Six populations of Warbling Antbird (Hypocnemis cantator) currently considered subspecies are more appropriately recognized as species, given the multiplicity of vocal differences that distinguishes them. These vocal differences are as great or greater than vocal differences documented between syntopic species-pairs in the family Thamnophilidae (Isler et al. 1998). Evidence is also provided that two forms currently considered subspecies are syntopic and that two others are parapatric without apparent physical barriers. Vocally, the pair of syntopic taxa were distinguished dramatically, but solely, by common calls. The finding that common calls were as diversified as songs in this species-group suggests that calls may be as important as songs in reproductive isolation. Future field studies should therefore focus on clarifying the function of different types of thamnophilid vocalizations and elucidating their role in speciation. This is the first contribution to a multifaceted analysis of the vocalizations and genetic structure of typical antbirds (Thamnophilidae) in Amazonia. In future work, results of the vocal analysis will be compared with a parallel genetic study, after which the two analyses will be integrated to suggest a phylogeny. The present study and preliminary studies of genetic differentiation (e.g., Bates et al. 1999) make it clear that the H. cantator complex has had a long evolutionary history that produced greater species-level diversity than was recognized previously.

Límites de Especies en Thamnophilidae: El Complejo de Hypocnemis cantator

Lek-mating Long-tailed Manakins (Chiroxiphia linearis) exhibit an unusual pattern of delayed plumage maturation. Each year, males progress through a series of predefinitive plumages before attaining definitive plumage in their fifth calendar year. Females also exhibit variation in plumage coloration, with some females displaying male-like plumage characteristics. Using data from mist-net captures in northwest Costa Rica (n = 1,315) and museum specimens from throughout the range of Long-tailed Manakins (n = 585), we documented the plumage sequence progression of males, explored variation in female plumage, and described the timing of molt in this species. Males progressed through a series of age-specific predefinitive plumages, which enabled the accurate aging of predefinitive-plumaged males in the field; this predefinitive plumage sequence is the basis for age-related status-signaling in these males. Females tended to acquire red coloration in the crown as they aged. However, colorful plumage in females may be a byproduct of selection on bright male plumage. Females exhibited an early peak of molt activity from February to April, little molt from May through July, and a second, more pronounced peak of molt activity in October. By contrast, males in older predefinitive-plumage stages and males in definitive plumage exhibited comparable unimodal distributions in molt activity beginning in June and peaking between July and October. Our data are consistent with selective pressure to avoid the costs of molt-breeding overlap in females and older males. Our findings have important implications for social organization and signaling in Long- tailed Manakins, and for the evolution of delayed plumage maturation in birds.

Desarrollo del Plumaje y Muda en Chiroxiphia linearis: Variación de Acuerdo al Sexo y la Edad

Songbirds typically have small-to-large repertoires of different song types used in complex patterns over a day or season, but what remains poorly understood are patterns of song use by songbirds that have a single, simple song. Here, on the basis of extensive field observations, we reveal how a male Chipping Sparrow (Spizella passerina) varies its simple, repetitive song to create a dynamic singing performance. During the day, and beginning shortly after males arrive on their territories, males typically sing long songs at a relatively slow rate from the tops of trees near the center of their territories. About two weeks after males have arrived, they begin to sing well before sunrise; during this dawn chorus, songs are brief and delivered rapidly, typically while males face each other on the ground at territorial boundaries. Each male sings this way during the dawn chorus throughout the breeding season, except when his female is fertile. By contrast, daytime singing essentially stops after a male pairs. The dawn chorus appears to mediate social interactions among territorial neighbors, whereas daytime songs function in long-distance territory advertisement, particularly for female attraction.

Comportamiento de Canto al Amanecer y Durante el Día en Spizella passerina

Using shared songs is believed to be an integral part of neighbor communication and territory establishment strategies among many avian species with repertoires. Previous studies of two western subspecies of Song Sparrows (Melospiza melodia) reported a high level of song sharing among neighboring males, whereas studies of an eastern subspecies have reported a very low level. The purpose of our study was to investigate another population of the eastern subspecies to determine whether higher song-sharing levels existed within its range. Every song in the repertoire of 29 males was compared with the songs of all other males to assess the number of shared songs. For each male, we calculated the mean song-sharing level with neighbors and non-neighbors. Males shared, on average, 33% of their repertoire with neighbors, significantly more than they shared with non-neighbors (27% of their repertoire). Two first-year males learned whole song types from several individuals and preferentially learned the song types shared among those individuals. Our results suggest that the eastern and western subspecies may not differ genetically in the way they learn songs, because song-sharing levels and song learning in our population were more similar to those of the western subspecies than to those of other populations within its own subspecies. Song-sharing differences among eastern populations may be explained instead by factors acting at the level of individual populations.

Niveau Élevé de Chants Partagés chez une Population de l'Est de Melospiza melodia

In spite of their putative importance in the evolution of certain traits (e.g., nocturnality, coloniality, cliff nesting), the effects of aerial predators on behavior of adult seabirds at colonies have been poorly investigated. We hypothesized that Tufted Puffins (Fratercula cirrhata) respond to danger posed by aerial predators by modifying their behavior to mitigate danger. We observed Tufted Puffins making repeated colony fly-ins and departures and characterized (1) the timing of this behavior, (2) the activity rate (number of birds arriving or departing), and (3) the risk-level of activity, with respect to predation danger posed by Bald Eagles (Haliaeetus leucocephalus) and Peregrine Falcons (Falco peregrinus). As we predicted, we found that Tufted Puffins (1) dilute danger by synchronizing their fly-in and departure activities, (2) reduce fly-in and departure activity rates when predators are present, and (3) switch to lower-risk fly-in activities (e.g., staying over water where they have an escape route from an aerial attack) when predators are present.

Réaction de Fratercula cirrhata au Danger de Prédation au cours des Vols d'Approche de la Colonie

The evolutionary relationship between the New World quail (Odontophoridae) and other groups of Galliformes has been an area of debate. In particular, the relationship between the New World quail and guineafowl (Numidinae) has been difficult to resolve. We analyzed >8 kb of DNA sequence data from 16 taxa that represent all major lineages of Galliformes to resolve the phylogenetic position of New World quail. A combined data set of eight nuclear loci and three mitochondrial regions analyzed with maximum parsimony, maximum likelihood, and Bayesian methods provide congruent and strong support for New World quail being basal members of a phasianid clade that excludes guineafowl. By contrast, the three mitochondrial regions exhibit modest incongruence with each other. This is reflected in the combined mitochondrial analyses that weakly support the Sibley-Ahlquist topology that placed the New World quail basal in relation to guineafowl and led to the placement of New World quail in its own family, sister to the Phasianidae. However, simulation-based topology tests using the mitochondrial data were unable to reject the topology suggested by our combined (mitochondrial and nuclear) data set. By contrast, similar tests using our most likely topology and our combined nuclear and mitochondrial data allow us to strongly reject the Sibley-Ahlquist topology and a topology based on morphological data that unites Old and New World quail.

Posición Filogenética de las Codornices del Nuevo Mundo (Odontophoridae): Ocho Loci Nucleares y Tres Regiones Mitocondriales Contradicen la Morfología y la Filogenia de Sibley y Ahlquist

Seven living species of passerines are identified or tentatively identified from the early Pliocene Fox Canyon locality (4.3–4.8 mya), Rexroad Formation, Meade Basin, southwestern Kansas. All seven species occur in Kansas today, primarily as winter residents or transients, and their migratory behavior may extend to the early Pliocene as well. A review of all known passerines from the Neogene of North America indicates that many modern taxa began to appear in the early Pliocene, much earlier than previously believed. This fossil evidence agrees with some mitochondrial DNA analyses for the estimated age of divergence for living species of longspurs (Calcarius lapponicus and C. mccownii), but similar estimates for the divergence of C. ornatus using cytochrome-b analyses is at least 3 my younger than indicated by the fossil evidence. The fossil songbirds, as well as other vertebrate taxa from the Meade Basin, also indicate a paleoenvironment of short-grass prairie and shrubland with wetlands and ponds nearby, similar to that found in the area today. This prairie-steppe habitat first appeared in the Meade Basin by the early Pliocene and remained relatively stable until the Pleistocene, when it periodically appeared and disappeared with climate change. High seasonal productivity associated with this habitat in the early Pliocene may have promoted migratory behavior and speciation events in songbirds during a period of relative climatic stasis.

Paserinos Fósiles del Plioceno Temprano de Kansas y la Evolución de las Aves Canoras en Norte América

Several bird-survey methods have been proposed that provide an estimated detection probability so that bird-count statistics can be used to estimate bird abundance. However, some of these estimators adjust counts of birds observed by the probability that a bird is detected and assume that all birds are available to be detected at the time of the survey. We marked male Henslow's Sparrows (Ammodramus henslowii) and Grasshopper Sparrows (A. savannarum) and monitored their behavior during May-July 2002 and 2003 to estimate the proportion of time they were available for detection. We found that the availability of Henslow's Sparrows declined in late June to <10% for 5- or 10-min point counts when a male had to sing and be visible to the observer; but during 20 May-19 June, males were available for detection 39.1% (SD = 27.3) of the time for 5-min point counts and 43.9% (SD = 28.9) of the time for 10-min point counts (n = 54). We detected no temporal changes in availability for Grasshopper Sparrows, but estimated availability to be much lower for 5-min point counts (10.3%, SD = 12.2) than for 10-min point counts (19.2%, SD = 22.3) when males had to be visible and sing during the sampling period (n = 80). For distance sampling, we estimated the availability of Henslow's Sparrows to be 44.2% (SD = 29.0) and the availability of Grasshopper Sparrows to be 20.6% (SD = 23.5). We show how our estimates of availability can be incorporated in the abundance and variance estimators for distance sampling and modify the abundance and variance estimators for the double-observer method. Methods that directly estimate availability from bird counts but also incorporate detection probabilities need further development and will be important for obtaining unbiased estimates of abundance for these species.

Incorporación de la Disponibilidad para la Detección en las Estimaciones de Abundancia de Aves

Recent work in Michigan's eastern Upper Peninsula suggests that terrestrial areas bordering northern Lake Huron provide important stopover habitat for spring migrating landbirds, principally because of the presence of emergent aquatic midges (Diptera: Chironomidae). Migrants were concentrated in lakeshore habitats abundant with midges during spring migration. American Redstarts (Setophaga ruticilla) and Black-throated Green Warblers (Dendroica virens) foraged and used habitat differently, depending on their distance from the lakeshore. Here, we describe results of an integrative study in which we sampled resources, quantified American Redstart foraging behavior, and estimated mass change in American Redstarts and five other common migrant landbird species to evaluate the importance of adult midges as an early season resource for spring migrants. Resource sampling and American Redstart foraging behavior suggested that more food was available in shoreline habitats than inland during spring migration. Furthermore, migrants gained mass in shoreline habitat during stopover, which supports the argument that nearshore areas provide important stopover habitat for spring migrants. Finally, resource sampling, mass change estimates, and American Redstart foraging behavior suggested that midges and spiders (Araneae: Arachnidae) provided an important early season resource for migrating landbirds. Evidence suggests that midges were responsible for elevated spider abundance at the shoreline and that birds foraged on both midges and spiders. Midges appear to play an important role in providing high-quality stopover habitat for landbirds migrating through Michigan's eastern Upper Peninsula.

Hábitat de las Paradas Migratorias a lo Largo de la Costa Norte del Lago Huron, Michigan: Insectos Acuáticos Emergentes como Recurso Alimenticio para las Aves Terrestres Migratorias Durante la Primavera

Assigning conservation priorities to areas used by birds during migration requires information on the relative quality of areas and habitats. The rate at which migratory birds replenish energy reserves during stopover may be used as an indicator of stopover-site quality. We estimated the rate of mass gain of 34 landbird species during stopover at a near-shore terrestrial site on the south shore of Lake Ontario in New York during 12 migration seasons from 1999 to 2004. The average rate of mass gain was estimated by relating a measure of condition to time of capture (hour after sunrise) with linear regression. Data from 25,385 captures were analyzed. Significantly positive rates of mass change were detected for 20 of 30 species during spring migration and 19 of 21 species during autumn migration. No significantly negative trends were detected in either season. Daily rates of mass gain across all species averaged 9.84% of average lean body weight during spring migration and 9.77% during autumn migration. Our regression estimates were significantly greater than estimates from traditional analyses that examine mass changes in recaptured birds. Analyses of mass changes in recaptured birds revealed a mean daily change of −0.68% of average lean mass in spring and 0.13% in autumn. Because of sampling biases inherent in recapture analyses, the regression approach is likely more accurate when the assumptions of the method are met. Similar studies in various habitats, landscapes, and regions are required to prioritize conservation efforts targeting migratory stages of the annual cycle.

Cambios de Peso Diarios de Aves Terrestres durante las Paradas Migratorias en la Costa sur del Lago Ontario

The tody-tyrant and flatbill assemblage, sensu Lanyon (1988a), includes 12 genera of tyrant flycatchers known variously as “tody-tyrants” and “flatbills.” Lanyon supported the monophyly of the group based on similar skull morphology and nest form, and built intergeneric relationships based on syringeal characters. However, these comparisons were made without a phylogenetic framework. A more recent study assessing relationships in the tyrant flycatchers using published morphological and behavioral data failed to recover monophyly of this assemblage (Birdsley 2002). Using DNA sequence data, we test for the monophyly of the tody-tyrant and flatbill assemblage and compare and contrast phylogenetic signals from mitochondrial and nuclear DNA character systems. We discuss our results in light of results from previous studies. We include representatives of the other major tyrant flycatcher assemblages for a total of 42 individuals (representing 27 tyrannid genera and 36 species). We sequenced 3,022 base pairs (bp) of three mitochondrial genes (ND2, ND3, and cytochrome b) and one nuclear intron (FIB5). Our results resolve many of the basal relationships of the tody-tyrant and flatbill phylogeny, but separate and combined analyses of data partitions are necessary to understand the nature of conflict among data sets. The tody-tyrants constitute a monophyletic clade, but the genera Hemitriccus and Lophotriccus are not monophyletic, and the limits of Oncostoma-Lophotriccus need to be revised with more complete sampling at the species level. The flatbills as defined by Lanyon are not monophyletic (Onychorhynchus and Platyrinchus are not true flatbills). Pseudotriccus and Corythopis are sister taxa and, together with Leptopogon and Mionectes, are allied to the tody-tyrant and flatbill clade.

Filogenia Molecular del Grupo de los Picochatos y Mosquiteros de la Familia Tyrannidae

Male and female birds can exhibit striking differences in morphology (dimorphism), including exaggerated plumage structures, size differences, and feather color differences, yet most species are considered to have identical sexes. Classification of a species as sexually monochromatic (identical coloration between the sexes) has traditionally been based on human visual perception. Research over the past two decades has shown that birds see each other and the world differently than their human investigators; these visual differences, combined with objective color measurements, suggest that traditional assessments of plumage coloration may be questionable from an avian visual perspective (Cuthill et al. 1999). I tested the avian reality of human categorization of sexually monochromatic plumages for North American passerines. I found, on the basis of plumage-reflectance data and modeled avian color-discrimination thresholds, that 91.6% of the presumed sexually monochromatic species I sampled are sexually dichromatic to birds, which confirms the rarity of sexually monochromatic bird species. This study informs future work as to potential sources of plumage signals hidden from human observers and generates testable predictions regarding avian sex-recognition via plumage signals.

La Coloración del Plumaje desde la Perspectiva de la Visión de las Aves Confirma la Rareza del Monocromatismo Sexual en las Aves Paserinas de Norte América

We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson’s Warbler (Wilsonia pusilla) migrating through five sites spanning a cross-section of the species’ southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial patterns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all five migration sites, we found a significant negative relationship between the date Wilson’s Warblers passed through the sampling station and δD values of their feathers. These data were consistent with a pattern of “leap-frog” migration, in which individuals that bred the previous season at southern latitudes migrated through migration stations earlier than individuals that had previously bred at more northern latitudes. We documented that this pattern was consistent across sites and in multiple years. This finding corroborates previous research conducted on Wilson’s Warbler during the fall migration. In addition, mean δD values became more negative across sampling stations from west to east, with the mean δD values at each station corresponding to different geographic regions of the Wilson’s Warblers’ western breeding range. These data indicate that Wilson’s Warblers passing through each station represented a specific regional subset of the entire Wilson’s Warbler western breeding range. As a result, habitat alterations at specific areas across the east-west expanse of the bird’s migratory route in the southwestern United States could differentially affect Wilson’s Warblers at different breeding areas. This migration information is critical for management of Neotropical migrants, especially in light of the rapid changes presently occurring over the southwestern landscape.

Patrones Espaciales y Temporales de la Migración de Wilsonia pusilla en el Sudoeste Detectados Mediante Isótopos Estables

When the reproductive value of sons differs from that of daughters, selection will favor broods biased toward the sex that can provide greater fitness benefits. In species where female choice is based on male ornamentation, females mated to highly ornamented males may experience a reproductive advantage by skewing the brood sex ratio toward sons. In the Common Yellowthroat (Geothlypis trichas), males with larger black facial masks are more likely to gain a social mate and sire extrapair young and, as a result, have increased seasonal reproductive success. Females mated to larger-masked males could benefit if they produced more sons. Given that larger- masked males are preferred as extrapair sires, females may also benefit by producing more extrapair sons. We tested these hypotheses during a five-year study of Common Yellowthroats in Wisconsin. Contrary to our predictions, females did not produce more sons when mated to males with larger masks, and extrapair young were not more likely to be male. However, sons were more likely to be sired by males with longer tarsi, which suggests that females may respond to male body size rather than to male ornament size.

El Cociente de Sexos en las Nidadas Está Relacionado con el Tamaño de los Machos pero no con el Atractivo en Geothlypis trichas

Despite their large vocal repertoires and otherwise highly versatile singing style, male mockingbirds (Mimus spp.) sometimes sing in a highly repetitive fashion. We conducted a playback experiment to determine the possible signal value of different syllable-presentation patterns during simulated male intrusions in the Tropical Mockingbird (Mimus gilvus), testing the hypothesis that more repetitive singing represents a stronger threat and generates a stronger aggressive response. Responses were measured in terms of approach and singing behavior and were analyzed using McGregor’s (1992) multivariate method. We also introduce the use of survival analysis for analyzing response variables for which subjects do not perform the behavior in question in at least one of the replicates (known as “right-censored variables” in the statistical literature). As predicted by theory, experimental subjects responded more aggressively to songs composed of a single note than to variable ones. However, versatility at the between-song level had an opposite effect: high song-switching rates generated stronger responses than low ones. Given the lack of a statistical interaction between within-song versatility and switching rate, we conclude that these two parameters may serve independent purposes and possibly transmit different information. We discuss the possibility that the signal value of variation in vocal versatility lies in the mediation of territorial conflicts, the attraction of female partners, the mediation of conflicts over access to reproductive females, or some combination of these functions.

Respuestas de Machos de Mimus gilvus a Variación en Versatilidad Vocal Dentro- y Entre-cantos

The distribution and abundance of food are primary factors affecting resource-use patterns in birds. Many bird species eat several food types, which may differ in their distribution and overall abundance. I studied foraging ecology of seven sympatric species of Tangara at Mindo, Ecuador, to determine whether the patterns of resource use differed between two food types: arthropods and fruits. Interspecific differences in arthropod-foraging were manifested in the fine segregation of microhabitat preference combined with different habitat use. By contrast, interspecific differences in fruit-foraging were manifested in preferences for different plant genera, often associated with different habitats. No evidence was found for spatial partitioning of the same fruit species. Interspecific overlap in fruit-for- aging was 3× higher than that in arthropod-foraging, and species of Tangara that frequently joined the same mixed-species flocks differed largely in arthropod-foraging but overlapped greatly in fruit-foraging. The differences in patterns between arthropod and fruit-foraging may be explained by the different characteristics of arthropods and fruits as food resources. High sympatry of species of Tangara and other omnivorous tanagers, in general, appears to be maintained not because fruits are abundant, resulting in little competition for them, but because these tanagers specialize on different microhabitats for foraging arthropods.

Segregación de Artrópodos como Recurso Alimenticio de Tangaras Omnívoras (Tangara spp.) en el Oeste de Ecuador

The demographic significance of parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds”) has been debated for years, because manipulative studies are few and mathematical models of cowbird-host systems have not led to tests of their predictions. We combine results from a cowbird- removal experiment (Smith et al. 2002, 2003) with a stochastic simulation model that we developed, to reassess the effect of cowbirds on the annual reproductive success (ARS) and nesting success in Song Sparrows (Melospiza melodia). Our model followed the breeding success of individual Song Sparrow nests and extrapolated to output variables including ARS, nest survival, and parasitism rates. We parameterized the model with field data from cowbird control sites (i.e., cowbirds not manipulated) and found that output variables matched those observed. We used the reduced parasitism rates observed on cowbird-removal sites, reran the model, and compared output with observed values. On removal sites, ARS was greater than predicted by the model, which indicates that the model failed to account for some biological phenomenon that occurred when cowbirds were in the system. To assess what this phenomenon might be, we conducted further analyses that indicated that cowbirds may facilitate nest predation by “conventional” predators. Using elasticity analyses, we show that cowbirds have their largest effect on ARS through egg removal and that conventional predators are more important than cowbirds in directly affecting nest survival rates. We report that to assess the effect of cowbirds on nest survival, researchers must avoid using the common technique of comparing survival rates of parasitized and unparasitized nests within populations.

Réévaluation de la Menace du Vacher

The ratio of hatch-year (HY) to after-hatch-year (AHY) individuals (HY:AHY ratio) can be a valuable metric for estimating avian productivity because it does not require monitoring individual breeding sites and can often be estimated across large geographic and temporal scales. However, rigorous estimation of age ratios requires that both young and adult age classes are sampled in an unbiased manner, an assumption that is rarely tested. We estimated HY:AHY ratios for Marbled Murrelets (Brachyramphus marmoratus), a threatened seabird, using at-sea surveys and captures to assess whether age-specific differences in behavior and distribution result in biased productivity estimates in central California. AHY and HY Marbled Murrelets were distributed similarly at sea, and HY individuals did not congregate in nursery areas. Moreover, dispersal by radiomarked AHY Marbled Murrelets out of our survey area occurred at a low rate, and AHY densities were constant over the survey period, which suggests that AHY immigration and emigration did not significantly bias productivity estimates. HY density increased linearly over the survey period as expected if little dispersal occurred, which suggests that productivity estimates were not significantly biased by HY dispersal. Finally, simulation analyses indicated that annual variation in the timing of breeding resulted in only small biases in HY:AHY ratios. HY:AHY ratios were corrected for the proportion of AHY Marbled Murrelets that were incubating and the proportion of HY individuals that had not fledged at the time of sampling. Mean corrected HY:AHY ratios were low on the basis of both at-sea surveys conducted from 1996 to 2003 (0.032; SE = 0.011) and captures conducted from 1999 to 2003 (0.037; SE = 0.028), implying that productivity was poor in central California. Estimating age ratios may be an effective way of monitoring changes in reproductive success and identifying environmental factors that affect Marbled Murrelet populations, though tests of assumptions are needed in other regions.

Le Rapport des Âges comme Estimateur de la Productivité: Tester les Hypothèses avec un Oiseau de Mer Menacé, Brachyramphus marmoratus

Males of several avian species are more vigilant than their female partners, particularly during the preincubation period. Male vigilance may function as a deterrent of extrapair copulation attempts (EPCs) or to ensure male survival, because males of sexually dimorphic species may be more conspicuous to predators than females. However, vigilant males may act as antipredator sentinels to enhance female survivorship, which may also allow females to feed and rest more efficiently, thereby enhancing their ability to form clutches. We attempted to distinguish between the “male benefits” and “female benefits” hypotheses by studying the behavior of unpaired males and paired Harlequin Ducks (Histrionicus histrionicus) during the preincubation period. Paired males were, on average, four times more vigilant than unpaired males and their mates, which suggests that elevated levels of vigilance by paired males does not function primarily for self-protection against predators. Males were not more vigilant during the female’s fertile period, contrary to the “paternity assurance” hypothesis. Male vigilance during feeding bouts was highest when pairs fed alone near shore—a condition in which feeding was likely more “risky.” Male vigilance was positively correlated with female feeding when females fed near shore, but not at other times. During resting bouts, males were vigilant 14 ± 0.01% of the time in all conditions. We suggest that male vigilance may be important to enhance female survival, especially when females feed under risky conditions.

Comportement de Vigilance chez Histrionicus histrionicus durant la Période de Pré- incubation au Labrador: Les Mâles Sont-ils Vigilants pour Eux-mêmes ou pour leur Partenaire Social?

Males of the polyandrous Australian Brush-turkey (Alectura lathami) build mounds of leaf litter, in which incubation heat is produced by microbial decomposition. Females lay eggs singly, at intervals of several days, over many months. For each egg, they select an incubation mound in which to lay, and they then typically copulate with the male mound-owner; mound choice is, thus, usually equal to mate choice. Freed from incubation and maternal care, these females can invest considerable time and energy in assessing and choosing their potential mates. Low or high incubation temperatures inside the mounds have negative effects on embryos and chicks, and temperatures vary considerably both between and within mounds. Here, I show that mounds with mean incubation temperatures ranging from approximately 32°C to 35°C received more eggs than cooler or warmer mounds. Similarly, when the size of each egg was compared with its temperature when found in the mound, larger eggs were deposited mainly in mound material at temperatures between approximately 32°C and 35°C, whereas smaller eggs were laid at temperatures above and below this range. Egg size was included as a factor describing female mate choice, because egg size in relation to body size is exceptionally large, which indicates considerable female investment. Overall, these results suggest that the temperature in the males’ incubation mounds considerably affects female mate choice.

Selección del Montículo y de la Pareja en un Megápodo Poliándrico: Las Hembras Ponen Más y Mayores Huevos en los Montículos de Nidificación con las Mejores Temperaturas de Incubación

We estimated annual return rate, fidelity, and breeding dispersal in a migratory population of Flammulated Owls (Otus flammeolus) in central Colorado. Return rates, based on capture-recapture histories of 39 males and 52 females from 1981 to 2003, were higher for males (84%) than for females (45%). Annual recapture probability was higher for females, because breeders are easier to capture than nonbreeders and females always attempted to nest, whereas some males were unpaired (did not nest) for up to four years. Territory fidelity was male biased (92%, vs. 56% for females, adjusted for undetected emigration), and mean tenure on territories was more than twice as long for males as for females. Females, but not males, had lower return rates to territories in the year following nesting failure compared with females whose nests were successful. Most males appeared to occupy one territory their entire reproductive lives, countering predictions of habitat-selection models that individuals should move to higher-quality habitats when they become available. We estimated that 74% of pairs retained the same mate in consecutive nesting attempts, but mates that bred together for multiple years had no reproductive advantages over mates that bred together for the first time. In most cases, females dispersed from territories if their mates did not return. When females dispersed, they went to territories where total productivity over the study and lifetime reproductive success of new mates were higher than on original territories, which supports the hypothesis that dispersal by females increases individual fitness.

Tasa de Retorno, Fidelidad y Dispersión en una Población Reproductiva de Otus flammeolus

By nesting near aggressive birds, timid species can reap the benefits of aggressive nest defense while avoiding the costs. Red Phalaropes (Phalaropus fulicarius; hereafter “phalaropes”) typically nest in grass-sedge marshes, but nests have also been noted in rocky coastal habitats. We studied the reproductive ecology of phalaropes at East Bay, Southampton Island, Nunavut, to determine whether their use of coastal nest areas reflected a protective nesting association with an aggressive larid, the Sabine's Gull (Xema sabini; hereafter “gull”). From 2000 to 2002, we found and monitored 29 phalarope nests with gull nests nearby (≤150 m away) and 26 without gulls nearby. Coastal phalarope nests were nearer to gull nests than expected by chance. No habitat differences were detected between coastal areas with and without gull nests, but only three phalarope nests were found in coastal areas without gull nests. Thermistor probes inserted in phalarope nests revealed that incubators with gulls nearby behaved less cryptically, taking more frequent and longer incubation recesses. In human-approach experiments, phalaropes with gulls nearby flushed earlier than those without gulls. In 2000 and 2001, hatch success was 17–20% higher for phalaropes with gulls nearby, but these nests had lower success rates than those without nearby gulls in 2002. These gulls are able to defend their nests from avian predators only; in 2002, arctic foxes (Alopex lagopus) were abundant, and their primary prey, collared lemmings (Dicrostonyx torquatus), were scarce. We suggest that phalaropes select coastal areas near gulls, but that this association is beneficial to phalaropes only in years when egg predation by arctic foxes is low.

Variation Annuelle des Bénéfices d'une Association pour Nicher entre Phalaropus fulicarius et Xema sabini

From 1994 to 2003, I annually surveyed terrestrial insectivorous birds in a 100-ha plot within continuous rainforest near Manaus, Brazil. I used spot-map registrations and radiotagged birds to estimate territory size and density on the plot for 13 species. As in the few previous studies of Amazonian birds, territory sizes were large (mean = 13.0 ha) and densities were low (mean = 3.4 pairs per 100 ha). The most common species, Formicarius colma, was the only species with >10 pairs per 100 ha, and one of four species (with Myrmeciza ferruginea, Conopophaga aurita, and Corythopis torquatus) to have territories of <7.0 ha. On average, each species occupied 34% of the plot, with only four species (F. colma, Grallaria varia, F. analis, and M. ferruginea) ever occupying >50% in any year. Territories appeared and disappeared between surveys; ∼71% of territories detected in a given survey were present in the next survey. The two rarest species, Myrmothera campanisona and Hylopezus macularius, were absent from the plot in some years. Across species, territory stability was positively correlated with abundance; more common species had more stable density among years than rare species. Although past research has shown territory stability for the most common species of Neotropical rainforest birds, my results suggest that rarer species, which constitute the bulk of the avifauna, may show greater fluctuation in abundance.

I compared my results to similar data from lowland rainforests in Panama, French Guiana, Ecuador, and Peru. Species richness was lowest in Panama, but comparable among the Amazonian sites. Panama also had the highest biomass and smallest territory sizes. Interestingly, relative abundances of species shared among sites were not necessarily similar. With the exception of Conopophaga spp., all species or replacement species shared among sites were at least twice as abundant at one site as at another. Relative abundance within genera also differed among sites for Sclerurus and Formicarius. The sparse data available so far suggest that individual species show considerable spatial variation in abundance across Amazonia, though the mechanisms and the texture of the patterns remain unknown.

Densidade, Tamanho do Território, e Dinamismo Espacial ao Longo Prazo das Aves Insetívoras Terrestres perto de Manaus, Brasil

Although the ultimate factors that influence the duration of avian incubation periods are well known, we know much less about the proximate mechanisms by which birds adjust incubation period in response to selection. We tested the hypothesis that an adjustment in eggshell porosity is one such proximate mechanism (i.e., that avian species with higher ratios of incubation period to egg size lay eggs with less porous shells). Eggshell porosity affects the rate of gaseous exchange between the developing embryo and the external environment; thus, to the extent that embryonic metabolism is diffusion-limited, eggshell porosity could directly determine incubation period. To test that hypothesis, we collected eggs from seven species of Alcidae, a family of marine birds that exhibits an unusual degree of interspecific variation in incubation period, and measured egg mass and eggshell porosity (determined by the number and size of pores and the thickness of the shell). Incubation periods were obtained from the literature. Egg mass and eggshell porosity combined explained 87% of the variation in incubation period among the seven species, which included at least one member of each of the six main alcid lineages. As predicted, eggshell porosity and incubation period were negatively related, after controlling for egg mass. Our results are consistent with the hypothesis that evolutionary changes in avian incubation period may be attributed, at least in part, to adjustments in eggshell porosity.

Taille de l’Œuf, Porosité de la Coquille et Période d’Incubation chez les Oiseaux Marins de la Famille des Alcidés

Established parks and nature reserves may be inadequate to preserve long-term biotic diversity, especially in tropical regions of Latin America where anthropogenic disturbance and land-conversion is an ongoing problem. Demand for economically productive land uses, such as cattle pastures or monoculture plantations, is one of the greatest threats to habitat and wildlife preservation. As a result, conservation biologists have turned to examining attributes of nonprotected lands to determine which land uses both support wildlife and make economic sense. I examined bird use of a plantation of Gmelina arborea (“white teak” or “melina” trees; hereafter “plantation”) in Guatemala to assess its suitability as bird habitat. Gmelina arborea is grown mainly for wood and paper pulp. Several compositionally different habitats were identified, based on the amount of natural vegetation grown within and among the plantation trees, forming a heterogeneous landscape. I detected 195 bird species from 45 families within this plantation-dominated landscape, and 144 species in plantation habitats combined. I observed a positive association between increased vegetative complexity and bird species richness; moreover, bird species richness attained levels statistically indistinguishable from those found in nearby forest fragments. Mixed plantation habitat containing 19–31% natural vegetative coverage supported bird communities that equaled or surpassed levels of species richness found by other researchers in shaded coffee (Coffea spp.) plantations. However, pure stands of G. arborea supported richness levels equal to those of grazed pasture; diversity levels associated with both these land uses were close to those reported for sun coffee plantations. Clearly, native vegetation played a significant role in enhancing bird species richness in the plantation habitat, and amounts of relative cover similar to or exceeding those in the plantation I studied should be considered in any management plan for G. arborea in Central America.

Rol Ecológico de Plantaciones de Árboles de Gmelina arborea en Guatemala: Una Evaluación de un Uso Alternativo del Suelo para la Conservación de las Aves Tropicales

Two attributes of many temperate passerine species are short-term territoriality and strongly fluctuating annual testosterone (T) profiles. Circulating T of temperate passerines can vary from undetectable levels in the nonbreeding season to higher, but fluctuating, levels during the breeding season. Males of many temperate species respond to territorial instability during the breeding season with transitory increases in T. In females, the hormonal response to aggression is more complex. Most temperate-zone passerine species that have been studied exhibit territoriality for less than three months. Here, I describe the year-round T profile of male and female Northern Cardinals (Cardinalis cardinalis), a temperate-zone species with prolonged territorial behavior (7 months). Circulating levels of T in female Northern Cardinals is relatively stable. Males show variation in T levels over the year and they may respond to territorial intrusions with increases in T. Of particular interest are the relatively high levels of T observed in female Northern Cardinals throughout the year, and measurable amounts of T in both sexes in the winter.

Testosterona en Cardinalis cardinalis: Posible Influencia del Comportamiento Territorial Prolongado

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.