The role of farm structure on bird assemblages around a Kenyan tropical rainforest

Although it is clear that the farmlands neighbouring fragmented forests are utilized by some forest birds, it is not clear how birds in general respond to farmland habitat mosaic. An effort was made to determine how bird density and foraging assemblages were influenced by farm structural characteristics and distance from forest edge. Thirty farms up to a distance of 12 km around Kakamega forest in western Kenya were studied. Farm structure entailed size, hedge volume, habitat heterogeneity, woody plant density, plant diversity and crop cover. Birds were surveyed using line transects and DISTANCE analyses and classified into six feeding guilds and three habitat associations. Size of farms increased away from the forest, as woody plant density, plant diversity, indigenous trees and subsistence crop cover declined. The most important farm structure variable was hedge volume, which enhanced bird species richness, richness of shrub‐land bird species and insectivorous bird density (R = 0.58, P < 0.01). Bird density increased with tree density while indigenous trees were suitable for insectivores and nectarivores. There were very few forest bird encounters. Agricultural practices incorporating maintenance of hedges and sound selection of agroforestry trees can enhance conservation of birds on farmland, though, not significantly for forest species.     

Impacts of an invasive willow (Salix × rubens) on riparian bird assemblages in south‐eastern Australia

We explored how a woody plant invader affected riparian bird assemblages. We surveyed 15 200‐m‐long transects in riparian zones in a much‐changed landscape of eastern Victoria, Australia. Abundance, species‐richness, foraging‐guild richness and composition of birds were compared in transects in three habitat types: (i) riparian zones dominated by the invasive willow Salix × rubens; (ii) riparian zones lined with native woody species; and (iii) riparian zones cleared of almost all woody vegetation. We also measured abundance and richness of arthropods and habitat structure to explore further the effects of food resources and habitat on the avifauna. We observed 67 bird species from 14 foraging guilds. Native riparian transects had more birds, bird species and foraging guilds than willow‐invaded or cleared transects. Habitat complexity increased from cleared to willow‐invaded to native riparian transects, as did abundance of native and woodland‐dependent birds. Native shrub and trees species had more foliage and branch‐associated arthropods than did willows, consistent with a greater abundance and variety of foraging guilds of birds dependent on this resource. Willow spread into cleared areas is unlikely to facilitate greatly native bird abundance and diversity even though habitat complexity is increased. Willow invasion into the native riparian zone, by decreasing food resources and altering habitat, is likely to reduce native bird biodiversity and further disrupt connectivity of the riparian zone.     

Variations in bird abundance in tropical arid and semi-arid habitats

Temporal variation in bird abundance was studied during a complete annual cycle in a thorn scrub, a thorn woodland and a deciduous forest in northeastern Venezuela. Abundance of site-attached and transient birds from different feeding guilds was determined by mist-netting at 2-week intervals. Diets were investigated by regurgitated samples. The overall avifauna was characterized by a low number of species but they were present all year despite showing strong seasonal fluctuations in abundance. The number of bird species and individuals peaked before and after the reproductive period. These high values probably were associated with movement of species feeding on plant food during the late dry season and the post-breeding dispersion of juveniles. Bird richness and abundance were lowest during the breeding season and in the early dry season when food abundance was low. Birds from different feeding guilds showed distinct patterns of seasonal abundance which tended to be similar at all three sites. Transient birds represented a large portion of the avifauna, particularly in nectarivores, frugivores and granivores during the dry season. We used a canonical correspondence analysis to demonstrate that bird abundance was correlated with breeding activity, rainfall seasonality and food abundance, with the influence of each parameter varying according to feeding guilds, spatial behaviour of individuals and habitats. Despite a great turnover in the occurrence of the diverse food types available, species composition remained strikingly constant during the year, with birds responding to seasonal changes primarily through a generalist feeding habit and a highly variable rate of transience.     

Dispersal modes affect tropical forest assembly across trophic levels

We examined assemblages of trees and two major groups of vertebrate seed dispersers, birds and primates, in Ugandan protected areas to evaluate the roles of dispersal limitation and species sorting in community assembly. We conducted partial Mantel tests to investigate relationships between community similarity, environmental distance and geographic distance. Results showed that environmental factors, specifically temperature and rainfall, significantly and more strongly structured tree assemblages than geographic distance. Analysis of tree dispersal modes revealed wind‐dispersed tree guilds were significantly dispersal limited but trees dispersed by animals were not. For assemblages of vertebrate seed dispersers, dispersal limitation significantly and more strongly structured assemblages of primates than species sorting whereas environmental factors significantly and more strongly structured assemblages of birds than dispersal limitation. We therefore examined whether trees dispersed by primates were more dispersal limited than trees dispersed by birds. We found consistent trends that primate fruit trees were more dispersal limited than bird fruit trees using three definitions of dispersal syndromes based on fruit color. Our results suggest that the dispersal abilities of primary consumers may affect the distribution of primary producers at large spatial scales.     

Comparing bird assemblages in large and small fragments of the Atlantic Forest hotspots

The Atlantic Forest (AF) is one of the five most threatened and megadiverse world hotspots. It is arguably the most devastated and highly threatened ecosystem on the planet. The vast scope of habitat loss and extreme fragmentation in the AF hotspots has left intact very few extensive and continuous forested fragments. We compared bird assemblages between small (<100 ha) and large (>6,000 ha) forest remnants, in one of the largest AF remnants in Argentina. We performed 84 point-counts of birds in four large fragments (LF) and 67 points in 25 small fragments (SF). We recorded 4,527 bird individuals belonging to 173 species; 2,632 belonging to 153 species in LF and 1,897 in 124 species in SF. Small fragments suffered a significant loss of bird richness, mainly forest dependent species, but the birds abundance did not decrease, due to an increase in abundance of forest independent and semi-dependent bird species (edge and non forest species) that benefit from forest fragmentation. The bird guilds of frugivores, undestory, terrestrial and midstory insectivores, nectarivores and raptors, and the endemic species of AF were area sensitive, decreasing significantly in richness and abundance in the SF. Terrestrial granivores were the only guild positively affected by forest fragmentation, containing mainly edge species, which forage in open areas or borders including crops. Our first observations on fragmentation effects on bird assemblages in the southernmost Argentinean Atlantic Forests did not validate the hypothesis on pre-adaptation to human disturbances in the bird communities of AF. On the contrary, we observed that forest dependent, endemic and several sensitive bird guilds were strongly affected by fragmentation, putting in evidence the vulnerability to the fragmentation process and the necessity to conserve large remnants to avoid reduction of the high biodiversity of AF birds.     

The conservation value of paddock trees for birds in a variegated landscape in southern New South Wales. 1. Species composition and site occupancy patterns

The use of paddock trees by birds was assessed in a grazinglandscape in southern New South Wales, Australia. Seventy paddock treesites were surveyed for 20 min each in the morning, and 36sites were surveyed again at midday in March 2000. During this time, thepresence and abundance of birds was recorded. Several site and landscapevariables were measured at each site. These included tree species, atree size index, a measure of the crown cover density around the site,and proximity to the nearest woodland patch. During formal surveys, 31bird species, including several woodland species, were observed usingpaddock trees. Data from bird surveys in woodland patches that wereobtained in a separate study in November 1999 were used to comparewhether there was a relationship between the abundance of a given birdspecies in woodland patches and paddock trees. Many birds commonlydetected in woodland patches were also common in paddock trees. However,some birds with special habitat requirements were absent from paddocktrees although they were common in woodland patches. Site occupancypatterns were modelled for several guilds of birds using logisticregression. Foliage-foraging birds were more likely to occupy clumps oftrees and sites with a high tree size index. Nectarivores appeared to bemore likely to be detected at sites more than 200 m fromwoodland, although this result was marginally non-significant(P = 0.08). The probability of detecting granivoreswas higher at sites with a low tree size index. Open country specieswere most likely to occupy large trees and sites that were located morethan 200 m from the nearest woodland patch. The value ofpaddock trees may have been underestimated in the past because a widevariety of bird species use paddock trees on a regular basis. Ensuringthe continued survival of paddock trees should be an important aspect offuture conservation and revegetation efforts.     

Use of Fruiting Trees by Birds in Continuous Forest and Riparian Forest Remnants in Los Tuxtlas,Veracruz, Mexico1

The composition of plant species in fragmented landscapes may be influenced by the pattern of visitation by birds to fruiting trees and by the movement of seeds among and within fragments. We compared bird visitation patterns to two tree species (Dendropanax arboreus, Araliaceae; Bursera simaruba, Burseraceae) in continuous forest and remnants of riparian vegetation in a region dominated by pasture in Los Tuxtlas, Veracruz, Mexico. We quantified frequency of visitation, fruit consumption, consistency of visitation (percentage of total tree observation periods during which a given bird species was recorded), and species composition of birds at individuals of both tree species in continuous forest and riparian remnants. Bird visitation rate, species richness, and fruit consumption rates were similar within both tree species in the two habitats. Species assemblages at D. arboreus were different between continuous forest and remnants. Species assemblages at B. simaruba did not differ by habitat. Our results demonstrate that habitat disturbance may influence avian visitation patterns, which may in turn affect subsequent recruitment patterns in some tree species. Our results, however, were not consistent between the tree species, suggesting that it is difficult to generalize concerning the effects of forest disturbance on avian species assemblages in fruiting trees.     

The Influence of Habitat Variables on Bird Communities in Forest Remnants in Costa Rica

This study examined the effects of forest structure (tree species richness, canopy height, percent canopy cover, understory density, tree density and DBH) and avian species traits (nest type and indicator list status) on the diversity, abundance and dissimilarity of bird communities in forest remnants and reforestation areas adjacent to Costa Rican banana plantations. Bird species richness and abundance were significantly related to tree species richness, canopy height and canopy cover in multiple linear regressions, the latter two forest structure variables being the best statistical predictors. Stratification of analyses by bird species indicator categories improved fits of regressions, because correlations with environmental variables differed in sign for different guilds of birds, a result likely to hold for other avifaunas. Analysis of avifauna dissimilarities among sites demonstrated that the species composition of bird communities was highly correlated with forest structure and tree species composition. Logistic regressions indicated that birds making protected (cavity, burrow, pendant, sphere and covered) nests were 2–6 times more likely to be present in the study avifauna than birds making open (cup, saucer, platform and scrape) nests and indicators of disturbed habitats were 11 times more likely to be present than indicators of primary forest. The forest structure data used were simple and inexpensive to collect, and data on avian traits were drawn from the literature. Thus, these methods could easily be replicated at other locations and would be valuable management aids and biodiversity assessment tools for conservation planning.     

Bird dietary guild richness across latitudes,environments and biogeographic regions

Aim To integrate dietary knowledge and species distributions in order to examine the latitudinal, environmental, and biogeographical variation in the species richness of avian dietary guilds (herbivores, granivores, frugivores, nectarivores, aerial insectivores, terrestrial/arboreal insectivores, carnivores, scavengers, and omnivores). Location Global. Methods We used global breeding range maps and a comprehensive dietary database of all terrestrial bird species to calculate guild species richness for grid cells at 110 × 110 km resolution. We assessed congruence of guild species richness, quantified the steepness of latitudinal gradients and examined the covariation between species richness and climate, topography, habitat diversity and biogeographic history. We evaluated the potential of current environment and biogeographic history to explain global guild distribution and compare observed richness–environment relationships with those derived from random subsets of the global species pool. Results While most guilds (except herbivores and scavengers) showed strong congruence with overall bird richness, covariation in richness between guilds varied markedly. Guilds exhibited different peaks in species richness in geographical and multivariate environmental space, and observed richness–environment relationships mostly differed from random expectations. Latitudinal gradients in species richness were steepest for terrestrial/arboreal insectivores, intermediate for frugivores, granivores and carnivores, and shallower for all other guilds. Actual evapotranspiration emerged as the strongest climatic predictor for frugivores and insectivores, seasonality for nectarivores, and temperature for herbivores and scavengers (with opposite direction of temperature effect). Differences in species richness between biogeographic regions were strongest for frugivores and nectarivores and were evident for nectarivores, omnivores and scavengers when present‐day environment was statistically controlled for. Guild richness–environment relationships also varied between regions. Main conclusions Global associations of bird species richness with environmental and biogeographic variables show pronounced differences between guilds. Geographic patterns of bird diversity might thus result from several processes including evolutionary innovations in dietary preferences and environmental constraints on the distribution and diversification of food resources.     

Assemblage structure and dynamics of terrestrial birds in the southwest Amazon: a camera‐trap case study

Habitat spatial distribution, seasonal variation, and activity patterns influence changes in vertebrate assemblages over time. Terrestrial birds play major roles in the dynamics of tropical forests, but there are few effective methods to study these species due to their cryptic coloration and elusive behavior. We used camera‐trap data collected during 16 mo (February 2017–June 2018) to describe the terrestrial avifauna in southeastern Peru, assess to what extent the composition of terrestrial avifauna changes among seasons and across two major habitats (terra firme and floodplain forests), and determine daily activity patterns of terrestrial birds. We used overlap analyses to examine temporal co‐occurrence between ecologically similar and sympatric species. Camera traps recorded 16 species, including eight species in the family Tinamidae. Capture rates were highest for Pale‐winged Trumpeters (Psophia leucoptera; Psophiidae) and Gray‐fronted Doves (Leptolila rufaxilla; Columbidae). Species composition did not differ between habitats or seasons, and capture rates between habitats only differed for White‐throated Tinamous (Tinamus guttatus). Overlaps of activity patterns were high between ecologically similar species and species found in terra firme habitats (White‐throated Tinamous and Cinereous Tinamous, Crypturellus cinereus) and in both habitat types (Pale‐winged Trumpeters and Gray‐fronted Doves). Low numbers of captures of possibly locally rare or less abundant species hindered a complete analysis of spatial and seasonal patterns of terrestrial bird assemblages. We suggest a greater sampling effort and greater spatial replication to better understand the spatial and seasonal dynamics of the terrestrial avifauna. Further studies that assess the mechanisms that allow the coexistence of sympatric tinamous would be valuable, both in our study area and elsewhere. The use of camera traps in long‐term monitoring projects proved to be an effective tool for monitoring terrestrial birds, identifying cryptic and often rare animals to species level, and providing valuable ecological information at species and community levels.     

Relationships between bird species and tree species assemblages in forested habitats of eastern North America

Aim We examined the relative influence of geographical location, habitat structure (physiognomy), and dominant plant species composition (floristics) on avian habitat relationships over a large spatial extent. Although it has been predicted that avian distributions are more likely to covary with physiognomy than with floristics at coarse scales, we sought to determine, more specifically, whether there remained a significant association between gradients in assemblages of bird species and dominant plant species within a general biome type, after statistically controlling for structural variation and geographical location of sampling sites. Location Our sample consisted of a subset of North American Breeding Bird Census survey sites that covered most of the range of eastern forests, from Florida to Nova Scotia, and west to Minnesota and North Dakota (up to c. 2500 km between sites). Methods We restricted our analyses to the single year (1981) that provided the largest sample of sites (47) for which vegetation data were available within ± 2 years of the avian surveys. We examined the relationship between avian community composition and tree species composition over this series of forested plots. Data were divided into four sets: (1) bird species abundances, (2) tree species abundances, (3) physiognomic or structural variables and (4) geographical location (latitude and longitude). We performed separate detrended correspondence analysis ordinations of birds and trees, before and after statistically partialling out covariation associated with structural variables and geographical location. To gauge the relationship between the two sets of species we correlated site scores resulting from separate ordinations. We also compared continental‐scale patterns of variation in bird and tree assemblages to understand possible mechanisms controlling species distribution at that scale. Results Both bird and tree communities yielded strong gradients, with first‐axis eigenvalues from 0.75 to 0.97. All gradients were relatively long (> 4.0), implying complete turnover in species composition. However, geographical location accounted for < 10% of the total variation associated with any ordination. Prior to partialling out covariation resulting from location and physiognomy, bird species ordinations were strongly correlated with tree species ordinations. The strength of association was reduced after partialling, but one bird and one tree axis remained significantly correlated. There was a significant species–area effect for birds, but not for trees. Main conclusions There was a significant relationship between bird species assemblages and tree species assemblages in the eastern forests of North America. Even after partialling out covariation associated with spatial location and forest physiognomy, there remained a significant correlation between major axes from bird and tree ordinations, consistent with the hypothesis that floristic variation is likely to be important in organizing assemblages of birds within a general biome type, albeit over a much larger spatial extent than originally predicted. Forest tree species ordinations differed from bird species ordinations in several ways: trees had a higher rate of turnover along underlying environmental gradients; trees appeared more patchily distributed than birds at this scale; and tree species were more spaced out along the underlying ecological gradients, with less overlap. By understanding the relationship between bird assemblages and forest floristics, we might better understand how avian communities are likely to change if tree species distributions are altered as a result of climatic changes.     

Bats are Not Birds – Different Responses to Human Land‐use on a Tropical Mountain

Land‐use intensification has consequences for biodiversity and ecosystem functioning, with various taxonomic groups differing widely in their sensitivity. As land‐use intensification alters habitat structure and resource availability, both factors may contribute to explaining differences in animal species diversity. Within the local animal assemblages the flying vertebrates, bats and birds, provide important and partly complementary ecosystem functions. We tested how bats and birds respond to land‐use intensification and compared abundance, species richness, and community composition across a land‐use gradient including forest, traditional agroforests (home garden), coffee plantations and grasslands on Mount Kilimanjaro, Tanzania. Furthermore, we asked how sensitive different habitat and feeding guilds of bats and birds react to land‐use intensification and the associated alterations in vegetation structure and food resource availability. In contrast to our expectations, land‐use intensification had no negative effect on species richness and abundance of all birds and bats. However, some habitat and feeding guilds, in particular forest specialist and frugivorous birds, were highly sensitive to land‐use intensification. Although the habitat guilds of both, birds and bats, depended on a certain degree of vegetation structure, total bat and bird abundance was mediated primarily by the availability of the respective food resources. Even though the highly structured southern slopes of Mount Kilimanjaro are able to maintain diverse bat and bird assemblages, the sensitivity of avian forest specialists against land‐use intensification and the dependence of the bat and bird habitat guilds on a certain vegetation structure demonstrate that conservation plans should place special emphasis on these guilds.     

The impact of cattle grazing regimes on tropical savanna bird assemblages

Globally, agricultural land use is implicated in the decline of avifauna. In rangelands (areas used for livestock grazing), bird community responses to grazing can be complex, species‐specific and scale dependent. A greater understanding of bird responses to grazing will lead to more meaningful management recommendations. We tested the hypothesis that foraging height predicts bird species’ responses to grazing, such that species using lower vegetation strata are most likely to respond to the impacts of livestock grazing. We examined the response of a tropical savanna bird community to four grazing strategies at a long‐term grazing trial in northern Australia. We predicted that ground‐foraging guilds would be more responsive to grazing treatment than foliage‐ or aerial‐foraging guilds. We analysed the bird community assemblage using generalised linear mixed models and examined individual species’ abundance in relation to microhabitat variables. We found that while ground‐foraging guilds were more responsive to grazing treatment, individual species dynamics within a foraging guild could be contradictory. For example, the red‐backed fairy‐wren decreased in abundance with increased grazing and was positively associated with grass and shrub (Carissa ovata) cover, whereas Australian magpies increased in abundance in the most heavily grazed paddocks. In general, the responses of bird species to grazing were more pronounced in guilds that forage closer to the ground, but whether the responses were positive or negative was driven by bird species ecology. Measures examining the responses of individual species are more useful than assemblage measures (such as richness) to describe the impacts of anthropogenic disturbance such as grazing.     

Conservation value for birds of traditionally managed isolated trees in an agricultural landscape of Madagascar

Isolated trees have distinctive economic, social and cultural value for the Betsileo people living on the edge of the protected forest corridor between Ranomafana and Andringitra national parks, in South-East Madagascar. Many of these trees are Ficus spp., traditionally protected and respected. At the landscape level, they are isolated features in a heterogeneous mosaic, providing fruit, shade and aesthetic services in open cultivated areas. Within the current management system, isolated trees may also contribute significantly to the provision of ecological services by enhancing bird diversity in open areas outside the forest. We identified practices and values linked to isolated tree uses and management through ethnographic data collection. Bird presence and abundance were sampled by 338 point counts in isolated trees and open areas of the agricultural mosaic. Isolated trees were occupied by 18 out of 32 (56%) bird species in the agricultural mosaic, including 8 (25%) endemic forest species. Endemic forest birds were significantly more numerous in isolated trees than in open habitats, both in species richness and abundance (mean P value < 0.001). Overall bird species richness was significantly higher in open areas containing isolated trees, than in areas without isolated trees. Bird species richness in Ficus spp. was significantly higher than in other isolated tree species, although no differences were detected in abundance or within guilds. Community-based management of isolated trees may thus represent an opportunity for convergence between bird conservation goals outside protected areas and local management values and practices.     

Forest patch size and isolation as drivers of bird species richness in Maputaland,Mozambique

Aim To examine the response of forest‐dependent and generalist bird assemblages and feeding guilds to patch characteristics of forest fragments in the context of island biogeography and metapopulation theories in an area that supports high levels of species diversity and endemism. Location Dune, riverine, sand and swamp forest fragments in southern Mozambique’s Maputaland. Methods We recorded 20 forest‐dependent and 69 generalist bird species at 220 survey points in 30 forest fragments that ranged in size from 5 to 7432 ha and that were 100 to 5100 m apart. We used linear regressions to relate the number of species to forest fragment size, isolation, perimeter, fractal dimension, shape and core area for frugivores, insectivores, granivores, nectarivores, carnivores and omnivores separately for forest‐dependent and generalist bird assemblages. We tested for modality in occupancy frequency distributions of species in forest fragments and used the binary matrix temperature calculator to determine whether the assemblages had a nested structure separately for forest‐dependent and generalist bird species. Results The number of forest‐dependent and generalist bird species categorized into the feeding guilds varied independently from forest patch parameter values. Occupancy models showed a random distribution for forest‐dependent birds, and generalists had a unimodal distribution. Both the forest‐dependent and generalist bird assemblages had a non‐nested structure. The presence of eight rare forest‐dependent and four endemic bird species in 22 of the 30 fragments contributed to the non‐nested structure of these bird assemblages. Main conclusions Fragmented forests did not induce the expected responses of the forest bird assemblages in that the number of species was not explained by patch characteristics, nor could we find evidence for metapopulation dynamics. Non‐nestedness may be caused by the few rare and endemic species occupying forest fragments with a wide range of patch characteristics. Knowledge of the response of species to forest fragmentation can benefit conservation planning catering for rare and endemic species. Our study suggests that all forest fragments in the region may have to be included in a conservation network to complement existing landscape‐based plans to protect the region.     

A test of pollinator specificity and morphological convergence between nectarivorous birds and rainforest tree flowers in New Guinea

Interactions between flowering trees in a representative sample of vegetation, and the birds that fed at their flowers, were studied for 2 years in lowland tropical hill forest in New Guinea. All 2,200 trees in a 3-ha plot were tagged, identified, mapped, and monitored monthly. Approximately 60% of all individual trees flowered during the study; all species that these flowering individuals belonged to were evaluated for bird visitation. Approximately 13% of the 164 resident species of New Guinea avifauna at the study site, especially honeyeaters and parrots, visited flowers. In the forest inventory plot, approximately 15–22% of all 86 tree species that flowered during the study were visited by birds; most of these tree species were canopy species. Results showed that there was no statistically significant correlation between bird species grouped by bill morphology and flower species grouped as morphotypes and ranked by nectar accessibility, although strong but unexpected bird/plant associations were evident. These associations may be related to variables such as body mass or perch size. These results are discussed in comparison with results from the Neotropics and Australia, and in terms of morphological convergence and pollinator specificity in pollination systems.     

Rapid colonization and turnover of birds in a tropical forest treefall gap

Ecological disturbance is an important factor that influences the abundance and distribution of species. Treefalls are a prominent source of disturbance in tropical forests, but robust characterization of community change after treefalls requires baseline data that are often not available. We capitalized on 25 yr of avian mark–recapture data from a lowland moist forest in central Panama to investigate the timescale of colonization and persistence of birds in a newly formed treefall gap. We compared bird species assemblages pre- and post-treefall to explore how the disturbance affected specific foraging guilds and overall assemblage structure (abundance and alpha diversity). We documented rapid colonization (i.e., within five months post-treefall) of the treefall gap by birds. Abundance and alpha diversity increased following the treefall, but both remained relatively constant in a nearby control plot. At the guild level, frugivores spiked in abundance and nectarivores (i.e., hummingbirds) increased in alpha diversity following the treefall. These results are in agreement with those of previous spatial studies of gap dynamics and suggest that certain tropical frugivores and nectarivores have a remarkable ability to rapidly find and exploit preferred resources and microhabitats embedded in a landscape matrix. Assemblage abundance and alpha diversity decreased back to pre-treefall levels within 1 and 4 yr of the treefall, respectively. Thus, even large gaps may provide only ephemeral benefits, highlighting the importance of periodic disturbance for landscape-level persistence of species that use gaps.     

Avian Habitat Preference in Tropical Forest Restoration in Southern Costa Rica

An important question for tropical forest restoration is whether degraded lands can be actively managed to attract birds. We censused birds and measured vegetation structure at 27 stations in young (6–9‐yr old) actively and passively restored pasture and old growth forest at Las Cruces Biological Station in southern Costa Rica. During 481 10‐min point counts, we detected a high diversity—186 species—of birds using the restoration area. Surprisingly, species richness and detection frequency did not differ among habitats, and proportional similarity of bird assemblages to old growth forest did not differ between restoration treatments. Bird detection frequency was instead explained by exotic grass cover and understory stem density—vegetation structures that were not strongly impacted by active restoration. The similarity of bird assemblages in actively and passively restored forest may be attributed to differential habitat preferences within and among feeding guilds, low structural contrast between treatments, or the effect of nucleation from actively restored plots into passively restored areas. Rapid recovery of vegetation in this recently restored site is likely due to its proximity to old growth forest and the lack of barriers to effective seed dispersal. Previous restoration studies in highly binary environments (i.e., open pasture vs. tree plantation) have found strong differences in bird abundance and richness. Our data contradict this trend, and suggest that tropical restoration ecologists should carefully consider: (1) when the benefits of active restoration outweigh the cost of implementation; and (2) which avian guilds should be used to measure restoration success given differential responses to habitat structure.     

Changes in desert avifauna associated with the functional extinction of a terrestrial top predator

We investigated how long‐term suppression of populations of a top predator, the dingo Canis dingo, affected composition of sympatric avifauna in Australian deserts, by surveying bird assemblages across ~80 000 km² of arid dune‐fields on either side of the Dingo Barrier Fence (DBF; a 5614 km‐long fence separating ecosystems in which dingoes are abundant from ecosystems in which dingoes are functionally extinct). Using fourth‐corner modelling, incorporating species’ traits, we identified apparent declines of sedentary birds that nest in low vegetation and small birds that feed primarily on grass seed, and increases in scavenging birds associated with the functional extinction of dingoes. Occupancy differed between sites inside and outside the DBF in 13 bird species. We hypothesise that these differences in bird assemblages across the DBF result, in part, from increases in kangaroos Macropus spp. and red foxes Vulpes vulpes in arid landscapes where dingoes have been removed. Our study provides evidence that the functional extinction of a large terrestrial predator has had pervasive ecosystem effects, including shifts in composition of avian assemblages.     

Covariation of flower traits and bird pollinator assemblages among populations of Kniphofia linearifolia (Asphodelaceae)

Globally, bird-pollinated plants can be separated into two groups, one consisting of species pollinated by specialist nectarivores, and the other of plants pollinated by occasional nectarivores. There are marked differences in nectar properties among the two groups, implying that there has been pollinator-mediated selection on these traits. This raises the possibility that variation in bird assemblages among populations of a plant species could lead to the evolution of intraspecific variation in floral traits. We examined this hypothesis in Kniphofia linearifolia, a common and widespread plant in southern Africa. Although bees are common visitors to flowers of this species, exclusion of birds from inflorescences led to significant reductions in seed set, indicating that the species is primarily bird-pollinated. We showed that bird pollinator assemblages differ markedly between five different populations of K. linearifolia, and that variation in flower morphology and nectar properties between these populations are associated with the dominant guild of bird visitors at each population. We identified two distinct morphotypes, based on corolla length, nectar volume and nectar concentration, which reflect the bird assemblages found in each type. Further work is needed to establish if a natural geographic mosaic of bird assemblages are the ultimate cause of differentiation in floral traits in this species.