At some sites in Ireland, Jackdaws can be a real problem when placing nest boxes for Barn Owls. They also nest in cavities, and once they find one they like, will line it with sticks until the size of the cavity is to their liking. They are such industrious stick collectors that they will quickly fill a large nest box cavity until there is just room for their nest and little more. This renders it useless to Barn Owls. Thankfully this has only happened at one of our sites so far, and if Barn Owls move in, only the most foolhardy of Jackdaws would go near it (see an example of this on this page HERE.
Although we normally recommend the type of nest box shown on this page HERE, there are one or two sites where a specially adapted box can be used to thwart Jackdaws. The double entrance on this box means the Jackdaws have trouble manoeuvring large sticks around the corners and into the main chamber, and the high second entrance also means that if the Jackdaws put sticks into the first, smaller chamber, the second will not be blocked. It seems to work!
This box was placed high in the rafters of a derelict school in Co. Kerry, last week. The design should deter any interested Jackdaws, and the outer covering of tarpaper will help keep out the elements in this rather exposed site. The rest is up to the Barn Owls...