This summer, new light-weight GPS (Global Positioning System) data loggers have been used to track Barn Owls in Ireland for the first time, revealing amazing detail on their foraging behaviour and providing insights on previously unknown aspects such as precisely which habitats birds use or avoid, how birds respond to poor weather, how much time they spend in farm yards, flight height and speed.
Until now, our knowledge of an individual's movements has been largely confined to the nest site. Nest cameras and nest visits and observations at the nest provide useful information, but once the owls head off to hunt we were, literally, in the dark.
The basis of using GPS data loggers on Barn Owls stems from the need to discover the factors which influence risk of collision for Barn Owls on major roads. Have a look through this blog and you will find many references to road casualties on, e.g., the Tralee Bypass (see HERE).
With this in mind, Transport Infrastructure Ireland and BirdWatch Ireland have initiated research to investigate the extent and impacts of road mortalities on Barn Owl populations, the factors which cause high casualty rates on a major road and whether it is possible to develop effective mitigation to reduce Barn Owl road mortalities.
A Barn Owl road casualty on the hard shoulder of the M8 in Tipperary, near Cahir, in February this year. Egis Lagan road maintenance staff contracted by T.I.I. record details of all such casualties on a daily basis along an 90 km stretch of the M8 (M.O'Clery).
The lightweight GPS tags are carefully fitted on the lower back of adult Barn Owls (under licence from NPWS/BTO), and are designed to fall off after approximately two to three weeks.
Adult Barn Owl ready to be released, with the GPS tag in place. It is lightweight enough not to hamper movement or flight, and designed to fall off the bird after about 10 days.(M.O'Clery, under licence from NPWS).
The GPS tag (M.O'Clery).
And what extraordinary revelations are coming from this information. For the first time, we can see exactly where, when and for how long an individual Barn Owl hunts. We can see exactly where a bird perched, for how long, where it next flew to, at what speed, and all with an accuracy down to just a metre or two.
Sample GPS data from a female Barn Owl at a site in north Kerry in July 2016 showing her movements over three nights (J.Lusby/M.O'Clery, under licence from NPWS).
We can see in some cases where a bird roosted for the day (sometimes many kilometres from their nest site), when they resumed hunting that evening, and which habitats they favoured while foraging. We can see where they quartered field edges, or perched in a high tree at the edge of a conifer plantation, and which barn they took shelter from during a downpour.
And what does all this tell us about Barn Owls and major roads? Three sites where birds were tagged had major roads within the owls' home ranges: the M8 was 2km from one nest; the main Tralee to Listowel road was 2km away from the second, and the Castleisland Bypass was 2.5 km from a third. All three Barn Owls hunted during that time along the major roads in their area.
By way of example, have a look below at the movements of a female Barn Owl as she hunts near Castleisland, Co. Kerry, in late July. The video starts with a view of her nest site, but we join her nearly 2km away, at a farmyard where she has been sheltering from torrential rain for four hours. It is now 1.30 a.m. and, as the rain finally lets up, off she goes. We can track her movements as she perches on trees and hedges and then, she arrives at the Castleisland Bypass...
And what does all this tell us about Barn Owls and major roads? Three sites where birds were tagged had major roads within the owls' home ranges: the M8 was 2km from one nest; the main Tralee to Listowel road was 2km away from the second, and the Castleisland Bypass was 2.5 km from a third. All three Barn Owls hunted during that time along the major roads in their area.
By way of example, have a look below at the movements of a female Barn Owl as she hunts near Castleisland, Co. Kerry, in late July. The video starts with a view of her nest site, but we join her nearly 2km away, at a farmyard where she has been sheltering from torrential rain for four hours. It is now 1.30 a.m. and, as the rain finally lets up, off she goes. We can track her movements as she perches on trees and hedges and then, she arrives at the Castleisland Bypass...
Video showing the movements of a female Barn Owl, Castleisland, Co. Kerry. The GPS device was scheduled to record one fix every five seconds - yellow fixes are where the bird was flying at speed, orange fixes indicate slower hunting flight and red is where the bird was stationary (J.Lusby/M.O'Clery, under licence from NPWS/BTO).
(You can click on the 'four arrows' symbol, bottom right, to see a full screen version of the video)
(You can click on the 'four arrows' symbol, bottom right, to see a full screen version of the video)
On one night she hunted along a 1km stretch of the Bypass for 55 minutes, crossed the road six times, and even perched on the central median for 17 seconds! The dangers to the Barn Owl are obvious, however this information also highlights the suitability of road-side grassy verges for foraging. On this occasion she does does not successfully capture prey, and moves on to forage elsewhere to try and provision the three chicks which are back at the nest site.
---
We have a huge amount of information to analyse from this season's GPS data, and there are still other tags to be retrieved, but we will keep you posted with more info and insights as we go...
---
We have a huge amount of information to analyse from this season's GPS data, and there are still other tags to be retrieved, but we will keep you posted with more info and insights as we go...
