Lesser Spotted Eagle Aquila pomarina in the Făgăraş Depression,Transylvania, Romania Jan van Diermen Abstract This report summarises data from the 2006 breeding season, unsystematically collected while performing a breeding population study of Great Grey Shrike Lanius excubitor. Study area measures 317 km 2 centred on the Olt river covering the bordering hill forest of the Transylvanian Plateau and the Făgăraş mountains. Lesser Spotted Eagles were seen during display in April, and from than on foraging and transporting food (mostly in bill). This gave a clue of prey choice, nest sites and reproductive success. Observations indicated that: Lesser Spotted Eagles take lizards as dominant larger prey, followed by voles and frogs, no chicks or young birds were seen to be taken unless the availability of such easy-to-catch and conspicuous items as Fieldfare Turdus pilaris fledglings that were taken by Common Buzzard Buteo buteo and Long Eared Owl Asio otus. from mid June onwards Carpathian eagles transport prey-items (including lizards of c.15g) over distances up to 7 km to the Făgăraş which seems hardly profitable from the cost-benefit point of view, Făgăraş breeders progressively foraged further away from their nest during chick rearing in June-July, Plateau birds show radial or fan shaped ranges, Fagaras birds may have elongated cone shaped ranges, reproduction in low vole years can be successful (estimated 57-63% of nests) exploring the high density of sand lizard. Important question remains what is the quality and importance of feeding habitat close to the nest. Future concern will be how to maintain or restore sustainable feeding habitat as natural floodplains loose their function. Also crop-management in commercial farming will reduce the chances of semi-natural systems as yet supported by low intensity farming. Intensive forestry may cause additional problems to breeding habitat. Lesser Spotted Eagles in Transylvania, Romania Lesser spotted eagles (LSE) are typical for the Carpathians and the Transylvanian Plateau. They breed in the woodland fringes bordering open landscapes and forage over a wider area of grazed hillsides and grassland plains, natural and cultivated floodplains. They bridge all habitat-gradients from woodland edges to floodplain and so are typical representatives of this landscape and its ecological values. Breeding population was estimated at 2800-3000 pairs in Romania 2004, being 20% of the Western-Palaearctic population (see, www.milvus.ro). Core areas are indicated as squares and the study area in yellow on the map to the left (Figure 1 without caption). Study area The study-area centres on the Olt river in the western Făgăraş Depression (county Sibiu). It ranges from the Transylvanian hills in the north to the Făgăraş edge in the south. The area measures 317 km 2 of which 63% is open area (48% pastures, 9% crops, 6% natural), 26% deciduous woodland, 2% orchards, 5% built up area. The Depression is intersected by parallel streams running from the Făgăraş mountains to the Olt-river. The Olt river has been transformed into barrages for electricity-production. Flooding no longer occurs. Where a vole-carrier dropped after 4 km of soaring and gliding, Racoviţa, July 10 th 2006 Methods, interpreting observations & calculating breeding population This report summarizes unsystematically collected observations. The first birds reappeared 30 th of March 2006. Pairs were seen to the end of April, from May females tended to stayed near nest sites (some heard begging) or on the nest to breed (eggs laid first half of May, young hatch mid June and fledge mid August). Some social foraging and persistent vocal interactions reoccurred from the beginning of June. Groups of 5-9 birds were seen together above feeding grounds, presumably including both failed pairs, breeders and immature birds. Nests were not searched for, birds disappeared in Fagus and Carpinus on the Făgăraş -side and in Quercus on the Transylvanian side. Observations on foraging birds helped estimating the breeding population. A minimum of 19 pairs were located through observations on repeated territorial display in April (4 territories), pair activity or food transport lasting in the egg stage (3 nests) and food-transport to the breeding female and subsequently the apparent hatchling seen in 29 instances (12 nests). The proportion of non-breeders was estimated at 10-16%.
Fig.2 Distribution of Lesser Spotted Eagle in study-area Făgăraş Depression, 317 km2, maximum dimensions 24x21 km, area limits in black, woodland an orchard green, altitude in 4 yellow shades from light <400 to bright >1000m ASL, inside study-area depicted as green contour-lines. Streams blue, Water bodies hatched blue, built up area & roads grey, horizontal hatch = arable fields. Circles: breeding sites, ô = successful, ô = failed, ô =only display seen. Grid 2x2 km squares: relative importance for mainly aerial hunting during periods of breeding and chick rearing in five shades from low to high(colours sand-yellow-orange-red-dark blood) derived from maximum density recorded on two standard-visits per month (4 per period). Symbols: prey transported southwards, transported northwards, strongly biased within periods towards places mostly frequented, but comparable between periods. Birds from the Făgăraş Mountains edge in the south preyed further from their nests, especially during chickraising transport frequently lasted over 15 easy minutes. Note the zone of squares just below the 500m ASL line in the south, where activity is low in July-August due to reduced cattle-grazing and pioneer woodland moving in. Distribution Territories were fairly regularly spaced, only the western part of the area seemed less suitable, especially on the Transylvanian side and near the industrial zone of Mărsa. I present dots on the map (figure 2), although they do not represent true nests. They indicate local success interpreted from birds with food dropping or disappearing. As some were observed from many kilometres away, locations are indicative. Food, direct consumption versus transport LSE is known to have a flexible diet, focused on voles in general but depending on conditions amphibians may prevail in the northern and reptiles in the southern limits of its range. In Romania it generally depends on voles to feed their chick (pers. comm. R. Zeitz, Milvus). The preceding winter was fairly rich in voles, but in 2006 there was no considerable spring increase in the population. It seemed to decrease by April and remained on a moderate level till August (due to mowing mice became more accessible by mid June). Birds foraged by hovering, hanging against the western airstreams, soaring or perching in trees. They also spent time on the ground collecting small prey items like beetles, grasshoppers and crickets (G. gryllotalpa and Gryllus campestris) both on arable fields, wet, grazed (with high density of anthills Formica-nests) and mown grassland. In total 41 transported food items were identified, being a very small sample compared to the daily needs of a successful pair. Dominant were reptiles: 21 mainly Lacerta agilis, one Lacerta viridis and possibly two Zootoca vivipara (>500m asl), one N. natrix, 14 voles (mainly Microtus arvalis, one C. cricetus, two mice probably Apodemus agrarius), 5 amphibians (once Hyla arborea, other presumed to be Rana dalmatina / Rana temporaria concluded from available animals on location) and one Mole Cricket G. gryllotalpa. Unidentified transported prey was not noted as I only took notice of birds at close range. Table 1 gives data on transported and directly eaten prey, the latter category involved birds of unknown status. Observation on birds eating prey in situ was hampered by poor visibility in high grassland or birds disappearing behind scrubs, reed beds or anthills. It probably emphasised on insects and juvenile frogs, in July-August particularly grasshoppers (definitely underestimated in counts of Table 1 & Figure 3). Breeding LSE focus on larger (heavier) items for transport to the nest, in this respect (the numerous but at 12-15 grams not heavy) lizards may have been less profitable than the (heavier but less available) voles.
Prey-handling transported (only breeders) eaten in situ (status unknown) Prey-group mammal 14 4 reptile 21 3 amphibian 5 8 insect 1 >>18 Σ 41 33 Table 1. Summary of observed prey taken by LSE, transported prey definitely only from breeders, prey eaten in situ may involve birds of any status, breeder, non-breeder or failed breeder. Period April- August 2006, number of observations per month was too small for analysis, but lizards prevailed may and July, mammals in June, amphibians in April and August, insects in June-August, but they were hardly detectable in May before mowing. Figure 3. percentage of items transported or eaten in situ per prey-category (total 73 items, 24 reptiles, 17 mammals, 13 amphibians and '19' insects). Only heavier prey fits for transport. Voles were expected to be more profitable for transport than reptiles. As reptiles outnumbered them and were transported at the same rate, voles seem to have been much less available. Figure 4. Hunting and altitude, former Olt floodplain below 400m ASL is most productive, highest zone may be important in period before chicks hatch when ranges from Făgăraş birds tend to be smaller. Feeding habitat In general LSE, once they left the forest edge, were observed feeding all over the open landscape, but appeared at highest density (even flocking) in the lower parts of the area near the river Olt and its tributaries (370-400m ASL). The Olt itself is turned into a row of artificial lakes for hydroelectricity, so its floodplain is not flooded anymore. Streams coming from the Făgăraş Mountains however keep the area wet. The Olt flood bed is traditionally cultivated. At this moment it holds a high proportion of extensively managed arable fields. These fields are mostly between 8 and 24 meters breadth and 100-300m long with a rich variety of cropmanagement, creating a huge edge-effect. Locally up to 40% of the managed area has been abandoned within the last 1-5 years. Dominant crops are maize and cereals, on large scale fields potatoes, mustard and wheat occur. Further uphill (above 400m ASL) extensively grazed grasslands, scrubs (also new zones with Viburnum and Betula as a result of reduced grazing activity), orchards (partly abandoned or bought by Italian investors) and strips or patches of Alnus-Salix woods along rivers and moors occur. Some rivers flow through broader (up to 700m) valleys with worn back slopes, creating attractive hunting conditions. As stated in Figure 4, hunting seems most profitable in lower altitude. April 5th, apparent nest site of Lesser Spotted Eagle, Quercus and Fraxinus, slope of Plateau, Colun April 3rd abandoned orchards, no mowing, no grazing, Betula pioneer wood takes over Sebeşu de Jos
Most lizards taken for transport were caught on semi-natural grassland, dikes and arid slopes ( 16 out of 21), most voles from Lucerne fields, grassland or abandoned fields ( 10 out of 13). Samples were too small and biased to make a reliable map on feeding-density, or to show seasonal cline in habitat-use. August 12th 2006, soaring A. pomarina, Sărata July 17th 2006, Liscov river worn back slope, Porumbacu May 9th 2006, Lacerta agilis caught, Porumbacu de Jos August 17th 2006, Perched LSE in willow, Sebeşu de Jos April 17 2006, Hyla arborea crouching, Hamba April 20 2006, Field vole Microtus arvalis lost meal, Colun It remained unclear to me whether substantial (early-morning or evening?) hunting in forest edges near the nest or near bogs at the foot of the Făgăraş mountains occurred. Possibly by birds perched in trees and therefore easily remaining unnoticed. The area below 400m, in fact almost identical with the former Oltfloodplain, is important too for other commensal species. Both Great Grey Shrike and Kestrel Falco tinnunculus reach their highest breeding density there. It is also frequented by feeding Hoopoe Upupa epops breeding further uphill, flying 2-3 km apparently especially to forage on Mole Crickets. Remarkable difference between vole eater Common Buzzard and LSE was that Buzzard repeatedly hunted Fieldfare Turdus pilaris fledglings, whereas LSE was not seen to do so, despite the opportunity lasting over a period of two months. Hunting for fledged Fieldfare was also witnessed from Long Eared Owl Asio otus.
Breeding success LSE, comparison with Kestrel, Common Buzzard & Long Eared Owl Judging from observed prey-transports in July-August 2006 12 out of 19 LSE pairs (63%) raised (one) young, giving a maximum (excluding non-breeders) yearling:adult age ratio of 24:76. Age ratios by the end of August 2006 averaged 15-22.3 % yearlings, so below the value expected from known breeders alone (avg. 18.7 ± 3.6 in 7 day-counts totalling 13 yearlings and 55 adults). Many chances for bias in this, because adults from outside study-area limits may prefer the Olt-valley, not all young were fledged or on the wing or I missed some failed pairs. I can't exclude any of the possibilities. Assuming the average is close to reality makes breeding success 12/21 pairs = 57%, and some 14 % non-territorial adult or immature birds present in the population (within assumed 10-16%). Below I compare the estimated LSE nest success (% of broods fledged) to my data on other known vole eaters in the area. Kestrels often did not raise young from their small clutches and to my surprise did not appear to take lizards frequently. I counted 3,4 and 4 eggs in three failed nests, of 14 nests only 5 (36%) fledged avg. 3.2 young. The breeding success of Common Buzzard was higher. Fledglings could be heard begging from 15 (71%) out of 21 breeding locations. This may reflect a more flexible feeding strategy than Kestrel s, but apart from the witnessed exploiting of Fieldfare-fledglings it was not studied in detail. Observed food-transports include 2 Fieldfare-fledglings, 7 voles, 1 juv. Rattus norvegicus, but again no lizard. Long Eared Owls were surprisingly successful in the village of Avrig, using the (absent) Barn Owls Tyto alba food niche. Five known pairs all raised young, two pairs even 4 and 5, which is high in this species. Outside the villages no chicks were noticed, and I had no idea about breeding density. In May-June three adults were found as road-victim under the Fieldfare colonies on 7 km of main road. These findings illustrate that Lesser Spotted Eagles in southern Transylvania may breed successfully in low- or moderate vole-years (or in any year) exploiting reptiles, the dense population of Lacerta agilis in particular (but N. natrix, L. viridis and closer to the woods Zootoca vivipara and Anguis fragilis are also present). Threats Main concern will be maintaining the quality of semi-natural habitats. Agriculture tends to either intensify or retreat. So unsustainable practise may take a giant leap at the cost of present values. Realistic threats are new commercial farming on large parcels with uniform methods, use of fertilizers and sprayings, cease of grazing village-herds and extensive mowing, control of water tables and drainage, controlling and exploring riverbeds all resulting in a reduction of habitat-transitions. These will seriously affect sustainability of the area for a wider scope of genera and species affecting the carrying capacity for raptors like LSE. The drainage canals running north from the natural bog-zone at the edge of the Făgăraş mountain-forests may have reduced the diversity in the open zones bordering the forest. Closing them might be the best option. I did not notice human interference with raptors or birds in general, but shooting was prohibited in most of the 2006 season because of bird-flu outbreaks (as close as 50 km east from the study-area). Forestry and tree felling may cause nests to fail, since low intensity-clear felling of mainly Carpinus betula and Fagus sylvatica in the lower Făgăraş mountains and Quercus sp. on the Transylvanian hills continued all-year round. There appears to be little environmental awareness, private nor professional. Concluding remarks My results indicate that the calculated LSE population density derived from the Milvus 2004 sample-census in this region is quite accurate, it might be somewhat too low in the southern Transylvanian Plateau. They also indicate that LSE in Transylvania may breed successfully in low or moderate vole-years because of the dense population of lizards, perhaps they simply do not depend on voles in any year in this region. LSE in southern Transylvania is a typical Natura 2000 target species, a challenge for sustainable management. It is of special interest to investigate the value of different habitats and to overcome the effects of new agriculture policies by appropriate management schemes. The loss of a naturally functioning floodplain may be hard to compensate but at least drainage of plateau pastures and lower fields should be minimized. Contact: diermenjan@gmail.com or hard to observe: hunting on foot, photo Aivar Veide, Estonia info@kentauro.nl