Jackdaws do Barn Owls a favour

Chimneys make up about a third of all Barn Owl nests and, though they can be in the smallest of cottages or the largest of derelict castles, they are usually only made suitable for the owls by the nest-building activities of Jackdaws.

Jackdaw (M.O'Clery)

From early spring to early summer these industrious crows set about building their stick nests, and when they find what might be a suitable nesting cavity, their instinct is to keep adding sticks until it is full enough to make a suitable shallow nesting platform. In a relatively short time they can fill a large Barn Owl nest box almost to the top with a mix of sticks, lambs wool and various bits of rubbish, tinfoil, twine and whatever else might have caught their eye. In one notable instance, an almost full pack of cigarettes was included in the structure. No doubt some farmer nearby was wondering where on earth his 20 Silk Cut Blue went.

Huge pile of sticks created by Jackdaws, Co. Tipperary, May 2016 (M.O'Clery).

Many a householder who has had to clear the debris of a Jackdaw nest from a blocked chimney can appreciate just how much material can be added and in larger cavities in buildings, such as chimneys and attic spaces, sticks can be added in an almost constant stream, creating some enormous piles. In the example above, the sticks reached a height of eight feet, nearly three metres, inside a derelict house in Co. Tipperary. How many hours of stick-collecting might this represent?

In another example below, Jackdaw sticks dropped down the high, open top of a chimney of a ruined house in Co. Kerry accumulated under the open base, rising to over head height, on top of which was a perfect secluded platform on which Barn Owls nested this summer.

Inspecting a Barn Owl nest on top of Jackdaw sticks, Co. Kerry, July 2016 (M.O'Clery, under licence from NPWS).

So although Jackdaws and Barn Owls are often competing for the same nest sites, Barn Owls are usually reliant on Jackdaws making the chimney suitable in the first place.

Below, some examples of Barn Owl nests in chimneys from this summer, all of which would not be suitable for the owls were it not for the hard work of the Jackdaws.

Three chicks in the blocked  chimney of a derelict mansion, Co. Kerry (M.O'Clery, under licence from NPWS).

This small cottage in Co. Kerry has its chimney blocked by a Jackdaws nest (M.O'Clery).

The same cottage chimney with a female Barn Owl and two chicks on their nest on top of the chimney blockage (M.O'Clery, under licence from NPWS).

Barn Owl chick in its nest site in a castle in Co. Tipperary, an old Jackdaw nest in a chimney shaft (M.O'Clery, under licence from NPWS).

Four Barn Owl chicks deep in the blocked chimney of a derelict house in Co. Tipperary. A perfectly dry and safe nest site (M.O'Clery, under licence from NPWS).

Two Barn Owl chicks in a relatively shallow blocked chimney in Co. Kerry. Such nests can be vulnerable to heavy rainfall, as they offer little shelter from directly above (M.O'Clery, under licence from NPWS).

Nationwide Barn Owl ringing and monitoring underway

A tremendous effort is being made at the moment to monitor and visit as many Barn Owls nests as possible this summer. This is tied in with a large project with BirdWatch Ireland and Transport Infrastructure Ireland (T.I.I) to examine Barn Owl mortality on the M8 Motorway in Tipperary and the Tralee Bypass in Kerry, more of which anon.

Barn Owl chick, Tipperary, July 2016 (Photo: M.O'Clery, under licence from NPWS).

 Results from the nest visits so far have been generally good, with 43 broods ringed so far, and several more to go so, in terms of numbers of broods ringed, it should be a record year. Brood sizes have been mixed, with nests in the Greater White-toothed Shrew range generally faring very well, with typically four chicks in most nests visited so far. Outside the shrew's range in, e.g., Kerry, brood sizes are well down on last year, with generally ones and twos at most nest sites, and only three nests with three chicks recorded so far.

Barn Owl, March 2016, at a roost site  in a castle near Thurles, Co. Tipperary (Photo: M.O'Clery, under licence from NPWS).

Timing of egg-laying this summer is also notably different within and without the shrew's range, with Barn Owls nesting one to two weeks earlier than the average egg-laying date of 7th May wherever they are preying on the White-toothed Shrew, and one to three weeks later in the areas outside the shrew range. Sites in Kerry have been notably late this season with several still on eggs in late June.

Barn Owl chick, Tipperary, July 2016 (Photo: M.O'Clery, under licence from NPWS).

Though the White-toothed Shrew seems to be having a positive effect on Barn Owl breeding numbers and brood sizes, there is still an issue with some nests within the shrew range where the chicks fall ill and die. The pattern is generally that the chicks start to lose weight around 25 to 30 days old, and die - seemingly of starvation - at around 30 to 40 days. Several such nests in Tipperary last week presented a particularly gruesome sight with, in one case, one weak and emaciated Barn Owl chick sharing a confined nest in a chimney with its three dead siblings. These fatalities occur in roughly 10 to 15 percent of nests within the shrew range, and is unknown outside of that, but the cause is as yet unknown. A parasite? Perhaps a virus, or bacteria unique to the shrew which is proving fatal to the chicks. It also seems to be an 'all or nothing' disease, whereby all the chicks in a brood succumb, or all are healthy and well.

Barn Owl nest site (circled) high on the inside gable-end wall of a castle in Tipperary. A site abandoned by the owls in recent years, but re-occupied again this summer. There were three chicks in the nest, all healthy and well fed. July 2016 (Photo: M.O'Clery, under licence from NPWS).

Site occupancy throughout Ireland seems particularly high this summer, with several cases of sites abandoned by Barn Owls in recent years being re-occupied this summer, particularly in counties Tipperary and Limerick. In Co. Kerry, despite the low brood sizes, the number of active sites is at least as high as the record year of 2015. 


Barn Owl nest site in a castle, July 2016 (Photo: M.O'Clery, under licence from NPWS).

Thanks to this years extensive survey work, as well as an increase in the number of nest boxes, an increasing level of contact with interested farmers and landowners, and a huge input from volunteers it looks likely that, by the end of this breeding season in September, we might well have a record number of known Barn Owl sites.

More info on the Co. Kerry sites on the Kerry Birding Blog HERE