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.

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.

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.

http://www.rte.ie/radio/mooneygoeswild/features/mooneycam/

Eerie Calls in the Night

I have been out on the prowl, over the last few nights trying to track down breeding Barn Owls. With most of the countries breeding population monitored at this point in the season, I am simply seeking some of the remaining outliers, to create a fuller picture of breeding status of this Red-Listed Species. Several of these sites have proven active and even seem to have bred, which is a positive in what has been an all round bad breeding season for many species.

Barn Owl - pictured by Padraig Cregg

Last night I visited a large ruined mansion not far from Banagher. The fact that the building wasn’t far from a road which gets a moderate level of usage allowed me some leeway in terms of my approach. I needn’t have worries though as I could hear calling Barn Owls has soon as the chunky thud of my diesel motor subsided. I could hear four birds in total, but it can be hard to be precise on the number of birds present as they may simply be moving about. I definitely saw three owls. My best guess was that there were two fledgling Barn Owls who were flying about along with their parents. The parents were calling back and forth to one another, a behaviour more typical of earlier in the season. This renewed courtship could result in a second breeding attempt by the parents, but given the bad season it is unlikely that it will amount to much. Barn Owls can have a second brood in a year but this is quite unusual in Ireland. In fact a brood as late as October has been recorded by BirdWatch Ireland staff.

Barn Owl white wash - pictured by Padraig Cregg

Although of course a nocturnal species, day time visits to likely buildings can be very informative also. Should you hear the stereotypical snoring begging call during the day it is most often a sign that the chicks are still quite young. Pellets and white wash, are, though the main daytime signs to watch out for. Above is a picture of Barn Owl white wash, note the thin white line almost like a dribble of white paint, which identifies it as Barn Owl white wash. Once birds are seen to be present, through day or nighttime observations, the building is revisited to ring the occupants, pictured below.  

Barn Owl ringing - pictured by Padraig Cregg

The Peregrine Falcon

The Peregrine Falcon is a beautiful bird, I think few would argue, but man-o-man what an ugly alarm call. I have been diversifying to a degree of late, moving away from my usual fair of Owls and Kestrels to the more regal Peregrine. Sitting atop their food chain has instilled a confidence to the species which other smaller raptors lack. Whenever I approach a nest site, the resident pair circle and berate my intrusion with their alarm calls. As with Barn Owls and Kestrels, ruined builds are an important nesting site for the species. Before entering into this field of work I would never have imagined or probably of have noticed the sheer number of ruined castles, mansions and cottages in the country. This second life of the buildings, makes them of great conservation importance. Fledgling Peregrines below.

The inside of a Peregrine occupied ruined building, is a veritable who’s who of the local avian community. The ground under foot crackles, with the crunch of miscellaneous bones of past meals. Although Peregrines are often implicated as racing pigeon glutens, Jackdaw carcases in my experience make up a large chunk of the diet. This is an unsurprising chose on the part of the Peregrines, due to the fact that Jackdaws are often also in residence in the ruins.

A lot of fiction surrounds Peregrines and the speeds which they can reach during a stoop while hunting. Let me try and clear this up, between 160km and 410km has been suggested by various authors. The truth is that birds have been seen to reach speeds of 200km and that speeds of 240km are theoretically possible for the species! During the stoop, Peregrines drop from a great height, folding their wings back and slightly away from their bodies, creating a tear drop shape. The unsuspecting prey is often killed in the midair collision, with the Peregrine’s talons aiming for the head. If the prey is still alive after collision, it is dispatched on the ground with the beak.     

Peregrines are a real success story; with the changes in the laws controlling the use of pesticides the species is making a comeback. Being both an urban and rural species, a close encounter with a Peregrine could be just around the corner, why not keep an eye out in your local patch for this sleek speedster.

Dusk on the Shannon, and all is well with the world.

The Shannon - by Padraig Cregg

Irish Stoat

I was on the way to work when a flash of brown, sped across the road. It was a stoat, with a rodent in its mouth. In its surprise and haste to avoid my car wheel it dropped its prize. Knowing their cheek, I pulled over, jumped out of my car with my camera in hand just in time to get this shot of the stoat returning to retrieve its meal. The Irish Stoat, which is an unique sub species, can be identified by the ragged edge of white on the chest, as apposed to the smooth edge seen on continental stoats.

Irish Stoat - by Padraig Cregg