Spit it out: does Canada Jay saliva help preserve their perishable food caches?

Background/Question/Methods

Species-specific adaptations that optimize food-caching have been identified across taxa. Canada jays (Perisoreus canadensis) are scatter-hoarding passerines whose large salivary glands produce copious amounts of saliva to fasten small boli (ca 1 cm X 2 cm) of perishable foods to arboreal cache sites. However, there may also be potential antimicrobial properties of their saliva, including lysosomal activity against Gram-positive bacteria and Carnobacterium spp., that could aid in the long-term preservation of cached food. We examined the effect of Canada jay saliva on cache degradation by deploying simulated caches in Algonquin Provincial Park, ON. Caches were boli of suet covered in: 1) saliva from Canada jays, 2) human (negative control), or 3) no saliva (control) placed in high-density polyethylene chambers drilled onto black spruce (Picea mariana), a preferred caching substrate, deployed from Oct. 2020 and retrieved Jan. 2021 then repeated from Oct. 2021 with a first retrieval date in Jan. 2022 and a second retrieval date in Apr. 2022, the latter of which marks a transition period for Canada jays from cached to fresh foods. To test for differences across treatments, a Kruskal-Wallis test then Dunn’s test were used to compare proportions of original cache masses that were lost during treatments.

Results/Conclusions

Mean mass loss of caches retrieved in Jan. 2021 (n=143) differed significantly across treatments (H(2) = 32.941, p < 0.001). Jay saliva-coated caches lost significantly less mass (5.4% ± 6.3) than human saliva-coated caches (10.0% ± 6.11) but did not differ significantly from the no-saliva control (5.1% ± 3.5). Caches retrieved in Jan. 2022 (n=80) differed in mean mass loss significantly across treatments (H(2)=51.495, p < 0.001). As in the earlier experiment, mean mass loss in jay saliva-coated caches (mean = 2.7% ± 2.0) was significantly lower than in human saliva-coated caches (mean = 14.0% ± 8.0) but did not differ significantly from control (mean = 3.5% ± 2.4). Our results suggest that Canada jay saliva lacks the chemical digestive function characteristic of human saliva and that this likely aids in preserving perishable food that may be stored for as long as 5-6 months.