Hunting and Feeding: Red Crossbill (Loxia curvirostra)

The red, or common, crossbill is a species of finch whose diet consists almost exclusively on the seeds of coniferous trees (Hahn, 1998). As such they have adapted a distinctive trait that enables them to deal with their specific diet. The unusual crossed bill of these birds allows them to prise open the tough cones of conifers before they ripen and open naturally (Uhlenbroek, 2008, pg 191). Their adapted bill comprises of an elongated upper bill and a shorter, crossed lower bill, which – while common to all crossbill species – can differ in size and shape between species and populations within a species according to their preferred type of cone, be it spruce, pine or larch (Marquiss, 2002).

In order to feed, the crossbill simply inserts its closed bill into a cone and opens the crossed tips, thereby prising open the scale of the cone and allowing the bird to eat the seed inside (Marquiss, 2002). Because of their highly resinous diet, these birds must frequently visit water sources in order to drink and clean off their bills (Uhlenbroek, 2008, pg 191).

The adaptation of this bill gives an advantage over other finches inhabiting the same area due to the ability of the common crossbill to breed whenever the cone crop ripens, even during the winter months (Hahn, 1998).

References:

Hahn, T.P. (1998). Reproductive seasonality in an opportunistic breeder, The Red Crossbill, Loxia curvirostra. Ecological Society of America, 79(7), 2365-2375.

Marquiss, M. & Rae, R. (2002). Ecological differentiation in relation to bill size amongst sympatric, genetically undifferentiated crossbills Loxia spp. International Journal of Avian Science, 144(3), 494-508.

Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.