Chickadees Use Individual Search Sequences To Forage For Food

Black-capped chickadees are food-storing passerines that are able to keep track of thousands of stored food locations called caches (Sherry, 1984; Healy & Hurly, 2004). They do this by using spatial memory, a cognitive adaption that allows for the most conservative use of their resources (Sherry, 1984; Tomback, 1980). For example, it is beneficial for them to not have to rebuild a shelter every time they leave one to search for food.

Finding their shelter after foraging is dependent on spatial memory. In chickadees, spatial memory also is important for food storage; in fact, many birds, including nutcrackers, jays, tits, and chickadees, rely on stored food to survive winter and to feed their young (Tomback, 1977; Roberts, 1979).

Chickadees are able to accurately relocate food they have hidden, or cached, recall which of their food sites have been emptied or discovered empty, and recall which kind of food is located at each cache site (Sherry, 1984). Moreover, the perceptual and motor experience of finding food, carrying it to a location, and storing it there, may be necessary to establish strong spatial memories in chickadees (Baker et al., 1988). Despite this fact, on average chickadees cache only 10 -15 % of the food they encounter in the wild during a day, suggesting that they do rely heavily on, and consume a large amount of, foraged food (Pravosudov, 1985).

Foraging animals can employ two strategies: win-stay to return to the location of food, or win-shift to avoid that location in the future (Olton, Handelmann & Walker, 1981). These strategies are cognitive adaptations to the depleting or replenishing nature of their food (Sulikowski & Burke, 2011) that can be tested in a two-phase procedure.

In Phase A, also known as the study phase, subjects are given the opportunity to search multiple locations until they find all of the food hidden there. After some interval of time, the subjects return for Phase B, also known as the test phase, to search for food again. When the locations that contained food are the same in the study and test phases, the subjects can use what is called a “win-stay” strategy to successfully return to the locations of food. When the locations that contained food are different between phases, subjects can employ what is called a “win-shift” strategy to avoid locations where food will not be found during the test phase.

Birds that forage on food resources that replenish use a win-stay strategy (Kamil, 1978) while birds that forage on resources that deplete use a win-shift strategy (Smith, 1974). Spatial memory for the locations of food, dangers, toxins, and shelter is essential for survival and development and is well studied in both rodents and birds (Schmid Hempel, 2011). However, the responses of many birds, including chickadees, to win-stay and win-shift contingencies is unknown.

Chickadees forage for foods that deplete after a single foraging bout (i.e., insects) and foods that replenish over time (i.e., seedheads); therefore, chickadees might be expected to flexibly employ win-shift and win-stay strategies while foraging in response to reward contingencies. Researchers at The University of Western Ontario’s Advanced Facility for Avian Research (AFAR) tested chickadees under conditions that promoted either win-stay or win-shift strategies and quantified their use of each strategy. They hypothesized that chickadees would alter their foraging strategy depending on the reward contingency.

First, chickadees foraged in multiple spatially dispersed sites located in trees during a study phase. Food was allocated randomly to these sites. In the win-stay condition, birds found food in the testing phase in the same set of locations as in the study phase. In the win-shift condition, birds found food in the opposite set of locations as in the study phase. Birds appeared to perform at chance when returning to locations that previously contained food in the win-stay condition and when avoiding locations that previously contained food in the win-shift condition. Rather than employ a win-shift or win-stay search strategy, chickadees used preferred search patterns that showed greater stereotypy under win-stay than under win-shift conditions.

In these experiments, the cost of searching the preferred possible food locations was low enough that the chickadees did not need to engage in a more effortful search strategy (i.e., one involving memory for win-shift or win-stay contingencies). Since chickadees forage year-round in the same locations, understanding the cause and mechanism of their individual search sequences warrants further investigation.

These findings are described in the article entitled Chickadees neither win-shift nor win-stay when foraging, recently published in the journal Animal Behaviour. This work was conducted by Nicole A. Guitar, Caroline G. Strang, Christopher J. Course, and David F. Sherry from the University of Western Ontario.