30 July 2020

2020 Barn Owl update

With the first Barn Owl broods now all ringed and boxes monitored, it's a good time to take stock and see how the season has gone. Averaging out the numbers in the table below, we can see that the project continues to grow and for the first time we have data from over 100 boxes which is a greeat achievement. The occupancy rate contineus to be relatively low, but we hope that previously unoccupied boxes will be taken up by new pairs as the years go by. Of the boxes monitored, clutch sizes appeared to be slightly down on previous years, but the subsequent brood sizes didn't necessarily reflect this. The figure of 3.2 hides a much more complicated story though.


2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Sites visited 32 34 32 44 41 47 64 85 87 106
Unoccupied 2 7 12 11 11 12 23 34 36 43
Occupied but no breeding 13 2 7 7 7 8 5 4 3 4
Average clutch size
(where observed)
4.8 4.1 3.6 4.6 4.6 4.6 5.3 5.2 4.7 4.6
Average brood size
(where observed)
3.1 3.1 2.4 3.5 3.5 2.8 3.0 3.3 3.0 3.2
Number of chicks ringed 33 46 19 63 70 47 90 126 119 170

It was apparent as the season progressed that brood sizes (and numbers of chicks ringed) was decreasing, but this is always hard to measure. But if we simply look at the number of chicks present at ringing through the season then a trend does seem to appear. The sample sizes are rather low, but we do think there's something in the data.

The much lower brood sizes later in the season we presume was due to the period of very unsettled weather, with plenty of rain. This makes feeding very difficult for adults which obviosuly has knock-on effects for chicks. We hope to be able to place cameras in numerous boxes over the winter (watch this space on that), which will give us much better data over the coming years.

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