An experimental test of seasonal and social influences on caching in black-capped chickadees, Poecile atricapillus

Caching (i.e. storing food for later) acts as an external energy reserve, increasing the probability of winter survival in small birds. For many species, high-intensity caching occurs in autumn when food is comparatively abundant. Theoretical models predict that reduced foraging predictability favours increased caching. Higher-ranked individuals often experience greater predictability in their access to food and are therefore expected to rely less on caching. We used radiofrequency identification (RFID)-enabled feeders to quantify the use of cacheable and noncacheable food in a free-living marked population of 91 black-capped chickadees, Poecile atricapillus , including the daily and seasonal caching patterns for individuals of different ranks. We used two separate proxies for dominance. First, we used sex (male or female) as a proxy for dominance because, in chickadees, males are dominant over females. Second, we used the number of feeder sites visited (one site or multiple sites), based on both theoretical and empirical work suggesting that subordinates use larger areas to meet their foraging needs, presumably due to their lower ability to monopolize resources. Contrary to our prediction that subordinates would cache more, we found that males had a higher use of cacheable food than females, and within sexes, individuals using a single feeder site had a higher use of cacheable food than individuals using multiple feeder sites. We also found a decline in the use of cacheable food, but not noncacheable food, over the course of the experiments (mid-October to mid-November), which was steeper for males and single feeder site users compared to females and multiple feeder site users. We suggest that higher use of cacheable food by males and single feeder site users in our study may be because the food provided was sufficiently limited such that dominants outcompeted subordinates, limiting subordinates’ access to cacheable food. Future work manipulating food abundance during the caching period is needed to test this hypothesis. • Season and dominance are both predicted to affect caching (food-storing) rates. • We studied use of cacheable and noncacheable food in chickadees in autumn. • Use of cacheable food declined in autumn–winter; use of noncacheable food was stable. • Dominants made greater use of cacheable food than did subordinates. • High food competition may limit subordinates' access to cacheable food.