Effects of forest fragmentation on genetic variation in endemic understory forest birds in central Madagascar

Summary This study focuses on some genetic consequences of habitat fragmentation in populations of four endemic bird species (Monticola sharpei, Terpsiphone mutata, Foudia omissa, andFoudia madagascariensis) living in the understory of forests in the Réserve Spéciale d'Ambohitantely on the Central High Plateau of Madagascar. The four species differ in their dependency on forest habitats, which may be related to their migration abilities between isolated forest fragments. Genetic variation was analysed on the basis of multi-locus fingerprints in order to study the influence of migration and habitat size on the genetic variability of local populations. There was no evidence that forest fragmentation affects any of the four species with respect to genetic variability.

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Effekte von Waldfragmentation auf die genetische Variabilität endemischer Vogelarten in Zentral-Madagaskar

Zusammenfassung Rund 53 % der Vogelarten Madagaskars sind endemisch. Viele dieser Arten sind an Waldhabitate gebunden und durch die Verinselung der madagassischen Wälder hochgradig bedroht. In dem vorliegenden Projekt wird die Auswirkung der Verinselung auf die genetische Variabilität und die genetische Differenzierung von vier endemischen Vogelarten am Beispiel des Reservats von Ambohitantely im zentralen Hochland Madagaskars untersucht. Ambohitantely beinhaltet mehr als 500 Waldfragmente von 0,64 ha bis 1250 ha. Untersucht wurden: 1. die WaldartFoudia omissa, 2.Monticola (früherPseudocossyphus)sharpei, eine Art mit starker Bevorzugung für primäre Waldlebensräume, die aber gelegentlich auch in Sekundärvegetation auftritt, sowie 3.Terpsiphone mutata und 4.Foudia madagascariensis, beides Arten, die sowohl in Wäldern als auch in offenen Landschaften vorkommen. Die unterschiedliche Abhängigkeit dieser Arten von Waldhabitaten und der damit verbundenen Möglichkeit, offene Landschaften zwischen den Waldfragmenten zu überbrücken, führte zur Frage, ob die Verinselung die genetische Vielfalt der untersuchten Populationen beeinflußt. Für die genetischen Analysen wurden Blutproben von Tieren aus drei Gebieten mit 1250 ha, 136 ha und 28 ha gesammelt. Die Proben wurden mit Multilocus-Fingerprints genetisch charakterisiert. Zum Untersuchungszeitpunkt konnte kein Einfluß der Fragmentierung auf die genetische Populationsstruktur der vier untersuchten Arten nachgewiesen werden.

     

Nesting success of native and introduced forest birds on the island of Kaua‘i

Forests of the Hawaiian archipelago are a global hotspot for conserving avian diversity and contain among the world's most imperiled species. Demographic studies are necessary to determine primary causes of Hawaiian forest bird population declines. We conducted research on the nesting success of multiple bird families on the island of Kaua‘i, allowing us to investigate the importance of factors related to breeding biology on forest bird declines at a community scale. Our study included two Hawaiian honeycreepers, ‘anianiau Magumma parva and ‘apapane Himatione sanguinea, a native monarch flycatcher, Kaua‘i ‘elepaio Chasiempis sclateri, and one introduced species, Japanese white‐eye Zosterops japonicus. Data from 123 nests showed that nesting success ± SE, estimated using program MARK, was low for ‘apapane (0.23 ± 0.10), but did not vary substantially among our other study species (‘anianiau = 0.56 ± 0.09, Kaua‘i ‘elepaio = 0.63 ± 0.08, Japanese white‐eye = 0.52 ± 0.11). Causes of nest loss for 51 nest failures included nest predation (43%), unknown (25%), empty after termination with no signs of nest predation (e.g. eggshell or chick remains in nest, disheveled nest) (24%), and abandoned clutch or brood (4% each). Kaua‘i ‘elepaio suffered more than twice as many nest losses to predation compared to our other study species, but also had the highest nesting success; and, ‘apapane suffered least to nest predation, but had the lowest nesting success. Further, rates of nesting success derived in our study were relatively high compared to multi‐species studies in mainland tropics. Therefore, although nest predation accounted for the greatest proportion of nest failures, it may not be a cause of forest bird population declines in our system. We suggest that future demographic studies focus on post‐fledgling, juvenile, and adult survival, in addition to the importance of double‐brooding and renesting attempts on annual reproductive success.     

Sources of variation in the nesting success of understory tropical birds

Survival of offspring is a key fitness component and, for birds, the threat of predation on nests is especially influential. Data on rates of nest success from tropical regions are comparatively few, conservation‐relevant, and essential for assessing the validity of models comparing the life histories and behavior or birds across latitudinal gradients. We monitored over 2 000 nests in the lowland forests of central Panama and, using the logistic exposure to model the fate of nests, explored the importance of variation in rate of nest success according to type of nest, height of nests, among years, in early versus late nests, and at different stages of the nest cycle. Analyses of over 1 400 nests for 18 species revealed considerable variation among species in the daily survival rate of nests (range among 18 species=0.91 to 0.98), but nest type and stage of the nesting cycle were generally influential on the probability of nest success. Cavity or enclosed nesters experienced greater nest success than open cup nesters and rates of nest loss were generally greatest in the nestling stage. We found limited evidence that height of nests affected probability of success, but no indication that timing of nesting effort was influential. Despite the occurrence of a severe ENSO event during our sampling, annual variation in nest success was not consistent among species. Interspecific variation in the rates and patterns of nest predation in our study, coupled with reports of high rates of nest loss at temperate latitudes, lead us to question long standing assumptions about latitudinal trends in rates of nest loss. We urge further work to understand the implications of nest predation on the evolutionary ecology of tropical birds.     

Nesting bird species in sun coffee, pasture, and understory forest in southern Costa Rica

We investigated avian nest distribution and success in understoryforest, sun coffee plantations, and pasture in southern Costa Rica. Nestsearching occurred in plantations and forest in 1999 and 2000 and in pastures in2000. Nests were monitored until they failed or fledged young. Antbirds(Thamnophilidae) were the most common understory forest nesters and were notfound nesting in the plantations or pastures. Common nesting species in theplantations included Turdidae, Tyrannidae, Cardinalidae, and Thraupidae, many ofwhich are typical of forest edge/canopy or open, scrubby habitats. Two speciesassociated with forest interior, Henicorhina leucostictaand Buarremon brunneinucha, were found nesting in theplantations. Pastures supported similar types of nesting species as theplantations, with the exception of the forest-interior species. Daily mortalityrates (DMRs) for above-ground cup-nesting species in plantations and pastureswere similar to those for species nesting in forest at our site and a site inPanama. The results indicate that conversion from forest to pastures and suncoffee plantations diminishes nesting habitat for forest-interior species, whilenumerous forest edge/canopy species and open-country species are able to nest inthese agricultural land-cover types. As a group, species nesting in theplantations and pastures do not have unusually high nest mortality rates,although species-specific studies are lacking. Nesting species distributionsacross habitat types and DMRs at our study site may be influenced by the largeamount of forest in the landscape.     

Spatial distribution of understory fruit-eating birds and fruiting plants in a neotropical lowland wet forest

Spatial distribution of fruit-eating birds and fruiting shrubs of the Melastomataceae and Rubiaceae were examined on a 10 ha plot in tropical lowland wet forest of Costa Rica. Many plant species and most birds exhibited considerable spatial variation in their occurrence on the plot, as indicated by the distribution patterns of shrubs with ripe fruits and captures in mist nets, respectively. In many cases, captures of fruit-eating birds were correlated with abundance of fruiting plants, particularly for species that rely heavily on fruits. In general, fruit-eating birds concentrated their use of the plot to areas rich in fruiting shrubs. This differential use of certain areas likely results in differential visitation to fruiting plants located in these areas and in a heterogeneous dissemination of seeds into the habitat.     

Influence of forest structure on density and nest success of mature forest birds in managed landscapes

Managing for forest wildlife requires attention not only to quantity but quality of forests within the landscape. We examined the extent to which local structural attributes and landscape context of forest stands explained variation in density and reproductive success of mature forest birds across 12 sites in southeast Ohio, USA, 2004–2006. Results suggest that several structural characteristics influenced bird–habitat relationships in our study. Densities of 3 songbird species (i.e., ovenbird [Seiurus aurocapilla], cerulean warbler [Setophaga cerulea], and scarlet tanager [Piranga olivacea]) were positively related to canopy openness, which is usually a function of canopy gaps. Habitat attributes described by ground litter, understory density, and canopy height were positively associated with densities of ground (i.e., worm-eating warbler [Helmitheros vermivorum]), or shrub nesting species (i.e., Kentucky and hooded warblers [Geothlypis formosa and Setophaga citrina], respectively). Furthermore, the number of small trees likely drove the positive relationship between density of wood thrush (Hylocichla mustelina), a subcanopy nester. After accounting for temporal variability in daily nest survival rates, the odds of nest survival for all species increased 10.5% for every 1% increase in canopy openness and decreased 1.4% for each 5% increase in understory vegetation density. Habitat–nest survival relationships were not apparent at the level of the individual species. Our results suggest that structural attributes produced by increasing habitat heterogeneity may be necessary for conservation of forest bird communities. © 2012 The Wildlife Society.     

Nesting characteristics of mourning doves in central New Mexico: Response to riparian forest change

Riparian forests of the American Southwest are especially prone to changes in composition and structure due to natural and anthropogenic factors. To determine how breeding mourning doves (Zenaida macroura) respond to these changes, we examined nest site use and nest survival in control plots, fuel reduction plots before and after mechanical thinning, and post-wildfire sites. The greatest number of nests (50%) were located in post-wildfire sites where resprouted vegetation and woody debris provided numerous nest sites in the understory. We found fewer nests in post-treatment fuel reduction plots (17%), where most were constructed in cottonwoods, and an intermediate number of nests in control and pre-treatment plots (33%), where most were constructed in exotic plants. The best-supported logistic-exposure nest survival model indicated that survival varied among years and with date. Models containing effects of forest type, study block, and nest site selection received little support, suggesting that survival was constant among plot locations, disturbance types, and nest sites. Our nest survival estimates were low relative to those from other studies, but productivity could offset mortality if adults make numerous nest attempts each year. Our results highlight the utility of woody vegetation and debris as understory nest sites for mourning doves and other riparian birds. Managers should devise methods to preserve or reestablish these nest sites when conducting fuel reduction, exotic vegetation removal, or post-fire restoration activities. © 2011 The Wildlife Society.     

Nesting behavior and breeding success of Hoatzins

ABSTRACT.   Hoatzins ( Opisthocomus hoazin ) are the only member of the family Opisthocomidae and are found only in forests in the Amazon and Orinoco river basin of South America. Although locally common in riparian habitats, information about their natural history is based almost exclusively on observations from gallery forests in the "llanos" (savannahs) of Venezuela. We investigated the nesting activities of Hoatzins in a primary rainforest in Amazonian Ecuador from 1995 to 2000. At our study site, Hoatzins live and breed in the inundated forests that surround lakes and river channels. Egg laying occurred from February to July and from September to November, but always peaked in April, May, and June. The mean clutch size was 2.4 ± 1.1 eggs ( N = 291; range = 1–7), but 51% of all clutches contained two eggs. The mean duration of the incubation period was 32 ± 1.5 d ( N = 20) and, overall, 17% of Hoatzin nests fledged at least one young. The main cause of nest failure was predation, with birds and snakes being the most frequent predators. Hoatzin reproduction was closely linked to the rainy season, and such timing may be influenced by increased food availability (high water levels cause leaf fall and the subsequent growth of new leaves coincides with the beginning of the feeding period of the young) and reduced risk of nest predation by mammalian predators when water levels are high. Our results indicate that the breeding biology of Hoatzins in tropical rainforest habitat, including small clutch sizes and low annual reproductive success, is similar to that of tropical passerines and provides further support for the existence of typical life history characteristics for tropical birds.     

Bird-habitat associations predict population trends in central European forest and farmland birds

Recent studies show differences in population trends between groups of species occupying different habitats. In Czech birds, as well as in many other European countries, populations of forest species have increased, whereas populations of farmland species have declined. The aim of our study was to test whether population trends of particular species were related to finer bird-habitat associations within farmland and forest birds. We assessed bird-habitat associations using canonical correspondence analysis based on data from a 400 km long transect across the Czech Republic. We calculated population trends of 62 bird species using log-linear models based on data from a large-scale annual monitoring scheme, which covers the time series from 1982 to 2005. Within forest birds, species with a closer association with lowland broad-leaved forest have had more positive population trends, whereas species with a closer association with montane and coniferous forest revealed more negative population trends. We attribute these opposite trends to the gradual replacement of coniferous forests by deciduous ones, which took place in the Czech Republic during recent decades. Our analyses revealed a hump-shaped relationship within farmland birds, species most closely associated with farmland habitat revealing the most negative trends, whereas species with intermediate association to farmland habitat showed the most positive population trends. Such a pattern can be explained by the abandonment of previously cultivated areas followed by the spread of unmanaged meadows and scrubland. Changes in quantity or quality of preferred habitats may thus represent major drivers of observed bird population changes.     

Seedling interactions in a tropical forest in Panama

Competition is believed to be a central force limiting local diversity and controlling the structure of plant communities. However, it has been proposed that the stressed understory environment limits total understory plant density to such low levels that competitive exclusion cannot be an important factor limiting the local diversity of understory plants. To evaluate the importance of inter-seedling competition, we performed a seedling competition experiment with five shade-tolerant species in a tropical moist forest in Panama. Three-month-old seedlings were transplanted into the forest singly or with their roots intertwined with a single conspecific or heterospecific seedling in all pairwise species combinations. If competition is important, performance (survival, stem height, and number of leaves after one and six years) would be expected to be lowest with a conspecific neighbor and greatest without a neighbor. The experiment was replicated in five 0.24-m² plots at each of 20 sites in tall secondary forest. To test whether seedling performance differed among treatments we fitted linear mixed models (LMM) and generalized linear mixed models (GLMM), treating species identity and microsite (site and plot) as random effects. The five shade-tolerant study species all experienced good establishment with relatively high survival and growth rates. The neighbor treatment consistently affected seedling performance, but the effect was always very small, both in absolute terms and relative to the much stronger species and microsite effects. Seedlings with a conspecific neighbor consistently performed worse than seedlings with a heterospecific neighbor, but having no neighbor generally did not cause superior performance relative to the other treatments. We conclude that direct competitive interactions are relatively unimportant among understory plants in humid tropical forests.     

Diversity of understory birds in old stands of native and Eucalyptus plantations

We compared the vegetation structure between old (>70 year) stands of planted diversified native forests and stands of Eucalyptus tereticornis embedded in a mosaic of Eucalyptus stands. We then tested for differences in the abundance, species richness, species composition, and ecological traits (forest dependence, sensitivity to forest fragmentation, and diet) of the understory bird assemblages inhabiting both kinds of stands. We expected differences in the structure of the bird assemblages because of the different origins and management strategies (contrary to native stands, Eucalyptus stands were selectively logged in the past). Three stands of each habitat (native and Eucalyptus) were sampled with mist nets during 11 months. Eucalyptus stands had a denser understory, whereas native plantations had a more developed vertical structure and a greater density of native trees. The abundance distribution of bird species was more homogeneous in Eucalyptus than in native stands. Eucalyptus had slightly higher species richness (36 species) than native stands (32 species). The composition of species and the occurrence of the diet, forest dependence, and sensitivity to forest fragmentation categories were similar between habitats. Some bird species (e.g. Turdus leucomelas), however, were more abundant in one habitat over the other. Old stands of Eucalyptus and planted native forest can harbor a diverse bird community similar in structure but not exactly equivalent for individual bird species. Planting native diversified forests and keeping set‐aside stands of the exotic tree should be viewed as complementary rather than alternative strategies for maintaining bird diversity within plantations.     

Genetic similarity and hatching success in birds

The ecological correlates of fitness costs of genetic similarity in free-living, large populations of organisms are poorly understood. Using a dataset of genetic similarity as reflected by band-sharing coefficients of minisatellites, we show that bird species with higher genetic similarity experience elevated hatching failure of eggs, increasing by a factor of six across 99 species. Island distributions and cooperative breeding systems in particular were associated with elevated genetic similarity. These findings provide comparative evidence of detrimental fitness consequences of high genetic similarity across a wide range of species, and help to identify ecological factors potentially associated with increased risk of extinction.     

Behavioural flexibility and invasion success in birds

Behavioural flexibility has long been thought to provide advantages for animals when they invade novel environments. This hypothesis has recently received empirical support in a study of avian species introduced to New Zealand, but it remains to be determined whether behavioural flexibility is a general mechanism influencing invasion success. In this study, we examined introduction success of 69 bird species in different regions of the world as a function of their degree of behavioural flexibility. Specifically, we predicted that species with relatively large brains and a high frequency of foraging innovations in their area of origin should show a higher probability of establishing themselves where they were introduced than species with small brains and low innovation frequencies. An analysis with general linear modelling (GLM) supported the prediction for relative brain size, even when controlling for phylogenetic biases and potential confounding variables. The only covariates that remained with relative brain size were plumage dimorphism, human commensalism and nest site. A pairwise comparison of closely related species also revealed that successful invaders showed a higher frequency of foraging innovations in their region of origin. This result held even when differences in research effort between species were considered. Overall, the results confirm and generalize the hypothesis that behavioural flexibility is a major determinant of invasion success in birds.     

Annual cycles in Jamaican forest birds

The annual cycles of forest birds in Jamaica were found to be very similar to those at higher latitudes. Most species bred between March and September, though a few possibly breed throughout the year, especially in cultivated areas. Primary moult followed immediately after breeding, and in some species was apparently arrested to allow a further breeding attempt. Several species were fatter outside the breeding season than during it, and this is interpreted as "winter fattening" comparable to that found in many birds at higher latitudes. Weights varied little but individuals retrapped were usually heavier outside the breeding season. In some species the first complete moult took place at the end of the first year, implying that the birds do not breed until at least two years old.     

Nesting success and within-season breeding dispersal in the Orange-breasted Sunbird Anthobaphes violacea

Nest predation is a primary cause of nesting mortality for many bird species, particularly passerines. Nest location can affect predation, and it has also been demonstrated that predation risk can alter nest site selection. Birds can limit predation risk by selecting specific habitat characteristics; by changing nest site characteristics between attempts; and by dispersing between nesting events. Here we report breeding data from a population of Orange-breasted Sunbirds Anthobaphes violacea (L.), for a single breeding season in the Jonkershoek Nature Reserve, South Africa. Neither shrub type nor nest height was found to affect the outcome of a nest. For subsequent breeding attempts, birds were not more likely to change the type of shrub in which they nested after a predation event than when the attempt was successful, nor did they change the height of their nest. However, we found that the distance between a nest and the subsequent one was significantly shorter after a successful nest than after an unsuccessful one. We interpret this as an adaptive strategy to avoid predation.     

Changes in the understory of Canadian southern boreal forest after fire

Abstract. We investigated changes in the composition and abundance of understory species after fire in the southern boreal forest around Lake Duparquet, Québec. Ten plots of 100 m² were sampled in each of eight sites varying in post-fire age from 26 to 230 yr, with 20 1-m² quadrats in each of these 80 plots. Variation in the understory was described by DCA ordination and interpreted as a regeneration succession series. Thickness of the organic layers, stand age and canopy composition were all correlated with vegetational change. This change was not constant throughout succession; some old sites showed an increase in the diversity and abundance of certain pioneer species. This was partly related to openings in the canopy resulting from a major outbreak of spruce budworm, which affected sites dominated by Abies balsamea. The ordinations were performed on both the 100-m² plots and the 1-m² quadrats. Heterogeneity within sites was larger at the 1-m² scale and there was a great deal of overlap in the position of the quadrats in ordination space. At the smaller scale of analysis, stand age and thickness of the organic layers were not correlated with the changes observed in the understory.     

林下植被的生物量分布特征及其作用

林下植被是森林生态系统的重要组成部分。研究林下植被的生物量特征及其生态作用对深入研究森林生态系统结构和功能有重要意义。本文归纳了森林林下植被的生物量分布特征与森林的类型、龄级和林分特征等因子之间的变化关系,分析了林下植被在维持森林生态系统营养元素循环、保持水土、指示森林环境状态变化、影响森林林分的生理生态特征和森林演替、保护动物的栖息地以及维持生态平衡等方面的主要生态作用。