We provide the first description of lek mating behavior in the Sooty-capped Hermit (Phaethornis augusti) based on four days of observation of unmarked birds at a lek in the Paria Peninsula of Venezuela. A minimum of six presumed males displayed within an area of 2835 m². Males displayed from an average of 2.5 perches per male located 1.10–2.25 m above ground on understory plant stems 2.5–4.0 cm thick. While present within the lek, hermits spent 75.9% of their time perched singing, 20.0% perched silent, 1.0% perched preening, 0.2% flying alone, 2.0% flying with a conspecific (in a chase), and 0.9% fighting with a conspecific. Lekking activity appeared to be most intense in the early morning and late afternoon, and least intense during mid-morning. The song comprised a squeaky phrase of about five syllables delivered by displaying males at an average of 27.7 songs (maximum of 33) per min. The behavioral displays resembled those of other lekking species of Phaethornis.

Curassows are among the most threatened Neotropical birds, so reliable methods for estimating their abundance are needed to discern distribution patterns and manage populations. Based on the assumptions that the distance to booming curassows cannot be determined reliably and that curassow calling is unpredictable, it has been suggested that curassow abundance should be estimated only through surveys using visual cues. Based on line-transect surveys of Great Curassows (Crax rubra) conducted in a lowland tropical forest in Costa Rica, we show that distance to booming curassows can be measured accurately in the field. We also show that line-transect aural surveys sample curassows over large areas across all forest vertical strata and provide precise estimates of their abundance, but are biased towards detecting males. In contrast, line-transect visual surveys sample only small areas of forest understory and are imprecise, but appear not to be biased towards any sex or age class. We argue that the assumption that curassow calling is unpredictable is not well supported, and we recommend the use of surveys using aural cues to estimate curassow abundance efficiently.

Fledging success is widely used as an index of reproductive success in avian studies, but survival of young after fledging is rarely estimated. In this study, I used radio telemetry to measure rates and causes of mortality of 63 Black-fronted Terns (Sterna albostriata) in the immediate post-fledging period on the Ohau River, South Island, New Zealand, in 1998–2000. Juvenile survival for four weeks after fledging was 0.795. Mean daily survival increased from 0.972 in the first week after fledging to 0.995 in the second week and 1.00 for the third and fourth weeks. Introduced predators such as feral cats (Felis catus) and Norway rats (Rattus norvegicus) were responsible for a minimum of nine out of 12 deaths, and all except one death occurred at the natal colony prior to dispersal. Larger, heavier juveniles that fledged at a younger age tended to have higher survival after fledging, but survival could not be accurately predicted based on measurements of growth. These results indicate that the post-fledging period can be an important period for mortality in young birds, and that survival until dispersal from the natal colony is the best measure of Black-fronted Tern reproductive success currently available.

Despite the fact that Lesser Scaup and Ring-necked Ducks are closely related and nest in similar habitats, the two species have inverse population trends. To evaluate the hypothesis that the difference in trends could be related to differences in reproduction, we compared nesting success of sympatric Lesser Scaup and Ring-necked Ducks in parkland habitat near Erickson, Manitoba. Data supported a model that allowed nest survival to differ by species more strongly than a model that did not. Daily survival rate of Lesser Scaup nests (0.941) was lower than that of Ring-necked Ducks (0.969). All Ring-necked Ducks nested over water, but only 57% of Lesser Scaup nested over water. Further, we found some evidence that nest survival was better over water than in upland locations. If our observed pattern of differential nesting success between species holds across broader areas, it may explain why Ring-necked Ducks are increasing across North America while Lesser Scaup populations are declining.

We designed a simple experiment to investigate whether the use of diurnal tape-lures could affect the composition of mist-netted samples of wintering Chiffchaffs (Phylloscopus collybita). It was found that use of spring-song tape-lures introduced a highly significant bias of the sex ratio (more males were attracted) but not the age ratio or body condition of the birds. A comparison with results from other studies and species suggests that the use of spring-song tape-lures introduce biases that are varied and difficult to predict.

This study describes annual variation in abundance and population status of non-breeding migratory shorebirds in flooding pampa grasslands of Argentina. We studied two Nearctic species, the American Golden-Plover (Pluvialis dominica) and the Buff-breasted Sandpiper (Tryngites subruficollis), and two Patagonian species, the Tawny-throated Dotterel (Oreopholus ruficollis) and the Rufous-chested Dotterel (Charadrius modestus), at Medaland Ranch in the Villa Gesell District of Buenos Aires Province, Argentina. Counts were made every 15 d between March 1996 and January 2000. Numbers of Rufous-chested Dotterels were generally highest toward the end of winter (July–September) indicating that the species uses this area as a stopover site. Tawny-throated Dotterels were present throughout the entire winter period (April–September). The Nearctic species spent the austral spring–summer months at Medaland (September–February) before returning to their breeding grounds in North America. Comparison of our numbers to historic counts indicates declines of Buff-breasted Sandpipers (especially during the past 25 yr) and American Golden-Plovers throughout the past century. Medaland Ranch is clearly an important wintering site for these four migratory shorebirds. The departure of Patagonian species and the arrival of Nearctic species always occurred within a short period of time (days), but the time factor between departure of Nearctic and arrival of Patagonian species was measured in months. Our observations tend to support the hypothesis that the migratory pattern of Patagonian shorebirds results from avoiding competition with Nearctic shorebirds.

We compared predation rates of artificial nests baited with different egg types with the predation rates on nests of the Brown-and-yellow Marshbird (Pseudoleistes virescens), a Neotropical passerine common in the same area, in Argentina. We used deserted natural nests as experimental nests, baited with either Japanese Quail (Coturnix coturnix) or Shiny Cowbird (Molothrus bonariensis) eggs. Each experimental nest was baited with one natural and one paraffin-filled egg. Experimental nests baited with quail eggs suffered lower predation and egg losses than those baited with cowbird eggs. The main cause of egg loss and nest mortality in “cowbird nests” was pecking behavior of cowbirds. However, when we removed the effect of cowbirds, differences still held. In this area, the Shiny Cowbird is common and is the main cause of reduced breeding success of several host species. “Quail nests” had higher nest and egg survival than active Brown-and-yellow Marshbird nests. In contrast, “cowbird nests” and active Brown-and-yellow Marshbird nests had similar nest and egg survival. Experimental nests baited with natural passerine eggs such as those of Shiny Cowbirds seem to approximate the natural nest and egg predation risk for passerines in our study area.

We examined whether surgically-implanted radio transmitters with percutaneous antennas affected behavior of Lesser Canada Geese (Branta canadensis parvipes) in Anchorage, Alaska. We implanted either a 26-g VHF radio transmitter or a larger VHF radio that was the same mass (35 g) and shape as a satellite transmitter in the coelom of adult females captured during molt in 2000. A control group of females was marked with leg bands. We simultaneously observed behavior of radio-marked and control females from 4–62 d following capture. We observed no differences in the proportion of time birds in different treatments allocated among grazing, resting, comfort, walking, and alert behavior. Females in different treatments spent a similar proportion of time in the water. Implantation of radio transmitters did not affect the frequency of agonistic interactions. We conclude that coelomic radio transmitters with percutaneous antennas had minimal effects on the behavior of Canada Geese.

The time of day of laying and the intervals between successive eggs in clutches of the Black-billed Cuckoo (Coccyzus erythropthalmus) have been incompletely documented. With observations bracketing the laying time of eggs, I determined that six eggs in four nests of the Black-billed Cuckoo were laid between 06:36 and 11:57 CST. Conspecific parasitism was recorded at one nest in which two eggs were laid on the same day, at 09:02 and 11:57; the second egg was likely the parasite's. Only one laying interval, of about 48 h, was determined accurately. There seems to be no best time for laying in parasitic cuckoos, because it may be dictated by host behavior.

We compared the effectiveness and reliability of mechanically egg-triggered set-cameras and time-lapse video cameras in identifying nest predators at active Dusky Flycatcher (Empidonax oberholseri) nests in Siskiyou County, California. We monitored 72 active flycatcher nests using camera systems from 1998 to 2000. Nest abandonment, hatching success, and daily survival rate did not differ between camera systems. Set-cameras were less reliable than video systems in successfully recording predation events (45% versus 95%). The nest predator assemblage between camera types differed significantly with more avian predators (primarily raptors) recorded at video-monitored nests. This may have been due to the failure of hawks and owls to take the trigger egg at set-camera nests during the nestling stage. We did not find a strong association between the condition of the nest (disturbed or undisturbed) after the predation event and the identity of the predator (mammalian or avian). We also documented disruption of the nest by visitors other than the original predator. These observations suggest that identification of nest predators based on nest remains can be highly inaccurate. We recommend the use of videography for accurate identification of nest predators. Results from studies identifying predators with egg-triggered cameras should limit conclusions to the incubation stage.

Tartar emetic is frequently used to force regurgitation in birds, allowing the study of diet while minimizing mortality. However, the responsiveness to the emetic in terms of regurgitation and mortality rates has been shown to be highly species-specific. A total of 369 individuals (44 species) present in an area of Brazilian Atlantic Forest received the tartar emetic during 410 treatment events. These birds were mainly insectivores, frugivores, and omnivores. Regurgitation occurred in 70% of the treatments, with an overall pre-release mortality of 10%. Average latency time was 20 min, and it was not correlated with average species body mass. Incidence of regurgitation was lower and mortality was higher in the first hours of the day. Incidence of regurgitation varied with feeding guild, taxonomic family, and body mass classes in univariate tests, but only with guild after the effects of family and body mass had been controlled for. Incidence of mortality was affected by family. Responsiveness did not vary between males and females. Mortality occurred more frequently among individuals that failed to regurgitate than among individuals that did regurgitate (85% vs. 15% of mortality events). Recapture rates were lower among treated individuals than among untreated individuals (10 vs. 13%), and lower among treated individuals that failed to regurgitate than among those that did regurgitate (8 vs. 11%), but these differences were not statistically significant. Treated and untreated birds presented statistically similar displacement rates between transects (32 vs. 42%). Our recommendation is that the tartar emetic should be used with caution, and alternative methods should be favored for those species presenting unsatisfactory responses to the tartar emetic. We also recommend that the use of this substance should be avoided in the first hours of the day, when the birds had little time to forage.

The accuracy of aerial estimates of avian aggregation sizes is variable across studies, and the relative importance of techniques and inter-observer error to this variation are poorly understood. Using a scaled physical model of a wading bird colony, we examined accuracy and variation in observer counts of simulated large numbers (200–6000) of densely nesting birds in vegetated situations. Observer estimates averaged 29% less than true numbers (under- and overestimates averaged together), and the mean absolute value of observer errors was 49% of true values. We found no effects of the size of the aggregation, the experience of the observer, the size of the previous aggregations surveyed by observers, the use of corrective lenses, or fatigue on degree of individual error. Over- and underestimates by individuals did not tend to cancel out in estimates by individuals of a “population” of colonies. Photographic counts of the same trials were significantly more accurate than observer estimates. We suggest that many studies using estimates of large numbers of birds may be confounded by similar errors. We urge that researchers use caution in interpreting the results of past surveys and develop ways to minimize, measure, and correct for visual estimation error within individuals and among observers.

Predation has consistently been identified as the most common cause of nest failure for Red-winged Blackbirds (Agelaius phoeniceus). During May and June, 2000 and 2001, we used infrared-triggered camera systems to identify potential nest predators on artificially relocated Red-winged Blackbird nests in eastern North Dakota. For some of the species observed, these observations represent the first documentation of predation on Red-winged Blackbird nests in the northern Great Plains.

I compared the breeding ecology of Collared Flycatchers (Ficedula albicollis) breeding in natural and artificial nest sites in old-growth, oak-lime-hornbeam stands of the Białowieża Forest, eastern Poland, from 1993 to 1999. There were no significant differences in laying date, clutch size, partial clutch losses, partial brood losses, or number of offspring fledged between pairs breeding in natural cavities and nest boxes; however, predation rates were significantly greater in natural cavities. Predation rates may be higher in natural cavities because, under natural conditions like that of the Białowieża Forest, predators may lack experience with artificial nest sites. These results indicate that studies using box-nesting bird populations should be regarded with caution, especially when they involve predation or predator-prey relationships.

Disturbance from human recreation may impact vulnerable life stages of beach-nesting plovers (Charadrius spp.). Although human recreation may decrease hatching success of Snowy Plovers (C. alexandrinus), we are unaware of any studies indicating an impact on chick survival. We tested whether the rate of chick loss in a breeding population of Snowy Plovers was lower on weekdays than on weekends and holidays, when beach visitation increases in most coastal areas. We used data collected on chick survival and the timing of chick loss in 1999 and 2000 at Point Reyes National Seashore, California. Observed weekend and holiday chick loss was 72% greater than expected in 1999 and 69% greater than expected in 2000. This suggests that increased human recreation on Point Reyes beaches over weekends and holidays negatively affected Snowy Plover chick survival.

Ecological studies and population surveys sometimes require information on the position of individuals. Because many birds are more audible than visible, we tested the potential of acoustic triangulation for locating Great Bitterns (Botaurus stellaris) within extensive reed marshes in the Camargue, France. During the breeding season, and predominantly at dawn, male bitterns produce a series of loud calls (booms). In the field, the direction of booming was estimated with a bearing compass by an observer walking along a linear path at the reedbed edge, taking enough measurements to cover a 90° wide angle between the first and last bearing. We used a probability model with an Andrews estimator to locate each bittern based on the intersection point of the bearings taken in the field. Bearing error was estimated by comparing these bearings with those derived from the real or estimated bird position. In a first experiment, we identified the factors influencing the variation in bearing error using six observers, 237 directional bearings, and 19 bitterns. In a second experiment, we quantified the bearing accuracy under optimal conditions based on three observers using 47 directional bearings to locate a bittern of known position. There was no observer effect, but wind speed above 10 km/h, occurrence of poor booms, and bittern distance under 200 m significantly increased bearing error. Bitterns calling normally under windless conditions could be located with a mean bearing accuracy of ±13.6°. Location accuracy depended primarily on the bird distance and number of bearing angles. We propose an optimal bearing effort to locate booming males in large reedbeds with an accuracy of a 40-m radius irrespective of the bittern distance. This protocol can be applied to other bird species once the bearing accuracy corresponding to their call and habitat has been estimated. Acoustic triangulation appears to be a useful, non-invasive, technique for locating bitterns and other bird species.