Ctenomys Talarum Research Articles

Mounting a specific immune response increases energy expenditure of the subterranean rodentCtenomys talarum(tuco-tuco): implications for intraspecific and interspecific variation in immunological traits

It was recently hypothesised that specific induced defences, which require substantial time and resources and are mostly beneficial against repeated infections, are more likely to be favoured in 'slow-living-pace' species. Therefore, understanding how different types of immune defences might vary with life history requires knowledge of the costs and benefits of defence components. Studies that have explored the energetic costs of immunity in vertebrates have done so with a focus primarily on birds and less so on mammals, particularly surface-dwelling rodents. In this study, we evaluated whether an experimental induction of the immune system with a non-pathogenic antigen elevates the energetic expenditure of a subterranean rodent: Ctenomys talarum (tuco-tucos). In both seasons studied, a significant increase in oxygen consumption was verified in immune-challenged tuco-tucos injected with sheep red blood cells (SRBC) compared with control animals. The increase in oxygen consumption 10 days after the exposure to SRBC was lower for female tuco-tucos monitored in the breeding season compared with females in the non-breeding season. Interestingly, antibody titres of female tuco-tucos did not decrease during the breeding season. Our results add new insight into the role of other factors such as basal metabolic rate or degree of parasite exposure besides 'pace of life' in modulating the interspecific immunological variation observed in natural populations of mammals.

Spatial learning abilities in males and females of the subterranean rodent Ctenomys talarum

Few studies have focused on sex differences in spatial learning in subterranean rodents. Ctenomys talarum inhabits complex burrow systems, with males occupying larger areas than females. We assessed spatial learning ability by measuring the capacity of C. talarum individuals to solve appetitive radial or longitudinal spatial tasks during the non-reproductive season. We found that, regardless of sex differences in home-range size, males and females performed similarly in both tasks, rapidly improving their spatial performance after the initial trials and maintaining an accurate performance during subsequent trials. Our results show that sex differences in home-range sizes may not always lead to the evolution of sexually dimorphic spatial abilities.

Effects of contrasting demographic histories on selection at major histocompatibility complex loci in two sympatric species of tuco-tucos (Rodentia: Ctenomyidae)

bij_1358 260..277 To explore the impact of history on selection and genetic structure at functional loci, we compared patterns of major histocompatibility complex (MHC) variability in two sympatric species of ctenomyid rodents with different demographic backgrounds. Although Ctenomys talarum has experienced a stable demographic history, Ctenomys australis has undergone a recent demographic expansion. Accordingly, we predicted that MHC allele frequency distributions should be more skewed, differences between coding and noncoding regions should be less pronounced, and evidence of current selection on MHC loci should be reduced in C. australis relative to C. talarum. To test these predictions, we compared variation at the MHC class II DRB and DQA genes with that at multiple neutral markers, including DQA intron 2, the mitochondrial control region, and 8–12 microsatellite loci. These analyses supported the first two of our predictions but indicated that estimates of selection (based on w-values) were greater for C. australis. Further exploration of these data, however, revealed differences in the time frames over which selection appears to have acted on each species, with evidence of contemporary selection on MHC loci being limited to C. talarum. Collectively, these findings indicate that demographic history can substantially influence genetic structure at functional loci and that the effects of history on selection may be temporally complex and dynamic. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 260–277. ADDITIONAL KEYWORDS: Ctenomys australis – Ctenomys talarum – expansion – population.

Predation upon the subterranean rodent Ctenomys talarum (tuco-tucos) by Buteo polyosoma (red-backed hawks) in coastal grasslands of Argentina

Differential predation upon tuco-tucos (Ctenomys talarum) by red-backed hawks (Buteo polyosoma) is reported, considering the characteristics that could lead to prey vulnerability and to predator selectivity. Predation was evaluated through analysis of 100 pellets and 20 prey remains collected in coastal grasslands at Mar de Cobo (Buenos Aires, Argentina) during winter (May to August) 2003–2004. The tuco-tucos represented the main component in the diet of red-backed hawks, registering a high consumption of sub-adult individuals (49.3%). Juvenile individuals (42.0%) were overrepresented and adults (8.7%) were underrepresented in relation to their field frequencies (14.4 and 43.1%, respectively), whereas sub-adults did not show significant differences. This high consumption of smaller tuco-tucos would be based on the higher vulnerability of young individuals to predation rather than raptor's handling constraints on bigger individuals. Our results indicate that a strong predator–prey relationship between tuco-tucos and red-backed hawks is established at the study area, and that tuco-tucos represent a key component for the survival of wintering hawks. Reportamos la depredación diferencial sobre el tuco-tuco (Ctenomys talarum) por el aguilucho común (Buteo polyosoma), considerando las características que podrían determinar la vulnerabilidad de la presa y la selectividad del predador. La depredación fue evaluada mediante el análisis de 100 egagrópilas y 20 restos presa recolectados en pastizales costeros de la localidad de Mar de Cobo (Buenos Aires, Argentina) durante el periodo invernal Mayo–Agosto de 2003–2004. El tuco-tuco representó el principal componente en la dieta del aguilucho común, registrándose un alto consumo de individuos subadultos (49.3%). Los individuos juveniles (42.0%) fueron sobrerrepresentados y los adultos (8.7%) fueron subrepresentados en la dieta en relación a sus frecuencias en el campo (14.4 y 43.1%, respectivamente), mientras que los subadultos no mostraron diferencias significativas. Este elevado consumo de individuos más pequeños radicaría en una mayor vulnerabilidad a la depredación de los juveniles más que en restricciones de manipuleo del predador sobre las presas más grandes. Nuestros resultados indican que existe una estrecha relación predador–presa entre el tuco-tuco y el aguilucho común, y que los tuco-tucos representan un componente clave para la supervivencia invernal de los aguiluchos.

Effect of diet quality and soil hardness on metabolic rate in the subterranean rodent Ctenomys talarum

The present work is aimed to establish, in Ctenomys talarum, the physiological and behavioral adjustments undergone by individuals when they are allowed to dig burrows in soils with different hardness and fed with diets of different quality. For each soil–diet combination, we estimated: resting metabolic rate (RMR), body temperature ( T b), body mass, digestibility, food consumption rate, transit time, reingestion rate, feces production and time devoted to feeding, resting, locomotor activity and coprophagy. Soil type and diet quality affected RMR, but response to soil hardness was verified later. Animals fed with high quality (HQ) diet showed similar body temperature irrespective of soil condition, while animals fed with low quality (LQ) diet showed lower T b under soft soil (SS). Individuals fed with LQ diet showed lower RMR and both, lower digestibility and high transit time of food than those fed with HQ diet. Moreover, increments in feeding and defecation rates were observed in the former group. Number of reingested feces did not differ between animals fed with diets of different quality. However, when incidence of reingestion was considered, animals fed with HQ diet showed higher values of feces ingestion. Either feeding, resting and activity patterns were arrhythmic. However, for animals fed with LQ diet a tendency to rhythmic coprophagy was observed and it could be considered as a way to optimize feeding. This study shows that RMR is limited by digestive efficiency which is influenced by diet quality, but also thermal stress may limit the conversion of assimilated energy into work and heat.

Short-term effects of an acute exposure to predatory cues on the spatial working and reference memory performance in a subterranean rodent

Spatial memory is important for animals to achieve successful foraging, reproduction, territorial defence and predator avoidance in structurally complex habitats. This cognitive function has been shown to be affected under stress conditions in surface-dwelling rodents. Here we used the Tala's tuco-tuco, Ctenomys talarum , a subterranean rodent that inhabits complex burrow systems, as a study model. This species has a highly developed spatial ability and individuals are regularly exposed to predatory stress while foraging on the surface. We examined the consequences of a single and brief exposure to predatory cues on the spatial working and reference memory performance. We trained wild-caught individuals (32 males, 36 females) in a six-arm radial maze (spatial working memory task) or a longitudinal maze (spatial reference memory task). Once the animals reached a memory performance criterion, they were exposed to a direct predatory cue (immobilization), an indirect predatory cue (cat urine odour) or both cues combined, and their memory performance was evaluated. Exposure to direct and combined predatory cues impaired spatial reference memory, increasing both the latency to achieve the goal and the number of errors during the test. Combined presentation of both predatory cues also negatively affected spatial working memory, but only for latency to achieve the goal. Our results suggest that use of spatial working memory during a predatory attack on the surface allows C. talarum to relocate burrow entries rapidly and hence increases survival probabilities.

Decreased glucose tolerance but normal blood glucose levels in the field in the caviomorph rodent Ctenomys talarum: The role of stress and physical activity

Hystricomorph rodents have a divergent insulin molecule with only 1–10% of the biological activity in comparison to other mammalian species. In this study, we used the subterranean rodent Ctenomys talarum as a model and performed blood glucose tolerance tests (GTTs) with trained and untrained individuals to evaluate blood glucose regulation and the possible role of physical activity as a compensatory mechanism. Additionally, we evaluated the variations in blood glucose during acute and chronic stress and gathered data in the field to evaluate natural-occurring variations in blood glucose levels. The GTTs showed that C. talarum have a diminished capacity of regulating blood glucose levels in comparison to other mammals and suggest that unexplored differences in the compensatory mechanisms, insulin structure and/or glucose transporters exist within species of hystricomorph rodents. However, blood glucose levels in the field stayed within the normal mammalian range. Physical activity did not prove to be a compensatory mechanism for blood glucose regulation. The individuals did not display important increases in blood glucose after acute stressors and managed to adequately regulate blood glucose during chronic stress. We suggest that the species may not face a selective pressure favoring a more tightly, mammalian like, capacity of regulating blood glucose levels.

Digestive strategies in the South American subterranean rodent Ctenomys talarum

Ctenomys talarum is a subterranean herbivorous rodent which due to its particular life style is frequently exposed to variations in surface environmental conditions (i.e. food quality and availability, temperature). Thus, unlike other subterranean rodents, C. talarum has to buffer both the surface and burrow challenging environmental conditions. We studied the occurrence of digestive strategies at different levels of C. talarum living in their natural habitat. We determined the dimensions of different parts of the gastrointestinal tract and organs along as the activity of key digestive enzymes (disaccharidase, N-aminopeptidase) in different parts of the gut in individuals seasonally caught. The results show that C. talarum exhibits characteristics in the gut at the biochemical level (high disaccharidase activities in small intestine, high N-aminopeptidase activity in the caecum and large intestine, and a seasonal differential modulation of N-aminopeptidase activity in small and large intestines), which could represent adaptive strategies to face seasonal variations in key environmental factors.

Phylogeographical structure in the subterranean tuco‐tuco Ctenomys talarum (Rodentia: Ctenomyidae): contrasting the demographic consequences of regional and habitat‐specific histories

In this work we examined the phylogeography of the South American subterranean herbivorous rodent Ctenomys talarum (Talas tuco-tuco) using mitochondrial DNA (mtDNA) control region (D-loop) sequences, and we assessed the geographical genetic structure of this species in comparison with that of subterranean Ctenomys australis, which we have shown previously to be parapatric to C. talarum and to also live in a coastal sand dune habitat. A significant apportionment of the genetic variance among regional groups indicated that putative geographical barriers, such as rivers, substantially affected the pattern of genetic structure in C. talarum. Furthermore, genetic differentiation is consistent with a simple model of isolation by distance, possibly evidencing equilibrium between gene flow and local genetic drift. In contrast, C. australis showed limited hierarchical partitioning of genetic variation and departed from an isolation-by-distance pattern. Mismatch distributions and tests of neutrality suggest contrasting histories of these two species: C. talarum appears to be characterized by demographic stability and no significant departures from neutrality, whereas C. australis has undergone a recent demographic expansion and/or departures from strict neutrality in its mtDNA.

Use of vegetation chemical signals for digging orientation in the subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae)

AbstractSensory modalities involved in the localization and selection of food represent critical information for understanding the foraging behavior of subterranean rodents. The objective of this study was to determine if a subterranean rodent that forages on aboveground plant parts, Ctenomys talarum, is able to detect the presence of odorous chemicals released by the plants into the soil to guide its excavation, as has been shown for subterranean species that forage on roots and bulbs. Individuals were introduced into an artificial Y‐maze, whose arms were filled with sandy soil in which plants either had or had not been growing (control). Digging activity exhibited in each soil type was recorded. The following plant species, present in the natural habitat of C. talarum, were used: Panicum racemosum (three different concentrations), Cortadeira sp., Margiricarpus pignatus, Ambrosia sp. and Raphanus sativus. The individuals allocated more time to excavation in the soil in which vegetation had been growing in comparison with the control for the five analysed plant species, except in the case of P. racemosum at its lowest concentration. The number of individuals that completed excavation in the tube‐containing soil in which plants had been growing was significantly higher than in the tube‐containing soil in which no plants had been growing, with the exception of P. racemosum at its lowest concentration and R. sativus. The results of the present study suggest that C. talarum have the ability to use olfaction to orient their digging while foraging even though members of this species consume mainly aboveground plant parts.

Subterranean rodents of the genusCtenomys(Caviomorpha, Ctenomyidae) follow the converse to Bergmann's rule

AbstractAim We analysed body‐size variation in relation to latitude, longitude, elevation and environmental variables inCtenomys(tuco‐tucos), subterranean rodents in the Ctenomyidae (Caviomorpha). We tested the existence of inter‐ and intraspecific size clines to determine if these rodents follow Bergmann's rule, to compare intra‐ and interspecific size trends and to assess the relevance of the subterranean lifestyle on these trends.Location South America, south of 15° latitude.Methods This paper is based on 719 specimens of tuco‐tucos from 133 localities of Argentina, Bolivia, Chile, Paraguay, Peru and Uruguay, representing 47 named species and 32 undescribed forms. Intraspecific analyses were performed forCtenomys talarumThomas, 1898 and theCtenomys perrensiThomas, 1896 species complex. Head and body length and weight were used for estimating body size. Geographical independent variables included latitude, longitude and altitude. Environmental independent variables were mean minimal and maximal monthly temperature, mean annual temperature, mean minimal and maximal precipitation, and total annual precipitation. To estimate seasonality, the annual variability of the climatic factors was calculated as their coefficients of variation and the difference between maximum and minimum values. Mean annual actual evapotranspiration (AET), and mean annual, January (summer) and July (winter) potential evapotranspiration (PET) values were also calculated for each locality, as well as annual, summer and winter water balance (WB). Statistical analyses consisted of simple and multiple regression and nonparametric correlation.Results Body size ofCtenomysdecreases interspecifically from 15°00′ S to 48°15′ S and from 56°33′ W to 71°46′ W, and is positively correlated with ambient temperature and precipitation. The best predictors of body size according to multiple regression analyses were mean annual temperature, the difference between mean maximum and minimum annual temperatures, annual PET, the difference between summer and winter PET, and annual and winter water balance. These patterns are repeated, but not identically, at a smaller geographical scale within the speciesC. talarumand the superspeciesC. perrensi.Main conclusions Tuco‐tucos follow the converse to Bergmann's rule at the interspecific level. At the intraspecific level some parallel trends were observed, but the smaller scale of these analyses, involving a very reduced variation of environmental factors, necessitates caution in interpreting results. The subterranean lifestyle probably insulates these rodents from the external temperature. The observed latitudinal body‐size gradients are more probably related to seasonality, ambient energy, primary productivity and/or intensity of predation.

Nutritional responses to different diet quality in the subterranean rodent Ctenomys talarum (tuco-tucos)

Nutritional response to different diet quality was examined in the subterranean rodent Ctenomys talarum (tuco-tuco). Animals maintained in captive conditions were fed with three plant species that differed in their fibre content. Tuco-tucos showed the ability to perform adjusts in short time lapse in response to diet quality; food ingestion, egestion and feces ingestion changed in animals under different plant species diets. Time budget, mainly time devoted to feeding and activity accompanied such changes. Coprophagy was practiced along the day and night following the arrhythmic activity pattern found for this species. Feces reingestion was not associated to resting. Furthermore, it was observed during fresh food ingestion, being pellets chewed. Soft and hard feces differed in morphological and nutritional characteristics.

Energy and distribution in subterranean rodents: Sympatry between two species of the genus Ctenomys

The low basal metabolic rate (BMR) observed in subterranean rodents, compared to that of surface-dwelling species of comparable size, has been proposed to be an adaptation to underground life. Two main hypotheses have been proposed to explain this finding, the cost of burrowing and the thermal stress. The former states that the low BMR is due to the high cost of extending the tunnel system whereas the other relates it to the possibility of overheating in burrows where evaporative and convective heat exchange are restricted. Additionally, both hypotheses related the energetics of subterranean rodent with spatial distribution. The genus Ctenomys is an excellent model to evaluate the cost of burrowing or thermal stress, since they are widely distributed, with members differing markedly in body mass. The aim of this study was to assess digging and basal energetics in two Ctenomys species that live in sympatry in a coastal grassland, but differ in their microspatial distribution by soil preference. We used the obtained energetic data to test both energy-distribution hypotheses. We measured BMR and digging metabolic rate (DMR) through open flow respirometry in two species exposed to soft and hard soils. In brief, DMR in Ctenomys talarum (100-170 g), as in Ctenomys australis (250-600 g), was unaffected by soil hardness. Within thermoneutral zone of each species, DMR/RMR quotient was lower in the smaller species. Our data did not support the thermal stress hypothesis, but the cost of burrowing hypothesis was not rejected. Other alternative hypotheses are proposed to explain the distribution of C. talarum and C. australis.

HOME-RANGE AND ACTIVITY PATTERNS OF THE SOUTH AMERICAN SUBTERRANEAN RODENT CTENOMYS TALARUM

Subterranean rodents are characterized by limited individual mobility and patchy distribution of local populations, all of which have been related to the great evolutionary diversification of this group. Because of their secretive habits, radiotracking becomes an essential tool to collect data systematically on characteristics of their space use, rate of movement, and daily patterns of activity. Compared to other subterranean species, the ctenomyids exhibit more activity above the surface. Despite this, a previous study showed that only 25% of the captive individuals analyzed presented rhythmic bouts of activity associated with light‐dark cycles. In our study, we used radiotelemetry to explore quantitatively the home-range dynamics and daily movements of the South American Talas tuco-tuco (Ctenomys talarum). As expected, the home ranges of males were larger than those of females. However, intraspecific variation in home-range size also was observed between 2 different study sites, possibly reflecting differences in body size and soil characteristics between the study sites. Rhythmicity in activity patterns was confirmed to be polymorphic in this species, as previously observed in captivity, and daily activity was mostly concentrated in the diurnal period. We suggest that the present study will contribute to generating important insights into home-range dynamics and daily patterns of activity of free-living subterranean rodents.

Effect of tunnel inclination on digging energetics in the tuco-tuco, Ctenomys talarum (Rodentia: Ctenomyidae)

Burrows play an important role for many species, providing them with shelter and access to food resources. For subterranean rodents, living underground imposes constraints on morphology and physiology. The convergence in burrow architecture among subterranean rodents has been related to the energy demands imposed by the cost of constructing an entire system. The low frequency of tunnels with downward angles steeper than 40 degrees appears to be a common feature in burrow design. In the subterranean habitat, movements through the soil are expensive and gravity can exert important restrictions on digging energetics when individuals push out the soil removed in steeper digging angles. The aim of this study was to determine the effect of digging angle on digging energetics in Ctenomys talarum. The mass of the removed soil and burrowing speed were similar while digging metabolic rate and net cost of transport were higher in individuals digging in tunnels with angles >40 degrees than in those digging tunnels with angles <40 degrees . The cost of constructing a burrow in the horizontal plane differed by 20% from others in which the natural representation of tunnels >40 degrees was considered. Even given that tunnels >40 degrees represented only 6% of the total burrow length, burrow architecture appears to be constrained by the high energetic cost of constructing in steeper angles.

ACQUISITION OF SUBTERRANEAN HABITS IN TUCO-TUCOS (RODENTIA, CAVIOMORPHA, CTENOMYS): ROLE OF SOCIAL TRANSMISSION

Abstract A test was conducted to investigate if mother–infant social transmission plays a role in the acquisition of subterranean habits in the rodent Ctenomys talarum. Thirteen infants were reared by their mother in an experimental aboveground habitat that precluded burrow construction. At the age of natal dispersal, young were allowed to dig in the soil typically inhabited by the species. All experimental tuco-tucos engaged in burrowing activities after short latencies (51 s ± 35 SD). Aboveground excursions lasted a few seconds and covered short distances, and there were no significant differences between experimental and control wild tuco-tucos. The structure of the burrows constructed by experimental tuco-tucos did not substantially differ from those typical for the species. It is concluded that vertical social transmission is not essential for the development of subterranean habits in C. talarum. The results are discussed regarding growing evidence on social transmission and its alleged role during e...

MAJOR HISTOCOMPATIBILITY COMPLEX VARIATION IN TALAS TUCO-TUCOS: THE INFLUENCE OF DEMOGRAPHY ON SELECTION

Although interactions between behavior, demography, and genetic diversity have been studied extensively for neutral molecular markers, relationships among these variables remain poorly understood for loci that are subject to selection. The genes of the major histocompatibility complex (MHC) provide a particularly appropriate opportunity to examine the impact of selection on genetic structure; the high levels of polymorphism characteristic of these loci are thought to be maintained by selective pressures arising due to pathogen exposure and inbreeding depression, both of which may be influenced by behavior and demography. To explore interactions among population structure, selection, and genetic diversity, we compared levels and patterns of MHC variability in 2 demographically distinct populations of the Talas tuco-tuco (Ctenomys talarum), a subterranean rodent that occurs in eastern Argentina. Specifically, we tested the prediction that selection on 2 class II loci (DRB and DQA) should be greater in the more dense, more inbred Mar de Cobo population. At both loci, allelism and heterozygosity were greater for Mar de Cobo than for Necochea. Similarly, for both loci, estimates of the intensity of selection (corrected for differences in effective population size) were greater for Mar de Cobo, as predicted based on demographic and behavioral differences between the study populations. Interlocus differences in variability are examined with respect to the apparent function(s) of these genes, whereas interpopulation differences in intensity of selection are evaluated with regard to the demonstrated behavioral and demographic differences between Necochea and Mar de Cobo.

Seasonal changes in body composition of Ctenomys talarum (Rodentia: Octodontidae): An herbivore subterranean rodent

Ctenomys talarum is a subterranean herbivorous rodent whose burrow systems exhibit particular characteristics, distinct from other subterranean environments. We studied seasonal variation in body composition of C. talarum in relation to energetic requirements. Body lipid content seasonally changed in C. talarum, related to reproductive cycle and thermorregulatory mechanisms. A decrease in protein body content was found only in spring. Ash content of females was lowest when most of them are in post partum estro. Observed variations in water body content could be associated with plant water content and/or metabolic regulation. Our results show the occurrence of seasonal variations in body composition in C. talarum, which could be related to the high cost of reproduction and the subterranean life style of this species.

Cost of foraging in the subterranean rodentCtenomys talarum: effect of soil hardness

Subterranean burrows provide inhabitants with shelter, a relatively stable thermal environment, and potentially access to food resources. However, one cost of living in such burrows is the energetically expensive mode of locomotion. Soil hardness and the physiological capabilities of animals are likely important factors that affect the cost of burrow construction, and hence, distribution of burrows. We assessed the effect of soil hardness on the cost of digging by captive individual Ctenomys talarum Thomas, 1898 in soft soils. Digging metabolic rate (DMR) was higher in harder soil than in softer soil (408.30 ± 51.35 mL O2·h–1vs. 267.59 ± 20.97 mL O2·h–1, respectively). In C. talarum, a higher soil hardness augments DMR by increasing, in terms of the cost of burrowing model, the costs of shearing and of pushing the removed soil. Additionally, these costs differ between C. talarum and other subterranean species (e.g., Thomomys bottae (Eydoux and Gervais, 1836)), depending on soil hardness and digging mode. Thus, the relationship between digging cost and soil hardness appears to be one of the most important factors that affect burrowing efficiency in subterranean rodents.

Winter Diet and Time-activity Budgets of The Red-backed Hawk (Buteo polyosoma) in the Coastal Grasslands of Buenos Aires Province, Argentina

Food habits of the Red-backed Hawk (Buteo polyosoma) were studied in the southeastern coast of Buenos Aires Province, Argentina, during autumn and winter of 2001–03. At the study area, the Red-backed Hawk was a specialist predator. On a numerical basis, 99.5% of its prey were small mammals, and little seasonal and annual variability in diet was observed. The diet was composed of murids—mainly field mice (Akodon azarae), pampas rice rats (Oligoryzomys flavescens), and vesper mice (Calomys spp.), and by octodontids (tuco-tucos [Ctenomys talarum]). The tuco-tuco was the most important prey, representing 55% of the diet biomass. The Red-backed Hawk exhibited a sit-and-wait strategy, indicated by the high percentage of time study birds were perched (78.8%). Feeding, comfort movements, and flight were also recorded (11.6%, 4.9%, and 4.7%, respectively). We observed 61 capture attempts on tuco-tucos, of which 42.6% were successful. Hawks displayed agonistic interactions with other bird species. The main aggressor (77.5%, N = 372) was the Chimango Caracara (Milvago chimango) that frequently consumed prey remains discarded by the hawks. Our work suggests a trend of preying on relatively more small mammals toward the southern end of its geographic range. The Red-backed Hawk in its wintering range seems to be a relative specialist predator mostly employing passive search as its main hunting strategy.