At home with the birds:Kalahari tree skinks associate with sociable weaver nests despiteAfrican pygmy falcon presence

Abstract

The way in which animals use habitat can affect their access to key resources or how they are buffered from environmental variables such as the extreme temperatures of deserts. One strategy of animals is to modify the environment or to take advantage of structures constructed by other 2 species. The sociable weaver bird (Philetairus socius) constructs enormous colonial nests in trees. These nests are frequented by Kalahari tree skinks (Trachylepis spilogaster) and the two species coexist over a large portion of the Kalahari Desert in South Africa. We tested whether lizards were more abundant in trees containing sociable weaver nests and asked whether the physical features of trees were important predictors of skink abundance. We then focused on potential costs of this association by examining the relationship between skink abundance and the presence of a potential predator, the pygmy falcon (Polihierax semitorquatus), which exclusively uses weaver nest colonies for roosting and nesting. Finally, we simulated a predatory threat to determine if skinks assess risk differently if a weaver nest is present. We found a significant positive association between the presence of weaver nests and skink abundance. In the absence of nests, the type of tree did not influence skink abundance. Skinks used weaver nests and were more likely to perch on the nest than the tree. When threatened with predation, skinks preferred to take refuge in nests. Surprisingly, the presence of nesting pygmy falcons in nests did not influence skink abundance, perhaps because of the abundance of nearby refuges within nests, tree crevices, or in debris at the tree base. We suggest that sociable weaver nests provide multiple benefits to skinks including lowered predation risk, thermal refuges and greater prey availability, although this requires experimental testing. In the current era of global climate change, sociable weaver nests may become a crucial resource for lizards seeking refuge as the Kalahari climate warms.

Ecological engineering across a temporal gradient: Sociable weaver colonies create year‐round animal biodiversity hotspots

“…Therefore, we suggest studies covering multiple years would be useful to fully evaluate the predictions of the SGH as it relates to the role of sociable weaver colonies. Furthermore, certain groups not included in this study, arthropods, amphibians and reptiles, are expected to benefit most from terrestrial engineers (Romero et al, 2015), and this is supported by studies that have shown increased abundance of invertebrates and reptiles at weaver colonies (Harvey et al, 2015;Rehn, 1965;Rymer et al, 2014).…”

“…Anecdotal data suggest a wide range of non‐obligate species also associate with these colonies (Maclean, 1973a). For example, Kalahari tree skinks Trachylepis spilogaster increase in abundance at trees that host weaver colonies (Rymer et al., 2014) while African pygmy falcons Polihierax semitorquatus , and some arthropods are obligately dependent on these structures (Harvey et al., 2015; Rehn, 1965). Nevertheless, the full importance of these nest colonies to the surrounding animal community is still unknown.…”

An integrated population model sheds light on the complex population dynamics of a unique colonial breeder

“…However, coupled with the positive effect of rainfall on reproductive output (Covas et al, ; Mares et al, ), less and later rainfall would most likely result in a negative impact on population growth rate through decreased fecundity. Even though total rainfall is forecasted to decrease, extreme rainfall events are likely to continue to increase (DEA, ; Mason, Waylen, Mimmack, Rajaratnam, & Harrison, ; Niang et al, ); whether and how these projected changes affect the persistence of this keystone species (Rymer, Thomson, & Whiting, ) remains to be seen.…”

Ecological engineering across a spatial gradient: Sociable weaver colonies facilitate animal associations with increasing environmental harshness

“…Colony presence increased the abundance of reptiles. Our findings support previous research that showed reptiles associate with weaver colonies (Rymer et al, 2014). However, we did not see variation between the differences in colony and non-colony trees across the aridity gradient.…”

“…Soils directly below colonies have particularly increased nutrient levels (Prayag et al, 2020) and this could result in direct effects on the local vegetation and animals. Weaver colonies have been shown to act as a resource to multiple species within the environment (Bolopo et al, 2019; Lowney & Charlton, 2017; Maclean, 1970; Rehn, 1965; Rymer et al, 2014) and maintain this impact throughout the year (Lowney & Thomson, 2021). Their facilitative role across their distribution remains unknown (Figure 1).…”