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Snowy Plover (Charadrius alexandrinus) nests (n = 415) were monitored to completion on an expansive alkaline flat in north-central Oklahoma in 1995–1996. We reported Mayfield Method nesting success but relied on apparent nesting success to compare differences in successful (hatched) and lost (depredated/flooded) nests in five 1000-ha areas, by microhabitat type, and inside versus outside electric-fence predator exclosures. Apparent nesting success differed by area in 1996 and over both years. Predation differed by area only in 1995, and flooding did not differ by area. Apparent nesting success and predation differed by microhabitat type in 1995 and over both years. Differences were observed among depredated and flooded nests inside versus outside electric-fence predator exclosures. Canids and gulls were primary predators. Nests associated with habitat improvements (1995) and near driftwood debris (1996) encountered higher predation, and nests near driftwood debris were more susceptible to flooding both years. We identified an area on the alkaline flat with the highest nesting success and lowest predation where future conservation efforts for Charadriiformes could be implemented.
The Red-cockaded Woodpecker population in Louisiana suffered massive habitat loss in the early 1900s resulting from large-scale clearcutting. We examined post-harvest aerial photographs of Fort Polk, Louisiana, from the 1930s to determine the extent of remnant forest and compared these remnants to current Red-cockaded Woodpecker clusters. Additionally, descriptive data—age, dbh, location—were gathered for all cavity trees within our study areas. Analysis of the photographs made it clear that the harvesting of the 1920s did not completely denude the landscape: trees remained in dense stands along streams and in scattered groups on some upland sites. These remnant trees corresponded to current woodpecker nest sites: on the two study areas, 84% and 100% of woodpecker clusters in 1997 were located on sites that contained trees from the 1930s. Over half of the current cavity trees on one site and over three quarters on the other site are remnant trees which survived the clearcutting. Those trees are the foundation of the habitat available to the Red-cockaded Woodpecker population on the sites today, and based on the nesting habits of this bird, the remnants probably provided the needed habitat to support a continuous or near-continuous Red-cockaded woodpecker population in the area through the post-harvest recovery period and up to the present day.
We summarize data on the breeding biology (based on seven nests) of the White-tailed Sabrewing (Campylopterus ensipennis; Trochilidae) at Tobago, West Indies. Breeding occurred during the dry season (February–April). Nests were placed 1.75–11 m high in small dicot trees, bamboo and palms in the forest interior, usually near streams. Two white eggs were laid in bulky (7–35-cm high), cup-shaped nests; one nest contained spines from a palm (Bactris sp.). The camouflaged nestlings were quiet. During the late nestling period, a female made 1.27 feeding trips/h (10.25 h of observation) to the nest; feeding sessions averaged 0.93 min with an average of 2.0 regurgitations/nestling, and recesses off the nest averaged 44.26 min. The female fed on arthropods and nectar, and vigorously defended the nestlings.
Bill measurement is important in many feeding studies. Traditionally, two alternative bill measures have been proposed: bill length measured from the tip to skull (i.e., total culmen), mainly used in Europe, and bill length measured from the tip to the anterior edge of nostrils, used both in Europe and America. However, the correlation between both measures as well as the analysis of what they are in fact measuring have not been explored yet. The aim of this paper is to test in the Citril Finch (Serinus citrinella) whether measurement of bill length from the tip to the anterior edge of nostrils and total culmen are measuring different components of bill length (e.g., ramphotheca vs. premaxilla), and to assess which is the best measure in relation to their measurement error. This is specially relevant in granivorous birds for which total culmen length differs from ramphotheca length. The correlation between bill length to nostrils and total culmen was moderate (r = 0.75). Multiple regression of total culmen (dependent variable) on the bill components included ramphotheca length (R2 = 52%) and marginally premaxilla length to nostrils (R2 change = 6%, P = 0.06). When using bill length to nostrils as dependent variable it also included ramphotheca length (R2 = 60%) and premaxilla length to nostrils (R2 change = 16%, P < 0.001). Measurement error was low for bill length to nostrils (ME = 1.6%) but high for total culmen (ME = 26.3%), making the latter measure not reliable. The replicability of total culmen is probably decreased in granivorous birds, compared to other passerines, by the fact that in these species the abrupt edge of the ramphotheca differs from the point at which the culmen meets the skull, which hinders the location of the end of culmen. All of this highly recommends that, specially in granivorous birds, the length of bill should be measured from nostril. Our results also show that both bill length measures are mainly measuring ramphotheca.
Incidental to a study of the breeding biology of other cavity-nesting species, we obtained data on an Apical Flycatcher (Myiarchus apicalis) female that remained for 6.5 yr (September 1990–February 1997) in the same area in the Cauca Valley, southwestern Colombia. The female was banded in September 1990, when incubating a two-egg clutch. Between September 1990 and April 1991 she made four nesting attempts, three of which were successful and produced eight young. Our work had two interruptions, but the female was recorded in the same pasture in 1993, 1995, and 1997, and we assume she remained there all the time. All nests were built in nest boxes, and were lined with fur, feathers, snake skin, and pieces of plastic, a typical trait of Myiarchus flycatchers. Mean clutch size was 2.6 eggs. The nestling period was 16–17 d, and fledglings left the nest at 80% of adult body mass.
In 1995, we discovered a population of the poorly known and critically endangered White-winged Nightjar (Caprimulgus candicans) in Yata'i (Butia paraguayensis) palm cerrado at the Mbaracayú Forest Nature Reserve, Paraguay. We provide the first description of the dislay of C. candicans, as observed in December 1995. The display, which appears to function primarily for mate attraction, took place in small arenas and consisted of a regular flight pattern between perches. Noises that accompany the display appear to be mechanical in origin. The modified shape of the outer remiges of male C. candicans suggests a role in the production of this display noise. Male territories were situated exclusively on the upper slopes of ridges in open grassland with a low palm density (termed campo sucio). Territories appeared to be relatively clustered, thus suggesting either a lek-mating system or male aggregation due to the use of specialized habitats as encounter sites for mating. Improved knowledge of the species behavior, breeding systems, and habitat use will facilitate its location at other sites and the development of habitat-based conservation management plans.
We estimated the annual population of Western Sandpipers (Calidris mauri) and Dunlin (Calidris alpina pacifica) stopping over on the Copper River Delta during peak spring migration 1992–1995. Our calculations required four components: total daily shorebird numbers, the daily proportion of each species, average length of stay, and the detection probability. For the 21-d period 26 April–16 May, annual population estimates for Western Sandpiper ranged from 1.2–4.1 million birds per year. Dunlin estimates for this same period ranged from 0.3–0.9 million. For both species, numbers were highest in 1993 and lowest in 1994. Power analysis determined that 15 yr of aerial surveys are needed to detect a 10% decline in Western Sandpiper numbers. Based on the proportion of birds in the Pacific Flyway stopping over on the Copper River Delta, we estimated the Western Sandpiper Pacific Flyway population was >2.8 million in 1992 and >4.3 million in 1995. These data indicate that the Copper River Delta continues to support the largest spring concentration of shorebirds in the Western Hemisphere.
During April–July 1997, we censused birds in three woodlands near Arnprior, Ontario, Canada using conventional point counts (n = 12) and point counts supplemented with “pishing” (n = 12), a well-known method for attracting various bird species. Overall, 3.6 (19%) more species were detected per census using pishing. Irrespective of statistical significance of individual species, 45 (74%) of the 61 species were detected on more days using pishing, whereas 5 (8%) species were detected on more days using the conventional method. A higher number of males and a higher number of visually detected species were recorded using pishing as compared to the conventional method, and these differences did not change with date. Pishing did not affect number of females detected nor number of species aurally detected. More individuals were detected using pishing as opposed to the conventional method, but the difference declined with date. Overall, 0.8 fewer unidentified individuals per census were recorded using pishing. Our results indicate that pishing in conjunction with conventional point count methods increases detectability and positive visual identification of passerine species in woodlands.
The nesting habits of Rock Wrens (Salpinctes obsoletus) were investigated at high altitude in the Sierra Nevada Mountains of California. Nests were built in cavities located under rocks or within rocky outcrops. The birds placed small, flat rocks inside the cavity to form a foundation for the nest cup, at the mouth of the cavity effectively decreasing the size of the entrance, and outside the nest cavity as if in a pathway. Eggs implanted with thermocouples provided records of egg temperature from which the females' incubation patterns were determined. Females roosted in the nest cavity and began diurnal incubation 3 days after beginning the clutch. Constancy of incubation was 71.0%, and mean egg temperature during full-time incubation was 34.4 C. Diurnal attentive bouts lasted a mean of 45.2 min and inattentive bouts 17.4 min.
We tested the assumptions of the Mayfield method (Mayfield 1975) using 416 Wood Thrush (Hylocichla mustelina) nests monitored from 1993–1997 in the Great Smoky Mountains National Park. We tested for differences in nest survival throughout the breeding season and throughout the nesting cycle. We compared the Mayfield cumulative survival curve with a modified version of the Kaplan-Meier with staggered entry. In addition, we compared the group of nests found during nest initiation with those found later in the nesting cycle. There was no evidence nest survival varied through the breeding season or with different stages of the nesting cycle. Furthermore, the Kaplan-Meier survival curve agreed with the Mayfield calculation. We found no evidence of heterogeneity. Validation of Mayfield assumptions is important because the method is widely used, allows for statistical comparisons, and is critical for estimating seasonal fecundity in bird populations.
The seasonal abundance of Neartic shorebirds in the Gulf of Maranhão, Brazil, was studied by censusing three sites from April 1991–March 1992. Censusing was conducted on Cajual Island and Panaquatira Beach at 15-d intervals and at 30-d intervals on Raposa Beach. Bird movements were analyzed by comparing census data from the Gulf of Maranhão with those presented by McNeil (1970) for northeastern Venezuela and by Spaans (1978) for Surinam. During fall migration, there were marked similarities in the abundance peaks of Short-billed Dowitchers (Limnodromus griseus) and Willets (Catoptrophorus semipalmatus) in both Surinam and the Gulf of Maranhão, which might indicate that these species reach these sites by non-stop flight across the Atlantic. Sanderlings (Calidris alba), Semipalmated Plovers (Charadrius semipalmatus), Ruddy Turnstones (Arenaria interpres), Black-bellied Plovers (Pluvialis squatarola), Semipalmated Sandpipers (Calidris pusilla), and Whimbrels (Numenius phaeopus) reached their fall peak much later in Maranhão than in Surinam, which suggests that these species reach the Guyana coast first, migrating later to the Gulf of Maranhão. During northward migration, Willets and Whimbrels did not show a spring migration peak in the Gulf of Maranhão, whereas a spring migration peak was recorded in Surinam, which suggests a route to the Guyana coast and from there across the Atlantic Ocean to North America. Red Knots (Calidris canutus), Sanderlings, Ruddy Turnstones and Black-bellied Plovers all had spring migration peaks in the Gulf of Maranhão, suggesting some transoceanic flight of these species from the Maranhão coast to North America. Semipalmated Plovers and Short-billed Dowitchers showed a small spring migration peak in the Gulf of Maranhão, whereas no migration peak was observed for Semipalmated Sandpiper. This suggests that these species start their movements towards the northernmost portion of South America earlier.
We compared the growth of late-hatched, competitively disadvantaged nestlings to that of their first-hatched, larger nestmates in 12 asynchronously hatching broods in a Wyoming population of House Wrens (Troglodytes aedon). Upon hatching, late-hatched nestlings weighed, on average, 48% as much as their heaviest nestmate (range 38–60%). Late-hatched nestlings gained significantly less mass per day (0.23 g, on average) than first-hatched nestmates between the ages of 3 and 7 days when mass gain is most rapid. Late-hatched nestlings also showed a strong tendency to grow tarsi more slowly than first-hatched nestmates over the same time period (mean difference: 0.16 mm/d). Primary feathers of late-hatched nestlings, however, grew slightly but not significantly more slowly those of first-hatched nestmates (mean difference: 0.05 mm/d). Reduced rates of mass gain and tarsus growth but normal rates of feather growth have been observed in competitively disadvantaged nestlings in several other passerine species in which broods hatch asynchronously. Maintaining normal feather growth may be an evolved strategy which allows late-hatched nestlings to fledge and travel with older nestmates and hence survive to independence. Alternatively, normal rates of feather growth may simply result from the nutrients required for feathers (i.e., proteins) being more available in the prey of small passerines than the nutrients required for other body components (e.g., calcium for bones).
The purpose of this study was to compare two survey protocols for estimating the size of Snow Goose flocks in winter. Compared to photo counts of the same flocks, visual estimates were biased low when flock size exceeded 2000 birds, and the degree of this bias increased with flock size. Correction factors required for visual estimates of flocks with 2000–4000 birds and >4000 birds were approximately 1.4 and 1.6, respectively. These findings have implications for traditional, annual surveys conducted on even larger populations of Snow Geese in other parts of North America and for other more criptic species, such as ducks and shorebirds.
Because brood size might affect nutrition or behavioral development of young Peregrine Falcons (Falco peregrinus), we explored the relationship of the size of the brood from which individuals fledged to their probability of surviving to become breeders in the midwestern United States. In our sample, the probability of an individual peregrine surviving to become a breeder was not related to size of the brood from which it fledged, based on 139 broods fledging 379 young of which at least 38 survived to become breeders.
Photographs that clearly disclose avian-nest predators are difficult to obtain, particularly when predators are small and exhibit subtle depredatory behavior. We exposed House Sparrow (Passer domesticus) eggs injected with Rhodamine B dye in camera-monitored ground nests for 12-d periods at 76 sites within mixed-hardwood forest stands in central Massachusetts, June–July 1997. Dye-injected eggs enabled us to recognize with certainty when eggs were breached at the nest because their contents were fluorescent pink and readily detected photographically. Eleven potential predator species were identified disturbing nests, of which eight were confirmed as predators. Eastern chipmunks (Tamias striatus) were the most frequent predators detected, along with fisher (Martes pennanti), raccoon (Procyon lotor), Blue Jays (Cyanocitta cristata), Black-capped Chickadees (Poecile atricapillus), red squirrels (Tamiasciurus hudsonicus), an Eastern Towhee (Pipilo erythrophthalmus), and a white-footed mouse (Peromyscus leucopus). White-footed mice were the most commonly detected species disturbing nests, but were photographed only once actually destroying an egg. The visual cue provided by dye-injected House Sparrow eggs confirmed depredatory behavior by eastern chipmunks, Black-capped Chickadees, an Eastern Towhee, and a white-footed mouse.
Eared Grebes (Podiceps nigricollis) marked with small radio-transmitters in 1995 and 1996 at a breeding site in south-central British Columbia, Canada, were subsequently detected in fall at Mono Lake (California) and Great Salt Lake (Utah). At least 50% of all marked birds were detected on Mono Lake, and data collected in mid-October suggested that this proportion was consistent across years. These observations largely confirm a fall migration pattern that had been previously based on leg-band returns. Radio-tracking also confirmed that some movement occurred between Mono Lake and Salton Sea. In terms of the number of marked birds detected, the internal antenna-type transmitter produced superior results over other (attachment) protocols but their short range (<2 km) means that they will be effective only at sites where the birds are both abundant and concentrated such as Mono Lake, Great Salt Lake, and Salton Sea.
We used aerial surveys and reports from experienced birders and biologists to identify potentially important sites for wintering shorebirds in coastal Florida. We visited 273 sites in November and December 1993 to assess use by shorebirds and, based on abundance and number of species, we selected the 60 most important sites. We visited these 60 sites at least 3 times between 16 Dec. 1993 and 1 Mar. 1994 and recorded 25 species among an estimated 30,501 shorebirds wintering at the sites. Dunlin (Calidris alpina), Western Sandpipers (C. mauri), Sanderlings (C. alba), and dowitchers (Limnodromus spp.) were the most commonly observed species. Coastal Florida was winter host to >3% of the estimated North American population of Wilson's Plovers (Charadrius wilsonia), Piping Plovers (C. melodus), and American Oystercatchers (Haematopus palliatus). Fifty-three of the 60 most important sites were on Florida's west coast. St. George Sound, Tampa Bay, and Florida Bay contained sites with the highest numbers and most species of shorebirds.
Population viability analyses for Piping Plovers (Charadrius melodus) are highly sensitive to survival estimates, especially those of adults. Thus, the discrepancy between the previous adult survival estimate for the Great Plains Piping Plover population (0.664, SE = 0.057) and estimates from other regions and closely related species prompted us to re-examine banding data for Great Plains plovers. We used published data plus three additional years of band resightings, data from banded juveniles, and a new modeling approach to estimate local annual survival rates of adults and immatures for a breeding site in central North Dakota in 1984–1994. Mean adult survival was 0.737 (SE = 0.092), and the temporal variance was 0.040–0.045. Immature survival was 0.318 (SE = 0.075), but true immature survival is probably higher, mostly due to unknown but likely high dispersal rates. Based on our revised survival estimate for adult Piping Plovers and projections from published plover population models, it is likely that the feasibility of recovering the Great Plains population is greater than previously thought.
Trapping territorial Black-billed Magpies (Pica pica) is challenging because magpies are extremely wary birds. We describe three successful techniques to capture territorial magpies during different periods of the breeding cycle. Funneled walk-in traps were more effective early in the breeding season (late February to late March) when snow covered the ground. A bal-chatri trap with an adult female magpie decoy captured 43% of targeted birds when female magpies were fertile and incubating. A mist-net with a mounted Great Horned Owl (Bubo virginianus) decoy in front of the net captured 52% of targeted birds when adults were feeding nestlings.
We examined vegetation characteristics around nest sites of the Hermit Thrush (Catharus guttatus) and Ovenbird (Seiurus aurocapillus) for three summers in the northern-and mixed-hardwood forests of northern Wisconsin and the Upper Peninsula of Michigan to test the hypothesis that nests with greater concealment are less vulnerable to depredation. Because these two ground-nesting passerines differ in terms of nest structure and behavior near the nest, they present an opportunity to examine how these two factors influence reproductive success in sympatric species. Depredation was the most common source of nest failure for both species, with Ovenbirds having higher nest success for data pooled across years. Side (but not overhead) concealment was correlated positively with nest success for the Hermit Thrush but not for the Ovenbird. Side and overhead concealment did not differ between the Hermit Thrush and Ovenbird. We found a substantial proportion of nests in ground pine (Lycopodium obscurum). Hermit Thrush, but not Ovenbird nests in ground pine were significantly more concealed than nests in other sites both from the side and overhead. Vegetative concealment at the nest microsite may be more important to the open-cup nest of the Hermit Thrush than to the domed nest of the Ovenbird. Because flushed Ovenbirds perform a distraction display and Hermit Thrushes do not, Ovenbirds may have an incentive to choose nest sites that offer less than maximum concealment.