The recent decline of the little owl in Britain calls for a greater understanding of the processes affecting populations of this species. The loss of suitable habitat and changes in land use practices are thought to be the main reasons for the decline of the little owl across Europe. The level at which these changes have impacted on the British little owl population is currently unknown.
Emily Joachim's Hawk and Owl Trust-backed PhD study into the decline of the little owl has come to the end of its first year. Emily believes that the decline in the British population of little owls could be linked with a reduction in the number of juveniles that survive the post-fledging period. If a juvenile little owl manages to gain enough experience, survives the post fledging period and secures a territory by October, it is much more likely to survive the winter and breed in the spring.
Emily reports a poor 2008 breeding season with too few young surviving their first six months. Radio-tracking was used to look at juvenile survival rates, time of fledging, post-fledging dispersal patterns and the causes of mortality in 17 little owls. The owlets were tracked until they were recorded as dead, lost or the tag battery had drained.
Five juveniles perished within the vicinity of the natal site during their first month post-fledging. Four were killed by predators and the fifth became trapped in an ash tree root and drowned when the adjacent water meadow rose. Three owlets were tracked between nine and 16 days after which their tags were classified as 'lost'. Emily suspects that these juveniles were also killed by predators whilst fledging, but as the tags were never found this cannot be confirmed. A further two were killed by predators on day 52 and 93 of this study. Emily does not believe that the tags impacted on the survival of the juveniles.
It is not all bad news though as five of the owlets were tracked between 84 and 182 days after which their tag batteries drained. Two of these juveniles took their flight of independence at the end of September, dispersing between 2km and 3km from their natal site. The remaining two tagged juveniles were recorded as 'lost' on days 41 and 62 of the study. Emily believes that these two juveniles took their flight of independence but she was unable to find them.
Why are so many juvenile little owls dying? This first year of research has highlighted the need for natal sites to be within a patchwork of habitats including hedgerows, dense vegetation and a network of branches, offering shelter for the young whilst branching. Without these habitat features, the juveniles fall to the ground and they have nowhere to hide from predators. Juvenile little owls start branching between three and four weeks and this is when they are most vulnerable.
Emily believes that the loss of suitable habitat means that little owls are finding it increasingly difficult to find territories that provide sufficient prey availability and accessibility, roosting and nesting sites with limited predation pressure. As a result, too few juveniles are surviving their first six months to go on and breed the following spring.
Emily Joachim's research is supervised by Dr Graham Holloway at The University of Reading and her fieldwork is supervised by Major Nigel Lewis MBE. The PhD is funded by a Biotechnology and Biological Sciences Research Council (BBSRC) studentship and is sponsored by the Hawk and Owl Trust and the World Owl Trust.
