Outstandingly high species diversity of raptors (diurnal raptors and owls) in Naliboki Forest

While observing and censusing raptors in Naliboki Forest, it was an outstandingly high species diversity of diurnal raptors and owls. Here is a possible explanation of this phenomenon.

First, the region of Naliboki Forest belongs to the transitional zone of the European forest, where northern and southern faunas significantly overlap.

Second, in comparison with mostly dry land forest massifs, that are common, Naliboki Forest initially consisted of both dry land forest habitats and extensive swamped openings. In 1960s-1980s most of large swamps were drained in Naliboki Forest, but several decades afterwards thousands of beavers appeared and they returned a lot of wetlands by creating thousands of ponds. In effect, the habitat heterogeneity in Naliboki Forest greatly increased. At the same time, rivers and other aquatic habitats (beaver ponds, floodplain lakes etc) are common in the terrain, too.

Third, because of climate change more southern species expand northwards, and some of them appear in the transitional zone, while the Naliboki Forest is situated transitionally.

Thus all these habitat components provide raptors with outstandingly high heterogeneity of environment that is full of diverse prey species (see Sidorovich, 2016 for the details).

In this post you will find which species of owls and diurnal raptors are observed in Naliboki Forest in the warm season (probably nesting), during autumn or spring migrations or in winter only. Basically we characterize the raptor distribution in the space and habitat variety of Naliboki Forest and point out population density, if such data is available.

Let’s talk about owls starting from relatively big species.

Eagle owl  Bubo bubo. Eagle owl is relatively rare non-migratory species of raptors in Naliboki Forest. However it nests in the terrain each year. The distribution and population density of the species vary in connection with the abundance of water voles. Because just this prey species is a crucial one during overwintering of eagle owls. The main localities, where eagle owls are regularly registered are S’miejnaje, Budy, Valasien’. Shubin. Lipovitsa, Kryvukha, Junitsa, Karaliova and Drazdy. On average the population density of eagle owl in Naliboki Forest is about one individual per 100 square km. That means that there are about nine couples of the species in the whole terrain.  

Snowy owl Nyctea scandiaca.  This northern owl species is rarely observed in winter in 1980-1990s, mainly in the period from the end of January till early March (4 out of 5 known observations). Snowy owls were seen within the extensive openings of the former darained swamps in the localities of Shubin, Budy, Hala Balota, Krasnaje and Valasien’.

Great grey owl Strix nebulosa. The great grey owl is a non-migratory species of birds, and it may be occurred  in  all large parts of Naliboki Forest. The data on the species abundance may be averaged as follows: approximately one pair of adult breeders per 30-40 km2 or about 5.6 individuals per 100 square km. It should be noticed that these data are not so precise as those related to the other owl species, because in April (when we usually do census of owls)  an artificial provocation of the great grey owl calling was not so effective to reveal them. Mainly we detected great grey owls hearing their daytime, sometimes night calling in March or early April, and also sometimes while seeing them.  Having such a rough data on the species distribution, nevertheless, we noticed a clear trend of lower number of great grey owls in the years of a higher density in eagle owls despite of the evident dependence of the great grey owl from the water vole population, too.  In a given year we have never found the both species of  these big owls nearby. However, we did not register any evidence of direct interference between the possible competitors. The last years there was registered the evident increase in the numbers of great grey owls in Naliboki Forest. In this terrain the owl species prefers to inhabit the places, there black alder swamps, spruce patches and grassy openings are interspersed.  

Ural owl Strix uralensis. In Naliboki Forest the Ural owl  is a rare non-migratory species of owls. Nevertheless, the Ural owl presence was revealed in both the northern half  of the terrain (the Jalowka and Tavaryshchyna localities in 2006-2009, the Klim locality in 2011, the Junitsa and Lysaja Hara localities in 2016) and in its southern half nearby the Kroman’ lake by Yurko & Duchyts (1998) and by us in the localitues of Rawtsy in 2014.  Basing on the data of the species census in 2002-2010 the average population density was about one individual  per 100 square km, but later in 2013-2015 it seemed to get commoner.  In this period Ural owls were registered in the localities of Valiavatka, Jalowka, Tavaryshchyna. Klim, Junitsa, Lysaja Hara, Jamna and Zarudny Bor.

Tawny owl Strix aluca. Widely spread and fairly common non-migratory species of owls. In 2000s the average population density of tawny owls in Naliboki Forest was about 74 inds per 100 square km. The last few years the numbers of tawny owls in this terrain evidently decreased in two times and even more.

Short-eared owl  Asio flammeus. In Naliboki Forest short-eared owls may be  mainly occurred  in the period of April-October. It is a rare species of owls that was seen for several times only in the localities of Jalowka, Hala Balota, Pawdniovaje Wiunishcha and Shubin. Plausibly the species nests in the terrain, but, perhaps, few pairs per a year only. For instance, in May 2014 a nest of the species was discovered in the former peatory of Hala Balota.  In May 2015 short-eared owl were numerically observed flying over the former peatory in the locality of S’viaty Kalodziezh.  Sometimes short-eared owls are registered in Naliboki Forest during winter.

Long-eared owl  Asio otus. The long-eared owls are mostly present in Naliboki Forest in the period of March-November. Some of them overwinter in the terrain, where such an individual mainly stays at drained lands. In non-migration period the number of  long-eared owls varied greatly in the terrain between different years. Presumably these changes in the species number are determined by the population cycling in Microtus voles that are the main prey of the predator. The  mean-weighted population density of  the long-eared owl in Naliboki Forest, taking into account the between-year variations,  was averaged as 8.6  individuals per 100 square km. Nearly all of the breeding pairs stay in drained lands and nest in a former nest of the magpie.

Hawk owl Surnia ulula. Almost every winter one or few times this rare owl species is observed in Naliboki Forest. Hawk owls were never seen in the forest in the warm season.  

Little owl  Athene noctua. The little owl is a rare non-migratory species in Naliboki terrain. We registered little owls in the Kliatsishcha village and its surroundings twice in 2004 and 2009 as well as once in the  Zabieriez’ village in 2012.  Later the species was found in the human settlements of Bor, Kliatsishcha, Bakshty, Jahadzien; and Aharodniki.  

Tengmalm’s owl Aegolius fureneus.  Tengmalm’s owl  is more or less common non-migratory species of owls. Basing on the data of the species census in 2002-2010 the average population density was 21.3 individuals per 100 square km. Tengmalm’s owl population changes in the large diapason from 5 to 60 individuals per 100 square km during 2002-2010.

Pygmy owl Glaucidium passerinum. Pygmy owl is a non-migratory species of birds, and it is one of the two most common species of owls. Basing on the data of the species census in 2002-2010 the average population density was 33.2 individuals per 100 square km.  The pygmy owl population changes in the large diapason from 3 to 68 individuals per 100 square km during 2002-2010

Now about diurnal raptors again starting from the their relatively big species .

Golden eagle Aquila chrysaetus. In Naliboki Forest the golden eagle was a rare sporadically occurred, but perhaps a residential species of diurnal raptors. In 2007-2009, 2011 and 2012 a pair and a single individual of adult golden eagles were regularly observed in the neighboring localities of Kazialiets, Halajbova Hrada and Hala Balota in the south-eastern part of Naliboki Forest. In March of 2008  a mating dance of golden eagles was observed in the Halajbova Hrada locality. Young golden eagles were registed in the area for six times in the period of 2008-2012. All these registrations suggest the species  nesting in the area. Nevertheless, our attempts (actually not much) to discover the nest failed. During  winters  adult and young golden eagles were occurred for five times in the valley of the Biarezina river in the downstream of the Patashnja hamlet in the period of 2004-2011. In February of 2009 adult golden eagle was scared from an elk carcass in the Vajnilawshchyna locality. Since 2013 in Naliboki Forest there were evidently more golden eagles. In the winter 2014-2015 subadult golden eagle was frequently occurred in the Nausts’,  Aziarskoje and Valiavatka localities. In January of 2015 adult golden eagles were regularly seen in  other areas: again in the Hala Balota and Kazialiets localities, and in Kaliuhi and Stas’kava localities. In the last area we observed adult golden eagle (once it was carrying a red fox cub) in the warm season 2015 for three times. In the winter of 2015-2016 in Naliboki Forest at least five golden eagles were registered: adult (small one perhaps male) and subadult in the Vol’ka river valley; adult (big one, perhaps female) in the Krasnaje, Kurhany and Hala Balota locality; adult (small one perhaps male) and subadult in the Kamarowskija and Asovyja localities.

Basing on the data represented we assume that approximately since 2005 there was, at least, one residential pair of the species in the Naliboki Forest. Since 2013 in Naliboki Forest the golden eagle became commoner and, perhaps, in the warm season 2015 even two pairs nested (one – around the Kaliuhi locality, another one at the Hala Balota locality somewhere in the Halajbova Hrada or Kukhnia or Junitsa localities).

White-tailed eagle  Haliaetus albicilla.  White-tailed eagle was regularly occurred in many places of Naliboki Forest in the 1950s: the localities of Pawnochnaje Wiunishcha, Dushylava, Lysaja Hara, Lotvin, Shubin, Krasnaje and Budy. In the beginning of 1980s the species did not nest in Naliboki Forest definitely, and, perhaps, only it sporadically visited the terrain. Since the beginning of the 2000s it began recolonizing of Naliboki Forest and in the beginning of the 2010s we knew two nests of the species in the localities of Kupalishcha and Dzieraminishcha. Moreover, a pair of adult  white-tailed eagles were regularly observed in  three  more places: the localities of Niarovy and Ulavina; Valasien’, Brodnaje, Budy, Pawdniovaje Wiunishcha;  Lotvin and Malaya Chapun’, where the predator nesting is plausible. In May-June of 2012, doing census of diurnal raptor in a part of Naliboki Forest (see the maps 5.1-5.5), we estimated   the species population density in the census plots as 0.3 individuals per 100 square km. This value suggests that it may be about 8 pairs of the species in the whole Naliboki Forest and its surroundings (associated with the terrain) on the area of 2.7 thousands square km.

Greater spotted eagle Aquila clanga.  In Naliboki Forest greater spotted eagle is a rare migratory species of diurnal raptors.  Since 2000 greater spotted eagle was observed on repeated occasions in the central and southern parts of Naliboki Forest.  Only in the mid-May of  2014 greater spotted eagle was twice observed in the swamped valley of the Biarezina river in the Niarovy locality that is in the northern part of the terrain. The data obtained on  greater spotted eagle suggest that it is a rare, but nesting species in Naliboki Forest.

Lesser spotted eagle  Aquila pomarina. Lesser spotted eagle is a relatively common species of diurnal raptors in the warm season in Naliboki Forest. They arrive in the end of April and then leave the terrain gradually in September-October. In 2012 the average population density of the species was about 7 individuals per 100 square km or, taking into account the main variation in the species distribution,  that was about 3-5 pair of breeding adults per 100 square km. There are  places that are populated by the lesser spotted eagle with markedly higher density – approximately 20-40 pairs per 100 square km. Such favorable habitats are situated in the group of localities, for instance, Hala Balota, Junitsa, Krasnaje, Symonava, Kurhany, Pawdniovaje Wiunishcha, Barki, Shubin, Budy, Krasnja Horka and Kryvukha; or Khmielishcha, S’viaty Kalodziezh, Dzieraminishcha and Vohminy; or Northern Wiunishcha and  Kupalishcha; or Niarovy, Kruhly Bor, Pieruch, Mylieva, Shchuchy Bor; or Paniamon’, Vojkava, Valasien’ and Haliandernia. The maximal local density of active nests of the lesser spotted eagle was found in the Barki-Shubin-Krasnaja Horka-Kryvukha and constituted about 9 nests per 10 square km.  All these places with the higher density of the lesser spotted eagle include habitats that favors foraging of the predator. Such habitats are as follows: abandoned and partly inundated peatories, open and swamped river valleys with old riverbeds and extended meadows on drained lands with drainage canals.  Conversely, in the sand dune areas (e.g. the Lysyja Hory, Siatryshcha, Siabryn’ and Liahavyja Hory localities) the species is nearly absent. Moreover, in the massive of spruce-prevailed forest (e.g. the direction from the Kliatsishcha village to the lake Kroman’) the lesser spotted eagle  is  rare in occurrence, too.

Short-toed eagle Circaetus gallicus. Short-toed eagle arrives in Naliboki Forest in the end of April and leaves the region in the end of September. It is a rare nesting  species in Naliboki Forest. In May-June 2012,  doing census of diurnal raptors, we knew two occupied nests (the Zapruddze and Kurhany localities) and one very plausible nesting plot (the Lotvin locality; the nest was unknown) in the fairly large  census area. Also, the species was observed in the localities of Rudnja Nalibotskaja, Zabalats’, Kaliuhi, Karytsietski Bor, Krasnaja Horka, Budy, Shubin, Asovyja, Masty, Niarovy and Ulavina. In May-June 2012 the average population density of the species  was 1.6 individuals per 100 square km. 

Black kite  Milvus migrans. Before the mid-1980s the black kite was a fairly common migratory species of birds of prey in Naliboki Forest. Nowadays it became quite rare. In 2010-2014 in a quarter of the terrain, where we studied on diurnal raptors we knew  only four nesting territories of the black kites in the localities of Malaja Chapun’, Junitsa, Hala Balota and Haliandernja. In May-June 2012 these nests were occupied and we did not find any other places of the species regular presence. So, the population density of the species was estimated as 1.9  individuals (or about one pair of breeding adults) per 100 square km.

Red kite Milvus milvus. The red kite is a rare sporadically occurred species of birds of prey. In May-July of 2010-2012 red kits were regularly observed in the four neighbouring localities of Patashnja, Karaliova, Zhabrachykha and Piashchany. A total red kites were seen there for 13 times. Once it was seen, while it was carrying a nest material. Following to the directions of red kite flights, the nest should be located 0.5-1 km southwards of the Patashnia hamlet on the right side of the Biarezina river. All these suggest nesting of the red kite in the place during two years, at least. Besides these observations red kites were twice registered in the drained area in the localities of Khmielishcha, S’viaty Kalodziezh, Dzieraminishcha and Vohminy in 1995 and 1999.

Common buzzard Buteo buteo. Common buzzards arrive in March and they gradually leave the Naliboki Forest in the period from late October till mid-December. Some of them overwinter in the terrain. It is the commonest species of diurnal raptors. In 2012 the average population density of the species was about 57 individuals per 100 square km or, taking into account the main variation in the species distribution,  that was about 20-38 pairs of breeding adults per 100 square km. There are  places that are populated by the common buzzard with markedly higher density – approximately 50-70  pairs per 100 square km. Such favorable habitats are situated in the following groups of localities: Hala Balota, Junitsa, Krasnaje, Symonava, Kurhany, Pawdniovaje Wiunishcha, Barki, Shubin, Budy, Krasnaja Horka and Kryvukha; or  Khmielishcha, S’viaty Kalodziezh, Dzieraminishcha and Vohminy; or    Northern Wiunishcha and Kupalishcha, Niarovy, Kruhly Bor, Pieruch, Mylieva and Shchuchy Bor; or Paniamon’,  Vojkava,  Valasien’ and Haliandernja. The maximal local density of active nests of the common buzzard was found in the group of localities of Barki, Shubin, Krasnaja Horka and Kryvukha and constituted about 18 nests per 10 square km.

Honey buzzards Pernis apivorus.  Honey buzzards arrive in the end of April and beginning of May and they gradually leave the Naliboki Forest in the second half of September. In 2012 the average population density of the species was about 13 individuals per 100 square km or, taking into account the main variation in the species distribution,  that was about 5-9 pairs of breeding adults per 100 square km.

Rough-legged buzzard Buteo lagopus. Rough-legged buzzard  overwinters in Naliboki Forest in number. They begin arriving mid-October or the beginning of November. In December of 2011 and 2012 we did census of  rough-legged buzzards in the central and south-eastern parts of Naliboki Forest. There were about 16 and 20 (mean 18) individuals per 100 square km.   We found that the majority of rough-legged buzzards (93% of individuals censused) stayed in open habitats that were as follows: abandoned and partly inundated peatories (14%), open and swamped river valleys with old riverbeds, mostly the Nioman valley (20%), and extended meadows  on drained lands with drainage canals (59%). Such favorable habitats are situated in the following groups of localities: Hala Balota, Junitsa, Krasnaje, Symonava, Kurhany, Pawdniovaje Wiunishcha, Barki, Shubin, Budy, Krasnaja Horka and Kryvukha; or Khmielishcha, S’viaty Kalodziezh, Dzieraminishcha and Vohminy; or   Pawnochnaje Wiunishcha and  Kupalishcha; or Niarovy, Kruhly Bor, Pieruch, Mylieva-Shchuchy Bor; or Paniamon’,  Vojkava,  Valasien’, Haliandernja. In the most suitable habitats  there were 3-19 (mean about 6 ) individuals per  10 square km.

In January and February there were censused markedly fewer rough-legged buzzards due to their migration southwards, and then in March their number in Naliboki Forest increased again. The last rough-legged buzzards leave Naliboki Forest by late April.  In the winter 2011-2012 we traced the rough-legged buzzard numbers in the extended opening in the localities of Khmielishcha, S’viaty Kalodziezh, Dzieraminishcha and Vohminy that used to be a large swamp before the draining in the 1960s-1990s. Nowadays, approximately a half of the opening is used for agriculture, whereas the other half was abandoned and overgrown with willow bushes and some trees or inundated and looks like a marshland with open waters.  There we estimated the following number of rough-legged buzzards on the area about 22 square km: end of November – 8 inds, mid-December – 19 inds, beginning of January – 17 inds, end of January – 5 inds, mid-February – 3 inds, mid-March – 12 inds, early April – 9 inds.

Goshawk Accipiter gentilis. Goshawk lives in Naliboki Forest year-round. It is not a rare species of diurnal raptors in the terrain, nevertheless, there are not so many of them as common buzzards. In 2012 the average population density of the species was about 8 individuals per 100 square km or, taking into account the main variation in the species distribution,  that was about 3-5 pairs of breeding adults per 100 square km.

Sparrowhawk Accipiter nisus. Sparrowhawk lives in Naliboki Forest year-round. Similar to the goshawk the sparrowhawk is not a rare species of diurnal raptors in the terrain, nevertheless, there are not so many of them as common buzzards. In 2012 the average population density of the species was about 6 individuals (or 3 pairs of breeding adults) per 100 square km.

Marsh harrier Circus aeruginosus. Marsh harriers usually arrive in Naliboki Forest in the first half April and they leave the terrain in September and October. In May-June 2012 the population density of the species was estimated as 4.9  individuals (2-3 pairs of breeding adults) per 100 square km. Mostly the marsh harrier nested in the reed marsh patches in all  abandoned peatories (the localities of S’viaty Kalodziezh, Hala Balota, Zhurawtsy, Kupalishcha, Masty, Lysaja Hara) and in more or less open valley parts of the Nioman, Biarezina and Islach rivers (especially in the localities of Haliandernja, Zialiona, Ulavina, Niarovy, Mylieva, Biely Bierah).

Montagu’s harrier Circus pugargus. Montagu’s harriers arrive in Naliboki Forest in mid-April and they leave the terrain in the first half of September. It is more or less rare species of birds of prey in Naliboki Forest. In May-June 2012 by doing census of diurnal raptors in a quarter of the terrain, we did not find any nesting areas (i.e. a location of frequent presence of the species). Nevertheless,  we know other places, where the species nested within Naliboki Forest (the localities of Ulavina, Zabiarez’ and Jatskava).   Plausibly, there is one pair of adult breeders of species per 400-600 square km of  the terrain. The species mainly nests within an open grassland in a high grass thicket.  Several times Montagu’s harriers were observed in Naliboki Forest during the late autumn and even in winter.

Hen harrier Circus cyaneus. Hen harriers usually arrive in Naliboki Forest in the first half April and they leave the terrain in October (but may be occurred in November too). In May-June 2012 the population density of the species was estimated as 4.4  individuals (2-3 pairs of breeding adults) per 100 square km. The species mainly nests in swamped clearcuts nearby open grasslands or agriculture fields. Few hen harriers were regularly observed in Naliboki Forest during the late autumn and in winter, particularly in the localities of Kliatsishcha, Shubin, Kazialets, Dzieraminishcha, S’viaty Kalodziezh and Prudzishcha.

Pallid harrier Circus macrourus. Since 2016 pallid harriers were registered for several times each warm season (including the nesting period). Mainly pallid harriers were seen in the localities of Pawdniovaje Wiunishcha, Krasnaje, Dzieraminishcha, Bielakorats and Shubin.

Peregrine falcon Falco peregrinus. Peregrine falcons are sporadically observed in Naliboki Forest during the species spring migration (late April-early May) and its autumn migration (late September-October). Mainly they were seen in the open parts of the localities of Shubin, Hala Balota, Pawdniovaje Wiunishcha, Mylieva, Niarovy and Ulavina. 

Hobby Falco subbuteo. Hobbies usually arrive in Naliboki Forest in the beginning of May and they leave the terrain in the end of September. In May-June 2012 the population density of the species was estimated as 4.4  individuals (about two pairs of breeding adults) per 100 square km. Mostly the hobby usually nested in an abandoned nest of ravens that situated in  old long-boled coniferous forest. In Naliboki Forest the predator hunts in various kinds of openings, first of all, among the nearest large meadows on drained lands. 

Merlin Falco columbarius. Merlin was a rare species in Naliboki Forest. In May-June 2012 the population density of the species was estimated as 1.6  individuals  per 100 square km. However,  the last several years the number of merlins in Naliboki Forest increased markedly (2-3 fold). The predator hunts in various more or less open habitats. Merlins were registered in the terrain from early April till mid-October.

Red-footed falcon Falco vespertinus. Red-footed falcon is a relatively rare species of diurnal raptors in Naliboki Forest. In May-June 2012 the population density of the species was estimated as 2.8  individuals  per 100 square km. The predator hunts in various more or less open habitats. Red-footed falcons were registered in the terrain from the end of April till the beginning of October.

Common kestrel Falco tinnunculus. Common kestrel is a relatively rare species of diurnal raptors in Naliboki Forest. In May-June 2012 the population density of the species was estimated as 2.6 individuals  per 100 square km. Kestrels hunt in openings. They were registered in the Naliboki Forest in the period of April-October.

Osprey Pandion haliaeetus. Osprey  was regularly occurred in several places of Naliboki Forest in the 1960s-1970s: the localities of Kroman’, Valasien’, in the Nioman valley nearby Liubcha, Dzialiatychy and Haliandernja, in the  Biarezina valley in the Patashnja locality. Nowadays, it looks like the species does not nest anymore in the terrain and may be observed there occasionally during its migrations. However, we still observed ospreys not rarely in the Nioman valley at the southern and south-western border of Naliboki Forest.

Imperial eagle Aquila heliaca. In Naliboki Forest imperial eagles were observed twice in the same Shubin locality in snowless December of 2018 and in July 2019.

Booted eagle Hieraaetus pennatus. In Naliboki Forest booted eagle is a rare migrating  species of diurnal raptors. Since 2007 the species was sporadically registered. Then  the species was observed regularly in the warm season (including the nesting period). most often booted eagles were observed in the localities of Pawnochnaje Wiunishcha, Zabalats’, Lysaja Hara, Patashnja, Nizki Bor, Kazialets, Valasien’ and Vialikaja Hrada. Any nest of the species is unknown. At the same time, we had no time and did not try to search for the  booted eagle nest.  However, the author support the assumption that the species regularly nests in Naliboki Forest.  In May-June 2012,  doing census of diurnal raptors, we registered two pairs of the booted eagle: the Zabalats’ locality and the Vialikaya Hrada locality. The estimated population density of the species  was 1.6 individuals per 100 square km.  Also, we saw the species in May and July of 2015 in the Kazialiets locality; and in May 2016 in the Nizki Bor and Navusts’ localities.

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