Can optimal caching models predict changes in diurnal feeder use patterns in black-capped chickadees ( Poecile atricapillus )?

Abstract

Many birds collect and store food for later use, a behaviour known as caching. Theoretical models predict that caching effort is concentrated in a single peak during the day, though the precise timing of that peak depends on multiple factors. We studied diurnal patterns of feeder used in a population of 50 individually marked black-capped chickadees (Poecile atricapillus) in late summer. We used total daily feeder visits (1 visit ≈ 1 sunflower seed) as a proxy for caching intensity because daily feeder visits (range 11–339 feeder visits per bird per day) often exceeded the required intake of about 45 sunflower seeds for chickadees at this time of year, consistent with a wide range of caching effort. Patterns of feeder use were always bimodal, and increases in hourly feeder visits occurred throughout the day with increased total daily feeder visits, however, the greatest relative increase in feeder visits was during midday. Post hoc analyses revealed that this population-level effect was driven by individual differences; some chickadees increased morning feeder visits with increasing total daily feeder visits, while others increased midday or end-of-day feeder visits. Future work should investigate drivers of these individual differences, including the role of interference competition.