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In May and June 2024, a die-off of Mexican mantled howler monkeys (Alouatta palliata mexicana) occurred in southern Mexico. This commentary documents the event, attributing it to extreme heatwaves, drought, wildfires, and habitat impoverishment. Despite their reported resilience to habitat disturbances, mantled howler monkey mortality rate in some areas reached 31%. Key evidence points to heatstroke as the primary cause of death, exacerbated by limited hydration and reduced dietary diversity in disturbed habitats. Immediate responses included community-led rescues (e.g., hydrating the monkeys), coordination of rescue activities by nongovernmental organizations (NGOs) (e.g., managing donations), involvement of scientists (e.g., monitoring of primate populations), and assistance from government officials (e.g., providing legal support for animal management). This event underscores the urgency of developing action plans to prevent and attend future crises. Among other actions, we highlight (i) establishing primate care infrastructure with medical and rehabilitation centers; (ii) developing protocols and training programs to ensure rapid crisis response; (iii) fostering collaboration among government, NGOs, and academic institutions for effective crisis management; and (iv) developing targeted research on climate change impacts, predictive models, and long-term health monitoring. We emphasize the critical need for coordinated conservation efforts to protect wild primates and maintain natural ecosystem resilience in the face of escalating climate challenges.

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Ecological niche modeling is used to estimate species distributions based on occurrence records and environmental variables, but it seldom includes explicit biotic or historical factors that are important in determining the distribution of species. Expert knowledge can provide additional valuable information regarding ecological or historical attributes of species, but the influence of integrating this information in the modeling process has been poorly explored. Here, we integrated expert knowledge in different stages of the niche modeling process to improve the representation of the actual geographic distributions of Mexican primates (Ateles geoffroyi, Alouatta pigra, and A. palliata mexicana). We designed an elicitation process to acquire information from experts and such information was integrated by an iterative process that consisted of reviews of input data by experts, production of ecological niche models (ENMs), and evaluation of model outputs to provide feedback. We built ENMs using the maximum entropy algorithm along with a dataset of occurrence records gathered from a public source and records provided by the experts. Models without expert knowledge were also built for comparison, and both models, with and without expert knowledge, were evaluated using four validation metrics that provide a measure of accuracy for presence-absence predictions (specificity, sensitivity, kappa, true skill statistic). Integrating expert knowledge to build ENMs produced better results for potential distributions than models without expert knowledge, but a much greater improvement in the transition from potential to realized geographic distributions by reducing overprediction, resulting in better representations of the actual geographic distributions of species. Furthermore, with the combination of niche models and expert knowledge we were able to identify an area of sympatry between A. palliata mexicana and A. pigra. We argue that the inclusion of expert knowledge at different stages in the construction of niche models in an explicit and systematic fashion is a recommended practice as it produces overall positive results for representing realized species distributions.

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Composition of the landscape matrix of surrounding forest fragments is thought to be critically important to the survival of arboreal primates because it offers structures that help the animals move between fragments and other foraging sites. However, little is known about the composition of the matrix used by these animals. The aim of this study was to quantitatively assess the importance of the landscape matrix and its effects on primate abundance, using black howler monkeys (Alouatta pigra) living in a landscape fragmented by the expansion of agriculture and pastures for livestock in southeastern Mexico. In 2008, a complete census of the monkeys was carried out across the 2000-ha landscape matrix, and for every site where we observed monkeys, we recorded canopy height, tree basal area, food-source abundance, and distance to the nearest fragment. A total of 244 howler monkeys, distributed among 48 groups (including six solitary males) were counted in the matrix. Mean troop size was 5.6 ± 2.8 individuals, and the mode was three individuals. The highest number of troops and greatest howler monkey abundance were recorded in the isolated trees, the eucalyptus plantation, and orchards. A generalized linear model revealed that monkey abundance tended to be higher in matrix elements with higher canopy height, greater food availability, and closest to rainforest fragments. These results suggest that it is necessary to take into account the many elements of the landscape when drawing up conservation and habitat management plans, particularly in order to establish connectivity among the fragments and elements of the matrix with native trees.

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Se describió el comportamiento de alimentación del mono aullador negro centroamericano (Alouatta pigra) en un fragmento de menos de una hectárea de selva húmeda perennifolia rodeada de pastizales de uso ganadero, árboles dispersos y huertos de mango en la región de Balancán (Tabasco, México). Objetivo: reportar la dieta y actividad del mono aullador negro en condiciones de hacinamiento durante el mes más lluvioso en Balancán, Tabasco, México. Materiales y métodos: las observaciones conductuales (81 h) se hicieron mediante la metodología animal focal de una tropa de A. pigra constituida por tres individuos (un macho adulto, un hembra adulta y un infante). Resultados: del tiempo total de observación, la alimentación representó el 15,97%, el descanso el 78% y la locomoción el 4,57%. En el área de estudio se registraron 14 especies de plantas, de las cuales 10 fueron consumidas por los monos aulladores. El 55% del tiempo de alimentación fue invertido al consumo de frutos, 27% a las hojas, 17% al tallo y 1% a los retoños. La especie de árbol más consumida fue Spondias mombin, con el 61% del tiempo invertido. Conclusión: al igual que otros estudios, se confirmó la tendencia alimentaria folívoro-frugívora del género Alouatta. Se provee información sobre la flexibilidad que tienen los monos aulladores negros para vivir y mantenerse en condiciones de extrema perturbación donde su hábitat es de 0,1 hectáreas con pocas especies de árboles para utilizar, lo que además obliga a los individuos a hacer uso del suelo para trasladarse. Palabras clave: Alouatta pigra, Dieta, Patrón de actividad, Frugivoría, Hábitat fragmentado...

Annotations on the feeding ecology of black howler monkeys in an overcrowded fragment in Balancán, Tabasco, México. We described the feeding behavior of Central-American black howler monkey (Alouatta pigra) in a fragment of less than one hectare of humid evergreen forest surrounded by grassland for livestock use, isolated trees and mango orchards, in the region of Balancán (Tabasco, México). Objective: To record the diet and activity of black howler monkeys in crowded conditions during the wettest month in Balancán (Tabasco, México). Methods and methods: The behavioral observations (81 h) were made using the focal animal methodology with an A. pigra troop made up of three individuals (1 adult male, 1 adult female and 1 infant). Results: Feeding time represented 15.97%, rest 78% and locomotion 4.57% of total time. In the study area we recorded 14 plant species, with 10 being consumed by howler monkeys. 55% of feeding time was devoted to the consumption of fruits, 27% to leaves, 17% to stems, and 1% to sprouts. Spondias mombin was the tree species most consumed, with 61% of the time invested on it. Conclusion: Like other studies, we confirmed the frugivore-folivore feeding tendency of the genus Alouatta. We provide information on the black howler monkey flexibility to live and maintain themselves in extreme perturbation conditions, where their habitat is 0.1 ha with few tree species to use, forcing individuals to move around the ground...

Anotações sobre a ecologia alimentar de bugios num fragmento superlotado (Balancán, Tabasco, México). Descreve-se o comportamento alimentar do bugio centro-americano (Alouatta pigra) num fragmento menor que 1 ha de floresta úmida perenifólia rodeada por pastos para uso do gado, árvores dispersas e pomares de manga na região de Balacán (Tabasco, México). Objetivo: Registrar a dieta e atividade do bugio em condições de superlotação durante o mês mais chuvoso em Balacán, Tabasco, México. Materiais e métodos: As observações de comportamento (81 h) se fizeram por abordagem animal focal de um grupo de A. pigra constituído por três indivíduos (um macho adulto, uma fêmea adulta e um infante). Resultados: Do tempo total de observação, a alimentação representou 15,97%, o descanso 78% e a locomoção 4,57%. Na área de estudo se registraram 14 espécies de plantas das quais 10 foram consumidas pelos bugios. O 55% do tempo de alimentação foi gasto para o consumo de frutas, 27% às folhas, 17% ao caule e 1% aos brotos. A espécie de árvores mais consumida foi Spondias mombin, com 61% do tempo investido. Conclusão: Assim como outros estudos confirma-se a tendência alimentaria folívora-frugívora do gênero Alouatta. Fornece-se informação sobre a flexibilidade que têm os bugios para viver e ficar em condições de extrema perturbação, onde seu habitat é de 0,1 ha com poucas espécies de árvores para seu uso. Forçando, além disso, aos indivíduos a usar o terreno para se deslocar...

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We evaluated the habitat and populations of the black howler monkey (Alouatta pigra) in the municipality of Balancán, Tabasco, southeastern Mexico, using a combination of field surveys and remotely sensed data. We identified 21,937 ha of remnant vegetation composed of 1,348 fragments. Fragments separated by up to 200 m were grouped into "clusters" of fragments in accordance with the maximum observed open distance crossed by A. pigra. A total of 11% or 84 of the 772 clusters identified through remote sensing were selected at random, and for these we determined the vegetation type, canopy height, area, and distance to the closest human settlement. In these same 84 clusters, which included a total area of 9,817 ha, from October to June of 2006 we located a total of 1,064 black howler monkeys, including 228 troops and 49 solitary monkeys. A. pigra was found in 62 (74.7%) of all clusters visited, with a cumulative area of 6,032 ha. Troops varied in size from 2 to 15 individuals (average 6.0+/-2.9 ind/troop). Adults were 67% (n=716) of detected individuals, whereas juveniles were 20.5% (n=218) and infants were 12.5% (n=133). We found black howlers to occur at an ecological density of 10.8 ind/km(2), which is low in comparison with A. pigra in other fragmented and conserved sites. We found a statistically significant relationship between the area of clusters and the abundance of howler monkeys (r(2)=0.2, F=10.47, gl=3, P=0.002). In addition, the probability of finding A. pigra was greater in secondary vegetation, riparian vegetation, tropical dry forest, undisturbed tropical oak forest, and palm forest (F=12, gl=3, P<0.0001), as compared with disturbed tropical oak forest. Our results provide data on the distribution, abundance, and population structure of black howler monkeys in a fragmented landscape in the southeast of Mexico. These data are a necessary prerequisite for conservation planning for this species.

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Uncommonly observed behaviors were systematically recorded in a troop (n = 9 individuals) of black howler monkeys (Alouatta pigra) inhabiting a small forest fragment (1.7 ha) in Leona Vicario, Balancán, Tabasco, Mexico. Between February 2002 and January 2003 (n = 499 h), we observed behaviors such as ground travel (85 occasions, total = 269 min/10.8% of total locomotion time), ground foraging (eight occasions, total = 50 min/0.84% of total feeding time) and drinking water pooled in tree holes (20 times, total = 93 min/0.31% of total activity time). Total time (412 min) for these non-resting behaviors (feeding and locomotion on the ground) is almost equivalent to time devoted to social activities (420 min). These behaviors indicate that howler monkeys may be responding to pressures imposed by the small size of the fragment by adopting diverse strategies to cover their basic nutritional needs in this environment. They accomplish this while exposing themselves to potential predation by coyotes (Canis latrans), as was observed once during the study. It is likely that these behaviors are occurring at an increasing rate among monkeys in fragmented landscapes.

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