| Abstract |
Crossbills (Loxia spp.) are unique among the canary relatives for their specialised feeding on conifer seeds. Cone-seeds are often protected by woody cone scales, which crossbills evolved to open with their crossed bills and ability to abduct the lower mandible. These adaptations, however, make crossbills inefficient exploiting in nonconifer seeds and, therefore, they need to locate cone-seeds throughout the year, every year. Since cone crop production can vary spatiotemporally, this requires nomadism and flexible timing of breeding. This chapter explains the challenges of exploiting diverse cone structures and seed sizes, how multiple crossbill species can co-occur where trade-offs in feeding performance on alternative conifers favour different bill structures and the critical task of finding conifers that hold seeds in their cones into spring and early summer. A current concern is that climate change is causing the early release of seeds resulting in periods of seed scarcity that reduce crossbill populations. |
