Highly social pinyon jays, but not less social Clark’s nutcrackers, modify their food-storing behaviour when observed by a heterospecific

Behavioural flexibility can be described as the ability to use information and generalise it across contexts. Social living is thought to favour behavioural flexibility. We used a food-storing (caching) paradigm, during which individuals either ate or cached food under different conditions, to investigate whether they could flexibly adjust their caching behaviour when observed by conspecifics and heterospecifics. We examined the location and number of caches made by two corvid species differing in sociality, highly social pinyon jays (Gymnorhinus cyanocephalus) and less social Clark’s nutcrackers (Nucifraga columbiana). Although pinyon jays cached a similar amount of food across conditions, they allocated more caches to areas less accessible to the observer when the observer spent more time close to the caching locations. Nutcrackers, however, reduced the number of seeds cached when observed by another nutcracker in comparison to when they cached alone, but did not significantly change their caching behaviour when observed by a pinyon jay. The differences in cache protection strategies, and the social cues (e.g., presence and behaviour of an observing bird) that elicit them, may be explained by the species’ social organisation. Overall, our results provide insight into understanding how pressures associated with the social environment may influence foraging behaviours.

Clark’s Nutcrackers (Nucifraga columbiana) caching Whitebark Pine (Pinus albicaulis) seeds in trees

On 17 September 2017, I observed two Clark’s Nutcrackers (Nucifraga columbiana) from 8–10 m distance as they cached seeds in a stand of dead Whitebark Pines (Pinus albicaulis) at 2500 m elevation on Saint Mary Peak in the Bitterroot Mountains of Ravalli County, Montana. Over 5 minutes, the nutcrackers created 14 caches in seven different multi-trunk tree clusters in an area of about 50 m2. All caches appeared to be single Whitebark Pine seeds, positioned 2–5 m (mostly 3–4 m) above ground in dead trees. Of the 14 caches, three were placed under loose pieces of bark on a trunk (one) or large limb (two), and the remaining 11 were in encrustations of American Wolf Lichen (Letharia columbiana) growing on branches of the dead trees. Nutcrackers are known to sometimes cache seeds above ground in trees during the late summer and autumn harvest of pine seeds, but usually not to the exclusion of other microsites. The ground at the Montana site was covered by 7–9 cm of fresh snow that fell the previous day, which may have encouraged the nutcrackers to place all of their seed caches above ground in trees.