Deforestation Simplifies Understory Bird Seed-Dispersal Networks in Human-Modified Landscapes

Global biodiversity is threatened by land-use changes through human activities. This is mainly due to the conversion of continuous forests into forest fragments surrounded by anthropogenic matrices. In general, sensitive species are lost while species adapted to disturbances succeed in altered environments. However, whether the interactions performed by the persisting species are also modified, and how it scales up to the network level throughout the landscape are virtually unknown in most tropical hotspots of biodiversity. Here we evaluated how landscape predictors (forest cover, total core area, edge density, inter-patch isolation) and local characteristics (fruit availability, vegetation complexity) affected understory birds seed-dispersal networks in 19 forest fragments along the hyperdiverse but highly depauperate northeast distribution of the Brazilian Atlantic Forest. Also, our sampled sites were distributed in two regions with contrasting land cover changes. We used mist nets to obtain samples of understory bird food contents to identify the plant species consumed and dispersed by them. We estimated network complexity on the basis of the number of interactions, links per species, interaction evenness, and modularity. Our findings showed that the number of interactions increased with the amount of forest cover, and it was significantly lower in the more deforested region. None of the other evaluated parameters were affected by any other landscape or local predictors. We also observed a lack of significant network structure compared to null models, which we attribute to a pervasive impoverishment of bird and plant communities in these highly modified landscapes. Our results demonstrate the importance of forest cover not only to maintain species diversity but also their respective mutualistic relationships, which are the bases for ecosystem functionality, forest regeneration and the provision of ecological services.

Community characteristics of forest understory birds along an elevational gradient in the Horn of Africa: A multi-year baseline

Tropical mountains are global hotspots for birdlife. However, there is a dearth of baseline avifaunal data along elevational gradients, particularly in Africa, limiting our ability to observe and assess changes over time in tropical montane avian communities. In this study, we undertook a multi-year assessment of understory birds along a 1,750 m elevational gradient (1,430–3,186 m) in an Afrotropical moist evergreen montane forest within Ethiopia’s Bale Mountains. Analyzing 6 years of systematic bird-banding data from 5 sites, we describe the patterns of species richness, abundance, community composition, and demographic rates over space and time. We found bimodal patterns in observed and estimated species richness across the elevational gradient (peaking at 1,430 and 2,388 m), although no sites reached asymptotic species richness throughout the study. Species turnover was high across the gradient, though forested sites at mid-elevations resembled each other in species composition. We found significant variation across sites in bird abundance in some of the dietary and habitat guilds. However, we did not find any significant trends in species richness or guild abundances over time. For the majority of analyzed species, capture rates did not change over time and there were no changes in species’ mean elevations. Population growth rates, recruitment rates, and apparent survival rates averaged 1.02, 0.52, and 0.51 respectively, and there were no elevational patterns in demographic rates. This study establishes a multi-year baseline for Afrotropical birds along an elevational gradient in an under-studied international biodiversity hotspot. These data will be critical in assessing the long-term responses of tropical montane birdlife to climate change and habitat degradation.

Comparing morphological traits of legs of understory birds inhabiting forest areas with closed canopies and forest gaps

Siri S, Ponpituk Y, Safoowong M, Nuipakdee W, Marod D, Duangkae P. 2020. Comparing morphological traits of legs of understory birds inhabiting forest areas with closed canopies and forest gaps. Biodiversitas 21: 1041-1048. Bird species exhibit different adaptations depending on their habitats. The morphological traits of each species represent adaptations that are impacted by environmental changes. We conducted a 3-year study from 2015 to 2017 to compare the leg morphology of understory birds that occur under closed canopies and in forest gaps in a hill evergreen forest in northern Thailand, with gaps in the natural forest representing forest disturbances. We captured 64 bird species over the study period and measured 11 leg morphological features for each individual. Ground-foraging birds were generally long-legged and climbing birds generally short-legged. Understory species living in dense forest areas were significantly associated with long claws, toes, and tibiae, whereas species occurring in gaps and open areas tended to have shorter leg structures. Results from classification tree analysis revealed that digit claw length is the most important trait for predicting which habitat a species is most likely to occupy. Our findings suggest that understory birds with long leg structures that live under closed canopies are most vulnerable to forest disturbances or the conversion of forests to large-scale open areas.