Social Group Size Research Articles

The effects of animal transfers on the reproductive success of female white rhinoceroses (Ceratotherium simum simum) kept in European zoos

The Southern white rhinoceros (Ceratotherium simum simum) has been kept in European zoos since the 1960s. However, captive breeding success has been low, with social group composition, group size, and available space all playing a role. Female rhinoceroses that have never bred or not bred for a long time have a particularly increased risk of developing reproductive tract pathologies, often resulting in infertility at a young age. One management measure to stimulate breeding is to transfer non-reproducing animals to other zoos. This study evaluated the success of transfers of 4 – 28 years old white rhinoceroses between European zoos. We analyzed n = 90 (45 males and 45 females) transfers of white rhinoceroses between 1990 and 2018. Fecal progesterone metabolite levels were analyzed for a subset of female rhinoceroses. The success of a transfer was defined as a calf born within five years. The success rate after female transfers was 26.7%; however, when the age limit of transferred females is set at 18 years, the success rate was 44.4%. The success rate after a male transfer was 23.2%. In transferred females, 83% of births occurred within three years after a transfer. Births following the arrival of a new male were distributed over five years. After a male transfer, endocrine data were determined in 26 of 82 females affected by the transfer. Positive development of estrous cycle activity after the arrival of the new bull occurred in 13 females. In summary, the success of the transfers in terms of offspring birth and endocrine stimulation of cycle activity was lower than anticipated, and sometimes a considerable amount of time elapsed before a calf was born. Nonetheless, transfers are essential to promote breeding. The relatively low success of the transfers analyzed in this study relates to the partially advanced age of the white rhinoceroses studied. Transfers of juvenile or adolescent females currently conducted between European zoos reveal a better birth rate than the present study.

Seasonal resource selection and movement ecology of free‐ranging horses in the western United States

AbstractUnderstanding factors driving resource selection and habitat use of different species is an important component of management and conservation. Feral horses (Equus caballus) are free ranging across various vegetation types in the western United States, yet few studies have quantified their resource selection and seasonal use. We conducted a study to determine effects of vegetation community, distance to water, and topographic variables on seasonal resource selection in 2 feral horse populations in Great Basin sagebrush (Artemisia spp.) ecosystems of west‐central Utah, USA: Conger Herd Management Area (HMA) and Frisco HMA. We deployed global positioning system (GPS) radio‐collars on 38 female horses and GPS‐transmitters braided and glued into the tail hair of 14 males, collecting locations every 2 hours for 1–4 years between 2016 and 2020. We calculated home range size and core use area of social groups (harems) and bachelor males using auto‐correlated kernel density estimators for each biologically defined season (breeding, fall, and winter) per study year. We examined seasonal home range size and overlap of harem groups and bachelor males and compared movement speed of bachelors and harems among seasons. We determined seasonal resource selection in a use‐availability framework using resource selection functions. We hypothesized that horses would select for areas of high herbaceous vegetation, that water would be a key variable in resource selection models like other equids, and home range size in winter would be largest because horses can eat snow for hydration and could therefore roam farther from surface water. Mean annual home range size was 103.12 ± 37.38 km2 (SD) for Conger harems and 117.47 ± 32.75 km2 for Frisco harems. At Conger there was no difference in home range size between harem groups and bachelor males, but home range size was smaller in winter than other seasons, whereas winter home range size at Frisco was larger than other seasons. Bachelor males moved at higher speeds than harems during all seasons, and harem groups from both populations had lower movement speeds in winter. Harem groups had distinct winter ranges with little overlap on breeding season ranges. In both populations, all horses selected for herbaceous vegetation types and avoided forest relative to shrubland throughout the year. Harems at Frisco were consistently located closer to water sources, whereas selection for water sources by Conger harems varied seasonally, with winter having the lowest selection. Harem groups at Conger had an average of 10.6% of their home ranges outside the HMA boundary and Frisco harems had up to 66.8% outside, likely because of the horseshoe shape of Frisco HMA in which shrub meadows (foraging areas) comprise the horseshoe center, which is outside the HMA. Our results highlight the importance of water sources, which were a key predictor of horse movement patterns in our study. We emphasize the utility of telemetry devices to understand resource selection of feral horses at a fine scale, enabling management to be more targeted and facilitate planning.

An empirical assessment of the institutional performance of community-based water management in a large-scale irrigation system in southern Mexico

Understanding irrigation performance by focusing on its institutional dimension can help improve water use and smallholder farmers' livelihoods. While many studies have evaluated the institutional performance of small-scale, farmer-managed irrigation systems, virtually no empirical studies have evaluated the performance of community-based water management institutions in large-scale irrigation systems with non-governmental bureaucratic administration. This study aims to fill this gap using a mixed-methods research design combining ethnographic work and a quantitative survey of 81 smallholder farmers' from four community institutions (ejidos) in an irrigation district in Chiapas, southern Mexico. While the management model implemented in the transfer of Mexican irrigation districts to users consisted of a bureaucratic administration entirely in the hands of contract agents, this study reveals the essential role of community institutions in local water management. However, although all four communities use water from the same irrigation district, the results revealed significant differences in the institutional performance of irrigation management. Using the Institutional Analysis and Development (IAD) framework developed by Elinor Ostrom, We showed that these differences could be explained by the biophysical attributes involved in irrigation (irrigation technique, access to groundwater resources, location of the water intake) and community characteristics (social capital and group size). The study recommends that water managers involve communities in the creation of farmers' associations, which could increase their social capital and thus the performance of local irrigation. Furthermore, the results suggest that farmers' views on the institutional performance of irrigation management should receive more attention in the large-scale irrigation system with bureaucratic administration. This knowledge can be particularly useful to improve the different levels of organization and thus water governance of irrigation districts in Mexico.

Repercussions of patrilocal residence on mothers' social support networks among Tsimane forager-farmers.

While it is commonly thought that patrilocality is associated with worse outcomes for women and their children due to lower social support, few studies have examined whether the structure of female social networks covaries with post-marital residence. Here, we analyse scan sample data collected among Tsimane forager-farmers. We compare the social groups and activity partners of 181 women residing in the same community as their parents, their husband's parents, both or neither. Relative to women living closer to their in-laws, women living closer to their parents are less likely to be alone or solely in the company of their nuclear family (odds ratio (OR): 0.6, 95% CI: 0.3-0.9), and more likely to be observed with others when engaging in food processing and manufacturing of market or household goods, but not other activities. Women are slightly more likely to receive childcare support from outside the nuclear family when they live closer to their parents (OR = 1.8, 95% CI 0.8-3.9). Their social group size and their children's probability of receiving allocare decrease significantly with distance from their parents, but not their in-laws. Our findings highlight the importance of women's proximity to kin, but also indicate that patrilocality per se is not costly to Tsimane women. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

The evolution of primate vocal communication: a social route

There is no doubt that different factors determine the evolutionary trajectory of a species' communication abilities. Beyond habitat, social life is likely a selection pressure. The hypothesis positing that living in a complex social system requires complex communication skills has gained ground. However, the measures used classically to tackle this question (i.e. number of call types and group size) fail to capture some of the subtleties of the evolution of communication systems. Integrative approaches comparing closely related species to highlight the possible relationship between the characteristics of their social systems, their ecological niche and associated vocal communication systems are required to further our understanding of this evolutionary puzzle. We first addressed this topic in two sympatric guenons, Diana monkeys and Campbell’s monkeys. Interspecies competition, and the niche specialisations this creates, appeared to be a key evolutionary driver of their repertoires. While most of their vocal units were shared, we found a diversification of alarm calls and socially meaningful vocal combinations, as well as a differential use of inconspicuous (less detectable) call structures. This was linked to differences in group size and degree of exposition to predators. Secondly, we compared the acoustic structures in macaques belonging to four species with contrasting social styles. We found that tolerant (Tonkean and crested) macaques displayed higher levels of vocal diversity (number of vocal units) and flexibility (degree of gradation) than intolerant (Japanese and rhesus) macaques in agonistic and affiliative (but not neutral) contexts. Lastly, because the core of communication is represented not only by what is expressed by an isolated caller, but also by the way vocal interactions are structured, we explored ‘conversational rules’ in apes. We found no relationship between classical social (group size, interaction rates) and vocal (repertoire size, call rates) complexity metrics. However, close call interaction patterns differed in line with the nature of societies. Orang-utan, the most solitary species, preferentially used repeated and isolated calls apparently outside of any vocal interactions. Chimpanzee, the most competitive species displayed a high proportion of overlapping vocalisations. Vocal turn-taking predominated in the most tolerant species (bonobo and gorilla). Even if primate vocal repertoires change slowly over evolutionary time, making them good phylogenetic indicators, socio-ecological niches may induce considerable local divergence at different levels: vocal repertoire composition, acoustic structure and contextual use of calls, and vocal interaction patterns.

Variation in plastic consumption: social group size enhances individual susceptibility to an evolutionary trap

Anthropogenic change forces animals to navigate novel conditions, including evolutionary traps formed by decoupling cues from their previously evolved meaning. One underexplored feature that could drive variation in response to traps is social context. We looked at how group size influences the behaviour of western mosquitofish, Gambusia affinis , group members, including eating novel foods. Individuals in larger groups were faster to recover after experiencing a predator cue and faster to feed on known food items. Moreover, fish in larger groups were more likely to try novel foods, including microplastics, a common evolutionary trap. We also found evidence of a group level behavioural syndrome, in which a consistent proportion of individuals performed a behaviour across assays (i.e. resumed general activity following a predator cue, ate known food and ate novel food). Our results provide evidence that group size can influence the severity of an evolutionary trap and that, regardless of group size, group identity can have a strong effect on individual behaviour. • We examined group size effects on mosquitofish behaviour across multiple contexts. • Fish in larger groups recovered more quickly following a predator cue. • Fish in larger groups began eating familiar food faster. • Fish in larger groups were more likely to try novel foods, including microplastics. • Group identity was also a strong predictor of individual behaviour.

Socioecological complexity in primate groups and its cognitive correlates.

Characterizing non-human primate social complexity and its cognitive bases has proved challenging. Using principal component analyses, we show that primate social, ecological and reproductive behaviours condense into two components: socioecological complexity (including most social and ecological variables) and reproductive cooperation (comprising mainly a suite of behaviours associated with pairbonded monogamy). We contextualize these results using a meta-analysis of 44 published analyses of primate brain evolution. These studies yield two main consistent results: cognition, sociality and cooperative behaviours are associated with absolute brain volume, neocortex size and neocortex ratio, whereas diet composition and life history are consistently associated with relative brain size. We use a path analysis to evaluate the causal relationships among these variables, demonstrating that social group size is predicted by the neocortex, whereas ecological traits are predicted by the volume of brain structures other than the neocortex. That a range of social and technical behaviours covary, and are correlated with social group size and brain size, suggests that primate cognition has evolved along a continuum resulting in an increasingly flexible, domain-general capacity to solve a range of socioecological challenges culminating in a capacity for, and reliance on, innovation and social information use in the great apes and humans.This article is part of the theme issue ‘Cognition, communication and social bonds in primates’.

Reimagining Critical Care Education During COVID-19 With High-Level Technology.

Methods of critical care (CC) education were quickly challenged when faced with the COVID-19 pandemic requiring social distancing and limited group sizes. A new delivery model was designed-one that included a smart video conferencing and recording system and an online platform to access education. Over the course of 4 weeks, the CC program was revamped to meet the immediate needs of CC new hires coming to this tertiary and quaternary medical center.

Large-herbivore nemabiomes: patterns of parasite diversity and sharing.

Amidst global shifts in the distribution and abundance of wildlife and livestock, we have only a rudimentary understanding of ungulate parasite communities and parasite-sharing patterns. We used qPCR and DNA metabarcoding of fecal samples to characterize gastrointestinal nematode (Strongylida) community composition and sharing among 17 sympatric species of wild and domestic large mammalian herbivore in central Kenya. We tested a suite of hypothesis-driven predictions about the role of host traits and phylogenetic relatedness in describing parasite infections. Host species identity explained 27–53% of individual variation in parasite prevalence, richness, community composition and phylogenetic diversity. Host and parasite phylogenies were congruent, host gut morphology predicted parasite community composition and prevalence, and hosts with low evolutionary distinctiveness were centrally positioned in the parasite-sharing network. We found no evidence that host body size, social-group size or feeding height were correlated with parasite composition. Our results highlight the interwoven evolutionary and ecological histories of large herbivores and their gastrointestinal nematodes and suggest that host identity, phylogeny and gut architecture—a phylogenetically conserved trait related to parasite habitat—are the overriding influences on parasite communities. These findings have implications for wildlife management and conservation as wild herbivores are increasingly replaced by livestock.

Using macroevolutionary patterns to distinguish primary from secondary cognitive modules in primate cross-species performance data on five cognitive ability measures

Species-level data on five cognitive ability measures from 69 primate species are used in conjunction with comparative phylogenetic methods to test for the existence of primary and secondary modules. The former are ‘hard wired’, and solve phylogenetically recurrent problems, whereas the latter are a function of domain general problem-solving mechanisms being applied to solving narrower problems, which yields the ability to spontaneously solve those problems once the solutions are learned. It is found that these abilities exhibit affinities for different macroevolutionary patterns relative to ‘Big G', and positive associations with dietary breadth and brain size. The analyses were also conducted using each ability residualised for G. It was found that the Ornstein-Uhlenbeck (OU) model best captured the macroevolution of residual tactical deception, and White Noise (WN) best fit the remainder. Residual tactical deception positively associates with brain volume, whereas the extractive foraging and innovation residuals negatively associate with this and the innovation residual negatively associates with social group size. The affinity of residual tactical deception for the OU model indicates that it may be a primary module under adaptive optimization selection. The predominance of WN in characterizing the macroevolution of the remaining residuals indicates that they may be secondary modules, under the influence of developmental and ecological (rather than phylogenetic) factors. Negative associations involving brain size (in two cases) and social group size (in one) suggest that the optimal conditions for cultivating these modules exist when these parameters are low.

A formalization of one of the main claims of “‘Dunbar’s number’ deconstructed” by Lindenfors et al. 20211

Lindenfors et al. claimed in previous work that the cortex size of humans does not relate to their social group size. We present here a formalization of that claim, stating that all things of class “relative neocortex size” that are in the context of a thing of class “social group” never have a relation of type “affects” to a thing of class “social group size” in the same context.

Sex, not social behavior, predicts fecal glucocorticoid metabolite concentrations in a facultatively social rodent, the highland tuco-tuco (Ctenomys opimus)

Social relationships may influence circulating glucocorticoid levels, particularly in group-living species in which individuals regularly engage in interactions with conspecifics. The effects of such interactions appear to vary, with greater social contact being associated with increased glucocorticoid concentrations in some species but decreased concentrations in others. These distinct responses raise intriguing questions regarding relationships among social behavior, individual phenotypes, and glucocorticoid physiology. To explore such relationships in a free-living mammal with a dynamic social organization, we quantified variation in baseline glucocorticoids in a population of highland tuco-tucos (Ctenomys opimus) from Jujuy Province, Argentina. These subterranean rodents are facultatively social, with lone and group-living individuals regularly occurring within the same population. To assess potential endocrine correlates of this behavioral variability, we examined differences in baseline fecal glucocorticoid metabolite (fGCm) concentrations as a function of social group size and composition as well as several metrics of social behavior derived from social network analyses. Despite marked variability in social relationships among the 37 (12 male, 25 female) free-living tuco-tucos sampled, none of the measures of social behavior examined were significant predictors of variation in fGCm concentrations. In contrast, individual variation in glucocorticoid metabolites was best explained by sex, with males having higher fGCm concentrations than females. These analyses provide the first characterization of the glucocorticoid physiology of highland tuco-tucos and underscore the potential importance of intrinsic phenotypic factors (e.g., sex) in shaping glucocorticoid variation in free-living mammals.

Applying Gregory Johnson's Concepts of Scalar Stress to Scale and Information Thresholds in Holocene Social Evolution

Although Gregory Johnson's models have influenced social theory in archaeology, few have applied or built upon these models to predict aspects of social organization, group size, or fissioning. Exceptions have been limited to small case studies. Recently, the relationship between a society's scale and its information-processing capacities has been explored using the Seshat Databank. Here, I apply multiple-linear regression analysis to the Seshat data using Turchin and colleagues' 9 “complexity characteristics” (CCs) to further examine the relationship between the hierarchy CC and the remaining 8 CCs which include both aspects of a polity's scale and aspects of what Kohler et al. call “collective computation”. The results support Johnson's ideas that stratification will generally increase with increases in a polity's scale (population, territory); however, stratification is also higher when polities increase their developments in information-processing variables such as texts.

Road-based line distance surveys overestimate densities of olive baboons.

Estimating population density and population dynamics is essential for understanding primate ecology and relies on robust methods. While distance sampling theory provides a robust framework for estimating animal abundance, implementing a constrained, non-systematic transect design could bias density estimates. Here, we assessed potential bias associated with line distance sampling surveys along roads based on a case study with olive baboons (Papio anubis) in Lake Manyara National Park (Tanzania). This was achieved by comparing density estimates of olive baboons derived from road transect surveys with density estimates derived from estimating the maximum number of social groups (via sleeping site counts) and multiplying this metric with the estimated average size of social groups. From 2011 to 2019, we counted olive baboons along road transects, estimated survey-specific densities in a distance sampling framework, and assessed temporal population trends. Based on the fitted half-normal detection function, the mean density was 132.5 baboons km-2 (95% CI: 110.4–159.2), however, detection models did not fit well due to heaping of sightings on and near the transects. Density estimates were associated with relatively wide confidence intervals that were mostly caused by encounter rate variance. Based on a generalized additive model, baboon densities were greater during the rainy seasons compared to the dry seasons but did not show marked annual trends. Compared to estimates derived from the alternative method (sleeping site survey), distance sampling along road transects overestimated the abundance of baboons more than threefold. Possibly, this overestimation was caused by the preferred use of roads by baboons. While being a frequently used technique (due to its relative ease of implementation compared to spatially randomized survey techniques), inferring population density of baboons (and possibly other species) based on road transects should be treated with caution. Beyond these methodological concerns and considering only the most conservative estimates, baboon densities in LMNP are among the highest across their geographic distribution range.

Social Group Size and Shelter Availability Influence Individual Metabolic Traits in a Social Fish.

SynopsisGroup living is widespread among animal species and yields both costs and benefits. Presence of conspecifics can restrict or enhance the expression of individual behavior, and the recent social environment is thought to affect behavioral responses in later contexts, even when individuals are alone. However, little is known about how social group size influences the expression of individual physiological traits, including metabolic rates. There is some evidence that shoaling can reduce fish metabolic rates but this variable may be affected by habitat conditions such as shelter availability via density-dependent processes. We investigated how social group size and shelter availability influence Eurasian minnow (Phoxinus phoxinus) metabolic rates estimated by respirometry. Respirometry trials were conducted on fish in isolation before and after they were housed for 3 weeks in a social treatment consisting in a specific group size (n = 4 or 8) and shelter availability (presence or absence of plant shelter in the experimental tank). Plant shelter was placed over respirometers for half of the duration of the respirometry trials, allowing estimation of minimum daytime and nighttime metabolic rates in both conditions (in the presence or absence of plant shelter). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope were also estimated over the entire trial. Minimum daytime and nighttime metabolic rates estimated while in presence of plant shelter were lower than when estimated in absence of plant shelter, both before and after individuals were housed in their social treatment. After the social treatment, SMRs were higher for fish that were held in groups of 4 as compared with those of fish held in groups of 8, while MMR showed no difference. Plant shelter availability during the social treatments did not influence SMR or MMR. Our results suggest that social group size may directly influence energy demands of individuals, highlighting the importance of understanding the role of group size on variations in physiological traits associated with energy expenditure.

The Structure and Dynamics of Endangered Forest Bird Communities in the Mariana Islands

I studied population densities of forest bird communities in the Mariana Islands of Saipan, Aguiguan and Sarigan in order to evaluate hypotheses concerning seasonal shifts in populations, habitat effects on densities, inter-island differences in densities, social group size and underlying reasons for community structuring. With the exception of one species, I found no evidence to support the hypothesis that seasonal shifts occur in populations. Hence, this island system differs in this regard from mainland tropical forests. I also found, contrary to theory, no evidence that the presence of altered habitat permits populations to be greater than they would be in their absence, as disturbed habitat had far lower densities of most species than native forest. Furthermore, I found no support for the hypothesis that social group size differs seasonally as a consequence of differential breeding activity, which is again contrary to findings for mainland tropical forests. A high density of nectar resources on two islands appeared responsible for high population densities of the Micronesian Myzomela on them. Inter-island density comparisons showed strong evidence for there being unfilled niches on Sarigan, thereby making the island a favorable site for species translocations. Examination of the prehistoric composition of Marianas forest bird communities indicated that they once resembled in density structure those of the comparatively pristine Palau Islands. Removing ecologically similar but now absent species from the original Mariana communities likely resulted in reduced competition for resources in ways that increased niche breadth and, thus, populations. The wholesale loss of species in the Marianas has led to communities in which three ecologically versatile species now account for the vast majority of individuals in the community.

Comparative connectomics of the primate social brain

Social interaction is thought to provide a selection pressure for human intelligence, yet little is known about its neurobiological basis and evolution throughout the primate lineage. Recent advances in neuroimaging have enabled whole brain investigation of brain structure, function, and connectivity in humans and non-human primates (NHPs), leading to a nascent field of comparative connectomics. However, linking social behavior to brain organization across the primates remains challenging. Here, we review the current understanding of the macroscale neural mechanisms of social behaviors from the viewpoint of system neuroscience. We first demonstrate an association between the number of cortical neurons and the size of social groups across primates, suggesting a link between neural information-processing capacity and social capabilities. Moreover, by capitalizing on recent advances in species-harmonized functional MRI, we demonstrate that portions of the mirror neuron system and default-mode networks, which are thought to be important for representation of the other's actions and sense of self, respectively, exhibit similarities in functional organization in macaque monkeys and humans, suggesting possible homologies. With respect to these two networks, we describe recent developments in the neurobiology of social perception, joint attention, personality and social complexity. Together, the Human Connectome Project (HCP)-style comparative neuroimaging, hyperscanning, behavioral, and other multi-modal investigations are expected to yield important insights into the evolutionary foundations of human social behavior.

Building blocks of language

Articulate language is a form of communication unique to humans. Over time, a spectrum of researchers has proposed various frameworks attempting to explain the evolutionary acquisition of this distinctive human attribute, some deploring the apparent lack of direct evidence elucidating the phenomenon, whilst others have pointed to the contributions of palaeoanthropology, the social brain hypothesis and the fact that even amongst contemporary humans, social group sizes reflect brain size. Theologians have traditionally (largely) ignored evolutionary insights as an explanatory paradigm for the origin of humankind. However, an increasing number are, of late, contributing to a worldview of humanity which accommodates both the epistemological realities of evolutionary biology as well as insights from theology. This includes reviewing and assessing the origins of articulate language and the physiological attributes necessary for its development. It is in this sense that the evolution of language is relevant from a theological perspective. The association between mental capacity and articulate language, already noted by Darwin, is relevant in explaining the larger group sizes found amongst humans, as is the incipient role played by the evolution of laughter in triggering the neuroendocrine system promoting bonding, to the eventual development of articulate language. Our aim is to review a selection of contemporary perspectives on the evolution of language, amongst others, reasons for the ease with which young children acquire language competency, and whether we may be hardwired for language from birth. Further reading is suggested in the footnotes.Contribution: This article is part of a special collection reflecting on the evolutionary building blocks of our past, present and future. It is based on historical thought and contemporary research with regards to the evolutionary emergence of language. It fits well with the intersectional and trans-disciplinary nature of this collection and journal.

Racial Categorization and Intergroup Relations in Children: The Role of Social Status and Numerical Group Size.

The aim of this review was to examine the effect of social and numerical group size on racial categorization and intergroup relations in children. We first described the development of racial categorization and the factors that increase the saliency of the race criterion in different contexts. Then, we examine the role of social status in intergroups relations and show that low status children express lower ingroup favoritism compared to their peers from high status groups. Few studies investigated the role of ingroup size on intergroup biases. Here, we look at this numerical variable through the proportion of children of different racial groups in the school environment. The results show that homogeneous environments contribute to the decrease of bias and negative attitudes. We discuss how identifying specific and interactive effects of the social and numerical group size would allow us to implement early and efficient intervention programs.

Climate-induced tree senescence leads to a transient increase in reproductive success of a large woodpecker species

Climate change-induced mortality of trees is a concerning phenomenon for global forest ecosystems. The rapid decay and death of long-lived trees can significantly impact forest dynamics, with effects that transmit through ecological networks, becoming more evident in organisms occupying high trophic levels, such as large and specialized woodpecker species. However, understanding how populations of high trophic level species respond to climate change is still a challenge. In this study it was analyzed 32-year data of social groups of the Magellanic Woodpecker (Campephilus magellanicus) in North Patagonia, a region facing increasingly frequent droughts and increased temperatures. A positive trend in the size of woodpecker social groups as a response to climate-induced tree senescence was tested. A causal structural equation model examining climate- tree senescence- woodpecker relationships was used. Increasing nonlinear trends and positive interannual growth rates (>10%) for tree senescence and group size were found. Lowland forest sites had higher levels of tree senescence and more numerous social groups. The causal model supported the positive effect of mean temperature on tree senescence and the positive association of woodpeckers with tree senescence. These results provide evidence of a climate-induced increase in tree senescence that causes an increase in the size of woodpecker social groups. It is suggested that accelerated decay and mortality of trees in the northern Patagonian forests will decrease the stocks of deadwood in the long term, threatening the persistence of this large woodpecker species.