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We describe the juvenile plumages of the Cinereous Mourner (Laniocera hypopyrra) and the Brazilian Laniisoma (Laniisoma elegans). Both L. hypopyrra and L. elegans possess a dramatically conspicuous plumage as juveniles in contrast to the generally cryptic plumage pattern exhibited by most juvenile birds. They are predominantly covered by cinnamon-orange feathers with black terminal spots, contrasting with the nest and the predominant colors of their environment. This colorful plumage presumably makes them more at risk from predation by visually oriented animals (e.g., raptors and primates), during one of the most vulnerable phases of their life, and strongly suggests these plumages function as a true, or false (mimicry), signal of ‘unprofitability’. Previous knowledge concerning the phylogenetic relationships between these two genera, and the juvenile plumage patterns of other species placed in the Tityridae indicate this shared character in L. hypopyrra and L. elegans represents a synapomorphy within this clade, thereby providing additional evidence of their relationship.
Glyphorynchus spirurus (Wedge-billed Woodcreeper) is one of the most common birds in the understory of many tropical forests of Central and South America but few studies have focused on its abundance and distribution. We use data from mist nets and direct observations over a 10-year period to examine patterns of abundance and distribution on two 100-ha plots (Harpia, Puma), ∼1.7 km apart in lowland forest of eastern Ecuador. Birds were captured in mist nets (96 nets/plot) that were open for ∼6 hrs/day for 1 day each in January and February; direct observations were made along transects within each plot during February (7 yrs) and April (4 yrs). We recorded 861 captures (447 recaptures) on Harpia and 963 captures (540 recaptures) on Puma; capture rates (birds/100 mist-net hrs) were slightly higher on Puma, largely a result of the greater numbers of recaptures. Number of individuals captured per year did not differ between plots. Mean (± SE) recapture distance within a year was less on Harpia (94.5 ± 6.1 m) than on Puma (121.6 ± 7.3 m) but recapture distances between years did not differ between plots (108 and 97 m, respectively for Harpia and Puma). Number of captures had a clumped distribution with some nets capturing many more individuals than others; number of captures per net was not correlated with captures at nearby nets. We recorded 490 Glyphorynchus during observations on Harpia (Feb samples) and 384 on Puma. Number of observations was greater on Harpia during 6 of 7 years. Numbers of observations had clumped distribution patterns on both plots; significant autocorrelations likely reflected the difficulty of detecting individuals by voice when >50 m from a transect. Comparisons with published data from other sites in Central and South America indicate considerable spatial variation in abundance but reasons for geographic variation in abundance need further investigation.
Song repertoire size and extent of song sharing provide information about social interactions that occur in songbird species. We recorded the songs of eight male Clay-colored Thrushes (Turdus grayi) in San José, Costa Rica during the 2008 breeding season. We classified 695 songs and 5,032 syllables using visual inspection of spectrograms and spectrogram correlation analysis to measure repertoire size and syllable sharing among a local group of males. Male repertoire size was 10–17 syllable types. Males shared on average 28 ± 15% (SD) syllable types from their repertoires with other males, but a larger proportion of syllable types remained unique to particular males. Extent of repertoire sharing and distance between singing males were not related. Presence of shared and individually unique syllables in the repertoires indicate that imitation, and perhaps improvisation, contribute to development of the song of Clay-colored Thrushes.
Members of the genus Zosterops are known for their colonizing ability and extensive phenotypic differentiation on numerous islands. There have been morphological and biochemical analyses of some Zosterops populations, but little study has been devoted to patterns of vocal communication signals, known to be important pre-mating barriers in many bird species and in possible diversification of taxa. I report on the song system of one subspecies of Zosterops in a mainland population and an island population 15 km distant. I used both a traditional subjective classification of song elements and the multivariate procedure of linear discriminant analyses (LDA) of measured sound features. The syllables constituting songs exhibited a low level of stereotypy, disallowing a lexicon of syllable ‘types’ to be constructed for individuals or a population. New syllables were continuously produced as a bird uttered more and more songs, possibly indicating an extremely large repertoire or an open-ended generation of vocal innovations. LDA indicated songs of the island population were moderately differentiated from and less variable than those of the mainland. This type of song system creates a problem for research on vocal signals, whether directed at comparisons between birds in a local area or between populations. I made a preliminary effort to address this problem and discuss my results in the framework of Zosterops and its propensity for evolutionary diversification.
Geographic relocations of migratory passerines have shown that adults can compensate for physical displacements; juveniles on their first migration, however, use an innate clock-and-compass strategy and are unable to compensate for displacement. We examined the effects of changes in magnetic inclination and intensity on orientation of adult and juvenile Australian Silvereyes (Zosterops l. lateralis) to learn if geomagnetic cues are used by a migratory passerine for geographic positioning. Silvereyes, captured in breeding areas in Tasmania, were physically transported to a location along their migratory route and assessed for orientation during autumn migration. Adults and juveniles exhibited seasonally appropriate, northeasterly orientation (19° and 23° east of magnetic North, respectively) when tested under the natural geomagnetic field. Birds were then exposed to changes in the magnetic field that simulated either southern (SimS) or northern (SimN) locations near the beginning and end, respectively, of their migratory route. Inexperienced juveniles continued to show seasonally appropriate orientation (3° and 358°, respectively) in both SimS and SimN magnetic fields. Adults, in contrast, exhibited changes in orientation but only when the experimental magnetic field was consistent with a geographical displacement that should require compensatory orientation (i.e., SimN). Adults exposed to a SimS magnetic field continued to show seasonally-appropriate orientation to the North (0°). However, adults exposed to magnetic fields simulating locations beyond their wintering areas (SimN) altered their orientation significantly, orienting bimodally and perpendicular (123°–303°) to their seasonally appropriate migratory direction. These results are consistent with the presence of an age- or experience-dependent magnetic geographic position sense in migratory Australian Silvereyes.
We used visual observations of banded individuals and satellite telemetry from 2007 to 2011 on Hawai‘i Island to document movement patterns of the Hawaiian Goose (Branta sandvicensis), commonly known as Nēnē. Visual observations of numbered leg bands identified >19% and ≤10% of 323 geese at one of two breeding sites and one of two distant non-breeding areas during 2007–2011. We used satellite telemetry to document movement patterns of 10 male Nēnē from 2009 to 2011, and log-linear models to quantify the magnitude and individual differences in altitudinal migration. Two subpopulations of Nēnē moved 974.4 m (95% CI ± 22.0) and 226.4 m (95% CI ± 40.7) in elevation between seasons on average, from high-elevation shrublands during the non-breeding season of May–August, to lower-elevation breeding and molting areas in September–April. Traditional movement patterns were thought to be lost until recently, but the movement pattern we documented with satellite telemetry was similar to altitudinal migration described by early naturalists in Hawai‘i prior to the severe population decline of Nēnē in the 20th century.
We studied the ecology and habitat selection of the Magellanic Plover (Pluvianellus socialis) in southern Patagonia during two austral summers. We searched for the presence of this rare species along the shores of 53 privately-owned lakes and portions of Lago Argentino across 12,000 km2 of steppe habitat in Santa Cruz Province, southern Argentina and compared characteristics of occupied and unoccupied lakes. Aeolian lunette size was a significant predictor of occupancy. Most lakes had only a single pair of breeding birds, although one had 14 pairs. No lake feature successfully predicted number of breeding pairs per lake. Territories were on cobbled beaches on the side of the lake with Aeolian lunettes, and at sites significantly closer to small streams and further from vegetation than random sites. Nest sites within territories had significantly less clay than unused sites. Clutch size was small (1–2) while hatching success was moderate (70%). Future studies of this species should focus on adult and juvenile survival, and the development of a demographic model that assesses the long-term stability of the population.
Activities of 29 male Cerulean Warblers (Setophaga cerulea) were quantified on two sites in West Virginia during May–June 2005. Singing and foraging were the most common of 11 observed behavioral activities (81.6%), while maintenance and mating behaviors were uncommonly observed. Male activity differed among vegetative strata (P = 0.02) with lower- and mid-canopy strata used most often (70% of observations), especially for foraging, perching, and preening. The upper-canopy was used primarily for singing, particularly within core areas of territories and in association with canopy gaps. Foraging occurred more than expected outside of core areas. Males were associated with canopy gaps during 30% of observations, but the distribution of behavioral activities was not significantly related (P = 0.06) to gap presence. Males used 23 different tree species for a variety of activities with oaks (Quercus spp.) used most often on the xeric site and black cherry (Prunus serotina) and black locust (Robinia pseudoacacia) on the mesic site. Tree species used for singing differed between core and non-core areas (P < 0.0001) but distribution of singing and foraging activity did not differ among tree species (P = 0.13). Cerulean Warblers appear to be flexible in use of tree species. Their use of different canopy strata for different behavioral activities provides an explanation for the affinity this species exhibits for a vertically stratified forest canopy.
We evaluated the influence of microhabitat vegetation cover on Red-crested Cardinal (Paroaria coronata) nest survival in natural forests in central eastern Argentina by monitoring 106 nests for 1,262 exposure days. Daily nest survival rates increased with vegetation cover above the nest and decreased linearly as the breeding season progressed. Increased concealment above the nest helped hide and protect nests from predators (mainly aerial predators). Earlier nesting attempts in the breeding season were more successful than those later in the season. This is the first study to evaluate the effect of microhabitat vegetation cover on daily nest survival rates of a south temperate passerine. We highlight the importance of microhabitat nest concealment on nest success of the Red-crested Cardinal.
I investigated the relationship between the probability of nest predation and nest-site characteristics: (1) nest height above ground, (2) number of branches attached to a nest, and (3) number of thorny branches around the nest for a population of Bull-headed Shrikes (Lanius bucephalus) breeding in Japan. Thirty-eight nests were located during 2008 and 2009 of which 16 were lost to predation, 14 were successful in fledging young, four were abandoned, two were parasitized, and two may have been partially depredated, although the actual reason is unclear. Neither nest height nor the number of thorny branches was correlated with breeding success. However, the number of branches was negatively correlated with probability of nest predation. The primary predators were believed to be birds, based on physical evidence at depredated nests. A high density of branches around nests of Bull-headed Shrikes may ensure they are not easily discovered and depredated by predators.
We investigated use of capsaicin, a chemical that evolved as a mammal-directed fruit-consumption deterrent for chili (Capsicum annum) fruits as a nest-predation deterrent. Capsaicin is unpalatable to mammals, but apparently undetectable by birds, and has been used as a selective mammal-repellent in several commercial applications. We placed imitation thrush (Turdus spp.) nests containing model and real eggs in a suburban site near Auckland, New Zealand. The majority of observed predation attempts in our experiments were attributed to introduced rats (Rattus spp.) based on comparisons of tooth-marks on damaged plaster eggs and tooth-marks made with rat skulls. Predation rates on imitation eggs treated with adhesive chili powder were lower than predation rates on eggs in other treatments (W = 201, n = 60, P = 0.05), including non-adhesive chili, adhesive paprika (capsaicin-free chili powder), non-adhesive paprika, and untreated eggs. Successive replicates of the same experimental paradigm in the same site revealed the predation rate on all imitation nests decreased with repeated placement of imitation nests and eggs. These results support the potential value for use of capsaicin-treated nests to deter mammalian predators of natural bird nests.
The Laughing Gull (Leucophaeus atricilla) was extripated as a breeding bird from New York State by 1900. Recolonization of coastal New York by this colonial waterbird occurred in 1979 with discovery of 15 breeding pairs in Jamaica Bay (Queens County) New York, New York. We conducted a survey of Long Island salt marsh habitats in 2008 to document if other breeding colonies of Laughing Gulls existed. We identified 66 individual possible breeding areas and field surveys were conducted in each area during June 2008. Many areas appeared to provide suitable nesting habitat (i.e., large areas of salt marsh dominated by Spartina), but no evidence of Laughing Gull nesting was found. A better understanding of Laughing Gull populations within the northeast coastal region and the effects of ongoing gull control near New York airports is needed for their conservation.
We studied the breeding biology of a Southern House Wren (Troglodytes aedon chilensis) population using nest boxes on Chiloé Island, southern Chile (41° S) to make latitudinal comparisons at the intraspecific level. There were no significant differences in body size between adult males and females, although wings were significantly longer in males. Clutch size averaged 4.3 eggs per nest, and brood size was 3.9 nestlings. Egg size averaged 17.3 mm in length and 13.2 mm in width. Incubation and nestling periods averaged 16 days each. The Southern House Wren on Chiloé Island has a larger clutch size than in the tropics, but a smaller clutch size than populations at the same latitude in the Northern Hemisphere. The Southern House Wren has larger eggs and a longer incubation period but a similar nestling period as House Wrens in the Northern Hemisphere.
We document the breeding behavior of the Red-bellied Grackle (Hypopyrrhus pyrohypogaster: Icteridae) from monitoring seven breeding groups during 4 consecutive years (2006–2009) in the central cordillera of the Colombian Andes. All nests were attended by three to seven individuals, representing family groups composed of adult males and females, as well as immatures from previous generations. Clutch size ranged from two to four eggs and was positively correlated with family group size. The incubation period was 15–17 days and nestlings left the nest when 16–18 days of age. Nestling success was relatively low (0.39), and mortality was caused by predation and harsh environmental events; however, groups attempted to breed after nest failures. The Red-bellied Grackle has a cooperative breeding system and individuals delay dispersal by remaining in natal territories.
The Yellow-olive Flatbill (Tolmomyias sulphurescens) is a small insectivorous passerine inhabiting Neotropic forests. Its breeding biology is poorly known despite its abundance and conspicuousness. We describe the nesting biology of Yellow-olive Flatbills from Atlantic Forest fragments in Belo Horizonte County, Minas Gerais State, southeastern Brazil. Eighty nests were monitored every 3–5 days from August to January between 1995 and 2000. Active nests were found from mid-September through late December with a peak from mid October through late November. First clutches were usually laid during the first rains, but prior to the main peak in annual rainfall. The Yellow-olive Flatbill builds closed, pencile nests on tree branches along streams or roads, principally of dark fungal (Marasmius sp.) fibers. Clutch size ranged from two to four white eggs. Incubation was irregular and hatching was asynchronous. Incubation and nestling periods were 20 and 23 days, respectively. Nesting success across all 5 years was 29% (mean among years = 31%, CI = 25–37%), and nest predation was the main cause of nest failure (49%). Mayfield estimates of nest survival were low (mean = 26%, CI = 17–36%), and the probability of an egg to produce a fledgling was only 10%. Fledging success was 0.8 fledglings per breeding pair, and chicks fledged at 107% (CI = 106–108%) of mean adult body mass. Our results do not support the purported pattern of long breeding seasons for tropical birds. The Yellow-olive Flatbill laid unusually large clutches, had lower nest survival, and greater fledgling productivity compared with other tropical passerines.
We studied species, functional groups, and habitat preferences of birds in five classes of agroforestry systems: agroforests, animal agroforestry, linear agroforestry, sequential agroforestry, and crops under tree cover in Tabasco, Mexico. Sampling sites were >2 km from natural forest fragments. Observations were made at 38 sites using 30-min point and transect counts in the morning and afternoon in the rainy season, season of northern winds, and dry season from June 2008 to May 2009. We observed 3,551 birds, which were assigned to 102 species: 72 were resident and 30 were migratory species. Overall efficiency of sampling was 82.4% and varied from 68.7% in linear agroforestry to 81.5% in animal agroforestry. Total species richness varied from 43 in sequential agroforestry to 64 in animal agroforestry. Species richness and Shannon diversity indices revealed no differences among agroforestry classes. Bird communities in animal agroforestry, linear agroforestry, and sequential agroforestry had similar species compositions, as did agroforests and crops under tree cover. Birds in all agroforestry classes were mainly forest generalists, although specialists of open areas were common, particularly in animal and sequential agroforestry. Only one individual of a forest specialist species was observed during sampling. Migrant species were mostly forest generalists, but some open area specialists occurred in animal agroforestry. Resident birds were distributed over all foraging guilds in all agroforestry classes, whereas migrants were mainly foliage-gleaning insectivores. Foraging guilds had different relative abundances among agroforestry classes. Structural diversity of agroforestry classes did not seem to influence bird species richness. Forest specialist species were virtually absent in agroforestry classes, but the avifauna in agroforestry is diverse and valuable in itself.
Mixed-species bird flocks are a prevalent characteristic of Andean avian communities. We describe the species composition of mixed-species bird flocks observed in a high mountain zone (3,000 to 3,450 m) of Quindío, central Andes, Colombia. The total number of species observed in mixed-species flocks was 42, and the mean number of species and individuals per flock were 5.1 and 11.5, respectively. Flock species composition was similar along the elevation gradient studied. Our observations suggest that five species (Margarornis squamiger, Iridisornis rufivertex, Conirostrum sitticolor, Mecocerculus stictopterus, and Diglossa cyanea) could be nuclear species in the flocks.
Monk Parakeets (Myiopsitta monachus) have been in Florida for >40 yrs, having been imported by the thousands for the pet trade. This conspicuous, charismatic species is now widely established, but relatively little is known about its population biology outside South America. We examined 845 parakeets from 385 nests from nest removals and collections by utility company personnel in 2003/2004 and 2006/2007 to document body size and aspects of reproductive biology and primary molt. Body measurements confirm Monk Parakeets in south Florida belong to the monachus subspecies. Adult males averaged 1.5 to 3.5% larger than females, but the body mass of females exceeded that of males during March–May, the period of egg development. The breeding season in south Florida commences in late winter/early spring with fledglings first appearing in the second week of June. Nest contents (eggs plus nestlings) averaged 5.6 for multiple-entry nests compared to 4.9 for single-entry nests. Over 94% of the adults we examined were replacing primary feathers during June–August. The extent and timing of breeding and molt in south Florida are virtually identical to those in South America, although offset by ∼6 months. Monk Parakeets in south Florida retain a fixed annual cycle characteristic of the ancestral population, but their flexible behavior enables them to adapt and thrive in new environments.
We studied geographic variation in the diet of Western Barn Owls (Tyto alba) along a urban-rural gradient in central-eastern Argentina and identified 5,231 prey items. Mammals were present in all samples, whereas birds and amphibians were present in 79.1 and 50.0% of the samples, respectively. There were significant differences in vertebrate assemblages consumed by Barn Owls at the opposite extremes of the gradient. Native sigmodontine rodents comprised 85.8% of the total prey items, especially towards periurban and rural areas. Exotic murid rodents were the main prey item in urban sites, while birds increased in frequency in urban and periurban areas. Food niche breadth and standardized food niche breadth values were higher at intermediate levels of urbanization ( = periurban). This ‘periurban peak’ in species diversity is a relatively well-known pattern, previously reported for taxa such as birds, lizards, bumblebees, and butterflies among others. The trophic habits of Barn Owls along this gradient were mostly similar to those reported in other studies in southern South America, where the main prey items were native rodents and food niche breadth values (measured at the level of Orders) were low. Western Barn Owls in our study maintained specialization as a micromammal predator.
‘Angel wing’ is a developmental wing deformity among birds that can cause flightlessness; it is mostly known from domestic birds, especially waterfowl, and has only rarely been reported among wild bird populations. We estimated that 460 (4.4%) Masked Booby (Sula dactylatra) chicks on Clipperton Island (10° 18′ N, 109° 13′ W) in the eastern tropical Pacific Ocean exhibited angel wing during March 2005. Both hatching-year birds and after-hatching-year birds exhibited the condition; the latter included seven flightless birds in adult plumage (i.e., minimum 2 yrs of age) which were still being fed by their presumed parents. The angel wing outbreak coincided in time with high nestling mortality, apparently related to food shortage, and we speculate on causal linkages.
Aggression between chicks and fledglings, at times ending in siblicide and cannibalism, has been mostly studied among nest mates. It is frequent among colonial-nesting birds and is usually related to competition for limiting resources (e.g., food and space) and competitive disparities between siblings, among other factors. We report three observations of full-grown Peruvian Pelican (Pelecanus thagus) fledglings attacking unrelated conspecific nestlings at a breeding colony in central Chile. One case ended in cannibalism. Five elements were common in all three cases: (1) nestlings that were attacked were left unattended by their parents in the nest, (2) nestlings that were attacked were newly hatched (up to 5 days of age), (3) aggressors were full-grown fledglings (60–75 days of age), (4) aggressive fledglings always attacked nestlings in groups, and (5) all cases were observed late in the breeding season. We suggest aggression toward and cannibalism of nestlings by fledglings are opportunistic behaviors, based on the opportunity of finding unattended nests and are triggered by food deprivation, although hormonal mechanisms may also be involved. Our observations constitute the first report of aggression and cannibalism by Peruvian Pelican fledglings.
Infanticide, the killing of dependent offspring, often provides direct or indirect fitness benefits to the perpetrator. Infanticide in socially monogamous systems, like that in many passerine birds, is typically performed by males in an attempt to gain access to potential mates. We observed infanticide by a female Barn Swallow (Hirundo rustica) in North America and, to the best of our knowledge, this is the first documentation of this behavior. A female pecked and threw out nestlings belonging to a neighboring pair of swallows. There were no obvious fitness benefits gained by this female, thus established evolutionary explanations are not applicable. Further investigations into the frequency of female infanticide, easily mistaken for predation, should be pursued to better assess the selective pressures driving this behavior.
We report the first evidence for intraspecific brood parasitism (IBP) of the open-cup nesting Pale-breasted Thrush (Turdus leucomelas) in southeast Brazil. Four of 15 nests followed from building stage onwards had evidence of IBP (27%), as detected from laying of two eggs in the same day in a nest (n = 2), laying of an additional egg after onset of incubation (n = 1), and egg laying before the end of nest construction (n = 1). Only a few cases of IBP have been reported for neotropical songbirds but it is likely more will be reported as they become better studied. We believe limited territory availability or nest loss during laying were potential causes of IBP in our study population.
Studies of spatial activity of songbirds during the nesting cycle have largely focused on male activity and neglected female space use, particularly outside the fertile period. We estimated the home-range size of seven female Dark-eyed Juncos (Junco hyemalis) 3 days after their nestlings had hatched. We used radiotelemetry to track female movements for 2 hrs on the afternoon of day 3 of nestling life, and 2 hrs on both the morning and afternoon of days 4 and 5. Female location and behavior were recorded every 10 min for the duration of tracking. Females exhibited a mean home-range size of 0.833 ha (range = 0.156–2.450 ha). Our estimate of home-range size during the nestling period was significantly smaller than a previous estimate of female home-range size during the fertile period in the same junco population. Home-range size varied greatly between individuals, and the observed differences may be attributable to variation in resource availability.
We used radiotelemetry to monitor movements and cover-type selection by independent fledgling Ovenbirds (Seiurus aurocapilla) at two managed-forest sites differing in mature-forest matrix: open-understory deciduous forest and dense-understory mixed-deciduous-conifer forest. Ovenbirds at each site made one to three single-day long-distance movements; those movements were of similar distance at the deciduous site ( = 849 ± 159 m) and the mixed-deciduous-conifer site ( = 1,133 ± 228 m). They also moved similar mean daily distances within stands at the deciduous site ( = 101 ± 12 m) and the mixed-deciduous-conifer site ( = 105 ± 11 m), and used areas of similar local vegetation density, but denser than that of their nesting habitat. Fledglings in the deciduous study area selected sapling-dominated clearcuts and forested wetlands over mature forest and shrub-dominated clearcuts. Fledglings in the mixed-deciduous-conifer study area generally used cover types in accordance with availability, and tended not to use shrub-dominated clearcuts. Our results suggest regenerating clearcuts may be important areas for independent fledgling Ovenbirds in landscapes that consist of otherwise contiguous open-understory mature forest, but not until saplings establish in those clearcuts, and not necessarily in forests where dense understory and naturally dense areas such as forested wetlands are common.
Tufted Titmice (Baeolophus bicolor) and Carolina Chickadees (Poecile carolinensis) often occur together in mixed species flocks during the non-breeding season and, as nuclear species, often initiate mobbing bouts. We compared the mobbing behavior of Tufted Titmice and Carolina Chickadees and, specifically, their tendency to approach five potential predators. We exposed flocks of chickadees and titmice to study skins of five species of raptors in 2008; raptors were categorized as either low-threat (rarely preying on chickadees or titmice) or high-threat (more likely to prey on chickadees or titmice). We noted the distance of closest approach by titmice and chickadees during trials, and whether a chickadee or titmouse spent more time within 5 m of the raptor. Titmice were more likely to remain within 5 m of both low (p = 0.0008) and high-threat (p = 0.0015) raptors. Titmice approached low-threat raptors closer than chickadees (p = 0.014). There was no difference in the mean distance of closest approach by chickadees and titmice during high-threat trials (p = 0.34). Titmice generally approached and remained closer to raptors during mobbing bouts than chickadees, possibly because larger titmice (∼ 21 g) are more likely targets of aerial predators than smaller chickadees (∼ 11 g). Titmice may be willing to take greater risks because the potential benefits (reduced risk of predation) are greater if mobbing causes potential predators to leave an area.
Effects of suburban development (sprawl), concurrent climate and increasing avian food on a population of Eastern Screech-Owls (Megascops asio) were studied for three decades using nest boxes and natural tree-cavity nests in residential yards and adjoining natural forest in central Texas. The suburban climate was warmer by 5.7 °C associated with suburbia's heat-island effect by the last decade of study. Nesting started earlier by an average of 4.5 days annually and fledgling productivity increased by 31.4%. Avian prey increased and contributed to 93% successful annual nests in a more stable population. Bird feeders and bird baths were likely enhancing factors at residences, where owls obtained prey and used bird-bath water for drinking and bathing.
The Austral Pygmy Owl (Glaucidium nana) is usually recorded as actively calling and foraging during daylight. We studied the diurnal activity of the Austral Pygmy Owl over 1 year in Cerro Ñielol Natural Monument in southern Chile totaling 339 hrs of observation. The most intense activity was recorded at mid-morning between 0900 to 1200 hrs when conspicuous perching and foraging attempts were observed. Vocalizations showed a pattern associated with the reproductive season. The contact pair call was most used throughout the year (54%), slightly less than the territorial call (46%).
I conducted the second austral autumn raptor count at Concepción Watch Site in the eastern Bolivian lowlands to document species composition, timing, and abundance of migrating raptors between 10 March and 6 April 2009. I counted migrants for 26 days (134.5 hrs) recording 6,979 migrating raptors of 16 species. Mississippi Kites (Ictinia mississippiensis) comprised 80% (n = 5,571), Black Vultures 11% (Coragyps atratus, n = 747), and Snail Kites 5% (Rostrhamus sociabilis, n = 396). The remaining 4% (n = 265) included 13 species and other unidentified raptors. I also recorded non-raptor species on migration from the lookout, including 36 Maguari Storks (Ciconia maguari), a flock of 11 Anhinga (Anhinga anhinga), and thousands of Barn Swallows (Hirunda rustica). My observations confirm previous records suggesting a significant raptor migration occurs at the Concepción Watch Site in the austral autumn. Raptor monitoring should continue at Concepción annually and the site used to promote raptor conservation and awareness in Bolivia.
We report the first cases of simultaneous double brooding known for Calliope Hummingbird (Stellula calliope) and Rufous Hummingbird (Selasphorus rufus) from observations of two females in Montana. Each female laid two eggs and started incubating while feeding large young in a nearby nest, and each successfully fledged young from both nesting attempts. Simultaneous multiple nests have been documented for five other hummingbird species that breed north of Mexico, suggesting the behavior is widespread in the family outside the tropics. Factors that might allow rapid renesting in temperate species include young that begin to feed themselves within a week after fledging, and longer day length that allows more time for females to forage than would be available in the tropics.