The Barn Owl project – An Update

Over the last two years (2007/2008) I have been monitoring barn owl nest and roost sites in Delta and Surrey. In total I have checked 143 potential nest/roost sites at least three times for any evidence of barn owl occupancy, and monitored 54 nest sites on a weekly basis over the last two years. A total of 134 barn owl fledglings have been banded and I have obtained valuable information about their growth and diet.  

I am happy to say that barn owls are still a common sight in the agricultural lands of Delta and Surrey and sometimes even in more urban areas. Throughout the study the barn owls have surprised me in how resilient they are in terms of the sites they choose to make their home, like a steel plate factory, a soil making plant, or a riding arena. Unfortunately they are not always very foresighted, and some of the narrow beams they choose to nest on put the chicks at risk of falling down when they get a bit older and feel like wandering around a little. So I am hoping we can be able to install some more nestboxes in such high risk areas.

Nesting & Chicks

The barn owl lays it eggs asynchronous, on average one every two days, this also depending on the weather. The most I recorded was 8 eggs, which can lead to over 250g weight difference between siblings when they all hatch.

In such circumstances the youngest ones have a hard time competing for food and will in most cases die of starvation in which the female will treat the dead chick as any other prey item and feed it to the remaining chicks, thus making sure nothing goes to waste.

The chicks grow tremendously the first five weeks, almost doubling their weight every week, exceeding the average weight of an adult when they are between 38-45 days old. 647 g was the heaviest chick recorded, almost 100g more than the average weight of an adult female. The chicks lose this baby fat when they develop their wings and their primaries and prepare for flight. Mastering flight doesn’t come without lots of practice and it is not unusual to see the parents doing quite a bit of coaching before the young barn owl decides to leave the nestbox and try its wings for the first time. Haven survived to this stage is an achievement in itself for any barn owl chick. Although the next stage; finding its own territory and mate may be an even bigger challenge in today’s Delta and Surrey.   

Results to date:
The number of eggs laid (2007:4.5± 1.4, 2008:6.0± 1.5) and the number of chicks hatched (2007: 3.5 ± 2.3, 2008: 5.4 ± 1.5) was significantly higher in 2008, but not the number of chicks that finally fledged from each nest site (2007: 2.2 ± 1.2, 2008: 3.0 ± 2.1). The range was 1-5 chicks fledgling from each nest site.

My monitoring of old barns, buildings and trees for barn owl occupancy showed that there has been a 38% decline in occupancy in Delta and Surrey over the last 18 years. However, 70% of this decline is because the roost/nest site is no longer available and has either fallen down, burned down, made inaccessible or been demolished.
The increase in traffic volume on highways is the main factor explaining why some barns which one would expect to be inhabited by barn owls remain unoccupied.  This indicates that barn owls are at high risk of becoming hit by vehicles and trucks when crossing and hunting in the grass verges alongside highways.

So in summary, my results so far are showing that the reduced availability of roost/nest sites and highways are the two main factors negatively affecting the barn owl population in Delta and Surrey.

Thank you so much for your cooperation and letting me have access to your barn/nestbox. Without your cooperation my research would not have been possible. If you have any further questions about my project or barn owls, feel free to email me, sofi.hindmarch@gmail.com or phone 778-238-7380.