Barn Owls, Kestrels & Long-Eared Owls

Report a Barn Owl, Kestrel or Long-Eared Owl Sighting to Padraig Cregg by email: or by phone: 087 7866357

Friday, 31 August 2012

Surveying 'with' Raptors

Surveying ‘for’ raptors is a well established discipline in ecology, however, the latest scientific research is now surveying ‘with’ raptors.

Golden Eagle (by John Carey)

The problem of climate change is increasingly being recognised politically and by the general public. The social, environmental and economic impacts of its actions are being felt worldwide. The equally important mechanism of environmental degradation; human-induced biodiversity loss, is threatening essential ‘ecosystem service’. Ecosystem services include clean water, air and soil, resources upon which our societies and economies depend. In order to overcome or prevent in the future, further, ecosystem service collapse, we must first identify, monitor and recognize the mechanisms involved. Therefore environmental monitoring is of paramount importance. All elements of the environment cannot be monitored given the complexity of the system. Therefore, the most informative and cost effective method must be sought. As a group raptors show considerable latent, potential as monitoring tools. They are often easily detected and monitored. Their presence or absence can be easily noted. As top predators, environmental effects are amplified within their communities. Raptors are typically highly sensitive to a range of environmental pressures, such as prey fluctuations, habitat change, human disturbance and contaminants.  

Marsh Harrier (by Killian Mullarney)

The role of raptor populations as valuable sentinels of environmental health is being increasingly recognised throughout numerous disciplines. As apex predators previous studies have found them invaluable indicators of the presence of pollutants, toxins and introduced species in the environment. The most well documented example, of proven, effective monitoring ‘with’ raptors, revealed changes in organochlorines in the environment. In Ireland, ecosystems are currently under the damaging effect of two introduced small mammal species and toxins. The introduction and expansion of two non-native small mammal species in Ireland, the Bank Vole and the Greater White-toothed Shrew could have wide ranging impacts within ecosystems throughout the country. Three distinct geographical areas have been defined in relation to small mammals, one with indigenous species only, another with indigenous plus the Bank Vole and a final type with indigenous plus both introduced species. The Bank Vole currently occupy a third of the land mass of Ireland. Genetic studies have established that the Irish population was founded from a small number of individual introduced from Germany in the 1920’s. The populations estimated rate of spread is 3 km per year. The Greater White-toothed Shrew occurs in a limited area within the range of the Bank Vole, it can occur at high densities and both species are now common within the regurgitated pellets of local raptors. This indicates a major shift in small mammal communities recently.

Studies have indicated that where the range of the Bank Vole and Greater White-toothed Shrew overlap they have a synergistic relationship which negatively effects the abundance of the Wood Mouse populations and can cause local extinction in the Pygmy Shrews. Interspecific competition and disease have both been implicated as causing factors. As the range of the two introduced small mammals expands so this negative effect for the Wood Mouse and Pygmy Shrew will be replicated into the new areas.

The effects of the Bank Vole and the Greater White-toothed Shrew are being felt by avian predators of small mammals. The Barn Owl, Long-eared Owl and Kestrel are in particular implicated. Barn Owl research has indicated that the Bank Voles and the Greater White-toothed Shrews presence in the diet can have profound effects on their breeding success. In areas of the south west where Bank Voles occur at high densities the species is seen to constitute 80% of Barn Owls’ diet.  Given the overlap in diet of these three species it can be envisioned that the Bank Voles and Greater White-toothed Shrews are impacting upon the Kestrel and Long-eared Owl also. Pygmy Shrews have been demonstrated to comprise 7%-14% of the mammalian composition of Barn Owl diets in Ireland. The Wood Mouse in Ireland represents 70% of the diet of the Long-eared Owl. Increasingly, the value of using apex predators as indicators of environmental health is being promoted. Are the introduced small mammals impacting the ecology of raptors and what consequences will their spread have for the future outlook of the wider countryside?

Raptors that prey on the Brown Rats or the House Mouse can fall victim to secondary poisoning. Due to the depleted small mammal community in Ireland these small mammals regularly occur in the diets of raptors in Ireland. Barn Owls within the Bank Vole and Greater White-toothed Shrew range may experience lower levels of secondary poisoning, a similar situation may be experienced by Kestrels and Long-eared Owls. 

Kestrel (Clive Timmons)

As small mammal specialists the Barn Owl, the Kestrel and the Long-eared Owl can act as biodeterminators, in establishing the wider significance of a small mammal introduction and secondary poisoning from rodenticides on Ireland’s ecosystems. By studying ecologically damaging agents in the environment 'with' raptors, efforts can be made to prevent, minimize and mitigate their effects in the future.

Wednesday, 8 August 2012

Raptor Facts and Figures

The breeding season is starting to slow down and show the first signs of it coming to an inevitable close. Kestrel fieldwork has been completed for the year, with close to 35% of monitored nests having failed or experienced predation. This is quite a bad success rate for Kestrels, who normally perform a lot better. No doubt the abysmal weather we have all suffered through will have played a central role in this. Barn Owls are known nationally to be the rarest of our three study species and are Red-listed in Ireland. In West Offaly this scarcity is replicated. There are roughly twice the number of Kestrels as Barn Owls and three times more Long-eared Owls.  

Barn Owl siblings - pictured by Padraig Cregg

The situation with Long-eared Owls in the country is less clear owing to less work carried out on the species nationally. In my home patch, of West Offaly, many of the traditional nest sites haven’t shown signs of breeding, ie calling chicks, however the overall numbers of breeding Long-eared Owl sites which we now know about has increased. This however is probable down to the increased efforts put into their monitoring this season. Mid August will see the completion of my final acoustic survey for calling Long-eared Owl chicks. On this date, a more comprehensive picture will emerge, but even at this point I can say that Long-eared Owls are the most common raptor species within my intensive study area in West Offaly.

Long-eared Owl - pictured by John Lusby

And on a completely unrelated note.....

Rowan trees grow the length of my garden, a linear orchard of seasonal berries for the avian community. But I had a thought, could predators and in this case a Sparrowhawk learn to associate an obvious prey food source like this with prey? Although hawks are numbered among the more intelligent of birds, this is possibly too great a mental leap. What I do know is my local Sparrowhawk is enjoying the frugivore birds in my garden. Bullfinches, Blackbirds and Starlings seem to be the favourites. A new selling point for the humble Rowan tree, ‘buy a Rowan attract a Sparrowhawk’....I’m sold.

Wednesday, 1 August 2012

Barn Owl Nest Watch 2012

John Lusby, Raptor Conservation Officer with BirdWatch Ireland, has partnered up of late with the Mooney Show on RTE Radio One. A camera has been placed (under license) in a Barn Owl nest box in Kerry. The webcam, which you can view by clicking on the link below, gives an intimate view of the breeding behaviour of Barn Owls.

The nest box was put in place in 2009, after a previous nest site in the roof of the building was destroyed, and the Barn Owls have nested there ever since.