Distribution of nonbreeding migrant birds in relation to variation in food availability has been hypothesized to result from the interaction of dominance hierarchies and variable movement responses, which together may have sex- and age-specific consequences. We predicted that site fidelity, movements, and abundance of Kirtland's Warblers (Setophaga kirtlandii) wintering on the island of Eleuthera in the Commonwealth of the Bahamas (hereafter "The Bahamas") would be correlated with food abundance but vary by sex and age. We found that the species' food resources (fruits and arthropods) typically declined during a winter but varied between winters (years) and study sites. Rainfall is a driver of variation in fruit abundance, as indicated by an information-theoretic evaluation of abiotic factors that influence fruit abundance. Despite variation in food availability, the proportions of fruits and arthropods in the diet of Kirtland's Warblers (88% of 90 fecal samples with both) varied little within or between winters or with sex or age class. Overwinter site persistence was low and variable among study sites (average = 43%, range: 11-67%); as predicted, site fidelity within and between winters differed by sex (males > females) and age class (adults > juveniles). However, knowledge of only sex and age was insufficient to predict site persistence in a model-selection framework in the absence of other contributing variables from the confidence set of models (i.e., food resources and/or habitat structure) for two model sets. These analyses further indicated that measures of food resources, either foliage arthropods or fruits, were reliable positive predictors of site fidelity, given the respective confidence set of models. Birds that shifted between study sites within a winter moved to sites with higher biomass of ripe fruit and ground arthropods, such that late-winter densities of Kirtland's Warblers were positively related to the biomass of fruits and ground arthropods. Sex and age differences in corrected body mass and fat were significant from midwinter through late winter, consistent with expected outcomes of dominance and experience. Differences in corrected body mass were evident by 16 April, when males had greater corrected mass than females, and by 26 April, when corrected mass of males was greater for adults than for juveniles. Late-winter rain had a positive effect on corrected body mass, corraborating previous Kirtland's Warbler studies that showed carryover effects on the breeding grounds and that survival in the following year was positively correlated with March rainfall in The Bahamas. Given that drought reduces the food resources and body condition of Kirtland's Warblers in The Bahamas, which negatively affects survival and breeding of Kirtland's Warblers in North America, conservation efforts in the Bahamas archipelago should focus on protecting the least-drought-prone early-successional habitats and sites with favored fruit species.
Migration has evolved to allow organisms to undertake life-history functions in the most appropriate place at the most appropriate time. Migration creates seasonal ecological linkages that have important implications for survival, population dynamics, response to climate change, and conservation. Although advances in bird-borne tracking technology have promoted knowledge of avian migratory ecology, major information gaps remain for most avian species, including seabirds. Ours is the first study to electronically track the migration and wintering of Northern Gannets (Morus bassanus; hereafter "gannets") from almost all of their North American breeding range, in multiple years and with multiple tracks from individual birds.Gannets used distinct wintering areas and aggregated in several major hotspots. Most adults remained along the northeast North American coast, and breeding populations displayed only weak migratory connectivity. Unexpectedly, the Gulf of Mexico was revealed to be an important wintering area for adults. Individual gannets displayed remarkable winter-site fidelity with extensive range overlap across years. Timing, rates of movement, and use of stopovers during migration depended strongly on winter destination and also on sex, colony, and year. Females left the colony prior to males in fall, but, contrary to expectation, earlier spring arrival of males was not detected. Variation in seasonal constraints was emphasized by faster and shorter spring migrations compared with fall. Migratory duration, distance, and timing of arrival and departure from the winter grounds were all repeatable, suggesting strong individual conservation in these traits, while variability in the timing of colony departure and arrival, migratory speed, and the extent of stopovers en route imply greater environmental influences on these behaviors.Three of 46 gannets displayed a radically different round-trip migration and overwinter strategy by undertaking the first recorded (and repeated), round-trip trans-Atlantic migrations to the coast of Africa, where gannets breeding in Europe overwinter. Trans-Atlantic crossings were as rapid as 5 days. Gannets breeding at all of the North American colonies located in easternmost Canada in Newfoundland made trans-Atlantic migrations. This contrasts with no such crossings by a much larger sample of gannets breeding in the species' largest North American colony (Bonaventure Island) in the Gulf of St. Lawrence. Similar trans-Atlantic migrations have not been recorded in the well-studied European colonies. The discovery of this trans-Atlantic connection has implications for interaction, connectivity, and phylogeographic radiation between the eastern and western Atlantic populations and suggests that migratory animals have a surprising capacity for successful movement beyond their known migrations.We discuss our results in the broader context of seabird migration. The observed patterns of migratory timing and scale-dependent connectivity present a novel opportunity to assess the ecological and conservation implications during migration and on the wintering grounds. The overall weak connectivity suggests that gannets, as a population, may have the capacity to respond to modest environmental change. However, the repeatability of some characters implies that any response may be slow because the population will respond, but not necessarily the individuals. The lability of migratory tactics in the population as a whole combined with remarkable individual consistency in some, but not all, migration parameters offers rare insight into the relative contributions of genetic and environmental factors controlling migration.
Population declines in songbirds are often attributed to regional habitat loss and fragmentation caused by land-use practices, which might be further aggravated by climate change. These concerns are particularly evident in the Intermountain West, where riparian areas are considered a priority for conservation because of predicted reductions in winter precipitation and increases in spring temperatures. These climatic changes might increase the susceptibility of species reliant on riparian areas to regional extirpation from loss of habitat. The Willow Flycatcher (Empidonax traillii) is a California species of concern because of precipitous population declines in the past three decades. In 1997, we established a long-term research program to determine population demographics and the effects of weather events and regional-scale meadow distribution and vegetative structure on nesting success of Willow Flycatchers. We monitored territory establishment and reproductive success of 786 territories and 850...
The survival probability of birds during the juvenile period, between the end of parental care and adulthood, is highly variable and has a major effect on population dynamics and parental fitness. As such, a large number of studies have attempted to evaluate potential predictors of juvenile survival in birds, especially predictors related to parental care. Lack's hypothesis linking body reserves accumulated from parental care to the survival of naive juveniles has organized much of this research, but various other predictors have also been investigated and received some support. We reviewed the literature in this area and identified a variety of methodological problems that obscure interpretation of the body of results. Most studies adopted statistical techniques that missed the opportunities to (1) evaluate the relative importance of several predictors, (2) control the confounding effect of correlation among predictor variables, and (3) exploit the information content of collinearity by evaluating indirect (via correlation) as well as direct effects of potential predictors on juvenile survival. Ultimately, we concluded that too few reliable studies exist to allow robust evaluations of any hypothesis regarding juvenile survival in birds. We used path analysis to test potential predictors of juvenile survival of 2,631 offspring from seven annual cohorts of a seabird, the Nazca Booby (Sula granti). Fledging age was the most important predictor of juvenile survival: fast-growing offspring survived best, when all other variables were held constant. Offspring sex was the next most important predictor, with juvenile males (the smaller sex) surviving better than females. Hatching day, an index of body weight, and wing length also showed important predictive ability, but cohort size, culmen length, and an index of clutch size and hatching success did not. Nestling growth was compromised under poor rearing conditions: overall weight fell, the number of days needed to reach fledging status increased, and the growth of some structures, but not others, was reduced. These effects were more pronounced in females, and the higher juvenile mortality of females accounts for most of the male bias in the adult sex ratio and its attendant "mate rotation" mating system in this population. Most previous studies did riot evaluate sex as a potential predictor of juvenile survival. Had we omitted sex from our models, we would have made two erroneous conclusions: that weight did not influence juvenile survival, and that small structural size enhanced it.
Historically, comparative study of the skeleton of hummingbirds has focused on systematics, emphasizing differences between hummingbirds and other birds and only rarely addressing differences within Trochilidae. This monograph covers both approaches, and comparisons within Trochilidae are framed within recently published, plausible phylogenetic hypotheses. The data are derived mainly from museum collections of anatomical specimens, covering similar to 256 species of 102 genera of hummingbirds, and 11 genera of other Apodiformes. Although the syringeal skeleton is included, emphasis is on the axial and appendicular skeletons.The first section deals with the syrinx and with skeletal features mainly associated with nectarivory and hovering, emphasizing characters that are unique to hummingbirds within Apodiformes. The syrinx of hummingbirds lies in the neck rather than the thorax and displays a unique bony knob on the surface of the tympanic membrane. During posthatching development, the upper jaw of hummingbirds undergoes metamorphic changes that produce a morphology uniquely adapted for nectarivory within Ayes. The ventral bars of the upper jaw lengthen and rotate to become lateral walls of an incompletely tubular bill that is completed by the closed mandibula, and lateral bowing (streptognathism) of the mandibula helps to seal the tube while a bird drinks nectar. Streptognathism of the opened jaw is used in display by some Hermits. The lamellar tip of the tongue required for nectar uptake also develops after fledging, while young are still fed by the parent. In Trochilines the nasal region changes from its configuration by bone resorption during posthatching development. Cranial kinesis in hummingbirds is poorly documented, but structural differences in the upper jaw of Hermits and Trochilines imply differences in cranial kinesis. The palatum of hummingbirds is distinguished from that of other apodiforms by extreme reduction of the lateral part of the palatinum, greater width of the ventral choanal region, and by a median spine on the vomer. Otherwise the vomer is variable in shape and not compatible with aegithognathism. Among cranial features, the basipterygoid process, lacrimale, and jugale are absent, and the interorbital septum is complete. The hyobranchial apparatus differs from that of other apodiforms in having an epibranchiale that is longer than the ceratobranchiale, and variably elongate in relation to body size. I hypothesize two modes of hyobranchial function-one applicable to moderate protrusion of the tongue (typical nectar eating), and another to extreme protrusion. The pelvis is less strongly supported by the synsacrum, and the proximal portion of the hind limb is more reduced than in other Apodiformes. By contrast, the tarsometatarsus and flexor muscles of the toes are well developed in association with perching and clinging. In the flight mechanism, features uniquely pertinent to hovering are distinguished from those that support stiff-winged flight-the latter common to both swifts and hummingbirds. Hovering is especially dependent on adaptations for axial rotation of the wing at all major joints, and on extreme development in hummingbirds of the unusual wing proportions (short humerus and forearm, and long hand) and enlarged breast muscles found in swifts. Osteological characters of the Oligocene fossil Eurotrochilus that can be compared with modern hummingbirds do not indicate nectarivory or sustained hovering in that taxon.In the second section, variations within Trochilidae are described and their distributions within the major clades (Hermits, Topazes, Mangoes, Brilliants, Coquettes, Patagona, Mountain Gems, Bees, and Emeralds) are specified. Most diverse are the jaw mechanism, nasal region and conchae, hyobranchial apparatus, cranial proportions, crests, and pneumatic inflation, structure of the ribcage based on number of ribs attached to the sternum, pectoral girdle, and various humeral characters. Other noteworthy but largely unexplained variation characterizes the hyobranchial apparatus of Heliodoxa, the humerus of the "Pygmornis group" of Phaethornis, sexual dimorphism in numbers of thoracic ribs, and synostosis of phalanges of the foot. Although Hermits display distinctive characters, their subfamily status is uncertain for lack of informative outgroups. Major trochilid clades are either weakly supported or unsupported by uniquely derived characters, but apomorphic variation within Mangoes suggests recognition of an Anthracothorax group of genera, and within Emeralds, a large Amazilia group. Each of the major trochilid clades displays considerable diversity in body size and skeletal characters, and numerous characters show parallel evolution within the family. Intraspecific variation is widespread, and selected examples are highlighted. Patterns of skeletal variations at multiple levels of phylogerty suggest that some variations characterizing higher levels had their origins at the intraspecific level.A list of unsolved problems of functional morphology of the skeleton in hummingbirds is offered. Especially intriguing are the many posthatchirtg changes in development of the feeding mechanism and the challenge of incorporating morphological data and their implications into models of evolution of hummingbird communities. Received 17 September 2012, accepted 8 February 2013.
We used PCR and DNA sequencing to screen for haemosporidian parasites (Haemoproteus and Plasmodium) in 2,488 individual birds from 104 species and 22 families, primarily understory suboscine passerines, captured in a lowland Amazonian forest in Ecuador as a first major step to understanding the transmission dynamics of this cosmopolitan group of parasites in this region. To assess diversity of avian haemosporidia in our study site, we identified putative evolutionary lineages of haemosporidia using the mtDNA gene cytochrome b (cyt b). We sampled birds over 9 years, which allowed us to assess annual variation in haemosporidian prevalence. Additionally, we investigated among-species variation in prevalence and tested relationships between traits of hosts and prevalence of haemosporidia in a comparative analysis. Finally, we estimated host specificity of each recovered parasite lineage and compared several indices with different details of host information. Prevalence of haemosporidia was 21.7% when we combined years and ranged from 5.6% to 91.2% among well-sampled host species. Prevalence varied significantly among years, ranging from 14.5% in 2006 to 33.2% in 2009. The hypothesis that haemosporidian prevalence increases with level of sexual dimorphism and decreases with foraging height of a host species received some support. We identified 65 unique cyt b haplotypes, some of which we considered variation within the same evolutionary lineage. In total, we defined 45 putative evolutionary lineages based on 363 identified parasites. Fourteen haplotypes were identical to haplotypes found elsewhere, sometimes on different continents. Host specificity varied greatly among parasite lineages. Collectively, our findings indicate that within a local Neotropical assemblage of avian haemosporidia, community organization is highly complex and part of this complexity can be attributed to differences in host life history; diversity, particularly of Plasmodium spp., is high; and individual parasite lineages can differ greatly in both abundance and number of host species.
Increases in anthropogenic noise (hereafter “noise”) exposure may negatively affect reproductive success for breeding birds because noise may mask sounds of approaching predators. However, we recently found that increases in noise amplitude positively influenced nest survival through a decrease in nest predation. On the basis of this result, we hypothesized that noise may result in (1) a numerical decrease in predators in noisy areas or (2) a functional predator response, in which predators are present but noise interferes with their ability to locate nests. We separated the effects of nest predation risk due to a numerical decrease in predators and risk associated with activity at the nest using artificial-nest experiments on control and noisy treatment sites and within a broad range of noise exposure. Our results concurred with results from natural nests regarding patterns of predation, which suggests that common predators may be less abundant in areas with increased noise exposure. Additionall...
Animals often exhibit predictable geographic variation in morphology, and such ecogeographic patterns reflect local adaptation to varying environmental conditions. The most common of these patterns are termed Bergmann's, Allen's, and Gloger's rules. I studied morphological variation in the Hawaii Elepaio (Chasiempis sandwichensis) and the Oahu Elepaio (C. ibidis), forest birds endemic to the Hawaiian Islands. I measured body size and plumage color of 223 live elepaios captured at 36 sites on Hawaii and 132 live elepaios captured at 23 sites on Oahu, and I examined 132 museum specimens from an additional 22 locations on Hawaii. I used multiple regressions to examine relationships of elepaio body size and plumage color to elevation and annual rainfall on each island. Size of Hawaii Elepaios varied among sites and was related to elevation and rainfall. Wing chord, tail length, and body mass had positive relationships with elevation, as predicted by Bergmann's rule. Proportional bill length and propo...
Many avian species have long been exposed to loud natural sounds such as streams, waterfalls, and wind. However, anthropogenic noise pollution is a relatively recent phenomenon that birds now have to cope with throughout much of the world. Early investigations on bird responses to noise tended to focus on physical damage to ears, stress responses, flight or flushing responses, changes in foraging, and other behavioral reactions. These studies were often conducted under laboratory conditions because determining effects of noise on free-ranging birds is particularly difficult, in that we rarely have the opportunity to isolate noise as a single testable variable. By coupling introduced noise on the landscape (e.g., from gas well compressors) with ecologically similar controls, investigators have recently found additional responses, including avoidance of noisy areas, changes in reproductive success, and changes in vocal communication. Numerous investigators have compared urban birds with their rural...
we used three site types to address whether noise from gas well compressors interfered with our ability to detect birds in the Rattlesnake Canyon Habitat management Area, San Juan County, New mexico: (1) gas wells without compressors (control), (2) gas wells with compressors turned off only during surveys (T-off), and (3) gas wells with compressors running during the surveys (T-on). we conducted 571 bird surveys at 294 point-count loca- tions, which were 50-150 m from gas well pads. we measured sound pressure levels (SPls) at point locations: control mean = 38.6 ± 3.0 (Sd) db(A); T-off mean = 55.0 ± 5.2 db(A), measured with compressors on; and T-on mean = 52.7 ± 4.5 db(A). w e observed significant differences in species richness, individual abundance, and bird diversity among site types; the differences existed between control and T-on sites and between T-off and T-on sites, but not between control and T-off sites. Species richness, individual abundance, and species diversity were all signifi- cantly and negatively influenced by SPl values. A significantly higher proportion of birds were detected on T-off sites compared with T-on sites for 13 species; this compares with only one species that was detected more at T-on sites than at T-off sites. Our results strongly suggest that noise emitted from gas well compressors significantly impaired our ability to detect birds. w e determined that the detection threshold is ~45 db(A), beyond which noise impairs human abil- ity to detect birds within 60 m. These results are relevant to bird surveys in areas where natural and anthropogenic noise may negatively bias detections.
Noise pollution can mask or distort bird songs, which can inhibit mating success, predator detection, and parental response to begging calls. We examined the impact of road construction noise on territory selection, reproductive success, and behavior of the federally endangered Golden-cheeked Warbler (Setophaga chrysoparia). To examine habituation and territory placement, we (1) used construction-noise playback to individual Golden-cheeked Warblers and evaluated occurrence of behavioral response as a function of distance from the roadway, and (2) established broadcast units that simulated construction noise to determine effects on territory selection. Among 88 surveys, six birds responded to construction-noise playback; all birds that responded were located ≥140 m from the road. We established three broadcast units per season in 2008 and 2009 to test for habituation. In each year, we placed broadcast units on the edges of randomly chosen territories identified during the previous field season. We...
Anthropogenic noise can limit the ability of birds to communicate by masking their acoustic signals. Masking, which reduces the distance over which the signal can be perceived by a receiver, is frequency dependent, so the different notes of a single song may be masked to different degrees. We analyzed the individual notes of mating vocalizations produced by Greater Sage-Grouse (Centrocercus urophasianus) and noise from natural gas infrastructure to quantify the potential for such noise to mask Greater Sage-Grouse vocalizations over both long and short distances. We found that noise produced by natural gas infrastructure was dominated by low frequencies, with substantial overlap in frequency with Greater Sage-Grouse acoustic displays. Such overlap predicted substantial masking, reducing the active space of detection and discrimination of all vocalization components, and particularly affecting low-frequency and low-amplitude notes. Such masking could increase the difficulty of mate assessment for l...
Human-altered landscapes often include structural features, such as higher lev- els of impervious surface cover (ISC) and less vegetation, that are likely to affect the trans- mission of avian vocalizations. We investigated the relationships between human habitat modifications and signal transmission by measuring four acoustic parameters—persistence, reverberation, and signal-to-noise ratio (SNR) of broadcast tones, as well as absolute ambient noise level—in each of 39 avian breeding territories across an anthropogenic disturbance gra- dient. Using a geographic information system, we quantified the amounts of different habitat features (e.g., ISC, grass, trees) at each site; a principal component analysis was used to identify which of these habitat features commonly co-occurred (e.g., "habitat suites"). Finally, we used a model selection process to explore whether the habitat suites predicted the acoustic parameters. Tone persistence was higher and reverberation was lower in more open, grassy habitats than in areas with more vertical anthropogenic structures. In more human-modified sites, ambient noise levels were higher, leading to lower SNR. In habitats with low levels of human modifica- tion, we found that even small increases in the total amount of open-grassy area will quickly improve the acoustic space of singing birds. However, our results also indicated that there may be a critical level of human habitat modification above which the addition of "natural" areas does not benefit avian communication. Thus, we recommend that managers focus their efforts on preserving pre-existing "natural" habitat, rather than attempting to introduce it into areas that have already received significant human modification.
—The breeding avifauna of northern Myanmar is extremely poorly known, largely because of unfavorable rainy-season conditions. Previous breeding-season surveys in this high-biodiversity region are lacking, and very few voucher specimens document breeding altitudes and periods. During June to July 2006, we conducted mist-netting, visual, and auditory surveys of the sub-Himalayan avifauna in Putao District, northern Myanmar. A total of 138 species were definitely recorded. Because of the preliminary nature of the surveys, only specific records and general patterns are discussed here. We netted juveniles of two species (Cyornis magnirostris and Dicrurus annectans) not previously known to breed in northern Myanmar. Most babblers (Timaliinae) were present in the same areas during the nonbreeding and breeding seasons, which supports the hypothesis that few, if any, migrate altitudinally. However, Jabouilleia naungmungensis was not encountered at the same low elevations in the breeding season as in the nonbreedin...
—Myanmar is a large, biodiverse country located between India and China in the west and east, and south of Tibet. Kachin State, situated in far northern Myanmar, is expected to be especially biodiverse because of its habitat and climatic diversity, ranging from lowland riparian areas to the high-elevation Himalayan Mountains. These areas of northern Myanmar are especially poorly known biologically, largely because of their difficult terrain, rugged mountains, and enormous rivers. We summarize the ornithological history of northern Myanmar and document the names, dates, and geographic areas (along with a bilingual gazetteer of names) of major ornithological expeditions. Because foreign naturalists made most of the bird collections, the resulting material is scattered around the world. We have compiled and organized information about past research and collections, and we suggest areas for future research investment. To date, few local areas within northern Myanmar have been surveyed, including the far north...
— Alca (Aves, Alcidae) has a comparatively rich fossil record with respect to other Charadriiformes, consisting of thousands of specimens. Despite the abundance of fossil material, richness in this clade has remained poorly understood, primarily because of the paucity of associated specimens. To address this issue, a combined morphometric and apomorphy-based method was developed that would allow referral of fragmentary and isolated specimens, which constitute ~97% of the Alca fossil record. Measurements of multiple variables from >2,000 Alca fossils were categorized by hierarchical cluster analysis and resulted in the recognition of species clusters. Discriminant function analysis was used to assess statistical support for these clusters and to identify the most informative measurements with respect to discriminating between on the basis of size. The reliability of this method was tested using the same measurements taken from 13 extant alcid and was found to be robust wi...
—Many species in Southeast Asia are hardly known in many aspects (biology, ecology, distribution, plumage characteristics), especially in the southeastern sub-Himalayan Mountains in the border region of Myanmar, China, northeast India, and Tibet. During a September 2005 survey of Naung Mung, Putao District, Kachin State, Northern Myanmar, we obtained specimens of three species evidently in first basic plumage, for which this plumage type was new, hardly known, or significantly different from that seen in specimens in collections or descriptions in the literature. After thorough examination, we identified these specimens as immature members of the following muscicapid species: White-tailed Robin (Myiomela leucura), including both a light and darker plumage type; Large Blue Flycatcher (Cyornis magnirostris); and Rufous-gorgeted Flycatcher (Ficedula strophiata). We discuss some taxonomic and biological implications of our findings.
— The encephalitic arthropod-borne viruses (arboviruses) can cause a variety of serious human and wildlife diseases, including eastern equine encephalomyelitis, western equine encephalomyelitis, St. Louis encephalitis, Japanese encephalitis, and West Nile neuroinvasive disease. Understanding how these pathogens are dispersed through the environment is important both in managing their health-related impact and in interpreting patterns of their genetic variability over wide areas. Because many arboviruses infect wild birds and can be amplified to a level that makes birds infectious to insect vectors, numerous workers have suggested that the movements of migratory birds represent a major way that these viruses can be transported on a local, continental, and intercontinental scale. Virus transport by birds can, in theory, explain the colonization of new geographic regions by arboviruses, why some arboviruses in widely separated areas are genetically similar, and how arboviruses annually recur in temp...
We analyzed passerine biodiversity and phylogeography in the Sino-Himalayan region with respect to neighboring areas, especially the Siberian taiga zone to the north and tropical Asia southeast of the Himalayas and mountainous parts of southwest China. Fresh results, informative about evolutionary processes in that area, were obtained mainly by the application of new methods in passerine systematics, acoustic and molecular genetic markers. It became evident that species with areas in the Himalayas and southwest China and, in addition, often with disjunct areas in Siberia, actually belong to swarms of closely related, mostly allopatric species. In many cases these differ markedly in vocalizations and are deeply split according to molecular genetic markers. External morphology of the constituent taxa quite often remained surprisingly homogeneous and thus resulted in traditional subspecies status of single populations at best. Other such well-differentiated taxa were often overlooked and only discovered by m...
