Golden-winged Warblers (Vermivora chrysoptera) and Blue-winged Warblers (V. pinus) are small, brightly colored Neotropical migrant birds that breed in eastern North America. Wherever the two species occur together, they hybridize to a limited degree, producing distinctive hybrid phenotypes. In recent decades, chrysoptera has experienced dramatic population declines across much of its range. Those declines have often been correlated with establishment and increase of pinus in the same areas, but it remains uncertain what, if any, role pinus has played in driving the decline of chrysoptera. In a first attempt at molecular genetic analysis of chrysoptera-pinus population dynamics, Gill (1997) reported cryptic, completely asymmetric, and possibly very rapid introgression of pinus mitochondrial DNA (mtDNA) into chrysoptera, causing what he termed “local cytonuclear extinction” of chrysoptera. As Gill (1997) noted, however, those results were based on relatively small samples from a single area in Pennsylvania. To begin to investigate the generality of Gill’s findings and to establish a baseline for long-term genetic and ecological studies, we intensively sampled one new study area (in southern West Virginia) and also sampled more broadly across two other areas (in Michigan and Ohio) that have experienced pinus invasions and chrysoptera declines. In southern West Virginia, introgression of mtDNA appeared to be roughly symmetrical: 15% (11 of 72) of pinus phenotypes possessed chrysoptera mtDNA, and 12% (17 of 137) of chrysoptera phenotypes possessed pinus mtDNA. Results from much smaller samples from Michigan and Ohio also failed to show any evidence of asymmetric mitochondrial introgression. The results we report here, based on mtDNA and plumage phenotype information for 337 birds representing much of the range of the two species, indicate that previous genetic results and inferences from Pennsylvania may not be broadly applicable to the many areas of contact between chrysoptera and pinus in eastern North America.

We describe a new species of Thamnophilus antshrike—T. divisorius (Acre Antshrike)—from the Serra do Divisor of Acre, Brazil. The new species is known from a single small ridge (though we expect that it is present on other, unexplored ridges in the Acre Arch uplands), and is common in the interior of shrubby woodlands on poor soil physiognomically similar to white-sand habitats in the Guianas and Amazonia. Thamnophilus divisorius is sister to T. insignis (Streak-backed Antshrike), a narrow endemic of pantepui, and forms a wellsupported clade with that species and T. amazonicus (Amazonian Antshrike). Thamnophilus divisorius occurs in a remote region within a national park in Brazil; despite its limited range, we are optimistic about its future survival.

Despite much interest in the conservation of landbirds during migratory stopover periods, relatively few studies have examined spatial and temporal variation in habitat use and identified important habitats for migrating landbirds in North America. We surveyed migrant landbirds in five habitats (mature forest interior, mature forest-agricultural edge, mature suburban forest, mid-successional pole-stage forest, and early successional shrub-saplingstage forest) in central Pennsylvania from late August to early October, 1997–1999. We used abundances of individual species and migrant guilds, species richness, and fruit availability to assess relative habitat quality for fall migrants and measured structural characteristics associated with migrant habitat use. Of 15 species that differed in abundance among habitats, species that breed in mature forest (n = 10) were typically broadly distributed among habitats during stopover, with highest abundance in edge-dominated forests (forest-agricultural edge and suburban forest) and lowest abundance in pole-stage forests. Mature-forest-breeding migrants also regularly used early successional forests, where as many individuals were recorded as in forest interior. Shrub-sapling-breeding species (n = 5) generally were more narrowly distributed among habitats and were most abundant in early successional and edge-dominated forests. We detected among-year differences in relative use of habitats by mature-forest-breeding species, which suggests that the relative quality of stopover habitats may vary from year to year. Fruit availability was highest in shrub-sapling and forest-agricultural edge habitats and was positively associated with abundance of primary frugivores in all three years, indicating that fruit may be driving habitat selection by that guild. Mature-forest-breeding migrants were positively associated with forests that had more understory vegetation and lower percentage of canopy cover (i.e. more tree-fall gaps), which suggests that migrants selected sites with greater vertical and horizontal habitat heterogeneity. Migrating shrub-sapling-breeding species were positively associated with small-diameter stems (0–2.5 cm) and negatively associated with percentage of canopy cover (i.e. characteristics of breeding habitats). Consistently high use of mature edge-dominated and early-successional forests by a wide diversity of landbird species during fall stopover indicates the potential importance of those habitats for migratory landbird conservation.

We studied the demography of an insular California Spotted Owl (Strix occidentalis occidentalis) population in southern California for 12 years. We used model selection based on information theory to examine the relationship between weather and reproduction and survival. Mean annual fecundity was 0.139 (SE = 0.050) for subadult females and 0.345 (SE = 0.028) for adult females. Adult females had higher fecundity than subadult females during all years, and fecundity in both age classes was higher when a wet year preceded a dry spring (i.e. breeding season). A model incorporating these factors explained 100% of the estimated temporal process variation in fecundity. Mean apparent survival was 0.796 (SE = 0.012), 0.880 (SE = 0.041), 0.692 (SE = 0.062), and 0.368 (SE = 0.038) for adult, second-year subadult, first-year subadult, and juvenile (first-year) owls, respectively. We found no temporal process variation in survival. Using a Leslie projection matrix, we estimated the finite rate of population change to be 0.906 (SE = 0.018) over the entire period of study (1987–1998), which indicated that the population declined ≈9% per year during the study. That rate of decline was higher than a rate (λ_1991–1998 = 0.921, SE = 0.020) we estimated for a shorter period (1991–1998) that matched the time interval used in a recent meta-analysis of Spotted Owl population dynamics. We believe that both the present estimates and those of the meta-analysis are valid, given their respective goals. The study population was characterized by relatively high, constant survival of territorial birds, low and variable annual reproduction, and relatively low juvenile survival. Because weather was strongly correlated with reproduction, fecundity rates for the species may decline during short-term droughts and when storms occur during the breeding season. Weather extremes may not, however, be sufficient to affect temporal variation in survival of Spotted Owls in this part of their range.

Avian species that persist in breeding in disturbed habitats are often thought to be less affected by disturbance than habitat specialists lost following disturbances, yet there is growing evidence that human-altered environments may negatively affect reproductive behavior and nest success of those generalists as well. We compared nest success of Blackcapped Chickadees (Poecile atricapillus) in two adjacent habitats: a mature mixed-wood forest (undisturbed) and a forest regenerating after logging (disturbed). Despite similar breeding densities, proportion of nests that successfully fledged young was lower in the disturbed habitat than in the undisturbed habitat. Abandonment was the most common cause of nest failure. A within-habitat comparison of the social rank of birds revealed that low-ranking birds had lower nest success than high-ranking birds in the disturbed, but not in the undisturbed, habitat. Clutch size and brood size of nests that progressed to the point of hatch did not differ significantly between habitats. Average total number of fledglings produced per pair, though not significantly different, was suggestively lower in the disturbed habitat. Across habitats, nests situated in snags with lower amounts of internal decay were more successful. Successful nests were also located in sites with higher canopy height, low understory density below 1 m, and higher understory density between 2 and 3 m—all attributes generally associated with undisturbed, mature forests in the region. Our results provide evidence that disturbed habitats may represent poor-quality habitat for this forest generalist, and that habitat quality differentially affects individuals, depending on their dominance rank.

A breeding population of Aplomado Falcons (Falco femoralis) remains in the desert grasslands of Chihuahua, Mexico, despite their extirpation in the nearby southwestern United States. We monitored falcon reproduction at 35 territories during 1996-2002, a period of severe drought in the region. To test the influence of prey abundance and vegetation on falcon reproduction, we surveyed avian prey abundance through plot counts in 1998-2002 and characterized vegetation at each plot. Aplomado Falcon productivity declined from 1.57 fledglings per occupied territory in 1997 to 0.63 in 2002 at the larger of two study areas, a trend consistent with cumulative effects of consecutive years of low rainfall. Reproduction in the smaller area remained low throughout the study. Both productivity and incubation start date were significantly associated with prey bird abundance. Summer rain most likely influenced falcon reproduction by affecting seed abundance and therefore abundance of granivorous prey birds the following winter and spring. Falcons nested in open grasslands with sparse woody vegetation, an adaptation likely related to higher prey vulnerability and fewer predators. However, important prey birds were positively correlated with woody-plant density, which suggests that proximity of shrublands increased nest-site suitability.

Recent evidence suggests that migration may be extremely important in limiting populations of migratory songbirds. Understanding the relationship between changes in cor- ticosterone secretion and energy reserves during migration is essential to understanding how environmental conditions such as weather, food availability, predation pressure, and habitat quality may be affecting birds en route. Several studies have found that baseline corticosterone is often elevated, and response to capture and handling stress reduced (migration modulation hypothesis), in birds sampled during the migratory period. However, because neither corticos- terone secretion nor energetic condition within groups of birds sampled either in laboratory or in field varied significantly (Holberton et al. 1996, Holberton 1999), it was unknown whether corticosterone secretion could be modulated to track changes in energetic condition within the migratory period. Here, we investigated patterns of corticosterone secretion associated with variation in energetic condition in 18 free-living Hermit Thrushes (Catharus guttatus) sampled during autumn migration. Mean baseline corticosterone (mean ± SE) was 37.22 ± 7.70 ng mL⁻¹ and increased during the 30-min interval up to 54.52 ± 6.01 ng mL⁻¹. Lean birds were more likely to exhibit higher levels of baseline corticosterone and a reduced adrenocortical response, compared with birds that had greater energy reserves. Collectively, the results support the migration modulation hypothesis and illustrate that baseline and stress-induced corticosterone secretion can be modulated to meet the changing energy needs of birds during the migratory period.

I investigated the causes and consequences of adult breeding-site fidelity, territory fidelity, and natal philopatry in Willow Flycatchers (Empidonax traillii) in southeastern Oregon over a 10-year period, testing the general hypothesis that fidelity and dispersal distances are influenced by previous breeding performance. Willow Flycatchers adhered to the generally observed tendencies of passerine birds for low natal philopatry and high breedingsite fidelity. Site fidelity (return to the study area) of adult males (52.0%) and females (51.3%), and median dispersal distances between seasons (16 m vs. 19 m) were similar. Previous breeding performance and residency (age-experience), but not study-site quality, explained site fidelity in females. Site fidelity of females rearing 4–5 young (64.4%) exceeded that of unsuccessful females (40.0%), breeding dispersal was less (successful: 15 m; unsuccessful: 33 m), and novice residents were more site-faithful than former residents. Probability of site fidelity was higher for previously successful females (odds ratio = 4.76), those with greater seasonal fecundity (odds ratio = 1.58), novice residents (odds ratio = 1.41), and unparasitized females (odds ratio = 2.76). Male site fidelity was not related to residency, site quality, or previous breeding performance. Territory fidelity (return to the previous territory) in females was best explained by previous breeding performance, but not by site quality or residency. Previously successful females were more likely to return to their territory of the previous season than either unsuccessful (odds ratio = 14.35) or parasitized birds (odds ratio = 6.38). Male territory fidelity was not related to residency, site quality, or previous breeding performance. Natal philopatry was low (7.8%) and similar for males and females. Site quality appeared to influence philopatry, given that no birds reared at a low-quality study site returned there to breed, and birds reared there dispersed farther than birds reared at two other study sites. My results partially support the hypothesis that site fidelity is an adaptive response: (1) previously successful females that switched territories underperformed those that did not switch (P = 0.01); and (2) previously unsuccessful females that switched territories outperformed those that did not switch, but not significantly (P = 0.22).

We studied the frequency of intraspecific brood parasitism and physical transfer of eggs between nests in colonially nesting Cave Swallows (Petrochelidon fulva) and Cliff Swallows (P. pyrrhonota) in south Texas in 2001. Although the eggs of the two species look similar, frequency of brood parasitism in each species was unaffected by presence of the other species, which suggests that the parasitism we observed was largely by conspecifics. We detected brood parasitism in 4.6–5.0% of Cave Swallow nests and in 10.7–11.9% of Cliff Swallow nests. Brood parasitism was not significantly related to colony size in either species, to eventual success of the host nest, or to overall colony nesting success (a measure of environmental risk). We detected evidence of physical transfer of eggs in 0.7–2.0% of nests of these species. Cliff Swallows parasitized nests more often than Cave Swallows, but the frequencies of brood parasitism and egg transfer in the two species in south Texas appeared broadly comparable to those reported for Cliff Swallows in Nebraska, despite geographic differences in habitat, seasonality, breeding phenology, and levels of sociality between the populations.

Information on area sensitivity and effects of habitat fragmentation has come largely from forest and tallgrass-prairie habitats. Research from other ecosystems is required to determine whether the fragmentation paradigm derived from those studies is applicable to passerine communities elsewhere. I examined the effects of habitat fragmentation on abundance and occurrence of nine species of mixed-grass prairie passerines in southern Saskatchewan. I conducted 190 point-counts in 1996 and 1997 on 89 pastures ranging in size from 8 to 6,475 ha. Sprague's Pipit (Anthus spragueii), Baird's Sparrow (Ammodramus bairdii), Grasshopper Sparrow (A. savannarum), and Chestnut-collared Longspur (Calcarius ornatus) were found to be area-sensitive, in that they were more abundant or occurred more frequently, or both, in larger patches of mixed-grass prairie. However, the ratio of edge to interior habitat was a better predictor of area sensitivity than patch size in most cases. Horned Lark (Eremophila alpestris), Savannah Sparrow (Passerculus sandwichensis), Clay-colored Sparrow (Spizella pallida), Western Meadowlark (Sturnella neglecta), and Brown-headed Cowbird (Molothrus ater) were insensitive to patch size, though occurrence of Clay-colored Sparrow and Western Meadowlark tended to be greater in smaller pastures. Vegetation structure was also found to be an important predictor of grassland songbird abundance and occurrence, in that it explained additional variation not accounted for by patch size or the ratio of edge to interior habitat. Although protection of large contiguous tracts of habitat is essential to conservation of native species, small native-prairie patches with minimal edge habitat also play a vital role in conservation of grassland birds.

The postfledging period is the least-studied stage of avian life cycles. Survival during this period has crucial effects on population dynamics. Survival of fledged young may be influenced by dispersal from their nest sites, because juveniles must cope with the hazards of novel environments. To better understand this important life stage, we used radiotelemetry techniques to study postfledging movements and survival of 50 juvenile Eastern Meadowlarks (Sturnella magna) at Prairie Ridge State Natural Area in Jasper County, Illinois, in 1999 and 2000. Juveniles began to move away from the nesting area in the third week after fledging. Most juveniles moved only 1–5 km from their birth site by the end of the study (90 days). Juvenile survival for the first 90 days after fledging was estimated as 56–69%. Mortality was greatest during the first week of the postfledging period, likely because of high rates of predation. Juvenile meadowlarks are flightless at fledging and thus are vulnerable to predators. We did not observe a second peak of mortality, as other studies have shown, at independence or when juveniles began to move away from their nest areas. The present study suggests that immediate postfledging movements may not be related to dispersal to future breeding sites, but rather occur in response to immediate needs for food resources and security from predators. Furthermore, the data suggest that presumed mortality patterns and estimated levels of juvenile survival are suspect; that interspecific variability of juvenile survival and postfledging movements may be considerable; and that detailed, longer-duration field studies are necessary to elucidate this important demographic period.

Songbirds (Passeriformes) occur in the fossil record of the Northern Hemisphere around the early Oligocene. It has recently been suggested that the major passeriform lineages diverged in Gondwana in the mid- to late Cretaceous and that the oscines, which include all extant European songbirds, originated on the Australian continental plate. Suboscines are assumed to have originated in western Gondwana. Although there is an abundant fossil record of songbirds in Europe, few attempts have been made to set those remains in a phylogenetic context. Our examination of fossil songbirds from three middle Miocene localities in Germany and France shows that many lack the derived morphology of the hypotarsus that characterizes extant Eupasseres (a taxon that comprises oscines and suboscines). We assume that these fossil taxa are outside the crown-group of Eupasseres, which indicates the presence of an ancient songbird avifauna in the Miocene of Europe, in addition to the few fossil Eupasseres already described in the literature.

Telemetry devices used on seabirds have been shown to affect their behavior, reproduction, and survival. However, studies have primarily been limited to larger species, and results are occasionally equivocal. We quantified tag retention time and effects of attaching subcutaneous anchor radiotransmitters on behavior, provisioning, and reproduction in the Common Murre (Uria aalge), a medium-bodied seabird. Between 1999 and 2001, we tagged 48 Common Murres on Tatoosh Island, Washington. Subsequently, 46 birds were detected during colony observation, radiotracking, or both. Activity budgets and time spent at the nest site did not differ between tagged birds and their untagged mates. However, tagged birds made fewer but longer trips away from the nest and provisioned their chicks significantly less than their mates did (0.07 ± 0.02 fish h⁻¹ and 0.18 ± 0.02 fish h⁻¹, respectively). Prey size and energy content did not differ. Despite the disparity in provisioning rates at the individual level, tagged pairs and control pairs had equivalent energy-delivery rates and reproductive success. Tagging effects did not persist in the long term, because percentage of tagged birds returning to the colony the next breeding season was similar to percentage of birds without tags, and tagged birds' reproductive success was comparable to that of the rest of the colony. Subcutaneous anchor attachments compared favorably to glued tags and implanted transmitters in terms of retention time and survival, respectively. We recommend using subcutaneous anchor transmitters for medium-bodied seabirds that employ flexible foraging strategies. Possible exceptions are years of poor food availability, when the capacity to absorb tag effects may be lower.

We tested grackles (Quiscalus spp.) to determine whether they retain egg rejection behavior in the absence of the selection pressure of brood parasitism. Neither Bronzed Cowbird (Molothrus aeneus) nor Brown-headed Cowbird (M. ater) parasitism was recorded in 797 Great-tailed Grackle (Q. mexicanus) nests. Cross-fostered Bronzed Cowbird nestlings, but not Brown-headed Cowbird nestlings, fledged from Great-tailed Grackle nests, indicating that Brown-headed Cowbird parasitism does not select for rejection in these grackles. Great-tailed Grackle populations sympatric and allopatric with Bronzed Cowbirds rejected 100% of model cowbird eggs. An allopatric population of Boat-tailed Grackle (Q. major), a sister species of the Great-tailed Grackle, also rejected 100% of model eggs. Egg rejection in the Boat-tailed Grackle has apparently been retained in the absence of parasitism for as long as 800,000 years since it split from the Great-tailed Grackle. The Common Grackle (Q. quiscula), which lays the most variable eggs among the grackles, also has the lowest level of egg rejection—which is consistent with the argument that it may have lost most of its rejection behavior in the absence of parasitism. With extreme intraclutch egg-variation, Common Grackles may be more likely to reject their own oddly colored eggs, which would select against rejection behavior in the absence of parasitism. Those results have significant implications for long-term parasite-host coevolution, because they suggest that egg rejection has been retained in most species of Quiscalus in the absence of parasitism. If typical of the world's avifauna, such retention may force brood parasites to specialize on a few host species and to rarely return to using old hosts, which would readily reject their eggs.

Nestlings of aerial insectivores adjust their energetics, behavior, and development of internal organs in response to food shortages and subsequent improvements in feeding conditions. Here, we present results of laboratory refeeding of Bank Swallow (Riparia riparia) nestlings, which were undernourished between 4 and 7 days of age. During a subsequent three-day-long refeeding, their body mass did not catch up with that of individuals continuously fed ad libitum. However, refed young managed to compensate for delayed growth of pectoral muscles, small intestines, and fully restored fat reserves. Their resting metabolic rates and body temperatures increased to values similar to those of nestlings fed ad libitum. In contrast, digestive activity of their guts (quantified as carrier-mediated intestinal brushborder uptake rate of L-proline) was reduced, as compared with the period of undernutrition. Likewise, high locomotor activity observed during food shortage was significantly reduced upon refeeding. Furthermore, differences in body mass between nest mates, which had earlier modulated both locomotor activity and physiological responses to food shortage, had no effect on mobility and physiology of refed nestlings. Our results indicate that even a short, three-day period of refeeding triggered conspicuous acceleration of growth and development of vital internal organs in previously undernourished nestlings. However, that was not accompanied by significant compensatory whole-body growth (defined as a period of above-normal rapid growth, relative to age).

We used capture-recapture analyses to describe juvenile and adult survival from 1993 to 2001 in a population of Sociable Weavers (Philetairus socius), a colonial, cooperatively breeding passerine of southern Africa. We examined temporal variation in survival and the role that the breeding season's length and environmental factors play in determining survival patterns in the population. Annual survival probability (mean ± SE) was 0.66 ± 0.02. In contrast to most passerines, juveniles and adults had similar survival probabilities; survival rates did not vary significantly between years. We found no relationship among temperature, rainfall, and survival. Relatively high survival rates in Sociable Weavers probably result from a benign climate and easy access to food in winter. Juvenile survival may also be enhanced by prolonged parental care and delayed dispersal.

A Gray-headed Albatross (Thalassarche chrysostoma) was recorded traveling, in the course of a foraging trip, at a minimum average ground speed of >110 km h⁻¹ for ∼9 h with virtually no rest. After taking into account the sinuosity of albatross flight, actual mean ground speed was predicted to be ≥127 km h⁻¹, achieved in association with high tailwinds during an Antarctic storm. Despite its high speed and the storminess of the sea, the albatross still managed to successfully locate and capture prey at a rate comparable to that achieved under less extreme conditions. This individual's performance suggests that albatrosses have the capacity to maintain positive energy budgets while quickly covering long distances and taking advantage of the strong winds that are frequent in the Southern Ocean.

For 1996–2003, we determined reproductive output and success of 70 Lilaccrowned Parrot (Amazona finschi) nests in tropical dry forest of the Chamela-Cuixmala Biosphere Reserve in western Mexico. Only 42% of nests had young that fledged; predation was the main cause of nest failure. Low brood survival in 2000 and 2003 caused significant between-year variation in the probability of nest success during the nestling phase of the nest cycle. Reproductive output of Lilac-crowned Parrots was low, with females producing an average of 0.99 fledglings on an initial investment of 2.6 eggs. The fecundity component of clutch size varied significantly between years, because of the high median clutch size recorded in 2000. Nestling survival also varied significantly between years, creating large interannual fluctuations in reproductive output. The most productive breeding season was 1999, with an average output of 1.7 fledglings on an investment of 2.7 eggs; whereas the poorest breeding season was 2000, with an output of 0.57 fledglings from 3.3 eggs. Loss of reproductive potential was greatest in 2000 and 2003, because of brood reduction through starvation of later-hatched nestlings, with hatching order influencing the probability of nestling survival. Mean number of nestlings per egg-laying female was associated with interannual fluctuations in precipitation resulting from the El Niño-La Niña weather cycle in the Pacific Ocean. Both nest predation and food availability may limit parrot reproduction in tropical dry forests, with populations of threatened species in dry habitats being vulnerable to effects of climatic variability and habitat fragmentation.

We explored characteristics and patterns of nest distribution, and their putative costs and benefits to breeding females, in polygynous Red-collared Widowbirds (Euplectes ardens). Red-collared Widowbirds differ from most other Euplectes species, in that male nestbuilding is reduced to simple nest-rings used in courtship; females alone position and build nests in the territories. Females used only 37% of available territory area for nesting and aggregated at the centers of territories, possibly to take advantage of male vigilance from prominent central perches or to avoid harassment by neighbors. However, irrespective of territory size or number of females on the territory, females maintained relatively even spacing, with nests ∼15 m apart. Nest predation rates were higher (28.2% day⁻¹) during the nestling period than during incubation (14.6%), but independent of the number of actively nesting females on a territory. During synchronous nestling stages, however, birds nesting close to other birds incurred higher predation costs. Females may, therefore, centrally clump their nests on a territory but maintain enough distance between nests to reduce nest predation. Females choosing unmated males (monogamous) received no greater costs or benefits than females settling with mated males (polygynous). Taken with our earlier finding of strong female preference for longertailed males (Pryke et al. 2001a), our results here suggest that females may gain indirect genetic benefits of higher-quality offspring without incurring the high costs of sharing territories.

In many bird species, Arctic-breeding and temperate-zone-breeding populations may have different behavioral and physiological adaptations that reflect trade-offs between immediate survival and reproductive success. Compared with their temperate-zonebreeding counterparts, Arctic breeders face shorter breeding seasons and less predictable environments. As a result, it may be necessary for Arctic breeders to employ immediate life-saving responses (facilitated through an acute adrenocortical response) that might come at the expense of immediate reproductive success. Regardless of latitude, the sexes may also face differences in the trade-off between immediate survivorship and reproductive effort. To investigate those hypotheses, we (1) measured the adrenocortical response of male and female Yellow Warblers (Dendroica petechia) at both ends of a north-south breeding distribution and (2) examined within- and between-sex variation in corticosterone secretion during distinct stages of the breeding season that represent significant differences in parental investment (e.g. incubation and nestling provisioning). As predicted, Arctic-breeding males showed a significantly reduced adrenocortical response during the nestling period (when their parental contribution was highest; mean reduction = 39%), whereas temperate-zone-breeding males showed no significant reduction (mean reduction = 12%). Arctic-breeding and temperate-zone-breeding females did not differ in their adrenocortical responses during incubation and provisioning stages, showed reduced responses when compared with temperate-zone-breeding males, and showed responses similar to those of Arctic-breeding males during the provisioning stage. These data support the hypothesis that, during the breeding season, a reduced adrenocortical response (1) is more likely to occur when the potential for brood loss is greatest and (2) is associated with the degree of parental investment by the sexes. The balance between cost(s) and benefit(s) of the adrenocortical response may vary with the relative risks to survivorship and breeding success, and may vary between populations facing different time and energy constraints.

Renesting decisions and annual fecundity are crucial for interpreting other demographic information, yet are infrequently reported. We used radiotelemetry to monitor female Dickcissels (Spiza americana) throughout the 1999 and 2000 breeding seasons in southeastern Illinois. Overall fecundity (regardless of whether females remained in the study area throughout the breeding season) was 0.61 ± 0.13 female fledglings per year. Of females that remained within the study area, 94% fledged young (1.25 ± 0.15 female fledglings per year). Most females (62%) that experienced nest failure emigrated from the study area (moved >10 km) in 2.8 ± 0.6 days; others (36%) initiated subsequent nests in 8.5 ± 0.8 days. After fledging ≥1 young, 95% of females ceased breeding for the season. Successful and failed nest sites were indistinguishable on the basis of vegetative characteristics. Moreover, replacement nests had similar vegetative characteristics and were similar distances from habitat edges, compared with initial nests, which suggests that female Dickcissels do not or cannot “improve” nest-site characteristics in response to nest failure. We observed two behaviors unusual in female Dickcissels: one bird that fledged two broods in one season, and the return of five females banded in 1999 to the study site in 2000.

Songbirds apply ants to their feathers during anting behavior, possibly as a method of reducing feather parasites. We tested polar and nonpolar ant secretions and pure formic acid for bactericidal and fungicidal effects on microbial ectoparasites of feathers. Microbial inhibition trials were run with the bacteria Bacillus licheniformis (strains OWU 138B and OWU 1432B) and B. subtilis; and with the fungi Chaetomium globosum, Penicillium chrysogenum, and Trichoderma viride. Ant chemicals were derived from Camponotus pennsylvanicus, Pheidole dentata, Aphaenogaster rudis, Crematogaster lineolata, and Lasius flavus worker-caste ants. Although pure formic acid strongly inhibited all bacteria and fungal hyphae tested, concentrations of formic acid found in the bodies of formicine ants did not. Neither hexane ant-chemical extracts nor ant suspensions in deionized water inhibited the microbial species. Consequently, the hypothesis that birds apply ants to control feather parasites was not supported.

Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) winter in Mexico and often arrive in the vicinity of their breeding grounds in the Sierra Nevada well before nesting is possible. Arrival at Tioga Pass, California (elevation 3,030 m), usually occurs in early May, but residual winter snow and adverse weather can delay nesting for weeks. We used radiotelemetry to determine whether prebreeding Mountain White-crowned Sparrows engaged in weather-related altitudinal movements during the waiting period between the end of spring migration and onset of breeding during 1995–2001, with a range of residual winter snowpacks. Interannual variation in arrival date and onset of egg laying was 18 and 41 days, respectively. We tracked females for two years and males for all seven years. During spring snowstorms (which occurred in four years), radiomarked individuals moved to lower elevation sites, where they often remained for several days. Departing birds left Tioga Pass by early afternoon and returned early in the morning after storms. More frequent storms during tracking increased the likelihood of facultative altitudinal movements, but heavier residual winter snowpack did not. Warm days increased the likelihood of birds returning to Tioga Pass from low elevation. This study demonstrates that facultative altitudinal movement behavior can be a common feature of spring arrival biology in montane-breeding birds.

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

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

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

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

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.