Edge Birds Research Articles

Southeastern Brazilian tyrannulets as flower watchers

Several species of insect-eating birds occasionally visit flowering trees or shrubs to feed on arthropods at flowers instead of nectar or petals. In southeastern Brazil, the Planalto Tyrannulet Phyllomyias fasciatus (10.3 g) and the Gray-headed Tody-Flycatcher Todirostrum poliocephalum (7 g) often watch flowers to get insects and can visit flowering trees for hours or for several days. We describe the foraging behavior of these two tyrannulets at flowering trees and also report observations on several other species, mostly tyrant-flycatchers and tanagers. As an opportunistic foraging strategy, flower watching can be expected to be more common among small, canopy or edge birds that sally or hover-glean to catch small insects on or near foliage.

The birds communities functional structure dynamics in the ash individual consortia under the influence of the climatic factors annual dynamics

The studying of the connections between the birds and consortia is impossible without their dynamics research. The amount of organisms that are part of the consortium is large enough and their significant part is active only for some year part, the full extent of the links detection is impossible without the seasonal dynamics analyses. The article is devoted to the bird communities in individual consortia of such edificator of the linden-ash-tree oak groves, as the ash (Fraxinus excelsior L.). This work material was collected in different seasons of 2004–2010 years in a linden-ash oak grove on the test plot No. 209 of the ecological profile of the NSC «Belgard Prisamar`e International Biospheric stationary», Novomoskovsk district, Dnepropetrovsk region. The individual consortia of 183 ash examples of three age conditions (virgins – virg, young generative – gl, mature and old generative individuals – g2–g3) were investigated. The ash consortia have in their composition topomorphs of the woodbirds, edge birds, and ubiquitous birds. Woodbirds are the dominant birds group. They completely dominate in the virginia ash consortia and significantly prevail over the ubiquitous on young generative trees. An edge birds group appears only on old and mature generative trees. Climamorphs are represented by year-round and seasonal bird species. The ratio of these two groups in consortia varies during the year, but in general, year-round bird species dominate. Therefore, the interaction system of the birds with ash has is quit stable. The virginal ash has seasonal species only in summer and autumn. The generative ashes of all the categories have the both climamorphe groups during the year. This indicates that a stable system of the birds with ash consortive interactions has been formed only with the fruiting beginning. The trophomorphs are the most diverse group of the morphs. Such biomorphs as zoophages, phytophages, omnivores are represented in the ash consortium. Within these biomorphs, second-order biomors were identified: seed-eaters, fruit-eaters, observers, sweepers, deep sweepers. The third order trophomorphs were also distinguished as the size links. The trophomorphs greatest variety was recorded for the young generative trees – 13 trophomorphs of the second and third orders. The mature and old generative trees have 12 trophomorphs. The virginal trees – only 2 trophomorphs. This is partly due to the neighboring tree species influence in the tree stand composition. It was found that the virgin trees have the lowest biomorphic diversity of the birds, and the generative trees have the highest one. This distinguishes ash from the other tree species. The reason of this is that the mature and old generative ash (g2–g3) has a crown located above the upper layer. The semi-open architecture of this tree crown is also facilitate to this. In such conditions birds don’t find enough places for their protection from predators, so they spend a little time on this tree, and don’t delay in its crown. The young generative ash crowns are within the upper and middle tree layers, so they have safer conditions for birds. The studies conducted in different seasons, also has found an interesting feature of the ash. Unlike other species, the ash is the least attractive for birds in the fall. In winter the birds visit this tree quite actively. The ash high fecundity and its seeds remaining on the tree branches in winter are the reason of this fact. As a result, some birds feed the ash tree fruits, while the other birds extract insects-phytophagous from it. The results of the research indicate that the ash is less attractive for the birds than the tired crown trees, such as oak, maple, linden. On the other hand, a significant part of the birds time budget on ash is spent for surveillance. Birds use ash as a place for review and control of their site. Therefore, ash can be recommended as an additional species in the artificial tree-stands creation.

Differing effects of fallow type and landscape structure on the occurrence of plants, pollinators and birds on environmental fallows in Finland

Long-term grassland fallow and short-term meadow fallow represent alternative fallowing strategies for biodiversity conservation on farmland. Conventional grassland mixtures are used to establish long-term grassland fallows, whereas short-term meadow fallows are sown with specific meadow seed mixtures and require regular re-establishment to maintain the abundance of sown species. This study examined the impact of fallow type and landscape structure on the species richness and abundance of four taxa: plants, bumblebees, butterflies and birds. Long-term grassland fallows and short-term meadow fallows were studied in four contrasting landscape types in Finland, differing in the cover of forest and perennial grasslands. The fallow type and landscape structure affected each species group differently, and the value of a particular fallow type was also modified by landscape setting. Bumblebees were most abundant in short-term meadow fallows, whereas butterflies benefited more from long-term grassland fallows. Species richness of plants and butterflies were higher in forested than in open landscapes. Long-term grassland fallows promoted species richness of butterflies as well as the abundance of foraging edge birds in forested landscapes, whereas short-term meadow fallows enhanced the abundance of foraging edge birds in open landscapes. In landscapes with high grassland cover, the breeding density of open farmland birds was higher in meadow fallows than in grassland fallows, while the reverse was true in landscapes with low perennial grassland cover. The fallowing strategy thus can be adapted to the landscape context depending on the specific objectives. For overall biodiversity enhancement, establishing and managing different kinds of fallows is important.

Living on the edge: range edge birds consume novel foods sooner than established ones

Lay SummaryFinding and exploiting novel resources are essential for survival in unfamiliar habitats. Here, we show that individuals at a range edge are faster to try novel foods than those in longer established areas but did not differ in response to novel objects. Although novelty may be associated with risks (e.g., predators, parasites, toxins), the potential of gaining a high nutritional value resource might outweigh risks in areas where familiar resources are relatively unknown.

Understanding landscape patterns of temporal variability in avian populations to improve environmental impact assessments

It is recognized that wildlife populations exhibit spatial and temporal variability in patterns of species richness across heterogeneous landscapes. This phenomenon can prove problematic for environmental practitioners when attempting to complete comprehensive environmental assessments (EAs) with limited field surveys. A better understanding of regional spatio-temporal patterns in population dynamics should enhance site-level decision-making. In this study, the variability of seasonal data across the Credit River Watershed, southern Ontario, is assessed for a hierarchy of conservation measures including species richness, and two conservation wildlife response guilds based on primary habitat and area sensitivity. Bird populations were monitored at 24 forest monitoring plots across the watershed by the authors twice a season from 2003 to 2010 following the protocol of Environment Canada's Forest Bird Monitoring Program. The monitoring plots are located within four land management zones identified as 1) urban, 2) transitional, 3) escarpment and 4) rural. Data from the monitoring program are used to compare species richness among plots across the watershed and among land management zones. In addition, the variability of records from each plot over the 8year period was determined by means of the Coefficient of Variation (CV) statistic. The mean variability of these records at each site within each land management zone was determined in order to assess whether the temporal variability of bird records might affect the integrity of short term assessments. Finally, a one-way ANOVA was applied to learn whether the result of short-term assessments may be further compounded by differences in the response of selected bird guilds to landscape heterogeneity. The results show that there is a significant difference in mean richness of forest birds among the four management zones. The ANOVAs indicate that significant difference is due to the temporal variability of a) breeding forest interior birds rather than edge birds or generalist species and b) breeding area sensitive species rather than area non-sensitive species. Recommendations are made that environmental assessments targeting forest interior bird populations need to plan sampling strategies that recognize this variability, especially for sites within the transitional and urban zones. Planning in the transition or urbanizing landscape should incorporate landscape ecology principles to sustain current levels of richness in forest species.

The trade-off between housing density and sprawl area: Minimising impacts to forest breeding birds

Increasing housing density is generally assumed to confer negative effects on forest breeding birds. This implies we should build at low density over the landscape to conserve these species. However, for a given human population, low-density development must cover a large area, resulting in sprawl. A pertinent question is then: at what housing density are the impacts of a given human population on forest biodiversity minimised? For a given human population, it is unclear whether the impacts on forest biodiversity are less where housing density is high and sprawl area is small or where housing density is low and sprawl area is large. We addressed this question using the abundance, species richness and evenness of forest birds in Ottawa, Ontario and Gatineau, Quebec, Canada. First, we counted breeding birds at 22 sites representing a range of housing densities. We then used these empirical measurements to estimate forest bird abundance, species richness and evenness in four hypothetical development scenarios representing the trade-off between housing density and sprawl area. With the exception of the Undeveloped scenario (i.e., continuous forest), forest birds and forest interior birds were most abundant in the Compact scenario and most speciose in the Semi-compact scenario, whereas forest edge birds were most abundant and speciose in the Dispersed scenario. All three bird groups were most even in the Compact scenario. We conclude that compact housing development (building at high density over a small area) minimises the impacts of a given human population on forest breeding birds.

An Experimental Analysis of Spatial Position Effects on Foraging and Vigilance in Brown‐Headed Cowbird flocks

AbstractSeveral observational studies have found that the costs and benefits of social foraging vary as a function of spatial position in the group. However, it is difficult to make mechanistic inferences because several confounding factors, such as food deprivation levels, food availability, neighbor distance, and group size can mask or amplify spatial position effects. We attempted to address experimentally the effect of spatial position on foraging and vigilance in a group, controlling for many confounding factors. We used enclosures that restricted physical but not visual interactions between brown‐headed cowbirds and manipulated spatial position, flock size, and neighbor distance. Pecking rate (number of pecks per trial duration) was not related with position, but instantaneous pecking rate (number of pecks per foraging bout duration) was higher at the edge. The proportion of time spent head‐up (scanning and food‐handling) was also higher at the edge. For pecking rate and proportion of time spent scanning, changes in neighbor distance influenced the behavior of edge birds to a lesser extent than central birds. These results suggest that cowbirds at the edge perceived greater predation risk and that during the limited foraging time available, edge birds tried to compensate by foraging at a faster rate.

Generalizability of neotropical bird abundance and richness models

AbstractPredicting the consequences of land‐cover change on tropical biotas is a pressing task. However, testing the applicability of models developed with data from one region to another region has rarely been done. Bird faunas were sampled along 3.0‐km routes in southern Costa Rica (Coto Brus) to develop statistical models to describe the abundance and richness of groups as a function of land‐cover characteristics. The relative value of the land‐cover models was assessed by comparing them with null models. The generalizability of the models was tested with data from north‐western Costa Rica (Monteverde) to determine whether the models were applicable to another area that has undergone significant land‐cover change in the last 60 years. The richness and abundance of understory, open‐country and edge non‐insectivore groups showed clear relationships with land‐cover variables, and the land‐cover models had lower prediction errors than the null models for Coto Brus. With one exception, useful models for canopy birds, edge insectivores and hummingbirds could not be developed. The land‐cover models of abundance of canopy insectivores, understory insectivores and non‐insectivores, and edge non‐insectivores were generalizable to Monteverde whereas the land‐cover models of abundance of open‐country birds and species richness for any of the groups were not better than null models for Monteverde. The results indicate that land‐cover models that describe the abundance or richness of various bird groups provide useful predictions in the area where the data were collected and that models of abundance of some canopy, understory and edge birds may perform well in areas that are similar in elevation, life zones and land use to the area from which data were collected. Land‐cover models of the abundance of other groups, and of the richness of the majority of groups, may be less generalizable to other areas, or it may be difficult to develop models at all.

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

AbstractVariation in foraging success in relation to spatial position in a group is little known in species that feed on mobile prey that can hide or flee upon disturbance by foragers. I examined the foraging success of individuals located either at the edge or at the centre of flocks of semipalmated sandpipers (Calidris pusilla) feeding on a burrowing amphipod (Corophium volutator) during migration stopover in the Bay of Fundy, Canada. The rates of pecking, prey capture and success were lower for individuals foraging at the edge than at the centre of flocks. Edge birds spent more time running and more time flying than centre birds. Edge birds moved away from the centre of the flock and made frequent short flights towards the centre. In contrast, centre birds rarely moved in a specific direction and flew mostly to relocate elsewhere with the whole flock. Sandpiper flocks foraged over a large area in a relatively short amount of time. In addition, amphipod density is high in this habitat. It thus appears unlikely that prey depletion or low food availability at the edges of groups could explain the spatial variation in foraging success. Low foraging success at the edges of flocks thus arose mainly because of time costs related to flock expansion and retraction. The effect of mutual interference among foragers and of predation risk by falcons is discussed with respect to flock expansion and retraction.

Competition, predation risk and patterns of flock expansion in barnacle geese (Branta leucopsis)

AbstractChanges in the spatial pattern of flocks of barnacle geese Branta leucopsis were examined in relation to individual behaviour during feeding visits to farm pastures. The flocks were photographed every 10–20 min, and the shape and location of the flock was determined from a plan view obtained from digitized images of the photographs. Flocks initially maintained a tight formation shortly after arrival, but then tended to expand with increasing residence time. The rate of expansion, however, was significantly greater in large flocks, with small flocks showing no consistent pattern. Observed rates of change in flock area were compared with those obtained from a simple model of flock movement in which individuals followed a random walk and moved at a constant speed. In contrast to the observed data, small simulated flocks (with relatively more edge birds) showed the greatest relative increase in flock area. This discrepancy between the data and the simulation can be explained mechanistically by differences in the behaviour of individuals in flocks of different sizes. In large flocks, birds at the leading edge of the flock had faster step rates and travelled further than birds in the centre and at the trailing edge. Rates of movement in small flocks did not vary with flock position. Levels of vigilance were higher during the first 10 min after arrival, in males, in smaller flocks and at the edges of flocks. Thus, upon arrival, flocks maintain a tight defensive formation with high vigilance, but with increasing residence time, vigilance decreases and larger flocks expand, suggesting a need for individuals to reduce feeding competition.

Bird species richness in vegetation fences and in strips of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of the lowland tropical rain forest has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas, Mexico, lowland rain forests are particularly diverse in the avian fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bird species. In these landscapes, linear strips of residual rain forest vegetation along streams as well as linear strips of vegetation fences (live fences) crossing the pastures might provide some connectivity to bird populations existed in forest fragments. We investigated bird species richness and relative abundance in one 6-km long section of live fences (LF) bordering a dirt road and in two 6-km long sections of residual forest vegetation along a river (MR) and one permanent stream (BS). We used point count procedures which resulted in the count of 2984 birds representing 133 species. At the LF site we detected 74% of the species, 72% at the BS site and 57% at the MR site. Only 38% of the species were common among sites. Neotropical migratory birds accounted for 34–41% of the species counted at all sites. While edge and open habitat birds accounted for 6–10% of the species and for 50% of the records at the three vegetation strips, about 90% of the species were forest birds. Distance to forest fragments and degree of disturbance of the vegetation seemed to negatively influence bird species presence at the BS and MR strips. Rarefaction analysis indicated that the LF strip was richer in species than the other two sites, but the occurrence of the three vegetation strips in the landscape seem to favor the presence of many more species. We discuss the value of these vegetation strips to birds as stepping stones in the fragmented landscape.

Flock Size and Position Effects on Vigilance, Aggression, and Prey Capture in the European Starling

We studied autumn foraging flocks of European Starlings (Sturnus vulgaris) foraging on grass lawns to determine how flock size (up to ca. 250 individuals) and position within the flock (edge vs. center) affect the birds' foraging behavior. The birds fed exclusively by probing their bills into the ground, gaping, and extracting beetle larvae or earthworms, which were directly observed by us. Neither flock size nor position affected the rate of prey capture. Edge birds, however, spent more time vigilant and probed less than center birds. Rates ofagonistic interactions did not differ between flock positions; therefore, the percentage of time actually spent foraging (i.e., walking, searching, and probing) was lower for edge birds due to their higher level of vigilance. The only behaviors affected by flock size were percentage of time spent vigilant and percentage of time spent foraging, but only for edge birds in flocks of 520 individuals. The rate of agonistic interactions did not increase with increasing flock size for edge or center birds. Probe rate was not correlated with prey capture rate, placing caution on indiscriminate use of probe (or peck) rate as an index of prey capture rate. The likely nature of the dispersion pattern of the starling's prey is discussed in relation to our results.

Reverse short-channel effects on threshold voltage in submicrometer salicide devices

A reverse short-channel effect on threshold voltage caused by the self-aligned silicide process in submicrometer MOSFETs is reported. A physical model of lateral channel dopant redistribution due to the salicide process is proposed. The injection of vacancies and lattice strain during TiSi/sub 2/ formation causes defect-enhanced boron diffusion which results in a nonuniform lateral channel dopant redistribution and hence a threshold increase in short-channel devices. In addition to the small gate edge birds beak and the nonuniform oxidation-enhanced diffusion (OED) redistribution of channel dopant due to the polysilicon gate reoxidation, the self-aligned Ti silicide process can be major cause of the observed reverse short-channel effect in submicrometer MOSFET devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamics of a Robin population outside the breeding season

This Belgian study of a partially migratory population found that 1110renient strategy was related to habitat. It was the woodland birds which departed in autumn, while woodland edge and garden birds took up winter territories close by.

Ecological Sources of Selection on Avian Sounds

This study describes selection derived from habitat acoustics on the physical structure of avian sounds. Sound propagation tests were made in forest, edge, and grassland habitats in Panama to quantify pure tone and random noise band sound transmission levels. The sounds of bird species in each habitat were analyzed to determine the emphasized frequency, frequency range, and sound type (whether pure tonelike or highly modulated). Forest habitats differ from grass and edge in that a narrow range of frequencies (1,585-2,500 Hz) has lower sound attenuation than lower or higher frequencies. Attenuation increases rapidly above 2,500 Hz. Bird sounds from species occurring at the lower forest levels were found to be predominantly pure tonelike with a frequency emphasized averaging 2,200 Hz, conforming to the predictions based on sound propagation tests. The edge habitat is characterized by a wide range of frequencies having a generally similar attenuation rate. Pure tone and random noise band sounds did not differ in attenuation rates. The sounds of edge birds have high variance in the frequency-emphasized component, and more are composed of both modulated and pure tone elements to a greater extent than forest or grassland species. It is suggested that this variance is a reflection of a relative lack of selection pressure from habitat acoustics. Grassland propagation tests showed a positive correlation between increasing frequency and increasing attenuation. It is hypothesized that information transfer may be based on temporal aspects of the signal since these are less distorted in temperature- and wind-speed-stratified open environments.

Populations and Local Extinctions of Birds on Barro Colorado Island, Panama

A 1960—71 study of populations of color—banded ant—following antbirds of three species on a tropical—forested lowland reserve, Barro Colorado Island, showed that the small species (Spotted Antbird, Hylophylax naevioides) remained stable at about 20 pairs/km2. A medium—sized species, the Bicolored Antbird (Gymnopithys bicolor), decreased from about 3 pairs to 1.5 pairs/km2. A large species, the Ocellated Antbird (Phaenostictus mcleannani), declined from 1.5 pairs/km2 to near extinction–only one female remained in early 1971. Two of three other species that regularly follow army ants showed relatively stable populations, but a third large species (Barred Woodcreeper, Dendrocolaptes certhia) declined from two pairs to local extinction. Prior to 1960 a very large ground—cuckoo that follows ants had already become extinct there. Thus, the three largest of the seven original species that regularly followed ants were gone or nearly gone by 1970. The decrease in numbers of regular ant—following birds was not made up by increases in occasional followers. Detailed studies of antbirds showed no clear reasons for declines, except that annual mortalities of adults were high in Ocellated Antbirds (about 30%) compared to Spotted Antbirds (15%—17%) and nest losses perhaps higher in the former (96% compared to 91%). Nest mortalities were slightly lower (88%) and adult mortalities intermediate (about 25%) in Bicolored Antbirds. Female Ocellated Antbirds had higher mortalities than males. The antbirds renest repeatedly during long nesting seasons, up to 14 times per year for Ocellated Antbirds. However, to replace females of this species under Barro Colorado conditions 19 nestings per year would be needed. Concurrent listing of all birds of the island showed that 45 species of breeding birds, 22% of the avifauna present when the island was made a reserve, had disappeared by 1970. No new species replaced them. Of the lost species 13 are forest birds, in danger if forests are cut elsewhere. The other species, second—growth and forest—edge birds, have been crowded out by growth of the forest. Loss of species from this tropical reserve, especially the part apparently caused by the small size and isolation of the reserve, poses problems for conservation and ecological studies of tropical biotas. It is suggested that large future reserves have corridor zones to each other, that is, that intensive human use not preempt too much area nor interrupt immigration of animals or plants from one refuge to another.