Berkut. Vol. 8. Is. 1. 1999. P. 71-77.

 

STUDY OF THE ICTERINE WARBLER

IN BULGARIA

D.N. Nankinov

Изучение пересмешки в Болгарии. - Д.Н. Нанкинов. - Беркут. 8 (1). 1999. - Южная граница ареала пересмешки проходит через Болгарию. Она гнездится изолированными участками в благоприятных местах на всей территории страны на высотах до 1200 м н. у. м. Наиболее многочисленна пересмешка на северо-востоке Болгарии. Весной прилетает в среднем 10.05, но в годы с ранней весной первые птицы могут появ-ляться и на месяц раньше. Наиболее интенсивная миграция проходит во второй половине мая. Пересмешка населяет светлые леса с преобладанием березы, тополя, белой акации и других лиственных де­ревьев. Откладка яиц происходит после 16.05, вылупление птенцов – после 28.05. Слетков можно наблюдать со средины ию-ня до средины июля, изредка даже до 6.08. С учетом этой даты период размножения пересмешки в Болгарии составляет 83 дня. Первые особи покидают страну после 23.07. 78,06 % встреч птиц приходится на лето, 60,76 % отмечены в августе (рис. 2). Самая последняя встреча – 29.10. Продолжительность пребывания составляет 204 дня. Питается преимущественно двукрылыми. Численность пересмешки значительно колеблется по сезонам и годам. Отмечены циклические изменения на протяжении 100 лет.

Key words: Icterine Warbler, Bulgaria, migration, breeding, habitat, singing, number, feeding.

 

1. Introduction

The Icterine Warbler (Hippolais icterina) is a typical migratory bird, who nests in Europe and the central part of West Asia and winters in Africa. A complex border of its range crosses Bulgaria. Its number fluctuates strongly during the different seasons and years. Still it is not registered on many places, but as P. Pateff (1950) wrote: “this doesn’t mean that there are no nests at all, and it is not observed until now, because of its rareness and probably it will be found soon”.

 

2. Methods and materials

We collected the materials on the distribution and biology of the Icterine Warbler during our field work in the country, mainly on the field stations “Rupite” (after 1976) and “Atanasovsko Lake” (after 1978). We organised and conducted a regular catch of birds with fine Japanese nets and their ringing with standard aluminium rings. We performed regular observations in the parks and the surroundings of Sofia. The data from the ornithological literature was processed and also some of our previous studies, performed along the seashore of the Baltic Sea.

 

3. Results and discussion

3.1. Former researches

The first report that the Icterine Warbler nests in Bulgaria belongs to W. Radakoff (1879), who found Sylvia hypolais nesting in Wallachia (near Bucharest) and in Bulgaria. After more than 10 years, on 14 and 17.06. 1890 O. Reiser (1894) recorded the nesting of the species (who he marked as Hypolais philomela (L.), Hypolais salicaria Bp.), near the village Kranevo (Varna). E. Klain adduced concrete information on the height and the location of a nest and on the number of the brood of the Icterine Warbler. The nesting of three birds, recorded near Svishtov on 20.05. 1932, is uncertain (Harrison, Pateff, 1983). During the period 2-20.06.1935 G. Heinrich shot 10 Icterine Warblers among a big nesting near the outfall of the river Kamchia. One adult male of them was described as a new race Hippolais icterina Borisi (Jordans, 1940). The typus of the new race is kept in Bonn (Germany), in the collection of the Zoolo­gi­schen Forschungsinstituts und Museum Alexander Koenig under number 38.796. Later it turned out that the Bulgarian Icterine Warblers are not very unlike in size, shape of the wing and coloration from those living in Europe. The length of the wing of the male birds varies within the limits 75-81mm (Jor­dans, 1940), 75-82 mm (Pateff, 1950). 69 Icte­rine Warblers ringed on the field station “Ru­pite” during the period July-September, had the following proportions in mm: wing 72,8 ± 5,4 (66-82), tarsus 21,9 ± 2,9 (18-25), bill 11,5 ± 0,9 (9-14). Its weight was 15,0 ± 2,6  g (10-23) (Nankinov et al., 1985).

The Ic­terine Warbler was found nesting on 23.06.1952 along a river near village Batovo, Balchik (Petrov, Zlatanov, 1955). Singing males were recorded during the breeding season on 7.06.1957 near Primorsko, (Balat, 1962) and on 28.05.1959 to the north of Zlatni Pyasutsi (Mauersberger, 1960). There was a big concentration of passing and nesting Ic­terine Warblers in 1960 in north-east Bulgaria. On 20.05 G. Mauntfort and J. Ferguson-Lees (1961) found a nest at 7 steps height on a poplar near the Lake Sreburna. The first egg was laid on the next day. Another 10 males were singing in the area and one – near the village Popina. 8 males were singing in the forests Baltata on 24.05 and during the period 6-10.06 their number varied between 1 and 3 birds. At the same time on 31.05.1960 M. Paspaleva-Antonova (1961a) found a nest with 4 eggs in a farm yard in the village Vetren. In another publication of the same author (Paspaleva-An­to­nova, 1961b) we read that during the period 1958-1960 nests with young were found and from 20.05 to 11.06.1960 a nest with 4 eggs. It is supposed (Paspaleva-Antonova, 1964) that during 1960-1963 the species was nesting in the thin upper part of the old beech forest over the monastery in the Lyulin Mountain. In June 1965 on the island Persina M. Paspaleva (1970) described how “the Icterine Warblers – invisible among the green leaves of the poplars, irritate the other birds with imitation”. Then the species was observed in the Youth Park in town Ruse (Braun, 1968). Icterine Warblers were recorded in the inland part of north-east Bulgaria, near the villages Davidovo, Pravenchi and Rujicha on 2.06. 1964, 8.061965 and 2.07.1967 respectively (Simeonov, 1975).

In south-west Bulgaria S. Simeonov (1971) shot a male bird with active testes on 8.05.1964 near the village Che­resh. He observed an adult bird with 4 flying young on 6.08.1968 near the village Koprivlen and also recorded how an adult bird feed young in a nest on 3.06.1969 near the village Vinogradi. The Icterine Warbler is recorded during the breeding season near the river Kamchia – 4.06.1974 (Schubert, Schubert, 1982), near the village Pchelin, Ihtiman – 15.05.1978 (a pair) and near the village Malka Verea, Stara Zagora – 17.05.1978 (Petrov, 1981). It is also announced as a nesting species of Vracha Mountain (Profirov, 1988). B. Milchev (1994) gave 18 finds in the breeding season mainly in the eastern part of the Bulgarian part of Stranja Mountain. A nesting in Sofia was recorded (Nankinov, 1982). Singing males were listen on 15 and 19.05.1972 in the Borisova Gar­den and on 17.05.1973 – in the Central Ce­metery of Sofia. It was observed on the Shumensko Plato in the summer. (Nankinov, 1996). Later the Icterine Warbler was recorded in the breeding season near Sreburna, Shabla, Varna, Yambol and in other places. It nested irregularly in Sofia (Borisova Garden, Central Cemetary, West Park, South Park, Boyana, Pavlovo, Knyazhevo), at the foot of the Vitosha Mountain near Vladaya, Dragichevo, Rudarchi, within the forest “Vithosha”, near dam lake Studena and to the south near the village Dren and town Dupnicha and also in the poplar and acacia belt near Kurilo and Negovan. Therefore the species breeds in favourable isolated nesting places on the territory of Bulgaria (Fig. 1), but mainly in the north-east part of the country.

 

 

3.2. Arriving in spring

Long standing observations in Sofia show that the Icterine Warbler arrives in spring after 10.05. Usually about this date it also appears in the other parts of the country. But in the years with early spring the species arrives in Bulgaria in the first days of May and even in April. Icterine Warblers were caught on the field station “Rupite” after 30.04 and along the Black Sea coast – after 21.04. There were 2 birds recorded in Vasilyovska Mountain on 28.04.1985 (Georgiev, Aleksandrov, 1988). But the most early observation of the Icterine Warbler in Bulgaria is the one on 9.04.1977 when on the slope of Lyu­lin Mountain near Gher­nia Kos were recor­ded and listen 3 singing birds. The spring migration is most distinguished in the second half of May (Fig. 2). Its main pass coincides with the going into leaf of its favourite trees species: birch (genus Be­tu­la), poplar (genus Popu­lus) and others and it continues no more than 2 weeks. Then the birds stay and sing in the outskirts of the forests, in the thin wood parts (especially when they are of birch and poplar) and also in parks, orchards and farm yards. The spring migration in Sofia was observed when “most of the birds” began singing on 4.05.1902. A new wave of passing birds with big number was on 17.05 and single individuals remained for about 2 days after that (Andersen, 1913). The spring concentrations are most remarkable in north-east Bulgaria. M. Paspa­le­va-Antonova (1961a) recorded a mass migration and shot 7 male birds from 16th to 20.05.1960 on the island Batin and also in the wood belt and the small island near the village Sreburna. Then (21-24.05) many passing Icte­rine Warblers were observed along the  Da­nube (near Sre­bur­na and Popina) and also along the Black Sea Coast in the forest Baltata (Mount­­fort, Ferguson-Lees, 1961). 5-6 individuals were observed only once during the spring migration on 26.05.1994 on the decorative bushes in small gardens in the town Gabrovo (Stoya­no­va, 1996).

 

 

Fig. 2. Occurence of the Icterine Warbler in Bulgaria.

Рис. 2. Встречаемость пересмешки в Болгарии.

 

3.3 Habitats

The habitats of the Icterine Warbler in Bul­garia are situated from the sea level to 1200 m. This are outskirts of woods, thin deciduous and mixed forests with clearings, glades, cuttings or with dense bushes. It prefers light woods with prevailing young bir­ches, black italian poplar (Populus cana­den­sis) or black locust (Robina pseudoacacia). It inhabits artificial forests among the field, riverside wood belts, dense forests, thin woods in marsh areas, gardens and parks in towns and villages and their surroundings, farm yards, orchards. According to M. Paspaleva-An­tonova (1961a, 1961b) this bird avoids dense birch forests, which were prevailing along our the Danube shore and because of that it had been rare there in the past. The replacement of the birch forests with plantation of black italian poplars influences on the number of the Icterine Warbler. However, now the Icterine Warbler is not rare along the Danube, but in close look – it is as common as the chaffinch (Fringilla coe­lebs). During the breeding season these two species inhabit the lower floor (from 1 to 3 m) of the poplar and the black locust belts along the Danube.

At 2 Icterine Warblers live in Sredna Gora, on Septemvriiski Rid, to the west of Pchelinski Mineral Baths, in formations of Querceta freinetti, on 10 km. route, with percentage of predomination 1,32 individuals (Simeonov, Petrov, 1982).

 

3.4. Breeding

According to weather the male Icterine Warblers begin singing right after their arrival or several days after that. Their song is imitative – the characteristic for the species sounds are mixed with part of songs of many other bird species.

Still E. Klain (1903) wrote that “in its song Icterine Warbler includes sounds of different birds for example the grey partridge (Perdix perdix), quail (Coturnix coturnix), warblers (genus Sylvia), thrushes (genus Turdus), swallows and others and unites these sounds harmoniously in its song”. According to N. Boev (1958) “when singing the crown feathers of the male bristle and its head grows round. It whistles “yit” as the warblers, twitters and warblers in danger “tik” and “churrtittiut”. Its song consists of different quickly changing sounds often it is a plagiarism – sings with borrowed times from other song birds and mixed with the characteristic “chuyii ... didljuf”.

In the songs of the Icterine Warblers living in Bulgaria can be found alarm sounds, calls and parts of the songs of the Chaffinch, Gol­den Oriole (Oriolus oriolus), Green Sandpiper (Tringa ochropus), Common Starling (Stur­nus vulgaris), Siskin (Carduelis spinus), Great Tit (Parus major), Swallow (Hirundo rustica), warblers (genera Phylloscopus, Ac­ro­cephalus), redstarts (genus Phoenicurus), thrushes, sparrows (Passer montanus, P. do­mesticus) and others. It sings most intensive from the beginning of May to the end of June, can be heard during the whole day and it coincides with the time when the birds build their nests, lay and incubate the eggs. Rarely in early and warm springs some males sing in April. Songs can be heard in the beginning of July when pairs have late or second hatches. Some explorers (Ptushenko, 1954) compare the song of the Icterine Warbler to those of the Blyrh’s Warbler (Acrocephalus dumetorum) and Marsh Warbler (A. pa­lust­ris), but it differs from their songs by the characteristic of the species sounds “ti-ti-hin” and “chrrr-knii”.

The nests of the Icterine Warbler are built more often at 1-10 m high on the branching of the main trunk (rarely on side branches) and are masked with small bands of the birch bark, with cobwebs, small feathers, moss, lichens, poplars, willow or other plant down. Inside the nest is cover with tender feathers and hairs. It lays 4-5 eggs. The female incubates mainly. Young hatch and fly away from 70 % of the laid eggs. Such is the nesting success of the Icterine Warbler (Malchevskii, Pukinskii, 1983). On M. Paspaleva-Antonova observations (1961a) the male bird stays away from the nest and does not participate in the incubation. This circumstance, together with the cautions of the female mislead the explorers that the Icterine Warbler is a rare bird. The incubating female leaves the nest only when the intruder comes nearer than half a me­ter and moves quietly from branch to branch and returns in a similar way when the explorer walks away. A nest, measured by M. Paspa­le­va-An­tonova, has the following proportions (mm): outside diameter – 86, inside diameter – 48, height – 73 and depth of the bed – 29.

The information on the feeding of the young and the adult Icterine Warblers is rather scarce. Scraps of small beetles (Coleoptera) and a spider were found in the stomach of a bird, shot in Petrich (Prostov, 1963). It is established (Prokofieva,1968), that the Icterine Warbler feeds its young mainly with tender and succulent food, like spiders (Areneidae) in the first days after the hatching. A great part of the food (from 48 % to 67 % in different nests) are the dipterans (Diptera) – mainly flies and gnats, butterflies (Lepidoptera), beetles, hymenoptera (Hymenoptera) and also bugs (Heteroptera), dragonflies (Odonata), centipede (Chilopoda) and others. The adult birds forage in the heads of the trees as well as among the shrubs, the grass cover, in the blossoms of some plants and on the ground, but no farther than 50 m from the nest. They catch insects flying like the flycatchers (ge­nera Muscicapa, Ficedula). Parents feed their young for more 10 days after their leaving of the nest and after that the family falls apart and individual birds can be observed. We recorded migrating Icterine Warbler picking different berries, most often dewberries (Rubus caesius).

Fragmentary information about 9 nests afford an opportunity to figure out the opening and the final terms of the breeding cycle of the Icterine Warbler. The first arrived icterine warbles do not breed immediately. Usually a month passes from the beginning of the migration of the first icterine warbles to the building of the nests and the laying of eggs. In the beginning of May the testes of the male birds activate (Prostov, 1963, Si­me­o­nov, 1971). The first eggs are found after 16.05. In later and second hatches eggs appear­ in the second half of May and to mid June. Young begin flying from mid June to mid July as most of the young leave the nests in the end of June an in the beginning of July. Such young bird was caught on “Rupite” on 15.07. 1981. S.  Simeonov (1971) spoke of late flying­ young (6.08). If we accept this date as final for the leaving of nests from the young Icterine Warbles, then the breeding season of the species in Bulgaria (from the laying of eggs to the leaving of the last young) extends for 83 days. The breeding period of this bird is shorter to the north. For example we observed 17 nests of icterine warbles near the Finch Bay (Baltic Sea) in 1966, 1969 and 1970. Their breeding season from the laying of the first egg (1.06) to the leaving of the last young (23.07) extends for 53 days. The breeding of individual pairs is shorter to the north (26-28 days) than to the south (31-32 days).

 

3.5. Autumn migration

The autumn migration of the Icterine Warblers cross the territory of Bulgaria starts in the end of July. This can be observed by daily caught and ringing of birds on the field stations. The first passing Icterine Warblers were ringed on 29 and 31.07 on “Rupite” and on 24.07 on “Atanasovsko Lake” and on 23.07 near the village Dren (Sofia). The real, regular migration starts (in different days through the years) between 1.08 (1981) and 19.08 (1984). The times of the autumn migration are rather mobile – from 23.08 to 21.09 or even to 29.10. However, August is the month of the main autumn migration. Then concentrations of dozens of birds can be observed – 19.07.1973 – 30 individuals in a poplar wood in the place Murtvichata, near the river Ma­ritsa, by the village Govedari (Pazardzhik). Many Icterine Warblers were recorded in the end of August 1977 along the Strouma Valley, near the station “Rupite”, when 30-40 birds were count each day. The main wave of birds passed till 1.09, and in the next years the migratory waves were earlier – 4.08. There were also concentrations on 8.09.1976 and 15.08.1982. The autumn migration gradually lessen in September, although in some favou­rable years the number of the Icterine Warblers in this month is equal to their number in August. For example, in 1903 most of the Icterine Warblers passed over Sofia in September (Andersen, 1905). The migration stops in October. Individual birds were recorded on 1, 2, 3, 10 and 28.10. In some years Icterine Warbler stays in Sofia till the second half of October (Nankinov, 1982). The last Icterine Warbler left the country on 29.101977 (field station “Rupite”). Calculating the time from the arrival of the first spring migrants (9.04) to the leaving of the last individuals (29.10) we can say that generally the Icterine Warbler stays for 204 days in Bulgaria.

 

 3.6. Fluctuation in the number

The collected information on the records of Icterine Warbler shows fluctuations in its number during the months (Fig. 2). As a whole the species is most numerous during the autumn migration, when 78,06 % of all individuals, observed in Bulgaria, are recor­ded (n = 971). 60,76 % passed in August. The spring migration is wearer – 15,45 % and in the breeding season only 6,49 % of the Icterine Warblers are recorded.

The border of the breeding range of the Icterine Warbler is on the territory of Bulgaria. Therefore, its number is subjected to considerable fluctuations through the years. These variations are registered in the annual observations of one and the same places, as well as during the regular caught and ringing of birds. For example the Icterine Warbler has different number during the years on the field station “Rupite” and in 1979 no bird was caught.

Except these annual or through the years fluctuations in the number of the Icterine Warbler, there are total cyclic changes in its population during bigger periods of time. For example the Icterine Warbler has been numerous in many areas in Europe in the beginning of the century. After that its number grew 5-6 time, reaching its maximum in 1960-1965. Then a new regression in the population of the species started (Dolnik, Paevskiy, 1979; Malchevskiy, Pukinskiy, 1983) and this regression continues in nowadays. During the 1960s the population of the Icterine Warbler in Bulgaria reached its maximum, then it was a common bird in north-east Bulgaria and along the Danube. When its number lessens the Icterine Warbler first leave the cultivated areas (parks and gardens in the towns) and after that the other habitats.

Therefore, it can be supposed that the total changes in the population of the Icterine Warbler occur in 100 years and in the middle of each century it reaches its top number in its whole habitat.

 

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Dimitar N. Nankinov

Institute of Zoology BAS

Boul. Tzar Osvoboditel 1

1000 Sofia

 Bulgaria