More amazing insights from Barn Owl GPS tracking

This summer, a huge effort was made to track the movements of Barn Owls by fitting them with small GPS data loggers. The results have been spectacular, and the staggering amount of detailed information is delivering new insights into the behaviour of this nocturnal and secretive species.

Barn Owl fitted with GPS data logger to assess habitat use and home range (J.Lusby, M.O'Clery, BirdWatch Ireland under licence from NPWS).

Adult Barn Owls were fitted with the devices at seven sites in Ireland in summer 2017, recording speed and exact location of the birds every ten seconds. Combined with the information from six adult Barn Owls from summer 2016 we now have 98 nights worth of data and are able to discover exactly where they went and when, where they hunted, how they moved about a landscape at night, where they roosted during the day, how long they spent perched, how long in hunting flight, which areas they favoured and which they avoided.

Here’s an overview of some of the sites. Further posts will show some of the specific findings as we interpret the huge amount of information.

(You can click on any of the images for a closer view).

Here's the GPS data from a Barn Owl site in Co Kerry, the information gathered from ten nights. This bird spent a considerable time hunting along the coast, not far from the nest site, even spending quite a time hunting nearby sand dunes. The owl which was tracked was a male and he proved to be the best hunter of all our tracked birds, delivering at least 48 prey items during the ten nights.

Another of our owls has a home range in Co. Tipperary, in a predominantly mixed arable and cereal-growing region. The owl ranged up to 3.2km from the nest site, well within range of the M8 motorway just 1.8km distant. The owl visited this motorway regularly over the nine nights of data we recorded. More on that on the blog soon.

At a third nest site in Co. Kerry, the female Barn Owl was tracked for 12 nights, revealing a much larger range than the Tipperary sites. This bird travelled up to 8.25km from the nest in search of food. These long range trips themselves have revealed some interesting aspects about Barn Owl foraging behaviour, but more on that soon.

Call back soon for more.

Barn Owl tracking - Tralee Bypass

Readers of this blog will recall several posts involving instances of Barn Owls being struck by vehicles on major roads (see HERE and HERE, for example).

Continuing with our project to discover the effects of major roads on Barn Owl populations (in conjunction with T.I.I.), in July 2017 we tracked a female Barn Owl whose home range included the Tralee Bypass (see a history of this nest site HERE). While we long suspected that the adult Barn Owls from this site might well be hunting along the Bypass, the findings from the GPS data loggers were astonishing... Over 11 nights, she hunted along the verges of the Bypass nine times, and crossed the road 14 times. She also frequently perched along the verges, spending around two hours close to the road. The dangers to the bird are obvious and yet, she and her partner managed to raise two chicks this summer.

You can click on the 'four arrows' symbol on the bottom right to see a full-screen view.

Barn Owl tracking of a female Barn Owl near the Tralee Bypass, July 2017 (J.Lusby/M.O'Clery, under licence from NPWS and BTO).

Please share this video on social media!

More on this project soon.

Unusual death of a White-tailed Eagle

Poison was the initial suspected cause of death when a White-tailed Eagle corpse was discovered in Kerry this summer. The cause, it turns out, was very different, and quite unexpected...

Read the article on the Rare Bird Alert website HERE

Moving house – relocation, relocation, relocation

At some Barn Owl nest sites around the country, especially the larger buildings such as derelict mansions and castles, it is not unusual for the adults to switch nest sites from year to year within the same building, or buildings. We are as yet unsure what triggers the switch to alternative nests, but the move can occasionally be forced upon them if the original nest site changes if, for example, Jackdaws fill the cavity with sticks. At other times, there is no obvious reason for the switch. It could also be to do with disturbance, or simply the preference of a new bird, or a mechanism to avoid a build up of parasites at the nest, if viable alternatives are nearby. 

By way of an example, at a large, abandoned farm complex in Co. Kerry, Barn Owls have been nesting for at least six years, though when first detected, they were nesting not in the suitable ruined building but in a cavity in a mature Beech tree adjacent to the buildings. 

Abandoned farm complex in Kerry. The first Barn Owl nest discovered here was not in the eminently suitable ruined buildings, but in the Beech tree just behind from where this photo was taken (M.O’Clery).

Checking the tree nest, from which three chicks fledged (M.O’Clery).

However, by the following summer, the owls had abandoned the tree cavity (it was still apparently suitable) and had instead moved to a section of blocked chimney in the main building.

Left) The second nest, a cavity in the wall with a partially blocked chimney shaft behind and, Right) the third nest site, a nest box in one of the outbuildings nearby (M.O’Clery).

 A nest box was installed in a nearby building, to secure the site in case the chimney became no longer suitable, and the year after that, the owls nested in the nest box. Three moves in three years, but all within 50m.

  

At another location (photo below), again in Co. Kerry, pellets were found under a chimney in a derelict mansion, but careful watching at dusk found there was no nesting taking place in the mansion – the chimney was used only as a roost.  

Derelict mansion in Co. Kerry, an obvious place to start the search for a Barn Owl nest (M.O’Clery).

However, further visits and careful watching at dusk finally located the nest, about 100 m away in the blocked chimney shaft inside a stone outbuilding, a building they shared with a pair of nesting Chough. They successfully raised two young that year, but a visit the following April showed some slates directly over the nest had blown off in winter gales and rain could now fall directly onto the nest, and it had been abandoned. 

The Barn Owl nest was found, not in the mansion, but in the outbuildings, behind the large grey door. (M.O’Clery).

A nest box was quickly made and installed in the outbuilding a few days later and, though there were no signs of owls present, when the box was revisited later that summer, there were three Barn Owl nestlings inside. The adult owls must have discovered the box quickly, because by working out the egg-laying dates from the chicks ages it seems they had moved into the box and laid eggs within about two to three weeks – the fastest uptake of a Barn Owl nest box yet!

Left) John Lusby visits the first nest, an open-topped chimney shaft, covered by a roof. One of the adult owls accessed the nest via the hole in the roof, the other more often flew in through the window and up onto the nest. Right) Once the first nest was rendered useless by missing slates, the owls quickly moved into the nest box placed just a few feet away. (M.O’Clery).

The story doesn’t end there however, because the following year, the nest box was once again empty, so yet again we needed to check the old mansion nearby at dusk and finally it was discovered they had nested that year in an old chimney within the ruin.

Left) The third nest site, arrowed, a cavity in the wall leading from an old fireplace in the derelict mansion. Right, the single chick fledged from this nest in 2015. (M.O’Clery). 

And finally, last summer, yet another evening visit was made to watch and listen at the old fireplace to see if they were nesting there again. Nothing… It was only when leaving the site well after dark that faint ‘snoring’ was heard from young chicks in a high chimney on the other side of the derelict mansion. So in the space of a few years, the owls nested in a chimney shaft in an outbuilding, a nest box in the same outbuilding, a fireplace in the derelict mansion and finally last year, in a high blocked chimney. What will they get up to next?

The fourth nest site, in a vertical chimney shaft in the old mansion (M.O’Clery). 

You can see a short video of the fourth nest at www.vimeo.com/175104175 or use your smart phone to access the video with the VR code above.

There are many other such examples of Barn Owls relocating within the same building, such as at a castle in Duhallow where they switched from a high window ledge to a small wall cavity on the opposite side of the castle, or a site in Kerry where three nest boxes were provided, and they have nested in two so far (and roosted in the third), and a cottage also in Duhallow where they nested in a small roof space in 2013, only to move into the deep blocked chimney in 2014.

So anyone monitoring Barn Owl nest sites and find the original nest empty, keep an open mind, as the owls may simply have relocated nearby.

All Barn Owl ringing and photography at the nest sites  is carried out under licence to NPWS and the BTO.

The great Firies Barn Owl brood of 2015

Ringing of Barn Owl chicks has been undertaken by BirdWatch Ireland since summer 2007, and is providing much valuable insight into their movements and longevity. Around 800 Barn Owls have been ringed, and the recovery rate is relatively high for this species compared with others, for example, about one in ten Barn Owls ringed are re-trapped or recovered (usually dead) at a later stage. For example, for Storm Petrels, this figure is about one in a hundred. Part of it is down to survey and ringing effort, and in part no doubt because of their beauty and rarity (and often their conspicuousness), dead Barn Owls are often reported to BirdWatch Ireland, most often as road casualties.

In total, breeding success has been monitored at over 800 sites in the Republic of Ireland between 2008 and 2016 and in that time 750 owlets were ringed nationally. A total of 74 ringing recoveries and controls (re-trapping of live birds) were recorded between 2008 and 2016. All this accumulating information is proving to be most valuable.

For instance, from the ringing effort in Ireland so far, we know that most young Barn Owls disperse five to about fifty kilometres from their nest site, but occasionally, some will travel much further. The map below shows the ringing recoveries nationally.

Ringing recoveries of Barn Owls in Ireland up to the end of 2015.

However, let’s divert momentarily to a Barn Owl nest site near Firies, in Co. Kerry. 

Cottage in Co. Kerry with three nest boxes. The chimney shaft itself was also a suitable nest site, though the owls never used it (M.)’Clery).

Unusually there are three nest boxes here, one inside the cottage, on in the adjacent barn, and one specially adapted to fit on top of the cottage chimney. This was done in 2009 essentially as an experiment, to see if this might ‘improve’ the nest site for Barn Owls (it certainly did), and to see which nest site might be taken up. Sure enough, Barn Owls moved in that winter and nested the following summer, in the chimney box. 

Left) The chimney nest box on the cottage in Co. Kerry. Right) One of the four chicks at this nest site in 2015 (M.O’Clery).

This has been one of our most productive nests, producing chicks each year since, even in 2014 when breeding success throughout Ireland was extraordinarily low following a record-breaking cold spring. We have ringed chicks at this site for six years now, but the brood of 2016 – four chicks – was to be particularly remarkable.

John Lusby ringed all four chicks on 10th July 2015, and two were subsequently recovered – remarkable in itself that two out of four would be found again - unfortunately both found dead on major roads. The first was killed along a stretch of the M8 in Co. Tipperary, fully 140 km from the nest site, and the second furthest distance recorded by any Barn Owl in Ireland.

The second was found dead on the dual carriageway on 11th February 2017, just NE of Derry. In a straight line this is a distance of just over 350 km, much the longest distance recorded by an Irish Barn Owl and just about doubling the previous record. Of course, the owl had been capable of flying since the previous August, so the distance travelled would be considerably more, and we have no way of knowing what route it took to get to where it met its’ fate.

Thanks to the monitoring and ringing work undertaken at great effort each summer, we are learning much about Barn Owl life histories including their dispersal patterns, distance travelled, and longevity - all vital knowledge in the future conservation of the species.

And while it was remarkable indeed that we recovered two of the four Barn Owls from this nest, and that two of this brood proved to be such long-distance travellers, there is still the intriguing possibility there might be two more from this brood of 2015 out there. Might we yet encounter more of this remarkable family? Wonder where?

All Barn Owl ringing and photography at the nest sites  is carried out under licence to NPWS and the BTO.

Very late Barn Owl nest

The typical egg-laying period for Barn Owls is the first week of May, though there is always those that nest earlier and later, sometimes much later, as is the case at this nest box in east Kerry.

Four newly hatched Barn Owl chicks, east Kerry, 10th August 2017 (M.O'Clery, under licence from NPWS).

The nest box was checked on Thursday 10th August and the young Barn Owls were just hatching. Eggs are laid one to two days apart, so there is always a difference in size between chicks, yet the oldest was only a few days old, and there were still two unhatched eggs. The eggs would have been laid in the first week of July.

If they survive, the chicks will be fledging in mid-October, an extremely late date.

A rival to the oldest Barn Owl in Ireland

While ringing Barn Owls in south Kerry a few days ago, this adult male was caught, at a nest box near Caherciveen. He was already ringed.

Male Barn Owl, near Caherciveen, 2nd August 2017 (C. Nelms).

The ring showed that he had been ringed as a chick at another nest site, about 10 km distant. He is, along with the male Barn Owl from near Tralee (see the post below) now the joint oldest known Barn Owl in Ireland. Nine years old.

Male Barn Owl, near Caherciveen, 2nd August 2017 (C. Nelms).

The story of Ireland’s oldest Barn Owl

A male Barn Owl found dead along the Tralee Bypass on 1st September 2015 (the 10th to be reported there since the Bypass opened in August 2013) caused us much concern for the future of his nest site nearby. We had already gleaned considerable knowledge of this site and had followed the fortunes of this male for several years. The story of this site, and the history of its owl occupants is now extremely detailed, and most interesting. His death ultimately led to the discovery at this site of Ireland’s oldest Barn Owl.

The scene of our story, a derelict stone barn near Tralee, Co. Kerry. There is also a large derelict house behind it in which the owls nested, before they started using a nest box installed in the barn in 2014 (M.O’Clery).

Although we don’t know where this male was hatched, our first encounter with him was when he was trapped and ringed at this nest site just outside Tralee. He was ringed on 22nd June 2013 and was already an adult, probably two years old.

Male (on the left and female Barn Owls from the nest site, in June 2013 M.O’Clery).

His nest in 2013 was in a wall cavity in the derelict house beside the barn, but they failed to breed that year, though both adults survived into winter, and in 2014 they moved nest to a high attic ledge in a different room in the same building.

Left) The derelict house where the owls nested in the first few years of the discovery of this site. Right) Nest in one year, on a mass of Jackdaw nests in the apex of the roof inside the house (M.O’Clery).

Unfortunately, 2014 was a disastrous year for Barn Owls generally and they again failed to breed, as was the case at most other nest sites in Ireland. Although the pair was seen perched by the nest in early spring 2014, visits later that spring and summer revealed only a lone male screeching each evening in a vain attempt to attract a female, until the activity petered out in June. He was unpaired that summer, the female presumably having died around the previous March or April.

Better news in early 2015 by which time he had found a new partner, and again they moved nest, into a nest box in a nearby barn, which we installed in autumn 2014. He was photographed again, perched on a beam just beside the nest box, in April 2015 (below).

The same male in April 2015, now paired up with a new female partner and nesting once again. She is inside the box, nearly ready to lay her clutch of eggs (M.O’Clery).

Five chicks were found inside the nest box in the barn in early June, the first brood of five recorded in Kerry at that time. Another visit in early August found that three chicks had survived and were just about ready to fledge.

The five chicks from the males successful 2015 nesting season (M.O’Clery).

He was found dead on the hard shoulder of the Tralee Bypass on 1st September that autumn. A sad end for this veteran male. Birds older than three are a rarity in Ireland, and it’s quite possible this bird had already survived many hunting trips along the Bypass up until now, as his nest is only a couple of kilometres away. His luck finally ran out.

Our fears that this could spell disaster for our nest site were unfounded. When it came time to check the site in early spring of 2016, to our surprise and delight, there, perched outside the nest box on a beam, was a male Barn Owl. It was clearly a male, with a remarkably ‘frosty’ shawl of white around his face, and from the photos, it was apparent he was already ringed. But where? And when? 

Just as the previous male had done, the new male, seen here in May 2016, often perched in the open on the nest box, or a beam nearby. Intriguingly, he was already ringed, but we would have to wait until the ring could be read to find out where and when (M.O’Clery).

Barn Owls are generally short-lived birds, and since ringing of Barn Owls began in Ireland in 2008 only a handful of birds ever caught and ringed have been three or more years old. Barn Owls kept in captivity regularly live to be 15 or even 20 years old, but they obviously don't face the same hazards as a bird in the wild. In Ireland, at least half of all birds which fledge from the nest will not make it to their first birthday, and it is rare indeed to find a five year old bird. There are a number of sites which we know have been occupied by Barn Owls for 20 or more years, but this does not mean it is the same individual owls in residence, rather there has been a whole series of recruitments over the years. 

So was this new male a youngster from the previous breeding season, and from where did he come? The question was finally answered a short while later when the ring number could at least be read, and the answer was rather astonishing. He turns out to have been ringed as a chick at a nest site in a castle in east Kerry, about 20 km away, in summer 2008. At eight years of age, he was the longest-lived wild Barn Owl so far recorded in Ireland.

Our veteran male’s birthplace, a castle in east Kerry, where he hatched in summer 2008 (M.O’Clery).

And while checking the site once more this April, there he was again, perched in the same spot outside his nest box. He had survived another winter. Almost nine years old now, and getting ready for another nesting season with his mate. Later this season, he successfully reared two chicks.

Now nine years old and going strong, Ireland’s oldest known wild Barn Owl dozes by day on his nest box, in April 2017 (M.O’Clery).

Now the question is, where on earth had he been in the eight years before he turned up at this site? Perhaps his previous partner had died, or his previous nest site was destroyed, just as the female at this site lost her partner. Was he nearby, on an overlapping territory perhaps, or did he wander far and wide in search of a new site and a new mate? We shall never know for sure, but like all veterans, he sure has a story to tell.

All Barn Owl ringing and photography at the nest sites  is carried out under licence to NPWS and the BTO.

Kestrel nest box update

Feeding time at the Kestrel nest box in Co. Kerry is a rapid affair. Both adults are out hunting full time now, and only visit the nest to deliver the next meal. Blink and you'll miss it! At the start of this extended clip, as the chicks doze, we see an adult suddenly arrive with prey only for it to be snatched immediately by the eldest. The youngster misses its moment and tries to grab a bit while the eldest knocks back its latest meal.

Kestrel chicks, Co. Kerry, 30th May 2017 (M.O'Clery, under licence from NPWS).

They are growing fast, and the biggest are really looking like proper Kestrels now, as wing and tail feathers emerge and the body feathers start to appear. There's quite a bit of stretching and wing-flapping now, even from the youngest. Providing food for these youngsters is now a full-time job for the adults. If the weather remains reasonably benign, they'll all get their fill. As it is, all are doing well, and are in good health.

More soon.

Kestrel chicks feeding time

A longer clip from today of the female Kestrel attending to her hungry brood of five chicks. First, we see her covering the chicks to keep them warm, though this is becoming increasingly difficult as the ball of white fluffy feathers continues to grow.

The female Kestrel 'brooding' her five young (M.O'Clery, under licence from NPWS).

Then we see her suddenly attentive to something outside the box, presumably the male is calling her to come and get his latest catch. She calls to him, flies out, and quickly returns with a Pygmy Shrew. We see her feeding the eldest chick, but it immediately drops it. The female, ever attentive, picks it up and pulls it apart into more manageable portions. In this case, the eldest chick seems to get it all in three chunks, but judging by the full crops (the bulge under the throat), all of these chicks are faring very well and are certainly not going hungry.

Kestrel nest box on the Dingle Peninsula, Co. Kerry (M.O'Clery, under licence from NPWS). Click on the 'four arrows' symbol to see it in HD).

Finally she heads of for a brief period, possibly to hunt herself. The frequency of the female leaving the chicks alone at the nest box will increase in the coming days as they become less vulnerable, more able to regulate their own body temperature, and more hungry.

More soon.

Kestrel update - junior takes a tumble

The Kestrel chicks in a nestbox on the Dingle Peninsula are doing well, and growing fast. We're getting lots of valuable video from this nest but, for the moment, here's a quick update and a short video clip of the youngsters. 

The nest box is high in this isolated Sitka Spruce on the Dingle Peninsula, Co. Kerry (M.O'Clery).

The nest box (M.O'Clery).

The male Kestrel now only visits the nest to drop off the latest catch. 

The male Kestrel drops off another tasty morsel. The female has been feeding the chicks a Pied Wagtail fledgling. The male has brought another bird to the nest, though the species is unclear

The female is now out hunting occasionally, but also still spending extended periods 'brooding' the youngsters (sitting on them to keep them warm). It won't be too long before they are big enough to be left on their own at the nest, both parents then able to hunt for the voracious, ever-growing young Kestrels.

Kestrel nestlings - junior takes a tumble, Dingle Peninsula, Co. Kerry (M.O'Clery, under licence from NPWS).

More on this nest site soon.

The reason you don't usually see Barn Owls by day in Ireland

While searching for new Barn Owl nest sites in Co. Tipperary, one castle had been picked out as having potential. The owner had seen a 'white owl' recently, one that was "screeching it's head off" a few weeks ago. Surely a Barn Owl? It would need an evening to sit nearby, quietly watching to see what, if anything, would emerge from the castle at dusk.

At most sites, Barn Owls will wait until near dark before emerging from their carefully hidden nest sites. This evening was to be different.

Castle in Tipperary (All photos and video: M.O'Clery, under licence from NPWS).

Did an owl fly out of the castle at last light? Not quite. The 'rule of thumb' while watching for emerging Barn Owls at dusk is 'twenty minutes after sunset'. This can vary quite a bit though, so it is always a good idea to be in place to watch a potential owl site at, or before, sunset.

Yesterday, sunset was 21:25pm, but at 21:15pm a quick movement seen out of the corner of the eye saw a Barn Owl emerge from a slender chimney, on a small tower separate from the castle, and fly off quickly out of view.

However, within seconds, the local Rooks and Jackdaws which had been gathering in small, noisy flocks just before heading off to roost, spotted the owl and gathered en masse and, emboldened by sheer numbers, and daylight, chased and hounded the Barn Owl. In seconds the air around the owl was filled with about 150 crows, a posse of agitated Swallows and even an extremely brave Pied Wagtail, all chasing the unfortunate owl across the yard. The photo below captures the moment when the Barn Owl decided enough was enough, as it flew straight back to the chimney and down, safely away from the agitated mob.

Some of the assembled lynch mob follow the Barn Owl down toward the chimney, as the owl retreats to safety.

Close-up of the above photo.

And, with barely a pause, the Barn Owl descends back into the chimney and out of harms way.

Over the next twenty minutes, in the gathering darkness, everything calmed down, the crows gradually went to roost in nearby trees, the last Blackbirds and Robins stopped singing and, finally, the Barn Owl emerged once again. A quick shake, a look around, and off to hunt, without the slightest hassle from the neighbours.

The Barn Owl decides the coast is clear, the crows have gone to roost, and heads off into the night, unmolested.

Hit the 'four arrows' symbol to see the video full size.

There are reasons Irish Barn Owls aren't seen in daylight. Ireland doesn't have Short-tailed Field Voles and some other small mammals which are often active by day, and hunted by Barn Owls in daylight in Norfolk or south England. The other reason, as illustrated here, is that Ireland has an extremely high density of crows, and any Barn Owl out and about by day in Ireland will sooner or later, be mobbed by crows. Mobbing is an instinctive behaviour triggered by the presence of a predator. Hunting is impossible when hounded by a baying mob.

Have a look at the comparison below between the Irish and British populations of Jackdaws and Rooks.

The Atlas map for Jackdaw, 2007-11, showing relative abundance Bird Atlas maps.

The Atlas map for Rook, 2007-11, showing relative abundance Bird Atlas maps.

Hard for any Barn Owl to be out and about in daylight in Ireland, as this owl found.