High Bird Species Diversity in Structurally Heterogeneous Farmland in Western Kenya

Tropical ecosystems are globally important for bird diversity. In many tropical regions, land‐use intensification has caused conversion of natural forests into human‐modified habitats, such as secondary forests and heterogeneous agricultural landscapes. Despite previous research, the distribution of bird communities in these forest‐farmland mosaics is not well understood. To achieve a comprehensive understanding of bird diversity and community turnover in a human‐modified Kenyan landscape, we recorded bird communities at 20 sites covering the complete habitat gradient from forest (near natural forest, secondary forest) to farmland (subsistence farmland, sugarcane plantation) using point counts and distance sampling. Bird density and species richness were on average higher in farmland than in forest habitats. Within forest and farmland, bird density and species richness increased with vegetation structural diversity, i.e., were higher in near natural than in secondary forest and in subsistence farmland than in sugarcane plantations. Bird communities in forest and farmland habitats were very distinct and very few forest specialists occurred in farmland habitats. Moreover, insectivorous bird species declined in farmland habitats whereas carnivores and herbivores increased. Our study confirms that tropical farmlands can hardly accommodate forest specialist species. Contrary to most previous studies, our findings show that structurally rich tropical farmlands hold a surprisingly rich and distinct bird community that is threatened by conversion of subsistence farmland into sugarcane plantations. We conclude that conservation strategies in the tropics must go beyond rain forest protection and should integrate structurally heterogeneous agroecosystems into conservation plans that aim at maintaining the diverse bird communities of tropical forest‐farmland mosaics.     

面向鸟鸣声识别任务的深度学习技术

在生态系统中,鸟类是重要的组成部分,对调节生态环境和监测生物多样性至关重要,甚至可以通过监测鸟群动向与监听鸟群异常鸣声对地震、海啸等自然灾害进行辅助预测和防范,为此,鸟鸣声识别和异常鸣声监测成为热门的研究方向。然而,由于传统鸟鸣声识别方法存在特征提取不充分等问题,导致识别率不高。本文采用融合特征的方法结合深度学习技术提取鸟鸣声特征,融合特征选择改良后的对数梅尔谱差分参数同原始信号参数拼接所得的特征;深度学习方法是基于Dense Net121网络结构,并融入自注意力模块与中心损失函数进行鸟鸣声识别。自注意力模块部分提高了关键通道的特征表达能力;中心损失函数可解决类内特征不紧凑问题。我们通过消融实验对比验证,对在Xeno-Canto世界野生鸟类声音公开数据集上选取的10种鸟类声音进行识别,准确率达到96.9%。代码已开源至Github:https://github.com/Carrie X6/-Xeno-Canto-.git。     

Predation by the hoopoe (Upupa epops) on pupae of Thaumetopoea pityocampa and the likelyinfluence on other natural enemies

The hoopoe (Upupa epops L.) is an insectivorousbird often preying on larvae and pupae of the pineprocessionary caterpillar (Thaumetopoeapityocampa Denis & Schiffermüller), the mostimportant defoliator of pines in Southern Europe andNorthern Africa. The first half of the breeding seasonof this migratory bird coincides with the pupal stageof the insect. Bird predation of pupae was quantifiedin two years in a Pinus nigra stand of northernItaly by periodic counting of the empty cocoons lefton the soil surface after extraction. The predationrate, estimated on 20 pupation sites representing thewhole stand, was 74.1% in 1993 and 68.3% in 1994.Predation was higher in the upper part of the soil andthen progressively decreased with increasing depth.The hoopoe may also prey on cocoons containing pupaeinfected by pathogenic fungi or parasitoids. Anexclosure experiment showed that the bird mayinterfere with these other mortality factors. Threepupal parasitoids, the ichneumonids Erigorgusfemorator Aubert and Coelichneumon rudis (Boyerde Fonscolombe) and the pteromalid Conomoriumpityocampae Graham, were significantly less frequentin the exposed sites. The fungus Beauveriabassiana (Balsamo) Vuillemin and the most abundantpupal parasitoid, Villa brunnea Becker (Diptera:Bombyliidae), caused the highest pupal mortality atboth protected and exposed sites. The bird seems to bean incompletely additive mortality factor acting onthe pest and it can also alter the relativemortalities imposed by the other natural enemies.     

Digit ratios, secondary sexual characters and condition in barn swallows Hirundo rustica

The second and fourth digit length ratio (2D:4D) is sexuallydimorphic in many vertebrates. This ratio has been suggestedto provide an estimate of steroid levels encountered duringprenatal development, which may have organizational consequencesfor physiology and behavior of adults. However, recent studiesshowed that the relation between digit ratio and steroids seemsinconsistent and may vary among species and populations. Wetested the hypothesis that digit ratios would be correlatedwith the expression of secondary sexual characters, using thebarn swallow (Hirundo rustica) as a model system. This was doneby testing whether variation in 2D:4D ratio was correlated withtail length and features of song, which are important secondarysexual characters positively correlated with circulating steroidconcentration in adult birds. Furthermore, we examined the predictionthat male and female digit ratios would correlate with bodymass in an antagonistic way. There was no significant sexualdimorphism in digit ratio, which may be due to low levels ofsexual selection in this population. Adult right 2D:4D ratiowas negatively linked to tail length but not to male song output.Moreover, right 2D:4D ratio was negatively correlated with bodymass in male and positively in females. These results are consistentwith high digit ratios reflecting low levels of testosteronein this bird species.     

Habitat Structure Affects Reproductive Success of the Rare Endemic Tree Syzygium mamillatum (Myrtaceae) in Restored and Unrestored Sites in Mauritius

Invasive alien plants affect the functioning of ecosystems by altering plant–animal interactions, such as pollination, which may impede natural regeneration of native plant species. In Mauritius, we studied the reproductive traits and pollination ecology of the rare endemic cauliflorous tree Syzygium mamillatum in a restored forest (all alien plant species removed) and an adjacent unrestored area (degraded by alien plants). Flowers of S. mamillatum were only visited by generalist bird species. Although the initial number of flower buds per tree in the restored forest tended to be higher than that of trees in the unrestored area, final fruit set and the number of seeds per fruit were lower in the restored forest. This corresponded with lower bird visitation rates in the restored area. Additionally, during budding stage, most trees were severely attacked by lepidopteran larvae, and bud loss through herbivory was higher in the restored forest. Thus, the difference in reproductive performance of S. mamillatum between the two localities was caused by contrasting herbivore attack and bird visitation behavior in restored and unrestored areas. Our findings illustrate the importance of restoration efforts in mimicking the original physical structure of habitats and interaction structure of interspecific relationships, and the difficulty of doing so given the imperfect knowledge and the reality that many native species have become locally extinct and replaced by exotic species.     

Bird community composition across an Andean tree‐line ecotone

Few studies have found strong evidence to suggest that ecotones promote species richness and diversity. In this study we examine the responses of a high‐Andean bird community to changes in vegetation and topographical characteristics across an Andean tree‐line ecotone and adjacent cloud forest and puna grassland vegetation in southern Peru. Over a 6‐month period, birds and vegetation were surveyed using a 100 m fixed‐width Distance Sampling point count method. Vegetation analyses revealed that the tree‐line ecotone represented a distinctive high‐Andean vegetation community that was easily differentiated from the adjacent cloud forest and puna grassland based on changes in tree‐size characteristics and vegetation cover. Bird community composition was strongly seasonal and influenced by a pool of bird species from a wider elevational gradient. There were also clear differences in bird community measures between tree‐line vegetation, cloud forest and puna grassland with species turnover (β‐diversity) most pronounced at the tree‐line. Canonical Correspondence Analysis revealed that the majority of the 81 bird species were associated with tree‐line vegetation. Categorizing patterns of relative abundance of the 42 most common species revealed that the tree‐line ecotone was composed primarily of cloud forest specialists and habitat generalists, with very few species from the puna grassland. Only two species, Thlypopsis ruficeps and Anairetes parulus, both widespread Andean species more typical of montane woodland vegetation edges, were categorized as ecotone specialists. However, our findings were influenced by significant differences in species detectability between all three vegetation communities. Our study highlights the importance of examining ecotones at an appropriate spatial and temporal scale. Selecting a suitable distance between sampling points based on the detection probabilities of the target bird species is essential to obtain an unbiased picture of how ecotones influence avian richness and diversity.     

A place to land: spatiotemporal drivers of stopover habitat use by migrating birds

Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been integrated with passage to understand the factors that determine where and when birds stopover during spring and autumn migration. Here, we introduce the stopover‐to‐passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south‐eastern US, the most prominent corridor for North America’s migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat function and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds.     

An integrated population model sheds light on the complex population dynamics of a unique colonial breeder

Climate models forecast increasing climatic variation and more extreme events, which could increase the variability in animal demographic rates. More variable demographic rates generally lead to lower population growth and can be detrimental to wild populations, especially if the particular demographic rates affected are those to which population growth is most sensitive. We investigated the population dynamics of a metapopulation of 25 colonies of a semi-arid bird species, the sociable weaver Philetairus socius, and how it was influenced by seasonal weather during 1993–2014. We constructed an integrated population model which estimated population sizes similar to observed population counts, and allowed us to estimate annual fecundity and recruitment. Variance in fecundity contributed most to variance in population growth, which showed no trend over time. No weather variables explained overall demographic variation at the population level. However, a separate analysis of the largest colony showed a clear decline with a high extinction probability (0.05 to 0.33) within 5 years after the study period. In this colony, juvenile survival was lower when summers were hot, and adult survival was lower when winters were cold. Rainfall was also negatively correlated with adult survival. These weather effects could be due to increased physiological demands of thermoregulation and rainfall-induced breeding activity. Our results suggest that the dynamics of the population on the whole are buffered against current weather variation, as individual colonies apparently react in different ways. However, if more and increasingly extreme weather events synchronize colony dynamics, they are likely to have negative effects.     

Selective predation favouring cryptic individuals of marine snails (Littorina)

Many gastropods have inherited conspicuous shell colour polymorphisms. A challenging question is, are colour frequencies under selection or is polymorphism owing to random evolutionary processes? The intertidal species Littorina saxatilis (a rock‐dweller) and L. obtusata (confined to macroalgae) both have genetically determined shell colour variation. In Iceland, Littorina obtusata are mostly cryptic on brown macroalgae by having brown or yellow shells (~95% of the snails), while Littorina saxatilis often appears conspicuous to the background of dark rocks owing to non‐cryptic colours (15–20%). This difference may be due to selective elimination of conspicuously coloured L. obtusata by visual predators, while L. saxatilis, largely living in another habitat, is not under a similarly intense colour selection. To test this hypothesis we increased the frequencies of conspicuous L. saxatilis in experimental populations (from <12 to 55%) and placed these in the seaweed zone, the main habitat of L. obtusata. Fifteen populations were released on isolated spots of seaweed and three of these were covered by net cages to exclude bird predators. One month later, yellow snails had increased in frequency within the patches, and to our surprise the result did not differ between bare and caged patches. This suggests selection favouring a colour that matches the background of fucoid seaweeds by visual predators able to enter the cages. Birds acted as important predators by picking 16% of the experimental snails in the uncaged spots, but were unable to enter the caged spots. However, the bird predation was non‐selective with respect to snail colour. For various reasons the most likely predators able to enter the cages were intertidal fish, these were thus responsible for the selection of non‐cryptic snails. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 137–144.