Oriental genera Sylviparus, Melanochlora, and Pseudopodoces. Within the clade of chickadees and gray tits (Parus, subgenus Poecile), three Old World species, Parus lugubris of the eastern Mediterranean and Balkan regions, P. superciliosus of high elevations in the Himalayas of western China, and P. varius of the Orient are sisters to all other species. The Eurasian crested titmice (subgenus Lophophanes) and North American crested titmice (subgenus Baeolophus) are sister groups. Our data suggest two colonizations of the New World by parids in the late Tertiary. The ancestor of modern Baeolophus colonized North America 4 mya, and the ancestor of all North American chickadees colonized North America 3.5 mya.

Phylogénie chez la mésange (Paridés): II. Relations entre les espèces basées sur des séquences du gène mitochondrial cytochrome-b

The diet of adult Canada Geese (Branta canadensis interior) and their goslings was determined during the brood-rearing season in a freshwater tundra habitat using esophageal contents from 25 adult females, 27 adult males, and 59 goslings. Habitat use by geese and the availability and quality of aboveground biomass in wet sedge meadows and around ponds in lichen-heath tundra were also evaluated throughout the summer. During the first four weeks of brood-rearing, adult Canada Geese ate primarily graminoids (>65%), especially leaves of the short form of Carex aquatilis and Eriophorum spp., which had the highest nitrogen concentration (2.5–3.5%). Although graminoids were also important for goslings, they consumed a greater variety of other plant species (68%) than adults, especially in the first two weeks, possibly because of their inexperience. Late in the brood-rearing period, as the nitrogen concentration of graminoid plants declined, adults shifted to a diet composed mainly of berries (>40%, mostly Empetrum nigrum). At that time, goslings consumed fewer berries (24%) and maintained a higher proportion of nitrogen-rich plants in their diet (53% leaves, mostly graminoids) than adults, presumably to complete their growth. Plant species consumed by geese over the summer indicated a preference for high-quality plants (i.e. those with a high nitrogen concentration). Consequently, wet sedge meadow, the habitat that offered plant species of highest quality, was the habitat most heavily used throughout the summer, particularly around peak hatch. Goose grazing had no effect on seasonal production of aboveground biomass of graminoids, probably because of the relatively low density of the goose population.

Écologie alimentaire de Branta canadensis interior pendant la période d’élevage des jeunes dans un milieu d’eau douce sub-arctique

Pleistocene glacial cycles have often been hypothesized to provide vicariant mechanisms leading to allopatric speciation in a wide range of southern South American (Fuegian and Patagonian) avian taxa. Few of those biogeographic hypotheses, however, have been rigorously tested using phylogenetic analysis. We examined sequence variation in three mitochondrial gene fragments (cytochrome b, ND2, and ND3) to construct a molecular phylogeny for the South American genus Geositta (Furnariidae) and to test the interrelated hypotheses that Geositta cunicularia and G. antarctica are sister species that originated from a common ancestor while isolated in glacial refugia during Pleistocene glacial events in Fuego-Patagonia. Sequence data were obtained for all 10 currently recognized species of Geositta as well as Geobates poecilopterus and two outgroup taxa (Upucerthia ruficauda and Aphrastura spinicauda). We found levels of sequence divergence among Geositta species to be high, ranging from 7.4% to 16.3%. Our phylogenetic reconstructions clearly indicate relationships among Geositta species that differ considerably from those of traditional Geositta phylogeny. These data also strongly suggest that Geositta, as currently defined, is paraphyletic, with Geobates being embedded within Geositta. Our data do not support the hypothesized sister relationship between G. antarctica and G. cunicularia. Instead, they suggest that Geositta consists of two distinct clades, with antarctica and cunicularia falling into different clades. The high levels of sequence divergence among Geositta species, lack of a sister relationship between cunicularia and antarctica, and placement of Fuego-Patagonian antarctica into a clade consisting of two high-Andean (saxicolina and isabellina) and one coastal-west-slope (maritima) species demonstrate that the evolutionary history of Geositta is much older and far more complex than a simple model of allopatric speciation in glacial refugia would suggest.

Filogenia Molecular del Género Geositta (Furnariidae) e Implicaciones Biogeográficas para la Especiación de la Aves en Tierra del Fuego y Patagonia

In many tropical bird species, males and females sing together in coordinated vocal duets. Although studies of duetting present unique opportunities for understanding conflict and cooperation between the sexes, very few investigations describe the similarities and differences between male and female singing behaviors. Here, we present the first detailed account of the singing behavior of Rufous-and-white Wrens (Thryothorus rufalbus), a resident tropical duetting songbird. Male and female songs share a similar structure, yet show pronounced sex differences. Male songs have lower frequency characteristics and more repeated trill syllables, and often sound louder than female songs. Males sing more than females, and only males show elevated song output at dawn. Both males and females have song repertoires. Males have an average repertoire size of 10.8 song types, whereas females have a significantly smaller average repertoire size of 8.5 song types. Although males share proportionately more of their song types with neighbors than females do, both sexes share more song types with nearby individuals than with distant individuals. Breeding partners combine their solo songs to create duets. Duets assume a variety of different forms, ranging from simple, overlapping male and female songs to complex combinations of multiple male and female songs. Most duets (73%) are created by females responding to male song. Males respond to female-initiated duets with shorter latencies than when females respond to male-initiated duets. Each pair sings certain combinations of song types in duets more often than can be explained by random association, which demonstrates that Rufous-and-white Wrens have duet types. The most common duet type was different for each pair. Our results show that Rufous-and-white Wrens have pronounced sex differences in song structure, singing activity, repertoire size, repertoire sharing, and duetting behavior.

Diferencias entre Sexos en el Canto y Comportamiento de Dueto en Thryothorus rufalbus

We observed territorial Purple-throated Caribs (Eulampis jugularis) on three Heliconia morphs (H. caribaea and the red-green and green morphs of H. bihai) on the island of St. Lucia, West Indies, to examine how calculated costs and benefits compared with observed patterns of Heliconia use. Across the three years of our study, H. caribaea territories defended by Purple-throated Carib males were significantly smaller in area and had higher densities of flowers than red-green H. bihai territories, and both kinds of Heliconia territories defended by males were smaller and had higher densities of flowers than the green H. bihai territory maintained by a female. In the period (0630 to 1400 hours) during which birds maintained territories, total maintenance costs were more than met by energy obtained from territories, but only 2 of 13 territories provided sufficient nectar to meet birds' energy requirements for 24 h. Birds supplemented their energy intake from Heliconia territories by foraging at flowers in the rainforest canopy, and the percentage of time a territorial bird spent foraging in the canopy was inversely correlated with energy production on its Heliconia territory. The smaller territory areas and higher flower densities of H. caribaea territories lowered males' foraging time and energy costs per flower on H. caribaea as compared with red-green H. bihai territories, theoretically allowing them to meet their energy demands in less time and at lower cost. Males' estimated foraging time and energy costs were greatest at the green morph of H. bihai; compared with females, they would save a higher proportion of time and energy by foraging at H. caribaea and the red-green morph of H. bihai. That asymmetry between males and females in relative gains from foraging at each of the three Heliconia morphs may further reinforce resource partitioning between them, in addition to differences in size and fighting abilities.

Economía de Forrajeo y Territorialidad en la Especie Sexualmente Dimórfica Eulampis jugularis en Tres Formas de Heliconia

American Crow (Corvus brachyrhynchos) populations are increasing across North America, often at high rates in urban areas. A monthly survey of American Crows in the Seattle Christmas Bird Count (CBC) circle suggested that winter counts reflected American Crow abundance at other times of the year, so we used CBC results for American Crows as a measure of population trend. In the Seattle area, local survival and fecundity appear unable to account for exponential population growth. We tested the hypothesis that juvenile dispersal from outlying suburban and exurban areas contributes to growth in the urban population by radiotagging 56 juveniles 5–46 km away from the central business district of Seattle and tracking their movements. Juvenile American Crows’ centers of activity were 0.2–22.2 km away from their natal territory during the first 3–12 months after fledging. An estimated 45% survived one year. Movements of dispersing American Crows varied in their consistency with simulated random-walk paths; the data suggested that, at the population level, American Crows were not drawn into urban areas, though some individuals may have been. Movements of dispersers produced a net influx into the city, because of greater reproductive success outside the city than in it. Simulations of urban population growth that included immigrants and emigrants accounted for most of the observed growth, which indicates the importance of distant suburban and exurban breeding pairs to urban population dynamics.

La Dispersión de Juveniles de Corvus brachyrhynchos Influencia la Dinámica Poblacional a lo Largo de un Gradiente de Urbanización

Attention has recently been focused on microbes that occur in the plumage of wild birds and can degrade feathers under laboratory conditions and in poultry-waste composters. In particular, Bacillus licheniformis, a soil bacterium, was found in the plumage of many birds netted in eastern North America, and poultry feathers were rapidly broken down when incubated in a suspension of this bacterium (Burtt and Ichida 1999). If feather-degrading microbes affect wild birds under normal conditions, they may have played an important role in the evolution of molt, plumage color, and sanitation behavior, such as sunning and preening. We performed the first test on whether a feather-degrading bacterium can degrade feathers of live birds housed outdoors under seminatural conditions. We found no evidence that B. licheniformis degraded wing feathers of Northern Cardinals (Cardinalis cardinalis) when applied twice (with a two-week interval) during the winter, despite the fact that it degraded Northern Cardinal feathers when incubated in our laboratory. In a second experiment, we found no evidence that B. licheniformis degraded feathers of European Starlings (Sturnus vulgaris) when applied twice (with a one-week interval) during the summer, despite the fact that birds were housed in humid conditions that should have favored the growth of B. licheniformis.

Las Bacterias que Degradan Plumas no Afectan las Plumas de Aves en Cautiverio

Biologically important acoustic signals must be transmitted from a signaler to a receiver. Over distance, however, sounds may undergo modification through attenuation, degradation, and masking. Recent anthropogenic habitat modification occurring in many places—in urban habitats, in particular—has rapidly changed local topography and atmospheric conditions and generated new patterns of noise that are likely to interfere with communicative signals. As part of a study of microgeographic song dialects in an urban population of Orange-tufted Sunbirds (Nectarinia osea) in Israel, we examined the environmental influences on song transmission and reception in a rapidly developing human-altered environment. We examined the physical properties of the two dialect song types, which exhibit a large difference of 2–3 kHz in the maximum frequency of the trill, using sound transmission measurements to test how both song types propagate through a highly obstructed habitat of buildings and vegetation. Additionally, we examined how ambient noise—in particular, low-frequency noise arising mainly from automobile traffic—affects the transmission of both dialect songs. Finally, using song playback, we investigated the consequences of sound degradation on dialect recognition and discrimination by sunbirds. The dialect containing higher frequencies in the trill was found to undergo severe frequency-dependent attenuation, in which the maximum frequency of the trill notes drops by >2 kHz over a distance of 70–100 m (less than two territories away). Also, the possibility that the use of higher frequencies in that dialect group's song is intended to overcome masking by urban ambient noise, which is concentrated mainly in lower frequencies, was not supported by our findings. Males singing the high dialect responded differently to playbacks of an intact and an attenuated form of their dialect song. Taken together, our results suggest that the dialect containing higher frequencies in the trill may be unsuitable for effective long-range transmission through this particular sunbird habitat.

Propiedades Acústicas de Dos Dialectos del Canto Urbano de Nectarinia osea

Breeding birds require high levels of energy and certain nutrients, such as calcium. The extent to which calcium limits reproduction in wild birds is unclear. We performed a supplementation experiment to determine whether calcium limits the reproductive output of free-ranging insectivorous Tree Swallows (Tachycineta bicolor), a species whose usual diet contains little calcium. Providing supplemental calcium in the form of crushed oyster shell did not affect clutch initiation date, but it caused birds that had not started constructing a nest when we first detected them on the study area to begin laying sooner, which suggests that calcium reduced the length of the prelaying period. Supplemented females produced larger eggs, and that effect was most pronounced among females in good body condition. There was a trend for supplemented birds to produce larger clutches, and their clutches had significantly greater total mass than those of control birds. Supplemented birds, in particular those breeding late in the season, also hatched significantly more eggs. Our results suggest that calcium availability may limit some aspects of avian reproduction, even in nonacidified landscapes like our study area, where levels of calcium in the soil are high.

La Disponibilidad de Calcio Limita el Rendimiento Reproductivo de Tachycineta bicolor en un Paisaje no Acidificado

Mercury, a common wetland pollutant, can affect wildlife populations through acute toxicity or through physiological effects that modify behavior and negatively influence reproductive success. We compared body-feather mercury concentrations of free-living male and female adult White Ibises (Eudocimus albus) during three breeding seasons in the Florida Everglades and examined the relationships among mercury, hormone concentrations, and body-condition scores. Female White Ibises consistently had lower mercury concentrations than males. Prebreeding females' estradiol concentrations were negatively correlated with mercury concentrations. However, we found no relationship between mercury and female testosterone, progesterone, and corticosterone concentrations. Incubating male White Ibises showed a significant positive relationship between testosterone and mercury concentrations, but no other significant hormonal correlations with mercury concentrations. We used a seven-year standardized data set of Great Egret (Ardea alba) chick-feather mercury concentrations as a measure of temporal changes in mercury bioavailability in the Everglades and related that measure to annual numbers of White Ibis nests. White Ibis nesting was negatively correlated with the mercury exposure index. Low numbers of nesting White Ibises may have been the result of fewer birds nesting or high abandonment rates. Our results suggest that mercury exposure may cause fewer birds to nest or more birds to abandon nests because of subacute effects on hormone systems. However, the results are correlative; they call for further investigation in free-living populations and in the laboratory.

Relaciones entre las Concentraciones de Mercurio, Hormonas y el Esfuerzo de Nidificación de Eudocimus albus en los Everglades, Florida

Masked gulls are believed, on the basis of morphological and recent molecular work, to be a monophyletic group within the Laridae, but relationships of species within the group are not well resolved. We used sequence data from four mitochondrial DNA genes (ND2, ND5, ATPase6, and ATPase 8) totaling >3,600 base pairs to clarify relationships among the species and test competing hypotheses about their origin and biogeography. Monophyly of the masked gulls was confirmed. We also found strong support for a clade including all Southern Hemisphere masked gulls as well as a lone Northern Hemisphere representative, the Black-headed Gull (Larus ridibundus). The Australasian taxa form a well-supported clade, in which the Black-billed Gull (L. bulleri) is sister to the Red-billed Gull (L. novaehollandiae scopulinus) of New Zealand and the Australian Silver Gull (L. n. novaehollandiae). Another well-supported clade includes the Black-headed Gull as sister to the South African Hartlaub's Gull (L. hartlaubii) and the Gray-hooded Gull (L. cirrocephalus) of Africa and South America. The strongly supported position of L. ridibundus within the “southern clade” suggests that it originated from a Southern Hemisphere ancestor and recently dispersed into the Northern Hemisphere. Estimates of divergence times using rate-smoothing methods are consistent with those from previous molecular work and suggest that (1) masked gulls diverged from other gulls <2 mya and (2) much of the radiation in the group occurred in the last 600,000 years.

Preuve moléculaire de la radiation récente chez les mouettes “masquées” de l'hémisphère sud

Because of the difficulty of following female songbirds through an entire breeding season, field ornithologists are seldom able to directly measure seasonal fecundity (defined as number of offspring produced per female during an entire breeding season). Instead, it is more commonly inferred from some measure of nest-productivity data (e.g. average number of offspring fledged per nesting attempt) using algorithms that make assumptions about the propensity of females to renest after a nest failure or after successfully fledging a brood. Recent analyses have often assumed set maximum numbers of nesting attempts and successful broods, and that all females breed up to those maxima. However, whereas data from songbirds intensively followed for an entire breeding season show that they are capable of up to 4–8 nesting attempts, many authors, in estimating seasonal fecundity, assume a maximum of only 1–4 nesting attempts. We applied a model to a Prairie Warbler (Dendroica discolor) data set (Nolan 1978) that allowed direct comparisons of (1) seasonal-fecundity estimates obtained assuming fixed maximum numbers of renestings and broods with (2) estimates obtained assuming that numbers of renesting attempts and successful nests are constrained only indirectly by length of breeding season. Although results under the latter assumption are concordant with Nolan's (1978) direct empirical measure of Prairie Warbler seasonal fecundity, estimates under assumptions of fixed maxima of renestings or broods are in serious error for many parameter choices. As such, our analyses disclose that essentially all estimates of seasonal fecundity in the literature derived by assuming a limited maximum number of nesting attempts or of successful broods are biased. Most commonly, when nest mortality is high, seasonal fecundity is underestimated; in some cases where nest mortality is low, seasonal fecundity is overestimated. We recommend that researchers estimating seasonal fecundity from nest-productivity data use a model that explicitly sets breeding-season length and thereby only indirectly constrains the possible number of nesting attempts and successful broods.

La Nidificación Repetida Determina la Fecundidad Estacional en las Aves Canoras: ¿Qué Sabemos? ¿Qué Deberíamos Suponer?

We describe a new species of Aratinga—A. pintoi (Sulfur-breasted Parakeet)—from open areas on the northern bank of the lower Amazon River in the state of Pará, Brazil. It was for a long time misidentified as a juvenile of A. solstitialis or a hybrid between that species and A. jandaya. It can be distinguished from other Aratinga species by the combination of the following characters: mantle and wing coverts green, suffused with pale yellow; underparts pale yellow, with pale orange restricted to belly and flanks; and feathers on the underparts with a dark rachis. On the basis of color characters and general morphology, we suggest that this new species should be a member of a group composed of A. solstitialis, A. jandaya, A. auricapillus, and, possibly, Nandayus nenday. A review of taxonomy and distribution of the group is also presented.

Uma nova espécie de Aratinga (Psittaciformes: Psittacidae) do Brasil, com comentários sobre a taxonomia do complexo de espécies Aratinga solstitialis

Estimates of nest survival are commonly used as indices of reproductive productivity in a wide range of studies, including examinations of population dynamics, habitat fragmentation, and wildlife management. However, the strength of the relationship between estimates of nest survival and of seasonal fecundity has rarely been tested. To examine that relationship, we used 16 years of demographic data from an intensively studied population of individually marked Black-throated Blue Warblers (Dendroica caerulescens). We found a positive relationship between Mayfield nest-survival estimates and seasonal fecundity (i.e. number of fledglings produced per female). However, seasonal-fecundity predictions based on nestsurvival values underestimated observed seasonal fecundity by an average of 33% and population growth rate by 20%. Our results suggest that, though nest-survival estimates may be useful as indices of pressures on a population (e.g. nest predation), care is needed in using them as the basis of conservation or management strategies or to make inferences about population-level processes.

Relación entre las Estimaciones de Supervivencia de Nidos de Mayfield y la Fecundidad Estacional: una Nota de Cautela

We investigated body-mass dynamics during incubation of Long-tailed Ducks (Clangula hyemalis) nesting in Canada’s central Arctic, 1998–2003. Long-tailed Duck females (n = 37) lost 7% of pre-incubation body mass during incubation; on average, females weighed 618 ± 15 g (mean ± SE) at clutch completion and 575 ± 11 g at hatch. Given the differences in body size, Long-tailed Ducks relied less on endogenous reserves than sympatric King Eiders (Somateria spectabilis), but lost less mass than similar-sized waterfowl species nesting in temperate climates. Preliminary data suggest that Long-tailed Ducks maintain similar or higher nest-attendance rates than temperate-nesting waterfowl of similar size, and we suggest that access to locally abundant, high-quality foods enable Long-tailed Duck females to maintain high incubation constancy without sacrificing female body condition. Nevertheless, Long-tailed Ducks appear to differ widely from most Arctic-nesting waterfowl in nutritional strategy for nesting.

Masse corporelle chez l’Harelde kakawi (Clangula hyemalis) au cours de l’incubation

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

Constancia de Múltiples Días como una Alternativa a la Combinación de Datos de Captura-Recaptura para Estimar la Duración de las Paradas de Aves Migrantes Neárticas-Neotropicales Terrestres

Over a seven-year period, we used mark-recapture in a population of Flammulated Owls (Otus flammeolus) in the Zuni Mountains, New Mexico, to estimate adult breeding-site fidelity, mate fidelity, natal philopatry, and dispersal distances. We also used DNA fingerprinting to examine the genetic population structure of Flammulated Owls among four mountain ranges in New Mexico and one range in Utah. Mark-recapture revealed that adults are site-faithful and tend to maintain pair bonds between years, whereas juveniles show little natal philopatry. DNA fingerprinting revealed very low differentiation among populations, even between the New Mexico and Utah ranges, with population subdivision (F_ST) estimates ranging from 0.00 to 0.04. Heterozygosity values were high within each mountain range and, together with the low F_ST values, suggest that this Neotropical migrant may have long-distance natal dispersal and frequent intermountain dispersal.

Datos de Marcado-Recaptura y Huellas Dactilares de ADN Revelan Alta Fidelidad a los Sitios de Cría, Baja Filopatría Natal y Bajos Niveles de Diferenciación Genética Poblacional en Otus flammeolus

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