PAC1":emn1encp said:
This morning some crow/rook things were trying to build a nest at the top of our chimney. Two fell down the chimney, one died the other had to be let out the window. I hope that will be an end to plans for our chimney. However as there were four or five of them hanging around I am not convinced. not least because last week they set the burglar alarm off by one of them falling down the chimney!!
Those would be Jackdaws, who are notorious for nesting in chimneys. Best deterrent is a mesh guard over the chimney. Rooks and crows both nest in tall trees, rooks in noisy colonies (rookeries) while crows are less social and very territorial.
All the corvids (raven, crow, jackdaw, rook, magpie & jay) will mob and harrass larger birds in their territories, mainly because the larger hawks and seagulls are both a threat to their young and compete for the same food resources. They harrass mammal preditors (fox, stoat, cats, dogs etc) for the same reason.
Although most of the corvids will take the nestlings & eggs of songbirds if the opportunity arises (as will foxes, polecats, stoats, rats & weasels etc) the domestic (and feral) cat is a much greater threat to their numbers particularly in more urban areas. When songbird numbers decrease, leaving only magpies, crows, seagulls and pigeons, the corvids (and seagulls) get the blame, but the change in numbers can also be explained by cats finding the songbirds easy prey, and the larger birds too much trouble. It is thought that one reason for increase in magpie (and other corvid) numbers is the amount of roadkill on our roads and discarded food waste on the streets, as they are primarily scavengers rather than hunters.
Small birds will also mob large preditors - I've seen gangs of swallows and housemartins join forces to mob a sparrowhawk which had attempted (and failed) to take a young housemartin in flight.
tekno.mage