Orkney Ringing Group

Orkney Ringing Group

Harray Loch

RAPTOR RINGING & MONITORING

Hen Harrier

Male Hen HarrierThe raptor species associated in everyone’s mind with Orkney is the Hen Harrier.  The Orcadian ornithologist Eddie Balfour began his studies of the species in the 1940s and, after Eddie’s death in 1976, they were continued by Nick Picozzi of the then Institute of Terrestrial Ecology (ITE).  Nick’s studies ended in 1980 but members of ORG continued to try to monitor at least all successful nests in subsequent years.  The polygynous breeding system of the species in Orkney makes it impossible to follow all nests as those of the subordinate females usually fail early.

A crash in the harrier population during the 1990s resulted eventually in funding being found to support a PhD study into the breeding success of the population.  This study was undertaken by Arjun Amar, based with ITE’s successor body, the Centre for Ecology & Hydrology (CEH).  Arjun’s work showed clearly that the problem was related to food supply and subsequent studies have begun to link this to the high numbers of sheep that were put onto the moorland fringes in the 1990s.

Arjun’s work spanned the period 1998-2000 and Hen Harrier Broodconcerns about the harrier numbers were sufficient to persuade the funding bodies to employ a Hen Harrier contract worker for several years thereafter.  JimWilliams fulfilled this role and during this period numbers and breeding success began to improve, partly it is thought due to a series of good springs and also, perhaps, because, sheep numbers on the moorland fringes had begun to decline.

As things improved, the need to fund studies was seen as less important and so it has fallen to staff of the RSPB and members of the ORG to continue the long-term data set on the species in Orkney.  Currently the population stands at about 60 females and about 20 males breeding in both the West and East Mainland, on Hoy and on Rousay.

Merlin

Merlin Chick The Merlin is the other raptor species receiving good coverage in Orkney.  Eddie Balfour had knowledge of about 25 breeding sites in the islands but did not cover them systematically.  Nick Picozzi, with help from Jeff Watson, also covered several sites each year in the late 1970s.  When Eric Meek came to Orkney in 1981 as the RSPB Officer, he began a programme of monitoring all known sites every year, helped by several other members of ORG. 

The Merlin population crashed in the mid-1980s, numbers falling to only six known pairs and, in 1986, no young at all were reared.  Various investigations were made into the cause of this crash but no clear conclusions could be drawn.  Since that time the population has recovered and now hovers around the 17-21 pair mark each summer.  As with Hen Harrier, the population is concentrated in the East Mainland, on Hoy and on Rousay with one site in the East Mainland and occasional breeding on Stronsay.

Kestrel

Kestrels on Orkney can be very secretive birds and their nests are often very difficult to find.  This applies especially to that part of the population which nests on the ground out the heather-covered moorland.  The Orkney population is probably about 15-20 pairs with, as well as ground-nesters, birds also utilising sea cliffs, inland crags, old buildings and old corvid nests in trees.  No systematic monitoring is carried out, territories being located during the course of the more intensive Hen Harrier and Merlin monitoring.

Peregrine

The Orkney Peregrine population is about 15 pairs and has not undergone the massive increase seen in parts of mainland Britain.  Something is still holding back the population and it has been speculated that this may be contamination by PCBs entering Peregrines through the marine food chain, many of our birds being seabird feeders.  The presence on the sea cliffs of enormous numbers of Fulmars and the effects of their oil-spitting defence mechanism, especially on newly fledged juvenile Peregrines, may also be important.  The Mainland Peregrine sites are monitored each year by Chris Booth while some of the sites on other islands are covered by ORG members and RSPB staff.  Few chicks are ringed because of the inaccessible nature of many of the nests.

Short-eared Owl

Finding Short-eared Owl nests is a very difficult and time-consuming business.  Even more than ground-nesting Kestrels, Short-eared Owls are extremely secretive on the breeding grounds and most nests are found by chance during the course of other work.

Orkney has a very important proportion of the national total of this species with perhaps as many as 60 or more territorial pairs in a good season.  Owl ChickTheir main prey is the Orkney Vole, studies by Peter Reynolds in the late 1980s as part of a PhD on the vole itself, indicating that more than 80% of the owls’ diet consists of this species.

However, a few pairs of owls also nest on Hoy where there are no voles and it would be of great interest to know more about what they eat on that island!