Date of the interview: 09 February 2010
In this interview Dejan Bordjan talks about the current situation and the biology of the White-tailed Eagle in Slovenia.
Markus Jais: What is the current situation of the White-tailed Eagle in the Slovenia (number of pairs, young fledged in 2009?)
Dejan Bordjan: Up till the year before last if you would ask anybody how many WTEs breeds in Slovenia, the most common answer would be 1-3 pairs, but not anymore. Then we revised our knowledge and gathered new data from almost all ornithologists in Slovenia and came up with the number of 7-11 pairs. What surprised us most was that some of the “new” discovered pairs bred well before the year 2000. I am sorry to say we are not regularly monitoring the nest or know the location of all nest for that matter. We can only say that in 2009 at least 6 pairs bred and at least 3 were successful in rearing at least one young.
Markus Jais: How has the population developed during the last 20 years?
Dejan Bordjan: In Slovenia there are very few historical data for WTE and no breeding records prior the end of twentieth century. The first breeding record comes from late 1980s from SE part of Slovenia in more or less continuous forest. I suspect that the main reason for settlement of that pair is in remoteness, the area was a highly protected military area, and because of several carcass dump sites for bears in vicinity. Probably at the same time another pair began to breed also in more or less wooded country, but also with intermittent lake with high importance for water birds.
In the late 1990s and in the beginning of the new millennia most of other pairs began to breed. It is apparent that Slovenian breeding population has increased steadily from 1990s till today to 7-11 pairs. The population is still increasing with observations of individuals in new areas. In the same time wintering population also increased with up to 11 individuals counted during International Waterfowl Count.
Drava River, © Dejan Bordjan
Markus Jais: Which habitat do the eagles use? How far from human settlement are most nests?
Dejan Bordjan: All WTEs nest in some kind of forest habitat. Most nests are located in lowland wet deciduous forest, two nests in mountain beech forest and two in a small forest fragment on a south facing slope. For feeding they mostly use larger rivers and fishponds, but they have been observed on smaller rivers, arable land, gravel pits and in forest. Four were also observed on migration above steep slopes with thermophilic vegetation far from any suitable wetland.
Markus Jais: In some European countries, at least some White-tailed Eagles seem to get more used to people. There are more and more nests in open agricultural areas or close to busy streets, villages or cities. Do you notice a similar trend in Slovenia?
Dejan Bordjan: We can’t say for sure that they are more used of people, but there are some indices that support the idea. There are definitely more observations of WTE in the last years and more observations of WTE closer to people and even some of hunting near and flying over human settlements. So far no nests have been found in open agricultural country or near any areas of high human pressure.
Markus Jais: Is there suitable habitat not yet used by the eagles?
Dejan Bordjan: Although Slovenia does not have a lot of optimal nesting habitat, there are still areas with suitable habitats for WTE to use in future. Such habitat lies especially in central and western Slovenia, where only one pair has been found so far.
Lake Cerknica, © Dejan Bordjan
Markus Jais: What tree species are used mostly for the nests and is there a difference in the breeding success between the different tree species?
Dejan Bordjan: So far we have not found many nests, but those that we have found were on oak Quercus robur or beech Fagus sylvatica. With so few nests found and almost no monitoring of nests we can not say that there is different breeding success on different tree species used.
Markus Jais: What is the main food for White-tailed Eagles in Slovenia?
Dejan Bordjan: Main food for WTE in Slovenia are fish and different species of water birds. Apart from that WTE also use carrion and hunt for small mammals such as foxes, hedgehogs and hares.
Markus Jais: How many White-tailed Eagles do spend the winter in Slovenia?
Dejan Bordjan: Every year during an International Waterfowl count, we also count WTEs, and counted individuals wary considerably between winters. This is probably the result of non appropriate census technique for WTE. Never the less up to 11 individuals were counted, leading to assumption that somewhere between 10 and 15 individuals regularly spent the winter in Slovenia.
Lake Cerknica, © Dejan Bordjan
Markus Jais: How many birds die from illegal poisoning, persecution and electrocution?
Dejan Bordjan: In relatively recent past we have only two records of human induced death in WTE. One bird was found with the gun shut wound in central Slovenia, far from breeding area and the other one was male with his beak blown off. That one died of starvation and it was found near our southern border, so it is also possible that it wasn’t even shot in Slovenia. So far no other cause of death was registered in Slovenia so far, luckily.
Markus Jais: How many birds die from lead poisoning? Are there efforts to make lead ammunition illegal or are hunters encouraged to use non lead ammunition?
Dejan Bordjan: If you mean WTE probably none. For other species this is something that we don’t know. It is possible that in some areas where there is heavy hunting pressure on mallards (one of few birds that is a game animal), there is also high mortality due to lead poisoning, but this has not been explored so far. Since we lack evidence for such mortality, there have been only minor efforts for making lead ammunition illegal.
Markus Jais: What other threats to White-tailed Eagles do exist in Slovenia?
Dejan Bordjan: So far the biggest threat is forestry works. We have records for two nest abandonment as a consequence of tree cutting near nest site in early nesting stage, in one case in spite of legal protection of the site during nesting period. For two nests we have evidence for disturbance by human presence, which in one case led to complete abandonment of nest.
Markus Jais: Which areas currently occupied by White-tailed Eagles are threatened by development like the construction of dams or highways?
Dejan Bordjan: Most areas are in no immediate threat from habitat destruction, since most nests are in areas that enjoy at least some kind of legal protection. In spite of that form time to time comes an idea to develop areas that is occupied by WTE, but so far we have managed to deter all such ideas.
Water Reservoir Medvedce, © Dejan Bordjan
Markus Jais: How much of the habitat currently used by the breeding pairs is protected? Are the areas around the nests protected from forestry work during the breeding season?
Dejan Bordjan: As I mentioned in the previous answer, most nests are in areas that enjoy at least some kind of legal protection. Few breeding pairs have all their breeding territory in a protected area. Two breeding or possible breeding pairs are in areas where there is little or no protection and one is in area that is protected, but it does not protect WTE directly. Where the nest site is known it also has legal protection from forestry work during the breeding season, but that doesn’t always help (see answer before).
Markus Jais: Do you ring juvenile birds and what has been learned by ringing and ring recoveries of White-tailed Eagles in Slovenia so far?
Dejan Bordjan: Due to our legislation and general lack of detailed study of population dynamics of WTE, there has not been any ringing of juveniles, and so far we also have no record of observation of WTE in Slovenia ringed elsewhere.
Markus Jais: What needs to be done so that the population can continue to increase and how do you see the future of the White-tailed Eagle in Slovenia
Dejan Bordjan: With some restoration of suitable habitats and with further colonisation of Slovenia, we could get 5-10 new breeding pairs, but not much more than that. Slovenia is more or less forested hilly country and especially in the south and west it lacks suitable wetlands. In eastern Slovenia most of suitable habitat has already been colonised.
Markus Jais: What organisations are working for the conservation of White-tailed Eagles in Slovenia?
Dejan Bordjan: There is no organisation that is specialised in WTE. DOPPS BirdLife partner in Slovenia puts most effort in protection of WTE, with help of mostly voluntary work from people from other organisations like Slovenian forestry service or Institute for Nature conservation.
Markus Jais: What other eagle species do currently breed in Slovenia and what is their status?
Dejan Bordjan: Besides WTE there are four eagle species that are confirmed or potential breeders in Slovenia. The most abundant is golden eagle with up to 40 pairs mostly confined to mountains of W Slovenia. It is showing a stable or slowly increasing population.
The second most numerous is Short-toed eagle with around 15 breeding pairs mostly confined to SE Slovenia. With exception of one pair they breed and hunt on Karstic dry meadows overgrown with pine trees and oaks. One pair inhabits intermittent lake with abundance of grass snake Natrix natrix.
Lesser-spotted eagle is the next species that breeds in Slovenia, with 1 pair in mature lowland forest of E Slovenia. Due to low population size it is very vulnerable to fluctuation of much larger Croatian population. In past few years it thus breeds irregularly.
There are some sings that booted eagle might breed in Slovenia, but that has not been confirmed yet.
Markus Jais: What was your most amazing experience with White-tailed Eagles?
Dejan Bordjan: Just last year, when we were monitoring lapwing migration on one artificial lake in NE Slovenia, I was counting on last day of monitoring. Up till that day we had not seen any breeding activity of a local par, besides courtship. The pair was observed on every day of monitoring, but on the last day they came to the lake and shared a fish and afterwards flew to the field not far from me, where they copulated several times. Since I Confirmed that breeding pair few yeas before I was honoured that it was me they showed part of their intimate life.
Markus Jais: Dejan, thank you very much for the interview.