Multiple Lineages of Avian Malaria Parasites (Plasmodium) in the Galapagos Islands and Evidence for Arrival via Migratory Birds

Haemosporidian parasites in the genus Plasmodium were recently detected through molecular screening in the Galapagos Penguin (Spheniscus mendiculus). We summarized results of an archipelago‐wide screen of 3726 endemic birds representing 22 species for Plasmodium spp. through a combination of molecular and microscopy techniques. Three additional Plasmodium lineages were present in Galapagos. Lineage A–infected penguins, Yellow Warblers (Setophaga petechia aureola), and one Medium Ground Finch (Geospiza fortis) was detected at multiple sites in multiple years. The other 3 lineages were each detected at one site and at one time; apparently, they were transient infections of parasites not established on the archipelago. No gametocytes were found in blood smears of infected individuals; thus, endemic Galapagos birds may be dead‐end hosts for these Plasmodium lineages. Determining when and how parasites and pathogens arrive in Galapagos is key to developing conservation strategies to prevent and mitigate the effects of introduced diseases. To assess the potential for Plasmodium parasites to arrive via migratory birds, we analyzed blood samples from 438 North American breeding Bobolinks (Dolichonyx oryzivorus), the only songbird that regularly migrates through Galapagos. Two of the ephemeral Plasmodium lineages (B and C) found in Galapagos birds matched parasite sequences from Bobolinks. Although this is not confirmation that Bobolinks are responsible for introducing these lineages, evidence points to higher potential arrival rates of avian pathogens than previously thought. Linajes Múltiples de Parásitos de Malaria Aviar (Plasmodium) en las Islas Galápagos y Evidencia de su Arribo por Medio de Aves Migratorias     

A Risk-Assessment System for Screening Out Invasive Pest Plants from Hawaii and Other Pacific Islands

Abstract:  Ecosystems of Hawaii and other Pacific Islands have been greatly affected by invasive pest plants, and ongoing, deliberate plant introductions make it likely that additional pest plants will become established. We tested the ability of a modified version of the Australian and New Zealand weed risk-assessment system to identify pest plants in Hawaii and other Pacific Islands. We used information taken from outside Hawaii to predict the behavior—"pest" or "not a pest"—of almost 200 plant species introduced to Hawaii and other Pacific Islands. The screening system initially recommended further evaluation of 24% of these species, but an additional secondary screening was applied to this group, thereby reducing the rate of indecision to only 8%. To independently test the accuracy of the screening system, we compared its decisions—pest or not a pest—to opinions of 25 expert botanists and weed scientists who had substantial field experience in Hawaii or other Pacific Islands. We asked the experts to rate each species as "major pest,""minor pest," or "not a pest" in native or managed ecosystems. The screening system correctly identified 95% of major pests and 85% of nonpests. Among minor pests identified by the experts, 33% were classified as nonpests by the screening system. Use of the screening system to assess proposed plant introductions to Hawaii or other Pacific Islands and to identify high-risk species used in horticulture and forestry would greatly reduce future pest-plant problems and allow entry of most nonpests. The screening process is objective, rapid, and cost-efficient. With minor modifications, it is likely to be useful in many parts of the world.     

Variation with Land Use of Immune Function and Prevalence of Avian Pox in Galapagos Finches

Introduced disease has been implicated in recent wildlife extinctions and population declines worldwide. Both anthropogenic‐induced change and natural environmental features can affect pathogen spread. Furthermore, environmental disturbance can result in changes in stress physiology, nutrition, and social structure, which in turn can suppress immune system function. However, it remains unknown whether landscape variation results in heterogeneity in host resistance to pathogens. Avian pox virus, a pathogen implicated in avian declines and extinctions in Hawaii, was introduced to the Galapagos in the 1890s, and prevalence (total number of current infections) has increased recently in finches. We tested whether prevalence and recovery trends in 7 species of Galapagos finches varied by elevation or human land use. To do so, we used infection data obtained from 545 wild‐caught birds. In addition, we determined whether annual changes in 4 aspects of innate immune function (complement protein activity, natural antibody activity, concentration of PIT54 protein, and heterophil:lymphocyte ratio) varied by elevation or land use. Prevalence and recovery rates did not vary by elevation from 2008 to 2009. Avian pox prevalence and proportion of recovered individuals in undeveloped and urban areas did not change from 2008 to 2009. In agricultural areas, avian pox prevalence increased 8‐fold (from 2% to 17% of 234 individuals sampled) and proportion of recovered individuals increased (11% to 19%) from 2008 to 2009. These results suggest high disease‐related mortality. Variation in immune function across human land‐use types correlated with variation in both increased prevalence and susceptibility, which indicates changes in innate immune function may underlie changes in disease susceptibility. Our results suggest anthropogenic disturbance, in particular agricultural practices, may underlie immunological changes in host species that themselves contribute to pathogen emergence. Variación con el Uso de Suelo de la Función Inmune y la Prevalencia de la Varicela Aviar en Pinzones de las Galápagos     

Recovery of the Kakerori: An Endangered Forest Bird of the Cook Islands

The Kakerori, or Rarotonga Flycatcher (Pomarea dimidiata) , is an endangered monarch flycatcher endemic to the island of Rarotonga, Cook Islands. This bird was reported to be common until the middle of the nineteenth century, but it declined before 1885 and was thought to be extinct early this century. A small population persisted in the rugged interior of Rarotonga; in 1987 the population stood at 38 birds but was in decline. We determined that introduced predators, especially ship rats (Rattus rattus) , were affecting breeding success. Through a program of experimental management, aimed mainly at rodent control, the population increased from a low of 29 birds in Spring 1989 to 60 birds in Spring 1993. The recovery can be attributed to both improved breeding success and increased adult survivorship.     

Activity patterns of giant petrels, Macronectes spp., using different foraging strategies

We studied foraging activity of giant petrels during the incubation period, by simultaneously deploying activity recorders and satellite transmitters on northern (Macronectes halli) and southern giant petrels (Macronectes giganteus) at Bird Island (South Georgia, Antarctica) between 29 October and 26 December 1998. Satellite tracking showed two types of trips: (1) coastal trips, all undertaken by male northern giant petrels, to the nearby South Georgia mainland, presumably foraging on seal and penguin carcasses on beaches, and (2) pelagic trips, foraging at sea for marine prey or potentially scavenging on distant archipelagos (e.g. South Sandwich, Falkland or South Orkney Islands). Activity recorder data were consistent with the types of trip defined by the satellite tracking data, with median wet activity (time spent at the sea surface) during pelagic trips being 41%, but only 14% on coastal trips. On pelagic trips, there was a significant negative correlation between the duration of wet periods and the speed of travel between satellite uplinks. Mean travelling speed between uplinks was greater during day than night for both types of trips, suggesting that giant petrels prefer to travel during daylight and are less active at night. The scarcity of wet periods during the night in giant petrels foraging to the South Georgia coast (median=3%, range=1-9%) indicates that such birds spent almost all night on land. Likewise, the scarcity of wet periods at night for three birds foraging 700-1,000 km south of Bird Island, where there is no land but abundant icebergs, suggests these birds were resting on the icebergs at night. In addition to the adaptations to scavenging on carrion, pelagic trips by giant petrels contain elements similar to those of albatrosses, indicating a complexity to giant petrel lifestyle hitherto unrecognised.     

Vivid birds respond more to acoustic signals of predators

Because conspicuous morphology such as colorful plumage may increase predation risk, we aimed to see if variation in plumage coloration could explain variation in avian anti-predator behavior. We included several measures of plumage coloration: human perception of vividness from images in field guides, total intensity from reflectance spectra of museum skins, contrasts calculated from physiological models of these spectra parameterized for both raptors and humans, chroma, and spectral saturation. We investigated how well these measurements predicted risk assessment in ten species of birds in St. John, U.S. Virgin Islands. We quantified how each species responded to playbacks of a predator’s calls and compared this response to that elicited by songs from a non-predatory, sympatric bird. We found that human-determined measures of vividness best predicted anti-predator responses of birds—more vividly colored species responded more to predators than duller species. No spectrophotometric variable explained variation in species reactions to a predator call. Our results suggest that vivid birds may compensate for their conspicuousness by being more responsive to the sound of predators and that more work is needed to better evaluate how animal coloration is quantified in comparative studies.     

内蒙古包头民航机场及周边地区鸟类组成及生态分布

2006年8月-2007年7月,对包头机场周边7km范围内的鸟类组成及生态分布进行了调查,共记录到鸟类153种,分属16目39科。其中留鸟31种,夏候鸟67种,旅鸟47种,冬候鸟8种。该地区繁殖鸟(包括留鸟和夏候鸟)有98种,占调查区鸟类总数的64.05%,其中北方型种类有81种,占繁殖鸟总数的82.65%,表现出明显的古北界鸟类区系特征。调查区分为湿地、林地、草地、农田、居民区、山地、跑道与停机坪7种生境类型,对各生境中鸟类进行了分析。     

Impact of Invasive Cane Toads on Australian Birds

Abstract: The cane toad (Bufo marinus), a large, toxic, American anuran, was introduced to Australia in 1935. Populations of many of Australia's reptiles (snakes, varanid lizards, crocodiles) and carnivorous mammals (dasyurid marsupials) have declined because these predators are killed by the toad's powerful toxins. In contrast to these well‐studied species, little is known about the cane toads impacts on Australian birds. We reviewed published and unpublished data on behavioral interactions between Australian avian predators and cane toads and collated distributional and dietary information to identify avian taxa potentially at risk from cane toad invasion. Cane toads are sympatric with 172 frog‐eating bird species in Australia, and an additional 8 bird species overlap with the predicted future range of the toad. Although many bird species thus are potentially at risk, behavioral observations suggest the risk level is generally low. Despite occasional reports of Australian birds being killed when they ingest cane toads, most birds either ignore toads or survive the predation event. The apparently higher tolerance of Australian birds to toad toxins, compared with Australian reptiles and marsupials, may reflect genetic exchange between Australian birds and Asian populations that encounter other bufonid species regularly and hence have evolved the capacity to recognize or tolerate this toxic prey.     

Introduced Birds and the Fate of Hawaiian Rainforests

Abstract:  The Hawaiian Islands have lost nearly all their native seed dispersers, but have gained many frugivorous birds and fleshy-fruited plants through introductions. Introduced birds may not only aid invasions of exotic plants but also may be the sole dispersers of native plants. We assessed seed dispersal at the ecotone between native- and exotic-dominated forests and quantified bird diets, seed rain from defecated seeds, and plant distributions. Introduced birds were the primary dispersers of native seeds into exotic-dominated forests, which may have enabled six native understory plant species to become reestablished. Some native plant species are now as common in exotic forest understory as they are in native forest. Introduced birds also dispersed seeds of two exotic plants into native forest, but dispersal was localized or establishment minimal. Seed rain of bird-dispersed seeds was extensive in both forests, totaling 724 seeds of 9 native species and 2 exotics with over 85% of the seeds coming from native plants. Without suitable native dispersers, most common understory plants in Hawaiian rainforests now depend on introduced birds for dispersal, and these introduced species may actually facilitate perpetuation, and perhaps in some cases restoration, of native forests. We emphasize, however, that restoration of native forests by seed dispersal from introduced birds, as seen in this study, depends on the existence of native forests to provide a source of seeds and protection from the effects of ungulates. Our results further suggest that aggressive control of patches of non-native plants within otherwise native-dominated forests may be an important and effective conservation strategy.     

The malaria parasite Plasmodium relictum in the endemic avifauna of eastern Cuba

Island populations are vulnerable to introduced pathogens, as evidenced by extinction or population decline of several endemic Hawaiian birds caused by the malaria parasite, Plasmodium relictum (order Haemosporida). We analyzed blood samples from 363 birds caught near Guantánamo Bay, Cuba, for the presence of haemosporidian infections. We characterized parasite lineages by determining nucleotide variation of the parasite's mitochondrial cyt b gene. Fifty‐nine individuals were infected, and we identified 7 lineages of haemosporidian parasites. Fifty individuals were infected by 6 Haemoproteus sp. lineages, including a newly characterized lineage of Haem. (Parahaemoproteus) sp. CUH01. Nine individuals carried the P. relictum lineage GRW4, including 5 endemic Cuban Grassquits (Tiaris canorus) and 1 migratory Cape May Warbler (Setophaga tigrina). A sequence of the merozoite surface protein gene from one Cuban Grassquit infected with GRW4 matched that of the Hawaiian haplotype Pr9. Our results indicate that resident and migratory Cuban birds are infected with a malaria lineage that has severely affected populations of several endemic Hawaiian birds. We suggest GRW4 may be associated with the lack of several bird species on Cuba that are ubiquitous elsewhere in the West Indies. From the standpoint of avian conservation in the Caribbean Basin, it will be important to determine the distribution of haemosporidian parasites, especially P. relictum GRW4, in Cuba as well as the pathogenicity of this lineage in species that occur and are absent from Cuba.     

Human Impacts on Regional Avian Diversity and Abundance

Abstract: Patterns of association between humans and biodiversity typically show positive, negative, or negative quadratic relationships and can be described by 3 hypotheses: biologically rich areas that support high human population densities co‐occur with areas of high biodiversity (productivity); biodiversity decreases monotonically with increasing human activities (ecosystem stress); and biodiversity peaks at intermediate levels of human influence (intermediate disturbance). To test these hypotheses, we compared anthropogenic land cover and housing units, as indices of human influence, with bird species richness and abundance across the Midwestern United States. We modeled richness of native birds with 12 candidate models of land cover and housing to evaluate the empirical evidence. To assess which species were responsible for observed variation in richness, we repeated our model‐selection analysis with relative abundance of each native species as the response and then asked whether natural‐history traits were associated with positive, negative, or mixed responses. Native avian richness was highest where anthropogenic land cover was lowest and housing units were intermediate based on model‐averaged predictions among a confidence set of candidate models. Eighty‐three of 132 species showed some pattern of association with our measures of human influence. Of these species approximately 40% were negatively associated, approximately 6% were positively associated, and approximately 7% showed evidence of an intermediate relationship with human influence measures. Natural‐history traits were not closely related to the direction of the relationship between abundance and human influence. Nevertheless, pooling species that exhibited any relationship with human influence and comparing them with unrelated species indicated they were significantly smaller, nested closer to the ground, had shorter incubation and fledging times, and tended to be altricial. Our results support the ecosystem‐stress hypothesis for the majority of individual species and for overall species diversity when focusing on anthropogenic land cover. Nevertheless, the great variability in housing units across the land‐cover gradient indicates that an intermediate‐disturbance relationship is also supported. Our findings suggest preemptive conservation action should be taken, whereby areas with little anthropogenic land cover are given conservation priority. Nevertheless, conservation action should not be limited to pristine landscapes because our results showed that native avian richness and the relative abundance of many species peaked at intermediate housing densities and levels of anthropogenic land cover.     

Spatial and Seasonal Patterns of Bird Communities in Italian Agroecosystems

Abstract:  Despite agricultural landscapes covering almost 60% of the total land area of Italy, knowledge of the effects of agriculture and its intensification on bird communities is still scarce. I analyzed the effects of land uses on bird diversity and community structure in different farmland habitats of lowland northwestern Italy. I surveyed breeding and overwintering birds with a hierarchically nested sampling design and used generalized linear and mixed models to investigate the relationships between the diversity and abundance of birds and habitat or landscapes attributes. The effects of agriculture on α avian diversity varied with season and spatial scale, whereas nonagricultural habitats (long-term fallows or woodlands) had a generally positive effect that was constant throughout time and space. As the amount of woodland habitat increased, spatial turnover (β diversity) of breeding birds decreased. Arable landscapes supported low levels of avian diversity throughout the year but were favored by emblematic farmland birds that have declined severely in Europe and in the study area. Farmland birds (40% of which are experiencing population declines) were more abundant or foraged more frequently in the less-disturbed habitat types such as fallows, grasslands, and winter stubbles and tended to avoid the prevailing cultivations (maize, vineyard, and wheat). Landscape simplification, the expansion of maize cultivation, winter plowing practices, and the conversion of highly diverse grasslands to tilled lands are likely to be responsible for the local decline of most farmland species (Skylark [Alauda arvensis ], Starling [Sturnus vulgaris ], buntings [Emberiza spp.], and wagtails [Motacilla spp.]) and for the increase of birds that are turning into agricultural pests (Hooded Crow [Corvus corone cornix ]).     

Black Rats, Island Characteristics, and Colonial Nesting Birds in the Mediterranean: Consequences of an Ancient Introduction

Abstract: The devastation of island faunas by alien species has been instrumental in raising concerns about the global threat to biological diversity. Colonial nesting species, often restricted to islands, have been affected severely. Eradication of introduced species as a means to alleviate the problem is usually done with little or no understanding of the mechanisms governing interactions between introduced and native species. Such an understanding could help target management action. We analyzed how island area, rock substrate, bird species biology, and presence of an introduced species, the black rat (   Rattus rattus ), interact to explain the distribution and abundance of colonial nesting birds on a set of 72 islands from six archipelagos in the western Mediterranean. Rats were introduced to this region over 2000 years ago, and these communities have had time to reach an equilibrium. Using general linear models, we show that rats have affected species distributions more on the smaller islands and on islands with an acidic or neutral rock substrate; larger bird species are more resistant. On the smaller islands, where rat densities are highest, larger colonial birds are negatively affected. On larger islands, where rat densities are lower and fluctuate form year to year, larger colonial birds can maintain healthy populations despite the presence of rats. Although rats caused local extinction or reduction in bird abundance, the presence of islands varying in size and/or substrate allowed most archipelagos to retain their suite of colonial nesting bird species, despite a presumably reduced abundance for most species.     

Avian Diversity and Functional Insectivory on North-Central Florida Farmlands

Abstract:  We studied the potential for native birds to control insect pests on farms. We assessed habitat factors correlated with diversity, distribution, and insect-foraging activity of native birds on farms in north-central Florida and then characterized common bird species that consumed insect biomass in crops as "functional insectivores" (birds most likely to contribute to pest control). Analyses of point-count survey data and foraging observations collected over 2 years on paired organic and conventional farm sites indicated that (1) farms supported most (82–96%) land birds known to breed in the region; (2) bird species richness and abundance varied significantly with matrix habitat and field border type (but not with year or farm management type); (3) the highest bird abundances were associated with mixed crop plantings, field borders, and adjacent matrix composed of forest and hedge; and (4) abundances of 10 species identified as functional insectivores were primarily influenced by crop type (mixed crops attracted significantly more insect foragers into fields than monocrops). We documented birds eating pest insects in crops and did not observe substantive crop damage by birds during growing-season observations. We advocate use of the term functional insectivore to emphasize the potential positive role of avian insectivory on farms during the growing season.     

Evaluating the Predicted Local Extinction of a Once-Common Mouse

Abstract:  In an earlier paper ( Pergams & Nyberg 2001 ) we found that the proportion of the prairie deer mouse ( Peromyscus maniculatus bairdii ), among all local Peromyscus museum specimens collected in the Chicago region, had significantly declined over time. This proportion changed from about 50% before 1900 to <10% in the last 25 years. Based on this proportion a regression model predicted the local extinction of the prairie deer mouse in 2009. To evaluate that prediction, we estimated current deer mouse abundance by live trapping small mammals at 15 preserves in Cook and Lake counties, Illinois (USA) at which prairie deer mice had previously been caught or that still contained their preferred open habitat. In 1900 trap nights, 477 mammals were caught, including 251 white-footed mice ( P. leucopus ), but only one prairie deer mouse. The observed proportion of Peromyscus that were prairie deer mice, 0.4%, was even lower than the 4.5% predicted for 2000. Here we also introduce a simple, new community proportions model, which for any given geographic region compares the proportions of species recently caught with the proportions of species in museums. We compared proportions of seven species collected in Cook and Lake counties and examined by Hoffmeister (1989) with proportions of these species that we caught. Ten percent of the museum community was prairie deer mice, but only 0.2% of our catch was. The current local scarcity of the prairie deer mouse is consistent with the regression-based prediction of its eminent local extinction. More conservation attention should be paid to changes in relative abundance of once-common species.     

Long-Term Population Changes of Native and Introduced Birds in the Alaka'i Swamp, Kaua'i

Abstract:  Within the last 30 years, five endemic bird species of the Alaka'i Swamp, Kaua'i, Hawai'i, have likely gone extinct. We documented population trends of the remaining avifauna in this time period to identify a common pattern in the Hawaiian Islands: decline of native species and expansion of introduced species. We conducted bird surveys over 100 km² of the Alaka'i and Kōke'e regions of Kaua'i in March–April 2000 to estimate population size, distribution, and range limits of seven native and six introduced forest birds. We compared the results with four previous surveys conducted over the last 30 years. Five of the seven native species we studied have fared well, maintaining sizeable populations (>20,000 individuals) and unchanged or increasing numbers. The endemic 'Akikiki ( Oreomystis bairdi ), however, declined from 6296 (SE ± 1374) to 1472 (SE ± 680) individuals and exhibited range contraction from 88 to 36 km². The 'I'iwi ( Vestiaria coccinea ) also experienced a decline and contraction, though not as severe. Populations of several introduced forest birds are increasing, but all species, excluding the Japanese White-eye ( Zosterops japonicus ), were at low numbers (<5,500 individuals in survey area). One introduced species, the Japanese Bush-Warbler ( Cettia diphone ) recently invaded, whereas another, the Red-billed Leiothrix ( Leiothrix lutea ), has been extirpated. Two hurricanes in the past 20 years appear to have most strongly affected nectarivores and may have contributed to the decline or extinction of several other species. Overall, native bird populations on Kaua'i have exhibited species-specific responses to limiting factors. Although most native populations appear stable, the extant native avifauna is vulnerable as a result of limited distributions and the potential for widespread habitat degradation.     

Establishment Success across Convergent Mediterranean Ecosystems: an Analysis of Bird Introductions

Abstract:  Concern over the impact of invaders on biodiversity and on the functioning of ecosystems has generated a rising tide of comparative analyses aiming to unveil the factors that shape the success of introduced species across different regions. One limitation of these studies is that they often compare geographically rather than ecologically defined regions. We propose an approach that can help address this limitation: comparison of invasions across convergent ecosystems that share similar climates. We compared avian invasions in five convergent mediterranean climate systems around the globe. Based on a database of 180 introductions representing 121 avian species, we found that the proportion of bird species successfully established was high in all mediterranean systems (more than 40% for all five regions). Species differed in their likelihood to become established, although success was not higher for those originating from mediterranean systems than for those from nonmediterranean regions. Controlling for this taxonomic effect with generalized linear mixed models, species introduced into mediterranean islands did not show higher establishment success than those introduced to the mainland. Susceptibility to avian invaders, however, differed substantially among the different mediterranean regions. The probability that a species will become established was highest in the Mediterranean Basin and lowest in mediterranean Australia and the South African Cape. Our results suggest that many of the birds recently introduced into mediterranean systems, and especially into the Mediterranean Basin, have a high potential to establish self-sustaining populations. This finding has important implications for conservation in these biologically diverse hotspots.     

Value of protected areas to avian persistence across 20 years of climate and land-use change

Establishing protected areas, where human activities and land cover changes are restricted, is among the most widely used strategies for biodiversity conservation. This practice is based on the assumption that protected areas buffer species from processes that drive extinction. However, protected areas can maintain biodiversity in the face of climate change and subsequent shifts in distributions have been questioned. We evaluated the degree to which protected areas influenced colonization and extinction patterns of 97 avian species over 20 years in the northeastern United States. We fitted single-visit dynamic occupancy models to data from Breeding Bird Atlases to quantify the magnitude of the effect of drivers of local colonization and extinction (e.g., climate, land cover, and amount of protected area) in heterogeneous landscapes that varied in the amount of area under protection. Colonization and extinction probabilities improved as the amount of protected area increased, but these effects were conditional on landscape context and species characteristics. In this forest-dominated region, benefits of additional land protection were greatest when both forest cover in a grid square and amount of protected area in neighboring grid squares were low. Effects did not vary with species’ migratory habit or conservation status. Increasing the amounts of land protection benefitted the range margins species but not the core range species. The greatest improvements in colonization and extinction rates accrued for forest birds relative to open-habitat or generalist species. Overall, protected areas stemmed extinction more than they promoted colonization. Our results indicate that land protection remains a viable conservation strategy despite changing habitat and climate, as protected areas both reduce the risk of local extinction and facilitate movement into new areas. Our findings suggest conservation in the face of climate change favors creation of new protected areas over enlarging existing ones as the optimal strategy to reduce extinction and provide stepping stones for the greatest number of species.     

Songbird Use of Gallery Woodlands in Recently Cleared and Older Settled Landscapes of the Selva Lacandona, Chiapas, Mexico

Many regions of Central America have undergone wide-scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern México. Two study areas were established on lands that had been cleared and settled 20–35 and 10 years previously. Our objectives were to assess the value of arroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance of songbirds in cleared areas settled at different times over a 35-year period. Arroyo vegetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest-dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation are protected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land-use practices currently in use.     

Species richness patterns along environmental gradients in island land molluscan fauna

The relationship between species richness and environmental variables may change depending on habitat structure, dispersal ability, species mixing, and community adaptation to the environment. It is crucial to know how these factors regulate the environment-diversity relationship. The land molluscan fauna of the Ogasawara Islands in the West Pacific is an excellent model system to address this question because of the high species endemicity (> 90%), small area, and simple habitat structure of the islands. I examined relationships among indigenous species composition, richness, and habitat condition, and especially productivity and forest moisture on the island of Anijima. Two major communities of snails could be distinguished by detrended correspondence analysis (DCA): one group dominated in a moist habitat with high productivity, and the other group dominated in a dry habitat with low productivity. However, species richness became highest at the intermediate condition between the habitats in which the two snail communities were dominant, so that species richness showed a hump-shaped relationship with moisture and productivity. In contrast, the species richness of the snail community in the moist habitat showed a monotonically positive correlation, and that in the dry habitat showed a monotonically negative correlation with moisture and productivity. Thus, the greater species richness in intermediate moisture and productivity resulted from the ecotone effect or community overlap at the transitional areas, where faunas with different ecologies can meet in a single site. These findings suggest that hump-shaped productivity-diversity relationships in land Mollusca would reflect the ecotone effect as a result of the mixing of species adapted to either fertile habitats or sterile habitats.