Communal Nesting in Asocial Abert's Squirrels: the Role of Social Thermoregulation and Breeding Strategy

Abstract

The social thermoregulation hypothesis states that endothermic species will communally nest to reduce energy expenditures on thermoregulation. The hypothesis predicts that the frequency of communal nesting should increase with decreasing ambient temperature. The potential costs of communal nesting (e.g., increased predation risk, resource competition, cuckoldry, parasite/disease transmission, or infanticide) could decrease the frequency of communal nesting especially for asocial breeding females with dependent offspring. We examined the effects of ambient temperature and seasonal reproductive activities on the probability of communal nesting in Abert's squirrels (Sciurus aberti) in the Pinaleño Mountains, Arizona. Most squirrels nested consistently with the same partner in mixed‐sex pairs. The proportion of individuals engaging in communal nesting increased with decreasing ambient temperature as predicted by the social thermoregulation hypothesis. The onset of the breeding season greatly reduced the proportion of individuals communally nesting. The negative relationship between ambient temperature and communal nesting supports the use of communal nesting in Abert's squirrels as a mechanism to reduce thermoregulatory costs during cold conditions. The abrupt drop in the frequency of communal nesting during the breeding season is likely due to female abandonment of this behavior. By avoiding communally nesting during the breeding season, females may prevent males from mating with them outside of mating chases, reduce resource competition, and protect offspring from infanticide, diseases, and parasites. Males may gain additional fitness benefits from nesting with females because familiarity with females increases dominance rank in mating activities.

Ecological drivers of group living in two populations of the communally rearing rodent, Octodon degus

“…Our observation that social groups were larger at Rinconada than Los Molles suggests that social group formation and maintenance is not driven by social thermoregulation. These findings depart from studies of single populations or comparisons of multiple populations in mammals (mostly rodents) where the extent of grouping tracks changes in ambient temperature (West 1977; Madison 1984; Stapp et al 1991; Edelman and Koprowski 2007; Taraborelli and Moreno 2009). However, our results are in agreement with studies on voles (Getz and McGuire 1997) and badgers (Johnson et al 2002) in which group size is uncoupled from ambient temperatures.…”

“…Johnson et al (2002) found no relationship between the thermal environment (a main determinant of energy expenditure) and the size of social groups across populations of badgers ( Meles meles ) throughout Europe. While these findings contrast with studies of single populations in rodents where the extent of grouping tracks changes in ambient temperature (West 1977; Stapp et al 1991; Edelman and Koprowski 2007), they support other studies (e.g., Getz and McGuire 1997), suggesting that social group size is not influenced by fluctuations in ambient temperature. Regarding reduced costs of burrow construction, burrow digging has been associated to the evolution of sociality across neotropical (Ebensperger and Cofré 2001; Ebensperger and Blumstein 2006) and African hystricognath rodents (Jarvis et al 1994).…”

Aerobic power, huddling and the efficiency of torpor in the South American marsupial, Dromiciops gliroides

“…Huddling has been reported as a mechanism to save energy in small eutherian mammals such as Darwin's leaf-eared mouse ( Phyllotis darwini ) (Bustamante et al, 2002), the Alpine marmot ( Marmota marmot ) (Arnold, 1988), Abert's squirrel ( Sciurus aberti ) (Edelman and Koprowski, 2007), the striped mouse ( Rhabdomys pumilio ) (Schradin et al, 2006), the Indiana bat ( Myotis sodalist ) (Boyles et al, 2008), the Cape ground squirrel ( Xerus inauris ) (Wilson et al, 2010), and the neotropical bat ( Noctilio albiventris ) (Roverud and Chappell, 1991). Such behavior is also observed among some Australian marsupials, such as brush-tailed phascogales ( Phascogale tapoatafa ) (Rhind, 2003), eastern pygmy possums ( Cercartetus nanus ) (Namekata and Geiser, 2009), and sugar gliders ( Petaurus breviceps ) (Quin et al, 2010).…”

Behavioural correlates of group size and group persistence in the African ice rat Otomys sloggetti robertsi

“…The social thermoregulatory hypothesis states that animals will huddle to reduce 158 energetic costs associated with thermoregulation (Edelman and Koprowski 2007) and 159 predicts that huddling will result in greater energy savings in larger than small groups 160 (Scantlebury et warm up (i.e. sun basking) on emergence from the burrow in the morning.…”