20 May 2013

Tawny having a tough time

The nests of Barn and Tawny Owl have been recorded in Lincolnshire and Nottinghamshire intensively since the mid 1980s. This has provided a wealth of information, which is used to look at many aspects of breeding success.

Adult Tawny Owl by Carol Greig

Adrian Blackburn and Jim Lennon, along with help from other ringers, checked 82 Tawny Owl nest boxes on 21-24 April 2013 in East Lincolnshire, and recorded an occupancy rate of just 17% (14 boxes). Squirrel, Jackdaw, Stock Dove and Great Tit were also recorded. In total in 2013, just 17 chicks were ringed from seven broods; half of these were provided by two surprisingly large broods of four chicks, with and one other containing three young while the remainder were the rest consisted of single nestlings or pairs of owlets. This is much lower than the average number of 36 ringed young recorded over the period 1996-2012 and far below the highest annual total ever, an impressive 62 chicks ringed in 2005.

There were still two nests with eggs on the last visit could potentially produce more chicks but are very unlikely too at this stage; the other five had failed either during incubation or soon after the chicks had hatched.  We posted previously about the hard time Barn Owls were having due to the cold spring, so finding that Tawny Owls were also having a hard time was not a great surprise.

Some reasonably healthy Tawny Owl chicks by Carol Greig
There is evidence of a lack of prey from the boxes with fewer voles and mice being found, these being replaced with more unusual items, including the hind leg of a hare, a Carrion Crow’s head and a few shrews. It is notable that the boxes in ‘prime’ deciduous woodland habitat, which usually produce the majority of offspring, fared worst, with those in suburban gardens achieving a much higher output. Could it be that small mammal populations in woods have become depleted during months of cold weather and poor vegetation growth, while garden rodent populations thrive on the artificial food provided for birds?  The situation is probably not helped by the breeding season for song birds being delayed by several weeks, potentially reducing the availability of young birds as prey.

Thanks to Adrian Blackburn and Jim Lennon for letting us know.

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