Do you ever find the food provided by the dining hall so undesirable, that you have to dig up those months-old snacks in your fridge or cabinet? Some animals in nature behave in the same way. When facing the threat of limited resources, animals return to the food storage they created during times of rich food resources. These strategies of collecting and storing resources for future use are called food caching. Food caching is widely used by birds and mammals to survive through periods of low food-availability. Some animals are short-term food-cachers, who retrieve their food within hours or days. Meanwhile, other animals are long-term food-cachers who keep their food in storage for upcoming low-resource seasons. However, animals in the wild do not have the fridge or cabinet like you do, so how would they optimize their caching sites to prevent their food from the susceptibilities?
In the study “Canada jays (Perisoreus canadensis) identify and exploit coniferous cache locations using visual cues,” Martin et al. (2022) studied cache-site selection of Canada jays. Canada jays are long-term cachers, storing their food to survive through the winter. To protect their long-term cache from potential degradation, Canada jays use behavioral strategies to select the optimal environment for cache preservation. Tree species provide a variety of cache-site characteristics, such as different structures, chemical cues, and visual cues, but the mechanisms causing preferences for certain tree species remain unexplored. Experiments have shown that food preservation in conifer tree species is better than in deciduous trees, but no evidence has shown whether Canada jays are actively or opportunistically selecting conifer trees as their cache sites.
To investigate cache site identification and exploitation, researchers asked three questions: (1) Are Canada jays able to discriminate among tree species for caching? (2) Do they make assessments based on olfactory cues of the trees? (3) Do they make assessments based on visual cues of the trees?
The researchers hypothesized that both olfactory and visual cues of conifer trees increase the preference of Canada jays. To conduct the study, researchers captured 8 adult Canada jays and induced their caching behavior prior to the experiment. The birds’ behaviors were recorded in a free-flight room.
To answer the first question, researchers allowed the Canada jays to freely cache in a room with four tree species that mimicked their habitat. The four species include two coniferous species, red pine and white spruce, and two deciduous species, red maple and white birch. The Canada jays showed a significant preference to first visit the white spruce, as well as to spend time on it and cache in its branches. Their caching rate and frequency on white spruce was statistically significant, which means that in a given time or a given number of visits, Canada jays showed a propensity to deposit more on white spruce.
This study continued to investigate the influence of olfactory and visual cues on cache site search. Since deciduous trees lack the volatile to produce the scent, the experiment on olfactory cues only utilized conifer odors by spraying four conifer scents on different caching boards. The four scents being used were white pine, white spruce, balsam fir, and easter hemlock. Canada jays did not show a difference in the number of visits they made, or the time spent interacting with boards with different scents. They also did not show significant interest in caching on the board with any particular scent. In the study of the visual cues, Canada jays were choosing their cache sites among artificial trees with the configuration of either 2, 4, 6, or 8 evenly spaced branches. They presented no preference to visit or spend more time on any tree configurations, but demonstrated a greater proportion of caches in eight-branch trees compared to other trees.
Results from the first experiment indicate that Canada jays were able to identify their ideal cache hosts in order to exploit the hosts’ beneficial locations. If the Canada jays’ site search is solely based on opportunity, there would not be a significant preference for first visit, spend time, and cache in the white spruce, which is a coniferous species. The olfactory cue experiment showed no support that Canada jays use olfactory cues to discriminate among the caching sites, because the number of visits, time spent, and number of caches did not differ among the boards with four different scents. The visual cue experiment showed that Canada jays preferentially cached in the trees with the most branches, suggesting that they exploited the configuration cues and actively selected the most desirable site.
In the study with various number of branches, researchers found that Canada jays tend to cache at the intersections of the trunk and branches, as well as the end of the branch. Based on the findings we have, we could form further hypotheses on why multiple-branch trees are more preferred by Canada jays.
Previous research has shown that conifer species are better at cache preservation compared to other tree species. The results in this study suggests that Canada jays actively select conifer trees, especially white spruce, as the host of their long-term food preservation. Therefore, we could form a possible explanation as to why there is a correlation between Canada jay territory occupancy and conifer density. The preference for conifer trees as cache sites helps us understand the dynamic between the birds and the environment, which in this case is that the preference drives Canada jay’s habitation into regions with rich conifer resources.
Martin, R. J., Fuirst, M., & Sherry, D. F. (2022). Canada jays (perisoreus canadensis) identify and exploit coniferous cache locations using visual cues. Ethology. https://doi.org/10.1111/eth.13273