Paula Lidia Enríquez

Human disturbance to nesting raptors can influence breeding success, especially during early breeding. This study examined the impact of researcher presence, a relatively low impact human disturbance, on eastern barn owls Tyto javanica javanica during monitoring of 57 nest‐boxes in oil palm plantations in Malaysia over a period of 30 months. We analysed the impact of number of researcher visits on breeding success of barn owls, and recorded the immediate response of barn owls to researcher presence, namely nest‐box return times. We investigated the influence of potential variables (number of visits, visit frequency, breeding stage, habitat, study site, etc.) on barn owl nest survival using a logistic‐exposure model. Additionally, we explored the influence of female return times on hatching success using generalized linear models (GLMs) and used generalized linear mixed models (GLMMs) to analyse variables influencing female return times. A total of 108 breeding attempts were recorded in this study and we found that researcher visits, specifically frequency of visits, had a significant effect on nest survival of barn owls, especially during the incubating stage. Breeding female barn owls showed moderate individual variability in return times, and had shorter return times in mature habitats and when incubating. Longer nest‐box return times also influenced hatching success and we recorded several cases of immediate predation on eggs and young in nests after females were flushed from nest‐boxes by researcher visits. We recommend that researcher presence be minimized with lower frequency and shorter duration of researcher presence during incubation to encourage higher breeding success in barn owls. We also recommend that nest‐box checks be conducted at dusk to ensure nests are not left unattended for extended periods.

Ecological studies on tropical raptors are limited, even for common species such as some vultures. This study analyzed the altitudinal distribution and abundance of four species — Black Vulture Coragyps atratus , Turkey Vulture Cathartes aura , Lesser Yellow-headed Vulture C. burrovianus and King Vulture Sarcoramphus papa — in Chiapas, Mexico. Records were obtained from various bird surveys conducted between 2003 and 2015, which followed transects of 2 to 3 kilometers. A total of 693 sampling points were used for this analysis, and records for each species were grouped based on the presence of more or fewer than 100 individuals at three altitudinal gradients (0–300 m, 300–1,400 m, and 1,400–3,000 m a.s.l.). Black and Turkey Vultures were found across all three altitudinal levels, with greater abundance at lower elevations. Lesser Yellow-headed Vultures were found only at lower elevations, while King Vultures were more prevalent at mid-elevations and less common at higher elevations. Long-term studies using standardized methodologies are needed in tropical regions to understand temporal and spatial variations in the distribution and abundance of these vultures, as they depend on the unpredictable and scarce availability of food.

Metals and metalloids are among the pollutants of greatest concern worldwide due to their damage to human and environmental health. Organisms such as birds are exposed to these contaminants. Mercury (Hg), lead (Pb), and arsenic (As) concentrations were analyzed in feather samples (n = 241) of five species of birds from southern Mexico (1937–2006) from scientific collections. Feathers concentrations showed relatively high concentrations of As > Hg > Pb, exceeding toxicity thresholds in birds. Carnivore species had the highest concentrations of As (x̄ 44.42 ± 6.34 SE μg/g), while the concentrations of insectivore and omnivorous species ranged from 5.71 ± 0.66 μg/g to 9.24 ± 1.03 μg/g. Temporal trends for metals and As showed the highest concentrations in the 1930s and 1960s. Mercury and As showed a significant annual increase in the 1930s and 2006. An increase in Pb concentrations was observed before 1937 and a decrease after 1979 until 2006. Some temporary trends in metals and As were similar to local and global emissions caused by forest fires, mining activities, fertilizers in agricultural practices, and the termination of the use of Pb as a petrol additive. Knowledge about metals and As was generated at sites that are currently protected natural areas and cultural historical areas. Anthropogenic activities prior to their declaration of protection and transboundary pollution may be potential sources of contaminants at these sites. The first baseline of the spatio-temporal trend in toxic element concentrations was established in five species for future research.

The spatial configuration and management of agricultural and other land‐use practices can affect ecological assemblages. However, the differences in how resident and migratory birds respond to land‐use are remain unclear, hindering our understanding of bird biodiversity responses to land use. In a tropical moist broadleaf forest landscape of southeastern Mexico, we assessed alpha, beta, and functional diversity as indicators of ecosystem functioning in resident and migratory birds across landscape‐ and habitat‐level gradients, incorporating distance to a protected area, understory vegetation cover, and three land uses: 1) primary forest, 2) secondary forest, and 3) cattle pasture. Compositionally, resident and migratory bird assemblages exhibited similar gradual shifts across land uses. However, while resident bird richness steadily declined with increasing distance from a protected area and simplification of understory vegetation structure, migratory bird richness did not change. Relative to primary forest bird assemblages, we found that migratory bird abundances were greater in secondary forest and cattle pasture, and migratory insectivores compensated for 68% of the abundance losses of resident insectivores in secondary forest and cattle pasture. Among these insectivores in secondary forest and cattle pasture, increases in migratory birds compensated for the abundance declines of resident birds that utilize foliage gleaning and sallying foraging methods. Our findings emphasize the importance of evaluating and managing landscapes around protected areas, highlight the distinct responses of resident and migratory birds to land use, and reveal the mechanisms that sustain ecosystem functions in modified landscapes.

The spatial configuration and management of agricultural and other land-use practices can affect ecological assemblages, but how resident and migratory species respond to land uses is not well known, hindering our understanding of the effects of land use on biodiversity. Here, we compare alpha and beta diversity and ecosystem functioning for resident and migratory birds across three land uses: (1) primary forest, (2) secondary forest, and (3) cattle pasture. Compositionally, resident bird assemblages exhibited gradual shifts across habitats with diversity steadily declining with increasing distance from a protected area and reductions in understory vegetation. In contrast, migratory bird community composition clustered into five distinct groups, shifting 50-60% less than resident assemblages across the same gradients with no declines in richness. We found that migratory bird abundance was greater in secondary forest and cattle pasture, and migratory insectivores compensated for 68% of the abundance losses of resident forest insectivores in secondary forests and cattle pastures. Among the insectivores, increases of migratory birds in secondary forest and cattle pasture compensated for the abundance declines of resident birds that utilize foliage gleaning and sallying foraging methods. Our findings underscore the importance of local landscape evaluation and management around protected areas, highlighting the unique responses of resident and migratory birds to land use and the potential mechanisms sustaining ecosystem functions in modified habitats.

Protected areas are of paramount relevance to conserving wildlife and ecosystem contributions to people. Yet, their conservation success is increasingly threatened by human activities including habitat loss, climate change, pollution, and species overexploitation. Thus, understanding the underlying and proximate drivers of anthropogenic threats is urgently needed to improve protected areas’ effectiveness, especially in the biodiversity-rich tropics. We addressed this issue by analyzing expert-provided data on long-term biodiversity change (last three decades) over 14 biosphere reserves from the Mesoamerican Biodiversity Hotspot. Using multivariate analyses and structural equation modeling, we tested the influence of major socioeconomic drivers (demographic, economic, and political factors), spatial indicators of human activities (agriculture expansion and road extension), and forest landscape modifications (forest loss and isolation) as drivers of biodiversity change. We uncovered a significant proliferation of disturbance-tolerant guilds and the loss or decline of disturbance-sensitive guilds within reserves causing a “winner and loser” species replacement over time. Guild change was directly related to forest spatial changes promoted by the expansion of agriculture and roads within reserves. High human population density and low nonfarming occupation were identified as the main underlying drivers of biodiversity change. Our findings suggest that to mitigate anthropogenic threats to biodiversity within biosphere reserves, fostering human population well-being via sustainable, nonfarming livelihood opportunities around reserves is imperative.