The avian beak is increasingly recognised as an important organ for thermoregulation, particularly in disproportionately large‐beaked taxa such as toucans and hornbills. We used infrared thermography to test the prediction that southern ground‐hornbills Bucorvus leadbeateri physiologically regulate the surface temperature of their beak (Tbeak), as well as that of their facial (Tfacial) and gular skin (Tgular) in such a way that these surfaces provide avenues for non‐evaporative heat dissipation in warm weather. Our data, collected over air temperatures (Ta) ranging from 11°C to 36°C, supported these predictions. At Ta < 20°C, Tbeak tracked Ta, but rapidly increased to values 6–12°C above Ta at Ta = 20–22°C. The Tbeak–Ta gradient was maintained at approximately 7°C between Ta = 22°C and 28°C, before decreasing linearly with Ta > 28°C. We also found evidence for active regulation of Tfacial and Tgular, with both surfaces regulated at approximately constant increments above Ta up to inflection Ta values of 22°C and 29°C, respectively. The presence of inflection Ta values corresponding with abrupt changes in physiological regulation of these surface areas suggests a high degree of physiological control. Estimates of heat exchange suggest that SGH may be able to dissipate up to 75% of basal metabolic rate via these surfaces, confiming the beak and areas of unfeathered skin play an important thermoregulatory role in these large, distinctive and threatened birds.

Differences in individual locomotor activity patterns may be linked to a number of ecological factors, such as changes in ambient temperature or photoperiod. Observations on subterranean mammals suggest that they exhibit diel rhythms despite the lack of visual cues in their underground burrows, but it is unknown how seasonality and individual characteristics affect their activity. In this study we use RFID technology to monitor daily activity patterns of wild, social Natal mole-rats (Cryptomys hottentotus natalensis) during the summer and winter to investigate how their activity varies with season and whether their activity depends on individual characteristics such as body mass, sex and reproductive status. We found that in winter, individuals were more active during the time with the highest soil temperatures, whereas in summer, they showed a bimodal activity pattern during early morning and late afternoon coinciding with cooler soil temperatures. Individual characteristics, including reproductive status, did not affect general activity indicating that reproductive and non-reproductive individuals contribute equally to cooperative behaviors. We suggest that the activity patterns may be a behavioral adaptation to avoid extreme burrow temperatures and a mechanism to maintain a stable core body temperature. We highlight the advantages of RFID technology to study wild small mammal movements.

Climate change has caused aridification which can alter habitat vegetation, soil and precipitation profiles potentially affecting resident species. Vegetation and soil profiles are important for subterranean mole-rats as increasing aridity causes soils to become harder and geophytes less evenly distributed, and the inter-geophyte distance increases. Mole-rats obtain all water and dietary requirements from geophytes, and thus digging in harder soils may amplify stressors (hyperthermia, dehydration- or exercise-induced damage). This study assessed the oxidative status of the wild common mole-rat along an aridity gradient (arid, semi-arid and mesic). Kidney and liver oxidative markers, including total oxidant status (TOS), total antioxidant capacity (TAC), oxidative stress index (OSI), malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. Liver oxidative status did not demonstrate any significance with the degree of the aridity gradient. Aridity affected the TAC and OSI of the kidney, with individuals in the most arid habitats possessing the highest TAC. The evolution of increased group size to promote survival in African mole-rats in arid habitats may have resulted in the additional benefit of reduced oxidative stress in the kidneys. The SOD activity of the kidneys was higher than that of the liver with lower oxidative damage, suggesting this species pre-emptively protects its kidneys as these are important for water balance and retention.

Co-operatively breeding mammals often exhibit a female reproductive skew and suppression of the subordinate non-breeding group members. According to evolutionary theory and the immunity–fertility axis, an inverse relationship between reproductive investment and survival (through immunocompetence) is expected. As such, this study investigated if a trade-off between immunocompetence and reproduction arises in two co-operatively breeding African mole-rat species, namely the Damaraland mole-rat ( Fukomys damarensis ) and common mole-rat ( Cryptomys hottentotus hottentotus ), which possess female reproductive division of labour. This study also attempted to investigate the relationship between the immune and endocrine systems in Damaraland mole-rats. There was no trade-off between reproduction and immunocompetence in co-operatively breeding African mole-rat species, and in the case of the Damaraland mole-rats, breeding females (BFs) possessed increased immunocompetence compared with non-breeding females (NBFs). Furthermore, the increased levels of progesterone possessed by Damaraland mole-rat BFs compared with NBFs appear to be correlated to increased immunocompetence. In comparison, BF and NBF common mole-rats possess similar immunocompetence. The species-specific differences in the immunity–fertility axis may be due to variations in the strengths of reproductive suppression in each species. This article is part of the theme issue ‘Evolutionary ecology of inequality’.