GPS data shows Barn Owl successfully hunts along Motorway verge

Another of our GPS data loggers has recorded the flight of a female Barn Owl in Tipperary hunting successfully along the grassy verge of the M8 Motorway.

The nest site in an abandoned mansion in Co. Tipperary (M.O'Clery, under licence from NPWS).

Inside the nest, two chicks are visible at the rear of a long shaft in a wall cavity, and the backside of a third can just be seen near the top. As this nest was inaccessible, this image was taken using a special nest inspection device to record the number of young (J. Lusby, under licence from NPWS).

She initially takes off from her nest site and, as in the previous post below, hunts along ditches, hedgerows and streams, perching occasionally in trees and on telegraph poles. She hunts along the edges of gardens at one point and perches on a telegraph pole in front of a newly built house for four minutes. About 1.8km from her nest site, after seemingly failing to successfully capture prey, she focuses on the grassy verges of the M8 Cork to Dublin Motorway.

Although she flies along the grass verges, parallel to the Motorway, for about 50 metres, she soon lands on a fence, and within 35 seconds it seems she made a successful capture. We know this because she immediately starts on the return journey to her nest which lies out of sight nearly 2km away, but this time in a direct straight line and at greater speed than when she is hunting. Her return flight does not follow any of the linear features in the landscape which she would use while hunting. The round trip has taken 35 minutes.

Barn Owl hunting along the grassy verge of the M8 Motorway in Co. Tipperary (J. Lusby/M.O'Clery).

The GPS data from this site covered only a relatively small span of time, just over one night, but we can see she made a successful hunting trip to the Motorway verges during that time. Although the GPS data has captured this hunting trip in extraordinary detail, it poses further questions about how Barn Owls interact with major roads and we will be trying to better understand how important road-side verges are for foraging Barn Owls through gathering more information on their behaviour and movements, both at this site and others along the M8 motorway, which is also the route where we have recorded large numbers of juvenile Barn Owls as road casualties.

Screengrab of the point where she meets the M8, and then flies along the grassy verge for 50m. The red dots show where she perched and caught prey (J.Lusby/M.O'Clery).

Using Google StreetView we can see the exact spot where she perched and caught prey on the Motorway verge(circled). She flew directly to her nest nearly 2km away from this point (Google StreetView).

This research is funded by Transport Infrastructure Ireland, with information on the extent of Barn Owl road casualties on the M8 facilitated by Egis Lagan.

More on this very soon.

Seeking out hedgerows

As we start to look through the information generated this season from GPS data loggers fitted on Barn Owls, one of the obvious and consistent features is how foraging Barn Owls seek out linear features in the landscape, particularly hedgerows, and also features such as stream and river edges, woodland edges, and the rough grass of road-side verges. This is expected, but never before have we seen the foraging preference of Barn Owls, and the importance of hedgerows and edge habitats, in such detail.

North Kerry landscape showing typical hedgerow, woodland edge and road margins, vital foraging habitat for Barn Owls (M.O'Clery).

We can see in this video of the movements of an adult female Barn Owl from a nest site in north Kerry. On a night in late July - in this case about 45 minutes of a 75 minute foraging trip - virtually all of her time is spent hunting along these features. 

The female Barn Owl just before release, with the 

data logger just visible above her tail (J.Lusby/M.O'Clery, under licence from NPWS/BTO).

The nest site of this female Barn Owl, in a derelict cottage in north Kerry (M.O’Clery, under licence from NPWS).

With the information recorded on the GPS data logger we pick up on her journey while she is perching in a tree 500m from her nest site. She then takes off to hunt along hedgerow, pausing to perch again on trees and bushes (red dots show where the bird is stationary), and several telegraph poles, where she stops, most likely to listen for prey. The slow hunting flight (orange dots) is almost entirely along hedgerow and field edges, and, with the interior of improved fields virtually ignored, the faster direct flight (yellow dots) is mainly to cross a field to get to the next foraging area along the field boundaries.

Video of foraging flight of a female Barn Owl in north Co. Kerry. The video pauses to show the actual view of the road along which she hunted, perching on each of the telegraph poles along the road, most likely listening for prey (J.Lusby/M.O'Clery, under licence from NPWS/BTO).

More on this very soon. If you wish to be notified about updates, you can 'Subscribe to' or 'Follow' the blog using the menus on the right.

Research on Barn Owl foraging behaviour is funded by Transport Infrastructure Ireland.

New technology reveals Barn Owl secrets

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...

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)

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...