Resource geometry and provisioning routines

Provisioners capture items both for delivery and for self-feeding. In doing so, they may travel directly to and from a single location, visit several patches on each excursion from a delivery point, or alternate excursions to different destinations. Prey suitable for self-feeding versus delivery have differing attributes, which means that they are often best sought in different places. Visiting separate patches to self-feed and to load prey for delivery requires more travel time than foraging for both types of prey at a single location, but both self-feeding and loading are faster if carried out in the most suitable patches. Here, we investigate how the distribution of different types of food resources around a central delivery point affects the routine with which a provisioner visits patches to forage. Our results show that each of several basic travel routines is best in some broad region of a parameter space that considers the loading time saved in relation to the extra travel time required. This framework provides a simple explanation for the variety of routines observed in nature and can additionally account for the circumstances under which provisioners concentrate loads for delivery by internal processing, known in some seabirds.