Ol’ Blue Eyes
Walking through Wivenhoe Park in the mornings, I see jackdaws already establishing their nest sites. Jackdaws pair for life and are cavity nesters seeking out holes in old trees, using nest boxes or even searching out chimneys. My sweep tells me he has noticed the progress of jackdaws north as more people report chimneys blocked by the untidy sticks that form the jackdaw nest. Pre 1965 chimneys are preferred; the most favoured being the 9” x 9” Victorian flue.
Inquisitive and intelligent they can be seen probing the grassland for insects and occasionally pinching shiny objects such as foil or even watches. Their distinctive grey nape marks them out from other members of the crow family but their most unusual feature is their pale blue-white eyes. Recent research suggests that this bright eye frightens off competitors. Apparently jackdaws avoid nestboxes when they see the pale eyes of another jackdaw inside.
The Cambridge Jackdaw Project monitored over 100 nestboxes and compared responses to different images including a dark circle, a jackdaw’s face with darkened eyes and the normal face with blue-white eyes. Jackdaws spent less time at the nestboxes with the bright eye image inside. Gabrielle Davidson, who carried out the work, admits that scientists are unsure of the reasons for differing eye colours within bird species; only ten per cent of perching birds have pale eyes.
As cavity nesters, jackdaws compete for the few sites available; the bright eyes may have evolved to act as a warning signal. Jackdaws are remarkably faithful to their nest site, staying close even through the winter months. Here in Wivenhoe Park, the jackdaws join a noisy roost on the nearby library building, not far, as the crow flies, from their nests in the old parkland trees.