Avian species diversity in different habitat types in and around North Nandi Forest,Kenya

Forest fragmentation and degradation leads to formation of modified habitats whose ability to support existing avifaunal diversity is still largely unknown. Bird diversity in indigenous forest, disturbed forest, plantation forest and farmlands adjacent to North Nandi Forest reserve was studied between January 2015 and June 2015. The distribution of bird feeding guilds in these habitat patches was also evaluated. Birds were surveyed using point counts, timed species counts and line transects and classified into six feeding guilds. A total of 3,232 individual birds of 151 species were recorded in the four habitats. Significant difference on bird abundance across the four habitats (F = 15.141, P ≤ 0.05, df = 3, 1121) was noted. Shannon–Weiner diversity index H′ for bird community ranged from 3.06 for plantation forest to 4.05 for disturbed forest showing a relatively diverse bird community. Insectivores (F = 3.090, P ≤ 0.05, df = 3, 297) dominated the foraging species assemblage in all the habitats significantly. Linear regression analysis revealed a strong linear relationship on bird species richness and abundance with vegetation variables (P < 0.01 in all cases). The results indicate that disturbed forest and indigenous forest support high bird species richness than plantation forest and farmlands. However, high bird abundance was observed in farmlands and plantation forest as opposed to indigenous forest and disturbed forest as they provide dispersal routes over a short distance and are important for creating corridors between primary forests.     

Functional composition and phenology of fruit-feeding butterflies in a fragmented landscape: variation of seasonality between habitat specialists

For butterflies, tolerance to the matrix may be an important criterion of habitat occurrence in fragmented landscapes. Here we examine the relative effects of habitat fragmentation and the surrounding agricultural matrix on the functional composition of fruit-feeding butterflies of the Atlantic rain forest in southeastern Brazil. Generalized linear models were used to detect the effects of landscape metrics on butterfly richness and abundance of the total assemblage and functional groups. Circular statistics were used to analyze the patterns of monthly abundance of the total assemblage and functional groups in the forest remnants and the surrounding matrices. In total, 650 butterflies representing 57 species were captured; species composition differed significantly between the forest fragments and the surrounding matrices. We recorded 22 forest specialists, 18 matrix specialists, 11 common species with matrix preference and six common species with forest preference. Forest connectivity favored the richness of forest specialists, while habitat fragmentation enhances the richness and abundance of matrix-tolerant species. Circular analysis revealed that forest specialists were more abundant in the rainy season while matrix-tolerant species proliferated in the dry season. Although maintaining connectivity of forest fragments may increase the mobility and dispersion of forest species, our results showed that landscape fragmentation modify butterfly assemblage by promoting an increase of matrix tolerant species with detriment of forest specialists.     

Possible effects of habitat fragmentation and climate change on the range of forest plant species

Global circulation models predict an increase in mean annual temperature between 2.1 and 4.6 °C by 2080 in the northern temperate zone. The associated changes in the ratio of extinctions and colonizations at the boundaries of species ranges are expected to result in northward range shifts for a lot of species. However, net species colonization at northern boundary ranges, necessary for a northward shift and for range conservation, may be hampered because of habitat fragmentation. We report the results of two forest plant colonization studies in two fragmented landscapes in central Belgium. Almost all forest plant species (85%) had an extremely low success of colonizing spatially segregated new suitable forest habitats after c . 40 years. In a landscape with higher forest connectivity, colonization success was higher but still insufficient to ensure large-scale colonization. Under the hypothesis of net extinction at southern range boundaries, forest plant species dispersal limitation will prevent net colonization at northern range boundaries required for range conservation.     

Avifaunal responses to habitat fragmentation in the threatened littoral forests of south-eastern Madagascar

Aim Madagascar's lowland forests are both rich in endemic taxa and considered to be seriously threatened by deforestation and habitat fragmentation. However, very little is known about how these processes affect biodiversity on the island. Herein, we examine how forest bird communities and functional groups have been affected by fragmentation at both patch and landscape scales, by determining relationships between species richness and individual species abundance and patch and landscape mosaic metrics. Location Littoral forest remnants within south‐eastern Madagascar. Methods We sampled 30 littoral forest remnants in south‐eastern Madagascar, within a landscape mosaic dominated by Erica spp. heathland. We quantified bird community composition within remnants of differing size, shape and isolation, by conducting point counts in November–December in 2001 and October–November 2002. Each remnant was characterized by measures of remnant area, remnant shape, isolation, and surrounding landscape complexity. We used step‐wise regression to test the relationship between bird species richness and landscape structural elements, after correcting for sampling effort. Relationships between bird species abundances and the landscape variables were investigated with Canonical Correspondence Analysis and binomial logistic regression modelling. Results Bird species richness and forest‐dependent bird species richness were significantly (P < 0.01) explained by remnant area but not by any measure of isolation or landscape complexity. The majority of forest‐dependent species had significant relationships with remnant area. Minimum area requirements for area‐sensitive species ranged from 15 to 150 ha, with the majority of species having area requirements > 30 ha. Surprisingly, there was no relationship between bird body size and minimum area requirement. Forest‐dependent canopy insectivorous species and large canopy frugivorous species were the most sensitive functional groups, with > 90% species sensitivity within each group. The distribution of four forest‐dependent species also appeared to be related to remnant shape where remnant area was < 100 ha. Main conclusions The majority of forest‐dependent species, including many that are considered widespread and common, were found to have significant relationships with fragment size, indicating that they are sensitive to processes associated with habitat loss and fragmentation. As deforestation and habitat fragmentation remain serious problems on the island, it follows that many forest‐dependent bird species will decline in abundance and become locally extinct. At the regional scale, we urge that large (> 200 ha) blocks of littoral forest are awarded protected status to preserve their unique bird community.     

Equilibrium biogeography and the size of nature preserves: An avian case study

Summary The results of seven breeding bird censuses on an upland site in Connecticut from 1953 to 1976 are analyzed and related to changes in vegetation and surrounding urbanization during the same period. Turnover of breeding bird species on the old-field portion of the site was due to vegetational changes that caused the extinction of species preferring open shrub habitats and the colonization of species preferring forest. Turnover of breeding birds on the forest portion was due to its increasing isolation from similar forest habitat, resulting in the local extinction of forest interior species and the colonization of species characteristic of suburban habitats. The study site is too small for the preservation of forest interior bird species. It must be coordinated with larger preserves in a regional context if it is to be useful in preventing the regional extinction of forest interior bird species.     

Distribution and abundance patterns of bird community and raptor populations in the Andaman archipelago

A qualitative survey of the terrestrial bird community (sixty-five species) and a quantitative analysis of the five-diurnal raptor assemblage were earned out on 33 islands of the oceanic Andaman archipelago in the Bay of Bengal Among seven geographical parameters, island area was the main determinant of species richness for both the whole bird community and each category of species associated with four habitat types Species richness decreased most markedly with island size in the smallest islands and in open habitat species The rarest forest species were the most extinction prone with decreasing island size Specific habitat selection was the most prominent ecological correlate of inter island species distribution Observed species distribution patterns did not fit the random species placement or equprobable occurrence hypotheses Raptors were primarily forest species, two of them restricted to forest interior, two more tolerant of fragmentation and one naturally associated with mangroves Unexpectedly, the two rarest and most area sensitive raptors were the two smallest species with a strong active flight, whereas the most abundant and widespread species was the most forest interior and endemic taxon Both raptor species richness, species frequency of occurrence and abundance indices decreased with island area, which was consistently the most significant determinant of every species' occurrence and abundance There was a significant correlation between abundance or frequency of occurrence of every raptor species and the proportion of their preferred habitat type No relationship was found between habitat niche breadth or local abundance of any species and their distribution range among islands The hypothesis of random composition of species assemblages on islands was not supported because of species specific habitat selection Any evidence of interspecific competitive exclusion was limited to the striking habitat segregation of the two congeneric serpent eagles A metapopulation structure was suggested by small population distribution patterns, observed sea crossing and the circumstances of an apparent extinction     

Sugarcane and Eucalyptus plantation equally limit the movement of two forest‐dependent understory bird species

Habitat fragmentation results in landscape configuration, which affects the species that inhabit it. As a consequence, natural habitat is replaced by different anthropogenic plantation types (e.g. pasture, agriculture, forestry plantations and urban areas). Anthropogenic plantations are important for biodiversity maintenance because some species or functional groups can use it as a complementary habitat. However, depending on plantation permeability, it can act as a barrier to the movement of organisms between habitat patches, such as forest fragments, reducing functional connectivity for many species. Anthropogenic plantations are becoming the most common land use and cover type in the Anthropocene and biodiversity conservation in fragmented landscapes requires information on how different plantation types affect the capacity of the species to move through the landscape. In this study, we evaluated the influence of the type and structure of plantations on the movement of two forest‐dependent understory bird species – plain antvireo (Dysithamnus mentalis) and flavescent warbler (Myiothlyps flaveola) – within a highly fragmented landscape of Atlantic Forest hotspot. Knowing that forestry plantation is assumed to be more permeable to dependent forest bird species than open ones, we selected six study areas containing a forest fragment and surrounding plantation: three with sugarcane plantation and three with Eucalyptus sp. plantation. We used playback calls to stimulate the birds to leave forest fragments and traverse the plantations. Control trials were also carried out inside the forest fragments to compare the distances crossed. We observed that individuals moved longer distances inside forest than between plantation types, which demonstrate that plantations do constrict the movements of both species. The two plantation types equally impeded the movements of the species, suggesting the opposite of the general assumption that forestry plantations are more permeable. Our results indicate that, for generalist species, plantation type does not matter, but its presence negatively impacts movement of these bird species. We highlight that plantations have negative influences on the movements of common bird species, and discuss why this is important when setting conservation priorities.     

Rapid colonization of a Hawaiian restoration forest by a diverse avian community

Deforestation of tropical forests has led to widespread loss and extirpation of forest bird species around the world, including the Hawaiian Islands which have experienced a dramatic loss of forests over the last 200–800 years. Given the important role birds play in forest ecosystem functions via seed dispersal and pollination, a bird community's response to forest restoration is an important measure of the success of such conservation actions. We evaluated the bird response to reforestation at an important bird sanctuary, Hakalau Forest National Wildlife Refuge, Hawai′i Island, using 26 years of bird count data. We show that most species from within the diverse avian community increased significantly, but species colonized the restoration forest at different rates. Distance from intact forest and time since restoration were both important predictors of colonization rate, interacting such that for most species it took more time to colonize areas farther from the intact forest. In addition, both forest cover and understory diversity helped to explain bird densities, but the effect varied among species, suggesting that different habitat requirements may help drive variation in colonization rates. This article provides the first detailed evaluation of how a diverse community of birds has responded to one of the largest, ongoing reforestation projects in Hawai′i.     

Evidence that creation of a Pinus radiata plantation in south-eastern Australia has reduced habitat for frogs

Loss and fragmentation of habitat resulting from the clearing of forests for agriculture and urban development threaten the persistence of thousands of species worldwide. The clearing of native forest to plant a monoculture of exotic trees may also reduce and fragment the habitat available for indigenous plants and animals. Metacommunity theory suggests that the species richness of a community in a patch of habitat will increase with patch size but decrease with patch isolation. We investigated whether replacement of native Eucalyptus forest with a plantation of Pinus radiata has reduced and fragmented habitat for frogs, leading to a lower species richness of frog communities in the pine plantation and in small and/or isolated remnant patches of native forest. We surveyed frogs at 60 sites at streams and wetlands in the pine plantation, remnant patches of native forest surrounded by pines, and adjacent areas of contiguous native forest near Tumut in New South Wales, Australia. Only two of eight species of frogs were recorded in the pine plantation, and regression modelling indicated that streams and wetlands in the pines supported fewer frog species than those in remnant patches or the intact native forest. In addition, species richness tended to be higher at wide, shallow swamps and marshes near the headwaters of streams, with herbs, grasses, shrubs, reeds, sedges and rushes in the emergent and fringing vegetation. There was little evidence to suggest that larger eucalypt remnants supported more species of frogs, or that remnants isolated by greater expanses of pines supported fewer species, but we had low power to detect these effects with our data set. Our results support the preservation of all remnants of native forest along drainage lines and around swamps, soaks and bogs, regardless of size. Where new pine plantations are established, for example, on cleared agricultural land, care should be taken to maintain the structural and vegetative characteristics of water bodies to ensure that they continue to provide suitable breeding habitat for frogs.     

Reversing habitat loss: deciduous habitat fragmentation matters to birds in a larch plantation matrix

Whereas matrix management has recently been suggested as a useful tool in biodiversity conservation, patterns and processes within matrices remain unknown. We examined the effects of the loss and fragmentation (configuration) of original deciduous habitats on birds in larch plantation matrix in the winter and during the breeding season in a montane region in Nagano Prefecture, central Japan. Birds were counted using a plot-count method from 32 (winter) and 46 (breeding) matrix (plantation) sites with a range of surrounding habitat loss and fragmentation at a 1600-m scale. Birds were assigned to species groups based on ecological traits, and three groups for which larch plantation would function as low-quality matrix were analyzed. Bird occurrences were explained primarily by habitat structure. Although the effects of landscape structure were less than those of habitat structure, three of five groups across the two seasons experienced significant landscape effects. All effects were of habitat fragmentation (scatteredness of deciduous habitats), i.e. two groups (flycatchers in the breeding season and tree nesters in both seasons) frequently occurred in matrix surrounded by highly scattered deciduous habitats. However, most of these effects were confounded by local habitat structure. That is, the variation in bird occurrences explained purely by fragmentation variables was <6%. Nonetheless, because these effects were marginally significant at p<0.10, there was some support for fragmentation effects after covariation with habitat structure was considered. Based on these results and associated theoretical studies, we hypothesized that habitat fragmentation leads to loss of individuals and is more important than habitat loss in landscapes with a structurally similar matrix. We also hypothesized that matrix within landscapes with highly scattered habitats should be managed with high priority.     

Bird Species Sensitivity in a Fragmented Landscape of the Atlantic Forest in Southern Brazil1

I tested whether terrestrial/understory habits, large body sizes, low tolerance to edge or to matrix habitat, and food/habitat specialization are characteristics of the most vulnerable bird species based on point counts conducted in 14 forest fragments in northern Paraná, southern region of the Brazilian Atlantic forest. In addition, the sensitivity level of each bird species to forest fragmentation in northern Paraná (high, medium, and low) was compared to the Viçosa region, another fragmented landscape of the Atlantic forest. Contrary to expectations, large body size and terrestrial/understory habits were not features clearly related to high sensitivity to forest fragmentation; but species with tolerance to edge did have lower sensitivity. I found also that specialized habitat/food were not good predictors of extinctions; the most specialized guilds, bamboo and vine‐tangle insectivores and trunk and twig insectivores, had a high number of species with low sensitivity. Patterns of sensitivity were compared for 75 bird species that occurred in both northern Paraná and Viçosa; higher incongruence occurred for 14 and 7 species considered as highly sensitive in Viçosa but were of medium or low sensitivity, respectively, in northern Paraná. These differences may occur because sensitivity to habitat fragmentation may vary from the center to the periphery of a species' geographic range. Geographic variation in patterns of sensitivity to forest fragmentation may be important for conservation planning.     

Effects of habitat transitions on rainforest bird communities across an anthropogenic landscape mosaic

We compared bird community responses to the habitat transitions of rainforest‐to‐pasture conversion, consequent habitat fragmentation, and post‐agricultural regeneration, across a landscape mosaic of about 600 km² in the eastern Australian subtropics. Birds were surveyed in seven habitats: continuous mature rainforest; two size classes of mature rainforest fragment (4–21 ha and 1–3 ha); regrowth forest patches dominated by a non‐native tree (2–20 ha, 30–50 years old); two types of isolated mature trees in pasture; and treeless pasture, with six sites per habitat. We compared the avifauna among habitats and among sites, at the levels of species, functional guilds, and community‐wide. Community‐wide species richness and abundance of birds in pasture sites were about one‐fifth and one‐third, respectively, of their values in mature rainforest (irrespective of patch size). Many measured attributes changed progressively across a gradient of increased habitat simplification. Rainforest specialists became less common and less diverse with decreased habitat patch size and vegetation maturity. However, even rainforest fragments of 1–3 ha supported about half of these species. Forest generalist species were largely insensitive to patch size and successional stage. Few species reached their greatest abundance in either small rainforest fragments or regrowth. All pastures were dominated by bird species whose typical native habitats were grassland, wetland, and open eucalypt forest, while pasture trees modestly enhanced local bird communities. Overall, even small scattered patches of mature and regrowth forest contributed substantial bird diversity to local landscapes. Therefore, maximizing the aggregate rainforest area is a useful regional conservation strategy.     

Forest bird diversity in Mediterranean areas affected by wildfires: a multi-scale approach

Fire is a key mechanism creating and maintaining habitat heterogeneity in Mediterranean landscapes by turning continuous woody landscapes into mosaics of forests and shrublands. Due to the long historical role of fires in the Mediterranean, we hypothesised a moderate negative effect of this type of perturbation on forest bird distribution at a landscape level. We conducted point bird censuses in Aleppo pine forest patches surrounded by burnt shrublands and studied the relationships between three ecological groups of bird species (forest canopy species, forest understorey species, and ubiquitous species) and the features of local habitat, whole patch and surrounding landscape. We used a multi-scale approach to assess the effects of landscape variables at increasing spatial scales on point bird richness. Regarding local habitat components, canopy species were positively associated with tall pines while understorey species with the cover of shrubs and plants from holm-oak forests. Forest birds were positively related to patch size and irregular forest shapes, that is, with high perimeter/size ratios. Thus, these species did not seem to perceive edges as low quality but rather favourable microhabitats. We did not detect any negative effect of isolation or cover of woodlands in the landscape on the presence of forest species after local habitat factors had been accounted for. Finally, only local habitat factors entered the model for ubiquitous species. We suggest that mosaic-like landscapes shaped by fires in the Mediterranean basin are not strongly associated with negative effects fragmentation on forest birds other than those related with habitat loss.     

Differential and delayed response of two ant species to habitat fragmentation via the introduction of a pine matrix

1. Ants are a ubiquitous and crucial component of Australian Eucalyptus forests, but responses to long‐term habitat fragmentation remain poorly understood. Two ant species were followed across a 21‐year history of pine plantation establishment and maturation in a southeast Australian Eucalyptus forest. 2. At Wog Wog in southeastern Australia, a Native Eucalyptus forest was clear‐cut to make way for plantation establishment and 12 remnant patches of forest were left intact and subsequently surrounded by a pine matrix. Pitfall traps were placed in the continuous native forest, remnant Eucalyptus patches, and the pine matrix between fragments, and were stratified based on proximity to remnant patch edges and habitat type. Two ant species are focused on that represent the only remaining data for the early years of the experiment. 3. While Leptomyrmex erythrocephalus (Fabricius), the rarer of the two species, was not affected by fragmentation in the short term, 21 years after fragmentation, it was less likely to occur in both the mature pine matrix and fragments than in continuous forest controls. Aphaenogaster longiceps (Smith F.) was equally likely to occur in the fragments, continuous forest, and pine matrix early in the experiment but by year 21 post‐fragmentation was less likely to occur in the pine matrix than fragments or controls. 4. Importantly, we only detected negative impacts of fragmentation on ant occurrence as the pine plantation matrix matured and isolated ant populations on fragments. 5. It is concluded that changes in matrix suitability and specific habitat characteristics influence ant persistence in Eucalyptus fragments.     

Improving national habitat specific biodiversity indicators using relative habitat use for common birds

It has recently been stated that the global goal of halting the loss of biodiversity by 2010 has not been met highlighting the urgent need to monitor trends in biodiversity. Our study suggests that existing indicators of bird biodiversity in Denmark are inaccurate and we present a new objective method for accurately assessing trends in specific habitats using common bird species. Bird species were selected for creating habitat specific indicators by calculating their relative habitat use (RHU) in nine different habitat categories. RHU indicates the degree to which a habitat is preferred (RHU > 2) or avoided (RHU < 0.5) by a species, relative to other habitats. Indicator sets were constructed for each habitat type using species with an RHU > 2 and revealed that existing habitat indicators, based on species lists from the Pan-European Common Bird Monitoring Scheme (PECBMS), often included species that did not in fact have preferences for those particular habitats in Denmark. Habitat specific indicators based on the new species selection method showed significant negative trends in three of nine habitat categories: coniferous forest, bog/marsh and heath. Habitat classes were further combined to create overall indicators for forest, farmland and freshwater. A comparison of these indicators with the existing indicators revealed a negative overall trend for forest habitat, which had previously been overlooked, suggesting that species selection is crucial for the development of informative indicators. The habitat specific farmland indicator confirmed the negative trend in the current farmland indicator. The methodology for indicator species selection presented here could potentially be applied for use in a global context for a wider range of taxonomic groups.     

Colonization of dynamic Mediterranean landscapes: where do birds come from after fire?

Aim Two main mechanisms may explain post‐disturbance species colonization patterns of early successional habitats such as those originated by wildfires. First, post‐disturbance colonization is not limited by the dispersal ability of the species to reach the newly created open areas and, secondly, colonization is limited by dispersal. Under the first hypothesis, we expect, at a regional scale, to find similar post‐disturbance communities to develop on recently burned sites. However, colonization limited by dispersal will lead to strong between‐site variations in species composition. Location To test these hypotheses, we studied the post‐fire colonization patterns of nine open‐habitat bird species in eight distantly located wildfires in the north‐eastern Iberian Peninsula. Methods We censused post‐fire bird composition by means of field transects and identified potential colonization sources from species–habitat suitability maps derived from atlas data. Results Our results showed strong significant differences in post‐fire species composition between burnt areas. Burnt areas located in areas with low probability of species presence before the fire event showed lower species occurrence and richness after the fire. Main conclusions These results do not support the idea that early successional stages and open habitats have a homogeneous community structure at regional scales and suggest that dispersal is a key constraint determining bird colonization of post‐fire habitats. Further attention should be paid to landscape heterogeneity as a key factor in determining population dynamics of open‐habitat species in the light of current and future land‐use changes in Mediterranean regions.     

Elevation‐dependent effects of forest fragmentation on plant–bird interaction networks in the tropical Andes

Tropical forests harbor diverse ecological communities of plants and animals that are organized in complex interaction networks. The diversity and structure of plant–animal interaction networks may change along elevational gradients and in response to human‐induced habitat fragmentation. While previous studies have analyzed the effects of elevation and forest fragmentation on species interaction networks in isolation, to our knowledge no study has investigated whether the effects of forest fragmentation on species interactions may differ along elevational gradients. In this study, we analyzed main and interaction effects of elevation and forest fragmentation on plant–frugivore interaction networks at plant and bird species level. Over a period spanning two years, we recorded plant–frugivore interactions at three elevations (1000, 2000 and 3000 m a.s.l.) and in two habitat types (continuous and fragmented forest) in tropical montane forests in southern Ecuador. We found a consistent effect of elevation on the structure of plant–frugivore networks. We observed a decrease in the number of effective bird partners of plants and, thus, a decline in the redundancy of bird species with increasing elevation. Furthermore, bird specialization on specific plant partners increased towards high elevations. Fragmentation had a relatively weak effect on the interaction networks for both plant and bird species, but resulted in a significant increase in bird specialization in fragmented forests at high elevations. Our results indicate that forest fragmentation may have stronger effects on plant–frugivore interaction networks at high compared to low elevations because bird species richness declined more steeply towards high elevations than plant species richness. We conclude that conservation efforts should prioritize the maintenance of consumer diversity, for instance by maintaining stretches of continuous forest. This applies in particular to species‐poor communities, such as those at high elevations, as the ecological processes in these communities seem most sensitive towards forest fragmentation.     

At the landscape level,birds respond strongly to habitat amount but weakly to fragmentation

Aim

It is usually thought that habitat fragmentation acts negatively on species survival, and consequently, on biodiversity. Recent literature challenges whether habitat fragmentation per se affects species richness, beyond the effect of habitat area. Theoretical studies have suggested that fragmentation may matter most when the amount of available habitat is small or at intermediate levels. However, a recent review suggests that the effect of fragmentation on species richness is usually positive. Here, we dissect the richness–fragmentation relationship. What is the effect size? Does it depend upon the amount of habitat cover? How do individual species respond to fragmentation?

Methods

Applying a macroecological approach, we empirically related avian richness and the probability of occurrence (p_occ) of individual species to fragmentation (number of patches), after controlling for habitat amount in 991 landscapes, each 100‐km², in southern Ontario, Canada.

Results

Species richness was strongly related to total habitat amount, but habitat fragmentation had no detectable additional effect. Individual species’ p_occ related strongly to habitat amount. For some species, p_occ also related secondarily to habitat fragmentation within landscapes. Logistic models revealed that p_occ related significantly negatively to fragmentation after controlling for habitat amount for only ~13% of forest‐ and 18% of open‐habitat species bird species. However, p_occ related significantly positively to fragmentation for even greater proportions of species, including some red‐listed species. Fragmentation effects were not stronger at low or intermediate levels of habitat amount within landscapes.

Conclusion

In earlier studies, negative effects of isolation were observed at the patch level in experimental manipulations. However, at the landscape level, avian species richness in southern Ontario apparently responds primarily to habitat amount and negligibly to fragmentation. We argue that the evidence is inconsistent with the hypothesis that reducing habitat fragmentation per se would be an effective conservation strategy for birds at the landscape level.

     

The effect of habitat on the range expansion of a native and an introduced bird species

Aim Range expansion across a heterogeneous landscape may depend on the habitat selected and used by the expanding species. If habitat selection influences range expansion then localities colonized by a species should contain a greater proportion of favoured habitat (and less non‐habitat) than other nearby localities not colonized. White‐winged doves (Zenaida asiatica) and Eurasian collared doves (Streptopelia decaocto) are two bird species that provide an excellent opportunity to test this hypothesis, because the geographic ranges of both species have been expanding in North America for more than two decades. Location Continental USA. Methods We used distribution data from the North American Breeding Bird Survey to test whether the landscapes occupied by each species contained a greater proportion of favoured habitat (urban land, grassland/pasture, shrub land and cropland) and a lower proportion of non‐habitat (forest land) than landscapes where doves were not found. We tested each species separately in each of three broad expansion areas, namely East, Central and West. We also compared rates of spatial spread between expansion areas and between the two species. Results As predicted, both species tended to occupy landscapes with greater proportions of urban land, shrub land and cropland but with less forest land compared with landscapes without doves, in all three expansion areas. Contrary to prediction, occupied landscapes tended to have slightly less grassland/pasture than unoccupied landscapes. Rates of spread differed between the two species and among expansion areas. Main conclusions Range expansion and the extent to which a species fills or saturates its range are influenced by the habitat ecology of the expanding species. Species colonize localities based on the availability of suitable habitat. However, the role of habitat in a species’ range expansion does depend somewhat on the greater geographical setting. Over large regional and geographical scales, range expansion (rate of spread and saturation) may proceed unevenly, suggesting that range expansion is a very dynamic and context‐specific process.     

Is the range size of migratory birds constrained by their migratory program?

Aim Intuitively, species in which the individuals migrate long distances between summer and winter quarters should be more likely to disperse and colonize new breeding areas than resident species. However, it has repeatedly been noted that many bird species with large ranges are residents. This paradox was tested on land birds breeding in the boreal forest of the Palaearctic, the largest uninterrupted stretch of habitat on earth. Methods The longitudinal distribution of two land bird communities on each side of the Eurasian continent, in Scandinavia and eastern Siberia, were used to test whether migratory birds indeed have a lower colonization success than resident birds. Results The migratory species are significantly less likely than resident species to have a range including both regions. The pattern held true even after controlling for latitudinal effects and local abundance, and was also observed at the level of genus and family. Main conclusions The relatively low colonization success of migratory species into new breeding areas may be because these new areas require novel migratory programs (migratory distance, direction and timing) in order for the birds to reach suitable wintering grounds.