Many bird species have amazing ways of adapting to changes in their environment, and a recent study in Britain has revealed that great tits, blue tits and other native species are tapping into a new food source as a counteractive measure against the effects of climate change. Some bird species have started laying their eggs too early in the year, most likely as a result of climate change, and this has resulted in their chicks hatching out before their food source is available, the food source being caterpillars that feed on newly sprouting oak leaves in spring. The new food source is the protein-rich larvae of invasive oak marble gall wasps which the birds access by pecking away the tips of the galls found on the oak trees. Researchers working on the project, Professor Graham Stone of the University of Edinburgh, and Dr Karsten Schönrogge of the Center for Ecology and Hydrology, noted that the evidence shows that the gall wasp larvae are not just an ‘occasional snack’, but rather a ‘really significant food source’.
The oak marble gall wasp (Andricus kollari) lays its eggs within the oak tree leaf buds via its ovipositor. This then develops into a round mass of green plant tissue which later turns brown and becomes hardened. Within this hardened gall there is a single wasp larva, and this is what the bird is after. These galls are found in their thousands on the Turkey oak trees (Quercus cerris) which were introduced into Britain in 1735. The first wasps that emerge are all female and go on to lay their eggs in the same manner, but without mating. The galls grow over winter and in early spring both males and females hatch, go on to mate, and the cycle starts again.
Credit goes to Dr Tracey Begg who had the task of cutting open more than 30,000 Turkey oak buds collected from eight sites in Scotland and England. Of the 3,000 galls she examined, Dr Begg found that on some trees up to half had been pecked open, leaving ragged marks, as opposed to the smooth hole wasps create when they emerge naturally, confirming that the birds are using the wasp larvae as a major food source.
