Wednesday, 23 June 2010

Varb Owls enjoy bumber start

It is quite an achievement. Thanks to the efforts of the local fishing syndicate, and support from EDF Energy, we now have Barn Owls again breeding on one of our local nature reserves. It is also quite an achievement for the owls, because the female is incubating a clutch of eight eggs. If all of these hatch then this will be one of the largest broods I have seen in a decade-and-a-half of watching and studying these magnificent birds.

The groundwork for such success was laid earlier in the year. While the provision of a suitable nest box has been particularly welcome, it has been the availability of small mammal prey that has enabled this particular female to produce such a large clutch of eggs. In turn, this highlights the importance of the habitat management being carried out on the reserve and the use of cattle to produce a grassland sward that can sustain such an abundance of Field Voles and shrews. For the owls, the real work will begin any day now, once the eggs hatch. Over the first week or so, the chicks will be unable to regulate their own body temperature properly and they will depend on their mother to brood them and keep them warm, the male bringing in food for the female to tear up and provide to the chicks. As the breeding attempt progresses, so the female will begin to leave the young unattended, helping the male to provide food for an increasingly demanding family.

Barn Owls initiate incubation once the first egg has been laid (most other birds don’t begin until the clutch is complete), with subsequent eggs laid at roughly two-day intervals. This means that the eggs tend to hatch over several days, resulting in chicks of different ages in the nest together. The eldest chick may be a week or more older than its youngest sibling. The adoption of this approach is very much a survival strategy, geared to increasing the chances that the owls will rear at least some young if times are difficult. It will be the oldest and largest chicks that will always get fed first, the youngest chicks only receiving food once the elder siblings are satiated. If food becomes scarce, then the youngest chicks will lose out and, unfortunately, are likely to starve to death. They then become food for the larger chicks. If all the chicks were the same age, then the chances are that they would all die if food became scarce. It may seem harsh but it is a neat strategy for a species whose prey may suddenly change in availability. Let’s hope that small mammals remain abundant on the reserve this summer.

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