Many nestlings respond to alarm calls with anti-predator behavior, but their physiological responses to such calls are poorly understood. Alarm calls could stimulate increased secretion of corticosterone to mobilize energy reserves in anticipation of an interaction with a predator. However, elevated corticosterone levels can be costly to nestlings because they induce catabolic reactions at a time when the birds are engaged in anabolic processes. Thus, there may be constraints on the secretion of corticosterone if the catabolic costs outweigh the behavioral benefits. Furthermore, many studies use baseline corticosterone levels as a correlate of body condition, and if nestlings respond hormonally when they hear alarm calls rather than when they are first handled by (or catch sight of) an investigator, then determination of baseline hormone levels would be difficult. To investigate this phenomenon, we broadcast taped calls of either adult conspecific alarm calls or songs of heterospecifics to 15–20 d old American Kestrel (Falco sparverius) nestlings. Playbacks were started when adults were absent, but adults returned and produced alarm calls at two control and three experimental nests. Blood was collected from randomly selected nestlings at each nest 13 min after the onset of a playback and within 2 min of opening the nest box, and the plasma was assayed for corticosterone. There was no difference in corticosterone values between nestlings that heard alarm calls and those that heard control vocalizations. Hearing natural kestrel alarm calls did not affect the results, although our small sample sizes resulted in low power to detect differences. These data indicate that 15– 20 d old kestrels do not increase corticosterone secretion in response to adult conspecific alarm calls, and suggest that studies of corticosterone secretion in nestling kestrels will not be affected by the occurrence of adult alarm-calling.

We compared the migratory bird assemblage at a high-elevation site in central New Mexico (Capilla Peak in the Manzano Mountains) with the bird assemblage at a low-elevation riparian corridor site (Rio Grande Nature Center State Park in Albuquerque). During fall 2001–2003, we used mist nets to sample these bird assemblages. We found greater species richness at the low-elevation site than at the high-elevation site, both overall and for most migratory and resident subgroups. However, at the high-elevation site we captured more species that may have had local origins at high elevations. Over the course of the study, capture rates were similar between sites, but there was greater annual variation in capture rates at the high-elevation site than at the low-elevation site. Several species were captured at higher rates at one site versus the other, and some were captured strictly at one or the other site. Our data showed that both sites supported many species in large numbers, and both riparian and montane habitats in the southwestern U.S.A. should be recognized for their importance as potential stopover sites for migrating birds.

The practice of obtaining white blood cell (leukocyte) profiles and heterophil/lymphocyte (H/L) ratios from avian blood smears has become increasingly popular to assess immune function in wild birds. I captured 28 House Finches (Carpodacus mexicanus) and made blood smears from samples obtained from them at 3, 30, and 60 min after capture to evaluate the effect of routine handling time on leukocyte profiles and H/L ratios. Total leukocyte counts decreased significantly with time, but the proportions of each leukocyte type remained the same over the 1-h time period. There was a nonsignificant increase in H/L ratios over time, but comparison with a group of birds held for 1 h before bleeding suggested that this was the result of the repeated bleedings, not handling time. I conclude that researchers should make every effort to obtain blood samples for making smears as soon as possible after capturing birds to ensure an accurate assessment of total leukocyte counts, but that routine handling times under 1 h do not affect H/L ratios.

House Finches are being increasingly studied because of their variation in male plumage, evolving migration, and susceptibility to mycoplasmal conjunctivitis. Researchers traditionally use two methods for capturing House Finches: a walk-in hardware mesh cage around a bird feeder and mist nets placed next to lure feeders. However, because one method relies on birds' willingness to enter a foreign structure to obtain food, while the other captures them while flying, these methods may not sample the same subset of the House Finch population. This possibility could have serious consequences for studies of plumage coloration, where sex and age ratios are important; for studies of migration, where measures of wing lengths reflect migratory ability; and for studies of mycoplasmal infections, where disease state and measures of health are important. I used data from a long-term monitoring project of House Finches that employs both capture techniques to test if any attributes of House Finches differed between mist-netted and cage-trapped birds. Of 1173 House Finch captures over 3 yr, I found no trap-related difference in the proportion of birds with conjunctivitis, nor in the proportions of males or in the ratios of molting versus non-molting birds. There was also no difference in House Finch tarsus lengths or weights between capture methods. However, a larger proportion of young birds were captured in cage traps, and wing lengths were greater in birds captured with mist nets. I conclude that in general, cage traps and mist nets sample similar subsets of House Finches, but that researchers should view their trapping data with these inherent age and size biases in mind.

Populations of Grasshopper Sparrows (Ammodramus savannarum) have been declining, and agricultural practices, such as grazing by domestic cattle (Bos taurus), are likely contributing factors. Grazing can alter the composition and structure of vegetation and influence prey availability, and such changes can impact the nesting success of grassland birds. Our objective was to examine the nesting success of Grasshopper Sparrows in grazed and ungrazed habitats on the Blue Grass Army Depot in Madison County, Kentucky. Clutch sizes of female Grasshopper Sparrows nesting in grazed and ungrazed areas differed significantly, with mean clutch sizes of 4.48 in ungrazed areas and 3.91 in grazed areas. In addition, nest success was higher in ungrazed areas (70%) than grazed areas (25%). Insect sweeps revealed that invertebrate biomass in ungrazed areas was greater than in grazed areas, and analysis of vegetation indicated that grazed areas had less litter, more shrubs, and shorter, less dense vegetation than ungrazed areas. Most unsuccessful nests were depredated, and the higher predation rates on nests in grazed areas may have been due to differences in vegetation structure. Shorter, less dense vegetation in grazed areas may make it easer for predators to observe adults and locate nests, while taller, denser vegetation in ungrazed areas may provide greater concealment. While the results of previous studies suggest that light to moderate grazing can produce habitat suitable for Grasshopper Sparrows, more intense grazing, as on our study area (one animal unit/ha), creates habitat less suitable for these sparrows.

Recordings of temperature fluctuations in the nests of birds can be used to infer incubation behavior such as the frequency and duration of off-bouts. Until recently, collecting temperature recordings from a large number of nests was limited by the size and expense of data logger equipment. In this paper, we describe software we developed to help simplify the analysis of recordings of temperature or mass fluctuations over time. The software program, called Rhythm, works in conjunction with Raven, a bioacoustical analysis program, to partially automate the measurement of incubation off-bout duration and related statistics such as percent constancy. This novel application of Raven combined with advances in data logger technology facilitates investigation in several areas of ecological and behavioral research.

We used four methods to compare the breeding chronologies of Marbled Murrelet at two sites at similar latitudes in British Columbia: Desolation Sound on the mainland, inshore of the Strait of Georgia, and Clayoquot Sound on the west coast of Vancouver Island. At both sites, we estimated breeding chronologies from the timing of (1) nest initiation dates determined by radio-telemetry, (2) the chick feeding period determined from observations of fish-holding adults, (3) hatch dates determined from observations of juveniles on the water, and (4) brood patch scores determined from captured birds. At Desolation Sound, these methods each produced a similar distribution of nesting dates, but at Clayoquot Sound, the distribution of nesting dates of radio-tracked birds were substantially biased towards later nests. Despite these methodological difficulties, we found that Marbled Murrelets at Desolation Sound bred ca. 30 d later than at Clayoquot Sound. Regional differences in breeding chronology of this magnitude, if not properly calibrated, would bias estimates of peak inland activity, and should be considered in forestry operations, the interpretation of census data, and the design of monitoring programs.

Fifty-six Dunlins (Calidris alpina) that died accidentally at banding sites in Buck Bay (southern Baltic Sea), Poland, between 1998–2001 were sexed by dissection and measured. Measurements and sexes of these 32 females and 24 males were used to derive a discriminate function to help predict sexes of the C. a. alpina race using phenotypic measurements (bill, tarsus, and wing). Another sample of 16 female and 19 male Dunlins was used to validate this function. The best discriminate function for predicting the sex of juvenile Dunlins in the Southern Baltic included bill, tarsus, and wing length. Among single measurements, wing length was the poorest predictor of sex. Bill length was the best indicator, correctly identifying 91% of juvenile Dunlins in the validation sample. Longer-billed females were more likely to be mis-classified than shorter-billed males. The bills of juvenile Dunlins migrating through the Southern Baltic region in the autumn are still growing, and it appears as if these long-billed juvenile female Dunlins take more time to reach their final bill size than males.

Poor reproductive success has contributed to the decline and low population size of the federally listed Western Snowy Plover (Charadrius alexandrinus nivosus), especially where it breeds on coastal beaches used by humans for recreation. From 2001–2004, we compared reproductive success of color-marked plovers breeding on ocean beaches with those on gravel bars of the lower Eel River in coastal northern California, one of six recovery units as identified by the species' recovery plan. In three of four years, more plovers (54–64%) nested in river than beach habitats, but this pattern was reversed in the last year of the study when 62% of plovers used beaches. Each year, a higher proportion of clutches hatched and more chicks fledged from river than beach habitats, producing a disproportionate number of yearlings recruited into the local population from the river. On average, river-nesting males tended significantly fewer eggs, hatched similar numbers of chicks, and fledged significantly more young compared with males breeding on beaches. Corvids were more prevalent in river habitats in two of four years, but beaches consistently had significantly greater human activity. These habitat differences in reproductive success exist despite efforts to manage predators (e.g., exclosures around nests) and humans (e.g., signs, fencing, and vehicle restrictions) on beaches and almost no management of river habitats.

Over the past 20 yr Warbling Vireo (Vireo gilvus) populations have declined in California. We monitored Warbling Vireo nests in the high elevations of the northern Sierra Nevada in the Tahoe National Forest near Truckee, California. Nest survivorship was low (29.9% Mayfield estimate) compared to Warbling Vireo populations outside of California, but similar to levels reported for other California populations. Brown-headed Cowbird (Molothrus ater) parasitism in the study population was low (7%). Warbling Vireo nest fate was related to nest-site location; successful nests in lodgepole pine (Pinus contorta) were situated on the west or “warmer” side of the tree, in the outer periphery of the foliage, and in areas with slightly less canopy cover compared to unsuccessful nests. These features of the nest site may help reduce the threat of predation and combat cold stress. Our results argue that Warbling Vireos in the northern Sierra Nevada have low nest survivorship (similar to populations in other areas of the state), and that successful nests are often found on thin branches well removed from the main stem.

Sibling competition selects nestlings to beg as quickly as possible when a stimulus in the nest entrance is presented. However, predation risk may select for nestlings to properly assess stimuli before begging, because nestlings that beg to erroneous stimuli may signal their position to a predator. The begging behavior of Coal Tit (Parus ater) and Great Tit (Parus major) nestlings to an artificial stimulus imitating a predator was examined. Sightless nestlings begged to the stimulus, but older nestlings did not. Developmental improvement of the sentient capacity, especially the acquisition of vision, might explain results of this study.

Long-term pair bonds and defense of territories year-round are common among tropical passerines. The boundaries of these territories tend to be stable, perhaps reflecting the need to defend an area that, regardless of conditions, provides sufficient food resources. If, however, these stable territories are not, even temporarily, sufficiently large, then intra-pair competition for available food may result, particularly in species with no sexual size dimorphism. With such competition, sex-specific differences in foraging behavior may result. Male and female Dusky Antbirds (Cercomacra tyrannina) are not size dimorphic, and pairs jointly defend territories throughout the year. Our objective was to determine if paired Dusky Antbirds exhibited sex-specific differences in foraging behavior. Foraging antbirds were observed in central Panama from February–July 2002 to determine if pairs partitioned food resources. Males and females exhibited no differences in foraging behavior, with individuals of both sexes foraging at similar heights and using the same foraging maneuvers (glean, probe, and sally) and substrates (leaves, rolled leaves, and woody surfaces). These results suggest that Dusky Antbirds do not partition resources and that territory switching, rather than resource partitioning, may be the means by which they gain access to additional food resources.

The nests of altricial bird species are host to a variety of nest ectoparasites that may develop high infestation levels and have a negative impact on chick growth, hematocrit, metabolic capacity, and survival before or after fledging. If ectoparasites affect chick development and fitness, then one would expect chicks to express behavior that might serve to limit the impact of parasites. We compared the behavior of nestling Blue Tits (Parus caeruleus) in nests with and without ectoparasitic blowfly larvae (Protocalliphora spp.). In parasitized nests, only 14.5% of the 15-s sampling periods were devoted to rest, whereas all chicks were resting in 32.5% of sampling periods for unparasitized nests. When nests were classed as active, repositioning occurred nearly twice as often in parasitized nests (83.5%) as in unparasitized ones (48.5%). Comfort behavior (e.g., preening) occurred more frequently in unparasitized nests (35.1%) than in parasitized (18.1%). The proportion of time spent repositioning increased linearly with parasite load. The daily energy expenditure of parasitized nestlings (2.3 kJ/g/d) did not differ significantly from that of unparasitized nestlings (3.1 kJ/g/d), and the tendency was towards lower energy expenditure in parasitized chicks. We cannot rule out the fact that our anti-parasite treatment increased the thermoregulatory costs of unparasitized chicks and obscured the energetic costs of parasites. However, we argue that Protocalliphora also can cause a depression in nestling body temperature that reduces metabolic rate, thus offsetting the costs of increased activity, while also reducing tissue growth rates.

The Chestnut-capped Blackbird (Agelaius ruficapillus) is widely distributed in South America, where it breeds in a variety of natural and man-made habitats. We studied the nesting of this species during two breeding seasons in rice paddies of Rio Grande do Sul, Brazil, a region where it is considered a pest on rice crops. Chestnut-capped Blackbirds build nests in rice paddies when the plants start to flower; thus, breeding phenology in this habitat is determined by sowing date. Clutch size averaged 2.5 eggs, and we found that clutch size tends to decrease the farther the nests are from the surface of the water. Incubation lasted 12.9 d on average, and hatching was asynchronous. The duration of the nestling period ranged from 12 to 17 d with an average of 13.9 days. Only 7.1% of nests were preyed upon, and none was parasitized by the Shiny Cowbird (Molothrus bonariensis). About 90% of nests produced at least one fledgling. These results suggest that the growth of the Chestnut-capped Blackbird population in Rio Grande do Sul may be due not only to the high availability of food during the nonbreeding season but also to the bird's relatives high breeding success in rice paddies.