Meeting Abstract
Diet specialists are particularly susceptible to fluctuations in food supply. A high degree of mobility allows some to use a Rich Patch Exploiter strategy, moving from one pulse of high food availability to another. Although this may allow them to spend most of their time in locations with abundant food, it may also require them to move long distances through regions where their specialized diet is not available. Two tactics for coping with this challenge are: (1) prepare for the move by laying down fuel reserves to be used during the movement, and (2) exploit other food sources besides their typical specialized diet while moving. Crossbills (Loxia spp.), and to a lesser extent pine siskins (Spinus pinus), are diet specialists, depending heavily on seeds of coniferous trees. As Rich Patch Exploiters, they annually move long distances through regions of few or no seeds in search of abundant conifer seeds. Both prepare for annual (spring/early summer) nomadic migration by depositing fat reserves to fuel long distance flight (tactic 1). However, since distance moved and destination vary from year to year, it seems likely that they may also need to employ tactic 2. Here we demonstrate that they rely heavily on insect foods (e.g., aphids, lepidoptera larvae) that are abundant on coniferous and other trees during the spring/early summer movement period. We also discuss importance of these insects to other components of their annual cycles (reproduction, plumage molt). Periodic reliance on alternative dietary components may be widely important in Rich Patch Exploiting diet specialists such as these finches.
