Aerial Feeding Research Articles

Body condition is associated with adrenocortical response in the barn swallow (Hirundo rustica L.) during early stages of autumn migration

Migration is an energy-demanding life-history period and also a significant population-limiting factor of long-distance migratory birds. It is important to understand how corticosterone, the main energy regulating hormone in birds, is associated with behavioural and physiological changes during migration. According to the migration modulation hypothesis (MMH), individual birds may express elevated levels of baseline corticosterone to facilitate fuelling, but down-regulate the adrenocortical response in order to protect skeletal muscles from the catabolic effects of the hormone. We measured the baseline and stress-induced levels of corticosterone in barn swallows (Hirundo rustica L.) during early stages of autumn migration. Here, we show that, while barn swallows clearly responded to the capture and handling stress by increasing the corticosterone level, the strength of this acute response was related to their energetic condition: birds with high body mass responded more rapidly and had lower peak values of corticosterone than lighter birds. Further, the baseline levels of corticosterone correlated negatively with the magnitude of the adrenocortical response. Barn swallows did not show elevated baseline levels of corticosterone in the course of autumn, which suggests that, instead of fuelling, the birds were actively migrating. Our results indicate that MMH also applies to aerial feeders, whose foraging habits differ from model birds of previous studies.

Bird species of conservation concern along urban gradients in Italy

The worldwide increase of urbanization requires better knowledge of its effects on biodiversity. We investigated the distribution of 41 breeding bird species of conservation concern along an urban gradient (centre, inner periphery, outer periphery, sparsely built up area) in Italian towns. We used data on the presence of bird species of conservation concern in each square of the grid of 27 urban atlases to obtain the frequency of each species in each sector. The frequency of species of conservation concern—for both passerines and non passerines—decreased in more urbanised sectors. An increased degree of urbanization is particularly unfavourable to the following groups of species of conservation concern: raptors (except Falco tinnunculus); galliforms; granivorous, ground-nesting passerines; and passerines of bush-shrub habitats. Our findings did not change substantially if we limited our analysis to small, intermediate or large towns. Our results confirm that urban areas are avoided by the majority of specialists and rare species. However, the frequency of aerial feeders and Jynx torquilla, Phoenicurus phoenicurus, Monticola solitarius and Muscicapa striata did not decrease in more urbanised sectors. Since these species include some whose main habitats are dwindling, urban areas might be a refuge for them. Conservation efforts in towns should preserve the conditions (presence of mature trees, habitat heterogeneity, availability of insects, suitable nesting sites in buildings) favouring these species.

Terrestrial birds as indicators of agricultural-induced changes and associated loss in conservation value of Mediterranean wetlands

Abstract During the last decades, agricultural intensification has modified the hydrology of Mediterranean wetlands, as has occurred in the Mar Menor coastal lagoon (SE Spain). Salt-steppe dominated wetlands, characteristic of transitional areas surrounding this lagoon and rich in biodiversity values, are threatened by changes in their water regime originated by land-use changes in the watershed. Traditional dryland cultures have also been replaced by irrigated ones. We assess the direct and indirect changes induced by agriculture on a terrestrial vertebrate community (steppe birds) especially sensitive to these ecosystem changes. This is made on the basis of several surveys of terrestrial birds (excluding aerial feeders and raptors) carried out between 1984 and 2008 in a representative wetland of the lagoon's continental margin (Marina del Carmoli). The changes in this bird assemblage reflect the hydrological modifications induced by agriculture at the watershed scale, which have significant effects on the relative representation of wetland habitats. Bird metrics and indices (species abundance, taxonomic composition, conservation value) describe these community changes as the combination of early declines in some species and families, and transient or late increases in other. In the long term, the family Alaudidae (and particularly species like Melanocorypha calandra) have lost importance to the benefit of Turdidae and Fringillidae. The area of salt-steppe explains a large part of the variation in the abundance of Alaudidae, while most variation of Turdidae and Fringillidae respond to the area of saltmarsh. Some Alaudidae seem to take advantage of the intermediate stages of saltmarsh expansion (Calandrella rufescens), or from the marginal irrigated crops fringing the wetland (Calandrella brachydactyla) that could compensate the loss of original agricultural habitats. Habitat changes in the wetland have occurred in three differentiated stages, and modify the steppe bird community towards a more heterogeneous assemblage including scrubland and palustrine species. Among three indices of ornithological value, only that based on the EU Bird's Directive Annex I species was negatively affected, but since the wetland has been designated a Specially Protected Area under this regulation, this represents a management failure. There exists some chance, however, to manage peripheral cropland in favour of biodiversity. The importance of monitoring in conservation evaluation and management is also stressed, since the terrestrial bird community of this wetland has not been regularly surveyed. In fact, its evaluation against the Bird's Directive criteria was made in a period of quick departure from the original, good ecological state of the wetland.

Understanding signal design during the pursuit of aerial insects by echolocating bats: tools and applications

Bats are among the few predators that can exploit the large quantities of aerial insects active at night. They do this by using echolocation to detect, localize, and classify targets in the dark. Echolocation calls are shaped by natural selection to match ecological challenges. For example, bats flying in open habitats typically emit calls of long duration, with long pulse intervals, shallow frequency modulation, and containing low frequencies-all these are adaptations for long-range detection. As obstacles or prey are approached, call structure changes in predictable ways for several reasons: calls become shorter, thereby reducing overlap between pulse and echo, and calls change in shape in ways that minimize localization errors. At the same time, such changes are believed to support recognition of objects. Echolocation and flight are closely synchronized: we have monitored both features simultaneously by using stereo photogrammetry and videogrammetry, and by acoustic tracking of flight paths. These methods have allowed us to quantify the intensity of signals used by free-living bats, and illustrate systematic changes in signal design in relation to obstacle proximity. We show how signals emitted by aerial feeding bats can be among the most intense airborne sounds in nature. Wideband ambiguity functions developed in the processing of signals produce two-dimensional functions showing trade-offs between resolution of time and velocity, and illustrate costs and benefits associated with Doppler sensitivity and range resolution in echolocation. Remarkably, bats that emit broadband calls can adjust signal design so that Doppler-related overestimation of range compensates for underestimation of range caused by the bat's movement in flight. We show the potential of our methods for understanding interactions between echolocating bats and those prey that have evolved ears that detect bat calls.

Seasonal dynamics of guild structure in a bird assemblage of the central Monte desert

Abstract Most studies of ecological guilds consider guild membership as a fixed attribute of species, and the guild structure as a fixed attribute of a community. Consequently, almost no study tackled the examination of temporal changes in the guild structure of a particular assemblage. We used data on foraging patterns of central Monte desert birds to assess seasonal differences in resource use by resident species, and to examine seasonal changes in the guild structure of the assemblage. From 1993 until 1999, we quantified the use of foraging substrates, manoeuvres, and height strata, and the utilisation of plants by 18 bird species. Resident species showed different kinds of seasonal dynamics, from no noticeable to drastic changes in their foraging patterns. Seasonal changes in guild structure were remarkable. Only two guilds were present all year round (ground foragers and foliage foragers), although they suffered important species turnover. Three other guilds had a seasonal occurrence: graminivores (during the non-breeding season), arboreal herbivores, and aerial feeders (during the breeding season). Two species changed from one guild to another between seasons. Both presence–absence of migrant species, and changes in the feeding ecology of resident species had an influence on the temporal dynamics of guild structure. These factors appeared to be related with changing resource availability, especially with the birds’ ability for facing lean conditions through migration and with the opportunistic use of seasonally superabundant resources. Our results undermine the trust in studies in which guild structure was assessed irrespective of temporal variations. We show also that guild membership is not a fixed attribute of a species: we should rather evaluate the individuals’ resource use in a given moment to assign them to a guild, instead of obtaining a single measure purporting to represent a species’ fixed attribute.

Does the migration programme constrain dispersal and range sizes of migratory birds?

AbstractAim It is generally believed that the migration programme constrains the dispersal and hence range sizes of migratory bird species. This conclusion is based on analyses of breeding ranges of migratory versus non‐migratory (resident) terrestrial bird species, and rests on the assumption that there are no ecological or evolutionary constraints on extending the non‐breeding range. To investigate this assumption, the abilities of migrant and resident terrestrial species to colonize new wintering areas were compared.Location Three major wintering regions of long‐distance migrants: South America, sub‐Saharan Africa and the Indian Subcontinent.Methods It was determined whether the relative numbers of residents and short‐ and long‐distance migrants were the same in those species that have dispersed to a novel wintering region as in the source species pools.Results At the species level, long‐distance migratory species are more likely to have non‐breeding ranges that include more than one of the above regions than resident species. This indicates that the dispersal of migratory species is less constrained than that of resident species. The pattern holds irrespective of the inclusion or exclusion of species associated with coastal, freshwater and wetland habitats, and also holds for ecological groups such as aerial feeders. The pattern is most pronounced between the regions separated by the strongest dispersal barriers (South America and sub‐Saharan Africa).Main conclusions It is unlikely that the migration programme per se constrains dispersal, but rather that difficulties in establishing new non‐breeding areas prevent range expansions in migrant species.

千葉県清澄山系におけるサンコウチョウの営巣環境

The breeding habitat of the Black Paradise Flycatcher Terpsiphone atrocaudata was studied in the Kiyosumi mountains, Chiba Prefecture. Five nests were found in the study area in 2004. The song areas in the three sites that were intensively monitored were similar in size (approximately 1.9 ha). All song areas comprised forestry plantations with low tree density, which appeared suitable for the aerial feeding habits of this species. All nest sites were near forest borders and the tree densities beneath and around them were low. The nests were built on vines or dead branches with canopy cover, but branches and leaves below them were scarce. These features of the nest sites probably provide access to the nests for parents and defense against nest predators. Although the Black Paradise Flycatcher is said to inhabit dark forests, my results suggest that it may prefer (at least partially) forests with low tree density as breeding habitats.

Aerial and aquatic feeding in the silver arawana, Osteoglossum bicirrhosum

The silver arawana, Osteoglossum bicirrhosum, hunts along shorelines and within flooded forests in the Amazon River basin and supplements its limited consumption of aquatic vertebrates by leaping from the water to obtain terrestrial and arboreal prey. We offered O. bicirrhosum prey both suspended above and submerged below the surface of the water. From high-speed digital recordings, we measured kinematic variables associated with the jaws, cranium, pectoral fins, and body during orientation and prey capture. Aquatic and aerial feeding events were kinematically distinct, with aerial events generally involving faster, larger movements and a distinct delay in the onset of lower jaw depression until the head had left the water. The comparatively large gape during leaping may facilitate prey capture by overcoming variability in the apparent position of the prey due to refraction, while the delayed onset of mouth opening may serve to reduce the effects of drag. This distinctive leaping behaviour allows exploitation of the terrestrial prey base, especially during seasonal inundation of the Amazon River basin when the aquatic food base is widely dispersed.

The influence of wing morphology and echolocation on the gleaning ability of the insectivorous bat Myotis tricolor

On the basis of its external morphology, Myotis tricolor (Temminck, 1832) should be able to both aerial-feed and glean. Furthermore, this bat is known to use broadband calls of short duration, reinforcing the prediction that it gleans. However, results from this study indicate that M. tricolor does not commonly glean. This conclusion was reached after studying the foraging behaviour of M. tricolor in a flight room. We presented M. tricolor with mealworms, moths, mole crickets, beetles, and cicadas in a variety of ways that required either gleaning and (or) aerial feeding. Although M. tricolor readily took tethered prey, it did not take any of the variety of insects presented to it in a manner that required gleaning. We therefore compared its wing morphology and echolocation calls with those of several known gleaners, Nycteris thebaica E. Geoffroy, 1818, Myotis lucifugus (Le Conte, 1831), and Myotis septentrionalis (Trouessart, 1897), and an aerial forager, Neoromicia capensis (A. Smith, 1829). In a discriminant analysis wing-tip shape was the only variable to provide some degree of discrimination between species, with M. tricolor having more pointed wing tips than the known gleaners. Discriminant analysis of echolocation-call parameters grouped M. tricolor with the other Myotis species and separated it from N. capensis and N. thebaica. However, M. tricolor did not use harmonics as did the other Myotis species. The apparent failure of M. tricolor to glean might therefore be due to its relatively pointed wings and narrow-bandwidth echolocation calls, owing to the absence of harmonics in its calls.

Relationships between external morphology and foraging behaviour: bats in the genusMyotis

A morphometric study of 41 species of Myotis revealed significant associations between morphological features and foraging styles, namely aerial feeding, gleaning, feeding over water, and trawling. Aerial feeders have small hind feet, short calcars, short ears, and narrow tragi. Gleaners have small hind feet, long ears, and wide tragi and tend to be larger in body size. Bats that feed over water have large hind feet, short calcars, short ears, and narrow tragi and tend to be smaller in body size. Trawlers have large hind feet and long calcars and tend to be larger in body size. The morphometric analysis also confirmed that some species of Myotis were intermediate in morphological features, coincid ing with alternation between foraging styles. The results support the view that the morphological features previously used to assign Myotis species to subgenera are more functional than phylogenetic, a position supported by recent genetic analyses. Examination of foraging styles from a phylogenetic perspective suggests that aerial feeding is ancestral and that subsequent diversification has been associated with partitioning and specialization into either gleaning or foraging over water and trawling. When the predictions from the multivariate analysis of the data for the genus Myotis are used with data from other bats, they suggest that 5 species of Nycteris are gleaners, while 11 species of Eptesicus are either aerial feeders or feed over water.

Hydraulic architecture of Monstera acuminata: evolutionary consequences of the hemiepiphytic growth form

The hydraulic architecture of the secondary hemiepiphyte Monstera acuminata was examined in native plants from Los Tuxtlas, Veracruz, Mexico, to determine how it compared to better‐known growth forms such as trees, shrubs, lianas and primary hemiepiphytes. Monstera acuminata starts its life cycle as a prostrate herb. As it ascends a tree or other vertical support, the stem becomes thicker, produces larger leaves, and may die back from the base upwards until only aerial feeding roots serve to connect the stem to the soil. Unlike the pattern of vessel‐size distribution along the stems of woody dicotyledons, M. acuminata has its wider vessels at the top of the stem, decreasing in diameter towards the base. Also peculiar is the fact that Huber values (axis area/distal leaf area) tend to increase exponentially at higher positions within the plant. Based on the hydraulic conductivity (kh) and leaf‐specific conductivity (LSC, kh/distal leaf area), the base of the stem potentially acts as a severe hydraulic constriction. This constriction is apparently not limiting, as aerial roots are produced further up the stem. The plants have remarkably strong root pressures, up to 225 kPa, which may contribute to the maintenance of functional vessels by refilling them at night or during periods of very high atmospheric humidity, as in foggy weather and rain. In common with dicotyledonous plants, vessel length, vessel diameter, kh, specific conductivity (ks, kh/axis area) and LSCs were all positively correlated with axis diameter. The features of the hydraulic architecture of M. acuminata may be an evolutionary consequence of an anatomical constraint (lack of vascular cambium and therefore of secondary growth) and the special requirements of the hemiepiphytic growth form.

Negative Relationship between Relative Tarsus and Wing Lengths in Malagasy Rain Forest Birds

The locomotory morphology of 32 species of rain forest birds in Madagascar was examined by using body mass, tarsus and wing lengths. Relative tarsus length was found to be longer when relative wing length became shorter and there was a significant correlation between them. Among 14 arboreal passerines, aerial feeding species shows longer wing, whereas longer tarsi is found in near-perch feeding species. This ecomorphological variation might allow ecological segregation in the Madagascar forest bird community.

Modifications des communautés d'oiseaux de la sapinière suite au ravage d'une épidémie d'insectes

This study addresses the relationships between changes in the structure of bird communities and changes in the composition and structure of forest vegetation resulting from an insect infestation. The study compares two balsam fir-white birch forests located in similar physiographic settings. One of these was protected against spruce budworm infestation through insecticide spraying over a ten-year period. Following the infestation, the unprotected, defoliated forest underwent significant changes in structure, particularly the mortality of the coniferous tree strata and the consecutive expansion of the deciduous shrub strata. Yet, despite the infestation, the defoliated forest had just as many bird species and individual birds as the healthy stand protected through the use of insecticides. In addition, half of the avian species occurred with the same frequency in both types of forest. Aerial feeders (flycatchers) and those found in the underbrush (including four species of Turdinae) best withstood this type of infestation, whereas all species that fed chiefly at the tops of conifers decreased in number. This decrease in population could be the result of changes in stand physiognomy (for species such as Boreal Chickadee, Pine Grosbeak and Blackpoll Warbler) or predator-prey relationships affecting birds that feed mostly on spruce budworm larvae (Yellow-rumped, Bay-breasted and Tennessee Warblers). As the defoliated forest became mixed with hardwood stands, some birds increased in number (Black-throated Green Warbler and Solitary Vireo). However, two other species, Winter Wren and White-throated Sparrow, both ground species, were more common in the defoliated stand, probably because of gaps in the forest and the accumulation of dead wood on the ground, where the infestation left openings in the previously dense stands of mature balsam fir. Key words: forest birds, balsam fir, Choristoneura fumiferana, insecticides

How Convergent Is the American Redstart (Setophaga ruticilla, Parulinae) with Flycatchers (Tyrannidae) in Morphology and Feeding Behavior?

ABsTRAcr.-Possible convergence between the unique aerial-feeding American Redstart (Setophaga ruticilla) and the tyrannid flycatchers was considered using skeleton, external morphology, substrate use, and locomotory feeding movements. The redstart is a typical paruline in the broader functional units of forelimb, hindlimb, and body axis, as well as in proportionate lengths of the main axial elements of both the forelimb and hindlimb. It retains and utilizes the advantageous features of the wood-warblers, including the capacity to hop rapidly through the vegetation. To this it has added the long and broad bill, and long rictal bristes (adaptations for aerial feeding) of the tyrannids. The wing shape remains woodwarblerlike, but it is convergent with the flycatchers in its low wing loading. The tail is long, as in the flycatchers, for better aerial control, but is spread and, apparently, used to flush insects from vegetation, as in the specialized Australo-Papuan fantails (Rhipidura). The redstart is a unique adaptive and ecomorphological type among north American passerines. Received 30 March 1993, accepted 19 August 1993.

Convergence in Aerially Feeding Insectivorous Birds

An analysis of bill, forelimb and hindlimb skeletal morphology of four families of aerial foraging birds (apodids, caprimulgids, glareolids and hirundinids) and closest related families of non-aerial foragers (charadriids and parids) was made to investigate possible convergence for acrial feeding in groups with very different phylogenetic histories. The correlated evolution of foraging mode and skeletal morphology was studied using the phylogenetically independent contrasts method in order to test a prediction of convergent evolution, and to assess the adaptive significance of morphological variation. Results show the existence of an ecomorphological pattern relating the aerial feeding technique with short, wide and flat bills, and short legs and pclvcs. We demonstrate that to properly test convergent hypotheses the effect of 'common ancestry' must be taken into account, otherwise spurious relationships can be obtained. This study also shows that in spite of the ecomorphological pattern shared for aerial foragers, they are segregated in the morphological space. We suggest the existence of some design limitations (phylogenetic constraints) which make certain morphological responses more likely than others.

Ecomorphological patterns of aerial feeding in oscines (Passeriformes: Passeri)

The hindlimb (myology and osteology) of swallows (Hirundinidae) is studied and compared with that of seven other passerine families to identify ecomorphological patterns. Muscular and osteological differences are found among swallow species and associations between morphology and foraging technique are examined. We explain morphological differences found in hirundinids as adaptations favouring flexion and adduction of the legs in these aerial foragers, which devote very little time to cursorial locomotion. This adaptive hypothesis is tested using a phylogenetic approach on the basis of an available molecular phylogenetic hypothesis. A clear ecomorphological pattern emerges relating foraging behaviour and pelvic morphology in hirundinids: aerial feeding technique is correlated with short distal leg segments, a large pelvis, a medial insertion of M. iliotibialis cranialis, an absence of pars accessoria of M. flexor cruris lateralis and a fused M. pubo-ischiofemoralis.

Ecomorphological patterns of aerial feeding in oscines (Passeriformes: Passeri)

The hindlimb (myology and osteology) of swallows (Hirundinidae) is studied and compared with that of seven other passerine families to identify ecomorphological patterns. Muscular and osteological differences are found among swallow species and associations between morphology and foraging technique are examined. We explain morphological differences found in hirundinids as adaptations favouring flexion and adduction of the legs in these aerial foragers, which devote very little time to cursorial locomotion. This adaptive hypothesis is tested using a phylogenetic approach on the basis of an available molecular phylogenetic hypothesis. A clear ecomorphological pattern emerges relating foraging behaviour and pelvic morphology in hirundinids: aerial feeding technique is correlated with short distal leg segments, a large pelvis, a medial insertion of M. iliotibialis cranialis, an absence of pars accessoria of M. flexor cruris lateralis and a fused M. pubo-ischiofemoralis.

Colonization of the Krakatau Islands by land birds, and the approach to an equilibrium number of species

The colonization of the Krakataus by resident land birds is re-examined in view of two additional good data points, 1951 and 1984-86, which were not available to MacArthur & Wilson (1967) in their seminal work on island biogeography. The bird data for all years were carefully assessed with respect to the explicit criteria needed for the calculation of rates of extinction, immigration and turnover; these parameters are defined and calculated. Calculated from data from the two most recent surveys, the equilibrium number of species ( S ) for Rakata, the largest island, is from 48 to 56 and for the archipelago as a whole from 44 to 58; the ranges reflect alternative assessments of the records. By fitting a colonization equation to data from all surveys, S for the archipelago is estimated as 36 species, and by a procedure attempting to account for cryptoturnover, 38 species. These estimates compare with 30 (MacArthur & Wilson 1967) and 40-45 (Mayr 1965). Thirty-seven species were present during 1984-86. The establishment of the secondary forest and closure of the canopy had the greatest effect on colonization parameters of resident land birds since 1883. Immigration and turnover peaked in the period 1908-21 and fell sharply over the next decade, when, in contrast, extinctions reached a peak. The species that have colonized the Krakataus are mostly wide-ranging species that are found in both Java and Sumatra and have wide ecological tolerances. The earlier colonists were open country, generalist species, but since forest formation there was an increase in the proportion that are true forest species and more specialist feeders; more recent colonists have been aerial predators and insect feeders. Analysis of the colonization data suggests that the first resident land birds colonized the Krakataus one or two decades after the 1883 eruption. The newly emergent island, Anak Krakatau, has provided early serai habitats for species that have been lost from the other islands of the archipelago because of ecological succession and consequently the island provides an ecological refuge, postponing the extinction of birds that depend on these open habitats. Anak Krakatau’s emergence and continued existence will reduce species turnover and delay the achievement of equilibrium on the archipelago.

Investigations of density interactions among breeding birds in ponderosa pine forests: correlative and experimental evidence.

We assessed the importance of interspecific competition among insectivorous birds breeding in northcentral Arizona's ponderosa pine forests. We examined density interactions among species using two analytic approaches; correlative and experimental. The correlative approach examined patterns of change in breeding densities over four years at the community level and within two foraging guilds; picker-gleaners and aerial feeders. The relationships between morphological and behavioral similarity with pairwise density interactions were also assessed. Our experimental approach involved placement of nest boxes on two treatment plots to increase breeding densities of secondary cavity nesting birds that were in foraging guilds with open nesting insectivores.We found little evidence of interspecific competition. Patterns of density fluctuations indicated large positive covariances among species at both the community level and within guilds. Pairwise density interactions were independent of morphological or behavioral similarity. Nest boxes significantly increased breeding densities of the secondary cavity nesters. However, these increases did not induce reprocal density changes in the open nesting species. Interspecific competition for food during the breeding season appears to be unimportant in ponderosa pine bird communities.

Comparison of Bird Populations in Remnants of Wandoo Woodland and in Adjacent Farmland.

Data were obtained during 2 yr at Baker's Hill, Western Australia, in farmland with no trees, scattered trees or clumps of trees and 3 types of open woodland. There were differences in the number of bird species found in each habitat, ranging from 25 in woodland habitats to 11 in open farmland. In autumn, there were more aerial feeders in open farmland and farmland with few trees than in farmland with many trees and woodland, but fewer in spring. There were more ground-feeding seed-eaters in farmland with trees than elsewhere, except in autumn. There were large seasonal reciprocal changes in the numbers of thornbills in farmland with many trees and woodland, indicating movement between habitats. Within the woodland habitats there were only small seasonal changes, but there were large differences in numbers of some groups between the 3 habitats.