Interview with Gordon Riddle about the Eurasian Kestrel the UKDate of the interview: 06 March 2011 The Eurasian or Common Kestrel is one of the most common birds in many European countries. But it is showing declines in some areas including Great Britain. In this interview Gordon Riddle talks about the biology and conservation of the Kestrel in the UK. Gordon has been studying this little raptor for almost 40 years in Britain. His latest book on the kestrel, Kestrels for company will be published in early May. See the interview and below for more details about the book. Markus Jais: What is the current status of the Common Kestrel in the UK?
Gordon Riddle: The kestrel is still relatively widespread in the UK but is undoubtedly in partial decline in many areas. From being the commonest raptor it has fallen to third place behind the resurgent common buzzard and the sparrowhawk. Its current status is amber, reflecting a 25-50% population decline. The conservative population estimate today is around 35,000 pairs but 50,000 were quoted in one paper. Markus Jais: How has the population developed during the last decades?
Gordon Riddle: Since the mid 1980s there has been a slow decline which has accelerated in the past decade. In England the population has fluctuated with steep declines in much of the north and west, and wherever there is intensive arable farming. High densities can however be found in many parts of southern and central England. In Scotland the fall in numbers is very significant. Latest figures indicate a decline in the UK between 1995 and 2008 of 20% while the corresponding figure for Scotland was 54%. The Scottish figures for 2008-09 are a staggering 64%. There seems to be a contraction of the kestrel population in the west of the UK including a rapid decline in Wales and Ireland. Markus Jais: What is known about the situation across Europe?
Gordon Riddle: In Europe the kestrel is classed as SPEC category 3 – a declining species, numbering between 330,000 and 500,000 pairs. It is still one of the commonest raptors in Europe with a mixture of stability in some countries and decline in others, for example France and some eastern European countries. The largest populations are in Germany, France, Russia and Spain.
Gordon Riddle with a healthy brood of 5 kestrels.
© Gordon Riddle
Gordon Riddle: I started working on the kestrel population in Ayrshire in 1972 and built up a long term monitoring programme which is still ongoing. The aim is to consistently target 35-40 nesting territories annually and gain complete coverage of the breeding cycle for each breeding pair. Nesting sites are a mixture of nest boxes in woodland, natural sites such as cliff ledges and corvids’ nests, and buildings. The kestrel work is only one element in the extensive coverage of raptors by the local Raptor Study Groups in Scotland. The combined data is collated nationally by the Scottish Raptor Monitoring Scheme. Markus Jais: What habitat do Kestrels prefer in the UK?
Gordon Riddle: The kestrel primarily preys on small mammals so the preferred habitat is open areas of unimproved or rough grassland. It readily occupies agricultural ground and also utilizes waste ground and parkland in cities. The southwest of Scotland, where my study area is located, has a high percentage of unimproved grassland habitat. In the days of conifer planting in the 60s and 70s the early years of the first rotation provided ideal ground for short tailed field voles and the kestrel responded by breeding in high numbers.
Kestrel female with brood in an old crow's nest.
© Gordon Riddle
Gordon Riddle: Although kestrels can breed in their first year they are not long lived. The strategy of a quick turnover of population depends upon high productivity and clutch sizes range from 3 to 6, with 7s and 8s not unknown. Broods of 4 to 6 are the norm in my study area. Natural factors such as adverse weather conditions can determine the timing of the breeding season and therefore the outcome. Earlier broods tend to produce the largest clutches and broods, and the young have better survival rates. Predation and competition from other raptor species is another factor. The direct impact of human activities on breeding success is relatively small. Markus Jais: What is known about the annual movements of Commons Kestrels in the UK? How many are sedentary and how many do migrate?
Gordon Riddle: The kestrel is a partial migrant and in the UK the picture is quite complex. The majority of adults from upland areas of northern Britain move south or to lower ground to avoid the snow cover and inclement winter conditions, joining up with migrating juveniles. This autumn migration is usually over by November. If winter territory is held on the lower ground it is by males, with females apparently travelling further south than the opposite sex. Other birds are more sedentary, for example in lowland farmland areas of eastern England pairs often remain together in winter. The wintering kestrel population in the UK also contains birds from Fenno-scandia and the Baltic coasts which often use oil installations as staging posts in the movement over the North Sea. Returning migrants in the spring join the winter residents in late February to the end of May. Markus Jais: What is known about the natal and breeding dispersal of juvenile birds after they leave their parent's territory? How many die during their first year?
Gordon Riddle: When the juveniles leave the family parties in late summer there is a random dispersal initially then a movement southwards, birds from Scotland and northern England reaching southern England by October with some crossing the Channel to northern Europe. Kestrels from England move to the Continent and some reach northern Africa. One of the birds I ringed travelled 3,079 kilometers to Teneriffe by November and there are other examples of similar long distance movements. The mortality rate in the first year is high at 50-60%, many inexperienced birds succumbing as the first severe weather of the winter sets in.
Kestrels take readily to nest boxes.
© Gordon Riddle
Gordon Riddle: The kestrel is under recorded in the UK and there is a need to encourage more people to become involved with the species. There has never been a national survey. The reasons for the declines are not fully known and factors such as the impact of competition and predation by recovering raptor populations, the effects of rodenticide poisoning, mortality due to windfarms all need further research. There is some evidence in recent years that vole cycles are changing with less extreme fluctuations than in the past, which could be another aspect of the decline. This also needs further investigation. Markus Jais: What is the main prey of Kestrels in the UK?
Gordon Riddle: The main prey of the kestrel is the short tailed field vole though passerines are taken in the latter part of the breeding season. Kestrel breeding performance in upland areas is tied into the 3-4 year vole cycle. In peak vole years the numbers of breeding pairs increases as does productivity while in poor years the number of pairs drops but, while barn owls sometimes do not even breed, the kestrel continues to produce albeit with lower outputs. In the latter part of the breeding season small passerines such as juvenile meadow pipits, starlings and skylarks feature in the diet. Markus Jais: Is there enough food for the Kestrels? Has intensification of agriculture and habitat destruction depleted the prey base?
Gordon Riddle: This is certainly a major issue. The intensification of farming in the past few decades has considerably reduced the amount of foraging ground which supports the small mammal populations on which the kestrel depends. Heavy grazing of grassland has undoubtedly reduced the amount of rough pasture available and extensive arable production has limited the amount of edges and corners over which the bird hunts. Incentives such as the ‘set-aside’ schemes was a step in the right direction but the new stewardship schemes do not seem to have the same uptake from farmers. Another factor which has reduced the kestrel’s prey base is the loss of excellent vole habitat with the maturing of the extensive commercial forestry plantations in Scotland in the 70s, 80s and 90s. The rough grass cover of the first rotation is in complete contrast to the often tangled mass of debris left on the forest floor in the second rotation which makes hunting much more difficult for the kestrel.
Classic unimproved grassland in the Ayrshire study area with nearby shelterbelt used for nesting.
© Gordon Riddle
Gordon Riddle: The main threats are the loss of foraging areas which support the small mammal populations on which the kestrel feeds due to the current levels of agricultural intensification and the maturation of afforested ground which afforded an unprecedented food source in its early development. Secondary poisoning through poor practice with chemical rodenticides is another possible negative man related factor while the competition and predation from recovering raptor populations is a natural phenomenon which may very well be much more important than first thought. Markus Jais: Is there competition with other birds like Barn Owls, Common Buzzards or Jackdaws?
Gordon Riddle: The kestrel’s relationship with other species is one of the most fascinating elements in its lifestyle. The recolonisation of areas by the goshawk can have a severe impact on kestrel populations locally, the kestrels being almost wiped out. There is also a degree of overlap in the feeding regimes of the recovering buzzard and barn owl populations. Both species compete with the kestrel for nest sites and the buzzard is known to kill adult and young kestrels. This is however probably a reversion to a more natural order of things which had been distorted in the 1960s and 70s when the number of kestrel pairs was in excess of all the other raptor species combined. Raptor populations had been severely depressed due to the combination of the extensive use of pesticides in agriculture and persecution from game shooting interests. Markus Jais: How do you see the future of the Common Kestrel in the UK and Europe and what should be done to protect them?
Gordon Riddle: What is really important is that complacency should not set in. The kestrel has never been a high profile species because of its ‘common’ tag and there must be greater attention paid to its status and conservation. In the UK it is only in the last few years that a new awareness of the kestrel’s situation has resulted in a momentum building up to address the gaps in knowledge regarding this species. With that knowledge conservation measures can be implemented to counter the negative factors. Possibly there is a natural re-adjustment taking place due to the recovery of depressed raptor populations and this ecological competition must always be borne in mind. However, the kestrel, because of its ability to respond positively to changes and its high productivity, has always shown the potential to ‘bounce back’.
Male kestrel brooding small young in the tower of a dam.
© Gordon Riddle
Gordon Riddle: The book ‘Kestrels for Company’ is a follow up to ‘Seasons with the Kestrel’ which was published nearly 20 years ago. The last two decades have seen huge changes in the raptor map of the UK and consequently on the status of the kestrel. The aim of the book is to raise the profile of the kestrel and stimulate action to improve our knowledge of this species, and the factors which are causing its decline, so that they can be addressed. Based upon the fieldwork and research carried out both in my study area and by others, the kestrel lifestyle and current decline is tied into the large picture of raptor conservation and politics. Chapters on the Seychelles, Mauritius and Cape Verde kestrels follow my great fascination for island populations and add a wider perspective. Markus Jais: What can people do to help the Kestrel?
Gordon Riddle: There are several ways in which people can assist with kestrel conservation. More research needs to be focused on the kestrel including an improvement in the monitoring coverage and work to explore the factors outlined in questions 11 – 13. Lobbying for more kestrel friendly government agri environmental policies to restore the rough grassland habitat through incentive schemes will also have a positive effect for other small mammal feeders such as buzzards, short eared owls and hen harriers. On a practical note the kestrel takes readily to artificial nest sites and nest box schemes can be extremely effective in areas where natural nest sites are a limiting factor. Markus Jais: What was your most amazing experience with Kestrels?
Gordon Riddle: Probably the most satisfying experience was when I free climbed the wall of a small lime kiln ruin to a nest hole which I assumed was empty as no bird had exited. As I pulled myself level with the opening I was eyeball to eyeball with a hen kestrel. If she had panicked and taken off she would have knocked me backwards but thankfully she eased back off her clutch of six eggs and stood there defiantly. After enjoying this stand-off for a full minute a slow retreat was the order of the day and I left the site with the data required and without putting her off the nest. A special moment indeed. Markus Jais: Gordon, thank you very much for the interview.