In 1996, an expedition of personnel from the Louisiana State University Museum of Natural Science and the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos made a trail from the east bank of the upper Río Cushabatay, departamento Ucayali, Peru, northeast to the top of a 1,538-m peak at 7°05′S, 75°39′W. The peak supports cloud forest from 1,200 m to the summit, and this “island” of habitat may be among the most isolated areas of cloud forest in South America. Among the depauperate cloud-forest avifauna we discovered a striking new species of Capito barbet, which apparently is the only member of the genus restricted to this habitat.

We introduce a phenotypic method to test for excess mortality in hybrids of the heterogametic sex, as expected from Haldane's rule, and apply this method to the unusually narrow hybrid zones between Hermit Warblers (Dendroica occidentalis) and Townsend's Warblers (D. townsendi) in the Pacific Northwest. Our test requires establishing comparable hybrid indices for male and female warblers. The hybrid index that we developed for females produced age-corrected distributions for phenotypically pure reference samples that closely matched those used by Rohwer and Wood (1998) for males. The similarity in these distributions enabled us to compare the relative frequency of males and females in hybrids and parentals. We detected no deficiency of hybrid females and thus no inviability in the heterogametic sex. Our failure to find evidence of the inviability component of Haldane's rule is not unexpected given the close relationship between these taxa; nonetheless, our methods should be generally useful for studies of hybrid zones.

The Southwestern Willow Flycatcher (Empidonax traillii extimus) is an endangered Neotropical migrant that breeds in isolated remnants of dense riparian habitat in the southwestern United States. We estimated genetic variation at 20 breeding sites of the Southwestern Willow Flycatcher (290 individuals) using 38 amplified fragment length polymorphisms (AFLPs). Our results suggest that considerable genetic diversity exists within the subspecies and within local breeding sites. Statistical analyses of genetic variation revealed only slight, although significant, differentiation among breeding sites (Mantel's r = 0.0705, P < 0.0005; θ = 0.0816, 95% CI = 0.0608 to 0.1034; Φ_ST = 0.0458, P < 0.001). UPGMA cluster analysis of the AFLP markers indicates that extensive gene flow has occurred among breeding sites. No one site stood out as being genetically unique or isolated. Therefore, the small level of genetic structure that we detected may not be biologically significant. Ongoing field studies are consistent with this conclusion. Of the banded birds that were resighted or recaptured in Arizona during the 1996 to 1998 breeding seasons, one-third moved between breeding sites and two-thirds were philopatric. Low differentiation may be the result of historically high rangewide diversity followed by recent geographic isolation of breeding sites, although observational data indicate that gene flow is a current phenomenon. Our data suggest that breeding groups of E. t. extimus act as a metapopulation.

We studied three Nearctic migrant species (American Redstart [Setophaga ruticilla], AMRE; Black-and-white Warbler [Mniotilta varia], BAWW; Black-throated Blue Warbler [Dendroica caerulescens ], BTBW) wintering in 14 isolated shade coffee plantations (0.1 to 8.7 ha) in the Dominican Republic to determine if site fidelity was comparable to that in tropical forests and if it decreased with plantation size. Site fidelity was measured as the percentage of wandering birds captured in mist nets, as overwinter site persistence of uniquely marked birds observed on the same sites (November to March), and as annual return of marked individuals to previously occupied sites (January to January). The percentages of wanderers in net captures were mostly lower than values reported for natural forests (AMRE 21%, BAWW 12%, BTBW 41%) and did not vary with plantation size. Overwinter site persistence (AMRE 65%, BAWW 65%, BTBW 76%) and annual return (AMRE 34%, BAWW 40%, BTBW 31%) in the plantations fell within the range of values reported for natural forests. Overwinter site persistence decreased with plantation size only in AMRE, although BAWW showed lower persistence in small plantations from early to midwinter. Annual return decreased with plantation size only in AMRE. Despite diminished site fidelity in small plantations, these birds showed some fidelity to small plantations, many of which were smaller than the mean size of winter home ranges.

Determining whether nesting attempts are successful can be difficult. Yet, current protocols for estimating nesting success do not address how uncertain nest fates should be handled. We examined the problem of nest-fate uncertainty as it relates to Mayfield estimation of nesting success and in analyses of factors that influence success. We used data from Minnesota to illustrate the potential effect of uncertain fate; 40% of Ovenbird (Seiurus aurocapillus; n = 127) nests and 30% of Least Flycatcher (Empidonax minimus; n = 144) nests had uncertain fates. How this uncertainty is incorporated into Mayfield estimates of success varied widely among researchers. In a survey of researchers who use the Mayfield method, 9 of 22 respondents (of 40 contacted) excluded nests with uncertain fate. Excluding uncertain fates is counter to how Mayfield first described his estimator and can result in severe downward bias. The remaining respondents (59%) included nests with uncertain fate but varied in how they terminated the exposure period. We developed a simulation model that calculated Mayfield estimates using different approaches and compared them with a known rate of nesting success. Magnitude of bias in Mayfield estimates varied considerably in our simulations. The approach with the least bias terminated exposure with the last observed active date for nests with uncertain fate, and with the midpoint between last observed active and first observed inactive dates for nests with known fate. In addition, information necessary to interpret and compare Mayfield estimates often is not reported. These values, including variance estimates and the period lengths used to estimate survival rates, should be reported with Mayfield estimates. Finally, nest fate is commonly used as a categorical variable in studies of factors affecting nesting success. In this approach, however, nests with uncertain fate must be excluded. An alternative approach is Cox regression, which incorporates nests with uncertain fate.

We used data from an 11-year study of Red-winged Blackbirds (Agelaius phoeniceus) to test the hypothesis that fledging success is a reliable index of recruitment at the population and the individual level. Natal philopatry was only 2.37% overall (3.51% for males and 1.49% for females) in our study population. However, the number of fledglings that returned as breeding adults from an annual fledgling cohort was significantly correlated with the size of the cohort. The correlation was also significant when males and females were analyzed separately, despite sex differences in natal philopatry, age of first breeding, and probable differences in mortality factors. Recruitment increased disproportionately with the size of the fledgling cohort. Thus, years of high production produced proportionately more breeding adults. At the individual level, the number of fledglings sired by a male in his lifetime was significantly correlated with the number of his descendants that eventually returned to breed in the study population. These results support the widely held assumption in avian field studies that fledging success is a reliable index of fitness.

We evaluated the influence of environmental and density-dependent factors (intraspecific and interspecific) on clutch size, brood size, and nesting success of Little Egrets (Egretta garzetta) in the Camargue of southern France. We recorded these reproductive parameters in most years from 1970 to 1998. We used a generalized linear modeling approach (model selection based on AIC) to examine the environmental effects of spring rainfall, winter temperature, and wind on these parameters. We also examined density dependence of these parameters based on the total number of Little Egrets and the total number of tree-nesting herons nesting in these mixed-species colonies. Clutch size was positively associated with rainfall and negatively associated with the number of Little Egret nests in the Camargue. Brood size was negatively associated with the number of Little Egret nests, although rainfall was only significant as an interaction effect with these two effects. Nesting success was negatively associated with the number of tree-nesting herons, the proportion of each colony consisting of Cattle Egrets (Bubulcus ibis), wind speed, and several interactions among these variables. Virtually all of the reproductive parameters that we evaluated were negatively associated with the number of Little Egret nests or the number of tree-nesting herons. Anecdotal evidence suggests that Cattle Egrets displace Little Egrets at some centrally located nest sites. Such sites are better protected from strong winds, which are a common cause of nesting failure.

I compared nesting intervals during three consecutive years in five species of temperate-nesting dabbling ducks (Mallard [Anas platyrhynchos], Northern Pintail [Anas acuta], Northern Shoveler [Anas clypeata], Blue-winged Teal [Anas discors], Gadwall [Anas strepera]) and assessed whether differences existed in timing of refractoriness. Most nesting by females of all five species ended by the summer solstice. Nesting ended earliest for Northern Shovelers and Northern Pintails and latest for Gadwalls. Some Mallards, Blue-winged Teal, and Gadwalls continued to nest into mid- and late summer, whereas Northern Shovelers and Northern Pintails did not. Mallards, Blue-winged Teal, and Gadwalls accounted for 99% (81 of 82) of flightless broods resulting from nests initiated during mid- or late summer in North Dakota and 98% (58 of 59) of flightless juveniles shot on or after 1 October by a random sample of duck hunters from across the United States. Early cessation of breeding by Northern Shovelers may have evolved in response to the species' limited flexibility in diet. Photorefractory mechanisms that limit most breeding to spring presumably evolved in response to severe constraints on reproductive success when nesting continued through summer (e.g. mortality of late-hatched young and molting females due to low temperatures). Interspecific differences in photosensitivity may account for variation in timing of cessation of nesting in late spring, but controlled experiments are needed to assess the possible role of non-photic influences. My results suggest that the refractory mechanisms controlling length of the breeding season in temperate-nesting dabbling ducks are more varied and complex than previously thought, with non-photic influences (e.g. water conditions, food availability, food quality) having a larger role than indicated by earlier research.

We used DNA fingerprinting to assess genetic structure of populations in Cory's Shearwater (Calonectris diomedea). We analyzed mates and parent-offspring relationships, as well as the amount and distribution of genetic variation within and among populations, from the level of subcolony to subspecies. We found no evidence of extrapair fertilization, confirming that the genetic breeding system matches the social system that has been observed in the species. Mates were closely related, and the level of genetic relatedness within populations was within the range usually found in inbred populations. In contrast to previous studies based on allozymes and mtDNA polymorphism, DNA fingerprinting using microsatellites revealed consistent levels of genetic differentiation among populations. However, analyzing the two subspecies separately revealed that the pattern of genetic variation among populations did not support the model of isolation by distance. Natal dispersal, as well as historic and/or demographic events, probably contributed to shape the genetic structure of populations in the species.

Species diversity and community composition of birds change rapidly along elevational gradients in Costa Rica. Such changes are of interest ecologically and illustrate the value of protecting continuous gradients of forest. We used mist nets and point counts to sample birds along an elevational gradient on the northeastern Caribbean slope of the Cordillera Central in Costa Rica. Sites included mature tropical wet forest (50 m); tropical wet, cool transition forest (500 m); tropical premontane rain forest (1,000 m); and tropical lower montane rain forest (1,500 and 2,000 m). We recorded 261 species from 40 families, including 168 species captured in mist nets (7,312 captures) and 226 detected during point counts (17,071 observations). The sample included 40 threatened species, 56 elevational migrants, and 22 latitudinal migrants. Species richness (based on rarefaction analyses) changed little from 50 to 1,000 m but was lower at 1,500 and 2,000 m. Mist nets and point counts often provided similar views of community structure among sites based on relative importance of difference categories of species (e.g. migrant status, trophic status). Nonetheless, important differences existed in numbers and types of species represented by the two methods. Ninety-three species were detected on point counts only and 35 were captured only. Ten families, including ecologically important ones such as Psittacidae and Cotingidae, were not represented by captures. Elevational migrants and threatened species occurred throughout the gradient, illustrating the need to protect forest at all elevations. A comparable study from the Cordillera de Tilarán (Young et al. 1998) demonstrated similar patterns of species change along an elevational gradient. Comparisons with that study illustrated that point counts are a valuable complement to mist-net studies. Both studies indicated the diverse nature of the avifauna along elevational gradients in Costa Rica.

In managed forests, riparian buffer strips typically are maintained to protect water quality. If properly designed, buffer strips also may act as wildlife reserves. However, forest managers have lacked the information to develop standards for buffer strips to maximize benefits for wildlife species. We assessed the conservation potential of 20-, 100-, and 200-m wide buffers for an area-sensitive songbird in boreal mixed-wood forest in Alberta. We measured abundance, territory characteristics, and pairing success of Ovenbirds (Seiurus aurocapillus) at treatment and control lakes one year before and after upland timber harvest. After harvest, Ovenbirds were absent from 20-m buffer strips. Harvesting did not significantly influence abundance or territory size in 100-m or 200-m buffers, although territories generally became narrower. Postharvest territory position did not change in 200-m buffers, but territories in 100-m strips shifted lakeward and included more habitat adjacent to the riparian edge than before harvest. Despite this shift in territory position, males that occupied 100-m strips successfully attracted mates. High availability of regional forest cover may have muted the more pronounced effects of habitat alteration observed in other studies. Our research is among the first to evaluate individual behavioral responses to the creation of forest edges. Our data indicate that 20-m buffer strips do not support breeding Ovenbirds, whereas 100- and 200-m buffers retain Ovenbirds during the year following harvest. Long-term harvest effects may differ from those we monitored and require study, particularly as timber extraction increases in the boreal mixed-wood ecoregion.

We estimated survival rates of adult Southern Buller's Albatrosses (Thalassarche bulleri bulleri) from 1948 to 1997 based on a long-term banding and recapture program at The Snares, New Zealand. Annual survival exceeded 0.95 from 1961 to 1968 and from 1992 to 1997 but declined to between 0.913 and 0.928 from 1969 to 1991. Reduced survival may have resulted from incidental mortality associated with longline and trawl fisheries in the foraging areas of these birds, but it must have been counterbalanced by changes in other population parameters because the population increased greatly in number from 1969 to 1997. Increased trawling activity in areas where albatrosses forage may have benefited the population by providing additional food, which may have enhanced the survival rate of recently fledged birds. We found no indication that survival rates differed between males and females, but an age effect occurred in which survival of birds with at least 25 years of breeding experience was lower than that of less-experienced and presumably younger birds.

Fruit preference by birds is a complex process based upon the morphology and spatial arrangement of fruits and on the physiological needs and capabilities of birds. In North America, most fruits can be divided into two groups based on nutritional content: those rich in sugars relative to lipids, and those rich in lipids relative to sugars. To investigate how fruit preference may change seasonally and to determine if it is correlated with physiological state, we designed a simple laboratory experiment using American Robins (Turdus migratorius) and artificial fruits. During summer and autumn, we offered eight robins a choice between synthetic sugar-rich and lipid-rich fruits of equal caloric value and then measured food intake and assimilation efficiency for each fruit type. Overall, robins preferred sugar-rich to lipid-rich fruits during both seasons. Robins had a higher assimilation efficiency for sugars than for lipids during both seasons, although assimilation efficiency of lipids increased significantly from summer to autumn. During experiments, robins consumed significantly more sugar-rich than lipid-rich fruits in summer but not in autumn. Coupling fruit intake with assimilation efficiency indicates that in summer, robins had a higher rate of energy gain from sugars than from lipids, but by autumn the rate of energy gain from lipids increased to nearly the same level as that from sugars. Our results suggest that robins prefer sugar-rich fruits because of their simple and fast rate of digestion, enabling higher rates of energy gain, but that lipid-rich fruits become important with the onset of autumn.

We studied sexual and individual differences in foraging and parental behavior of King Cormorants (Phalacrocorax albiventer) during the brood-rearing period at Macquarie Island. King Cormorants exhibit sexual dimorphism in size, with males being 16% heavier than females. Females foraged mainly in the morning and males in the afternoon. Five females were shallow divers (1.9 to 6.8 m), and seven females were deep divers (19.6 to 28.0 m); males dived deeper (15.6 to 44.2 m) than both groups of females. The amount of time spent on the bottom (“bottom time”) relative to the dive cycle was higher for shallow-diving females (x̄ = 40 ± SD of 13%) than for males (x̄ = 26 ± 4%) and deep-diving females (x̄ = 27 ± 3%). Total daily dive time and bottom time per day did not differ significantly among groups because shallow-diving females dived more often (x̄ = 211 ± 81 dives per day) than males (x̄ = 68 ± 21) and deep-diving females (x̄ = 70 ± 7). Provisioning rate, trip duration, and proportion of time at sea did not differ significantly for males, deep-diving females, and shallow-diving females. Females, especially shallow divers, compensated for their shallow and short dives with more frequent dives. Consequently, male and female King Cormorants provisioned their chicks at similar rates despite large individual variation in foraging behavior.

We used behavioral, physiological, and parasitological measures to document effects of acute malarial infections on activity budgets of experimentally infected juvenile Apapane (Himatione sanguinea). Five of eight birds died within 20 to 32 days after exposure to a single infective mosquito bite. Infected Apapane devoted less time to locomotory activities involving flight, walking or hopping, and stationary activities such as singing, preening, feeding, and probing. The amount of time spent sitting was positively correlated with parasitemia and increased dramatically after infection and between treatment and control groups. Birds that succumbed to infection experienced a significant loss of body mass and subcutaneous fat, whereas surviving Apapane were better able to maintain body condition and fat levels. When rechallenged with the parasite five months after initial infection, surviving birds experienced no increase in parasitemia, indicating that they had become immune to reinfection. Regardless of the outcome, infected birds experienced acute illness that would have left them unable to forage or to escape from predators in the wild.

We compared predation of artificial open-cup nests baited with Japanese Quail (Coturnix coturnix) eggs with predation of natural open-cup nests during 1997 and 1998 in a Louisiana pine forest to assess the assumption that predation of artificial nests is an index to that of natural nests. Cameras were placed at randomly selected natural and artificial nests in shrubs to document predators. Predation at artificial-nest plots was positively correlated with predation at adjacent natural-nest plots overall, although inconsistently by year. Artificial nests were almost exclusively depredated by corvids, but quail eggs were too large to be broken by small-mouthed mammalian predators. American Crows (Corvus brachyrhynchos) appeared to be important predators of natural nests. Predation of natural nests was independent of predation at other nests, but predation of artificial nests by crows was spatially and temporally clumped. Crows may have learned the location of artificial-nest plots, and predation of artificial nests increased significantly between years, contrary to predation of natural nests. Predation of artificial nests did not exhibit seasonal variation like that of natural nests. Overall, predation of artificial shrub nests did not accurately mimic that of natural shrub nests. Changes in procedures for artificial-nest studies that reduce spatially and temporally clumped predation and prevent the exclusion of small-mouthed predators could increase the suitability of such studies as a model for predation at natural nests. However, the difference in labor effort between studies of natural nests versus artificial nests that incorporate the changes we recommend likely would disappear, which would reduce the attractiveness of artificial-nest studies as an experimental model.

I used mark-recapture analysis and radio telemetry to characterize winter movement patterns of six grassland sparrows in southeastern Arizona. Mark-recapture data were generated by banding birds captured during repeated flush-netting sessions conducted on a series of 7-ha plots over three consecutive winters. This resulted in 2,641 captures of 2,006 individual sparrows of the six species. Radio telemetry was conducted concurrently on 20 individuals of four of these species. Recapture data and radio telemetry indicated that Cassin's Sparrow (Aimophila cassinii) and Grasshopper Sparrow (Ammodramus savannarum) were the most sedentary, followed by Baird's Sparrow (Ammodramus bairdii), Vesper Sparrow (Pooecetes gramineus), Savannah Sparrow (Passerculus sandwichensis), and Brewer's Sparrow (Spizella breweri). Grasshopper, Baird's, Savannah, and Vesper sparrows tended to remain within fixed home ranges during winter. With the exception of Savannah Sparrows, whose movement behavior varied among study sites, movement patterns remained constant within species across years and study sites despite radical fluctuations in the absolute and relative abundances of all species. Interspecific differences in movement pattern suggest that species in this system partition niche space according to the regional-coexistence mechanism. Abundances of the most sedentary species, Cassin's, Grasshopper, and Baird's sparrows, were poorly or negatively correlated with summer rainfall at the between-year landscape scale, whereas abundances of the more mobile Savannah, Vesper, and Brewer's sparrows were strongly positively correlated. This is consistent with the theoretical prediction that movement constrains large-scale habitat selection, favoring mobile species in fragmented environments.

We investigated the use of stable-isotope analysis as a direct means of tracing allocation of endogenous protein and lipid reserves to reproduction in five gulls (Larus canus, L. delawarensis, L. californicus, L. argentatus, L. philadelphia), four terns (Sterna caspia, S. hirundo, S. paradisaea, Chlidonias niger), and one jaeger (Stercorarius parasiticus) breeding on Great Slave Lake (GSL) in the Northwest Territories. Our approach was based on assumptions that (1) body tissues of birds just arriving at GSL from their assumed marine-associated wintering habitats would have stable-isotope ratios more enriched than those of birds in equilibrium with the local GSL foodweb, and (2) mobilization of these reserves to reproduction could be traced by the isotopic measurement of egg macronutrients. As predicted, the pectoral muscle of six species of arriving birds was more enriched in ¹³C (x̄ = −21.5‰) and ¹⁵N (x̄ = 12.7‰) than was that of postbreeding birds (¹³C, x̄ = −23.5‰; ¹⁵N, x̄ = 9.9‰) or hatching-year birds raised at GSL (¹³C, x̄ = −24.3‰; ¹⁵N, x̄ = 9.0‰). Abdominal fat of arriving Herring Gulls and Mew Gulls was more enriched in ¹³C (x̄ = −19.7‰) than the fat of other species (x̄ = −23.4‰), indicating lipids of marine origin. We compared isotope values of the local GSL foodweb with dietary values predicted from isotope measurements of egg macronutrients if diets were entirely derived at GSL. Isotopic analysis of lipid-free egg yolk, yolk lipid, and shell carbonate suggested that for most species, little if any endogenous protein reserves were used for reproduction, with the possible exception of Caspian Terns, whose egg protein and egg lipid values, and Common Terns, whose egg protein values, were more enriched in ¹³C than those of the other species. Although endogenous nutrient reserves likely were important to birds during migration and the initial settling period at GSL, local food supplies were adequate to provide nutrients for reproduction.

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.