Ernst, Alena rakovská




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THE ROOK (CORVUS FRUGILEGUS L.), ITS NESTING IN THE SLOVAKIA AND RELATIONSHIP TOWARDS AGRICULTURAL LAND
Jana PORHAJAŠOVÁ, D. ERNST, Alena RAKOVSKÁ
Department of Environmental Sciences and Zoology, Slovak University of Agriculture in Nitra,

Tr. A. Hlinku 2, 949 76 Nitra – Slovakia, Jana.Porhajasova@uniag.sk
Abstract: The rook (Corvus frugilegus L.) is one of the greatest corvine birds dependent on open agricultural land. With the onset of spring, hundreds of thousands of rooks flocks which wintered in Slovakia, this area leaves and returns to its breeding grounds in north-eastern Europe. Wintering populations will be replaced by our rooks, in Slovakia nesting, which wintered in France and Spain. Nesting populations of rooks in Slovakia are much smaller, rarer and more vulnerable in comparison with populations wintering in Slovakia. These rooks populations occurs only in vicinity of its breeding colonies, situated mainly in the lowlands and uplands of Slovakia. Many farmers these elegant birds perceive negative, mainly as pests of crops, not as important functional component of agro-ecosystem, where rooks provides important sanitation function, contributes to biodiversity increasing and to biological regulation of pests. Listed function in agro-ecosystems except, but the whole society too, its total usefulness prevails over its harmfulness because rookeries provides nesting opportunities for the critically endangered red-footed falcon (Falco vespertinus L.). Research focused on monitoring of nesting areas of rook was realized in 2010 - 2013 in the western part of Slovakia - in whole area of Podunajská nížina, where natural conditions and agricultural land utilization offers to rook best conditions for its nesting. During evaluated period in monitored territory were situated several tens of rookeries. Some of them, where we noticed active nests, were relatively old and stable. Among such includes rookeries located for example in the cities Trnava, Hlohovec and Piešťany, where rooks have found the most suitable conditions for breeding in the urban environment, in parks on trees. However, rooks were there strongly dependent on the surrounding open agricultural land because of food. We found, that for nest tree selection by rook is not decisive the species only, but mainly height of tree and layout of branches in treetop, which must hold a large number of nests situated close to each other. In these cities there were mainly species: Pinus sylvestris, Platanus acerifolia and Populus nigra. In 2010 in monitored area we noticed 2416 nests, in 2011 the number dropped to 2323 nests, in 2012 increased to 2454 and in 2013 we observed till 2656 nests. The results of research indicate a slight increase of nesting populations of rooks in Slovakia.
Key words: rook, western part of Slovakia, agricultural land, monitoring, nesting
Introduction

The rook (Corvus frugilegus L.) is considered as intelligent, docile and very social bird. It is one of the greatest representatives of corvine birds, order singers - passerines (Seed et al., 2006). It is species with Palaearctic type of extension, occurring mainly in Europe but also in Central and Front Asia. Worldwide there are extended 60 – 220 millions of individuals (Brenchley, 2009). The European breeding population of rook is quite large; represents more than 10 million pairs (BurfieldBommel, 2004). Rook is a migratory bird. With the onset of spring will be wintering population of north-eastern Europe replaced by our rooks, nesting in Slovakia, which wintered in the south-western parts of Europe, especially in France and Spain (Literák, 2008). Our populations are much smaller and more vulnerable and are not as common as many, especially farmers and urban dwellers believe. It occurs only in the vicinity of its breeding colonies - rookeries. The biggest rookeries in Slovakia were located in the western and eastern parts of the country, in the Podunajská and Východoslovenská nížina. In Slovakia rooks currently nests primarily in Podunajská nížina, which is in the long term considered as its most important nesting area. In this area there are several old and stable rookeries, for example in the cities: Trnava, Hlohovec and Piešťany (MošanskýTrnka, 2002; Kaľavský, 2011). First nesting of rook in western part of Slovakia was recorded as early as 1965. However, information about its breeding occurrence in this area was incomplete, so the aim of the research in 2010 - 2013 was to obtain comprehensive overview of the current enlargement of rook nesting in this area.

Rook nests mainly in the lowlands, hollows and uplands (Luniak, 1972). It is bound to open agricultural land with groups of trees, windbreaks, hedgerows, or small forests (Brebchley, 2009). In recent decades has been recorded a significant degradation of appearance and function of agricultural land, therefore rooks currently finds suitable conditions for nesting especially in parks in larger cities, where nests in colonies. The nest is usually generally built on a tall tree, while tree species is not decisive. Decisive is the height of tree and arrangement of branches (Kasprzykowski, 2008).

Rooks searches for food by walking on the ground on lawns near human settlements, but most often in flocks on plowed fields and stubbles in agricultural land (MacdonaldWhelan, 2008). In animal food components prevails especially insects together with its larvae, also are represented largely various snails and slugs, a little less rodents and other small vertebrates (OrŁowski et al., 2009). Appointed author on the basis of the analysis of the stomach content of rook chicks found that all of the components of the food taken of approximately 46.5 % was food of animal origin, 41.2 % consists of mineral components, and only 12.2 % of the diet was of plant origin. Animal food component consisted mainly of larvae and images of several insect species while predominant was order beetles, many of which were pests of field crops. In plant food components were dominant cereal grains. The mineral component was represented by small stones, small fragments of brick and sand grains.

Despite its high intelligence, elegance and a significant contribution to the ecosystem, between farmers, hunters and inhabitants of urban agglomerations, rook is erroneously regarded as useless, even the harmful animal. However, in reality it is only a historically harbored negative attitude which some people to rook still maintain (Kaľavský, 2011). Importance of rook lies mainly in biological pest control (OrŁowski et al., 2009), the possibility of organic food production - the presence of rookeries in agricultural land can reduce the farmers costs to plant protection against pests and thereby contribute to more ecological production of healthy food for the humankind (Kasprzykowski, 2008), increasing of biodiversity (Lacko-Bartošová et al., 2005), providing nesting opportunities for critically endangered red-footed falcon (Falco vespertinus L.) which occurrence is dependent on existence of rookeries, where searches and occupies abandoned nests of rooks (Gúgh, 2009), sanitation services to the ecosystem - removing of garbage, dead animals or different food debris (RobertsJÄhnes, 2013).
Material And Methods

Research was conducted in the years 2010 - 2013 in the western part of Slovakia - in the Podunajská nížina, which is the most important nesting area of rook in the Slovakia. Based on the data collected about the number of nests in all nesting localities was assessed overall development of rook nesting abundance in this area. Monitoring was realised once a year, usually during April, usually just before the foliage of nest trees (after foliage tree leaves limiting nest counting). During this period, all active nests, i.e. nests occupied by pairs of rooks, were visible clearly. In individual years were in this territory selected 3 nesting areas located in the cadastral of the cities: Trnava, Hlohovec and Piešťany (Figure 1). All nesting areas were located in close proximity to the intensively used agricultural land. During the monitoring was recorded and subsequently evaluated: 1. species of tree with active nests; 2. nests in each nest tree; 3. total number of nests in the rookery; 4. development of nesting abundance of the same rookery during the whole monitored period. Information about the breeding occurrence were recorded in tables and then inserted into the online database of Slovak Ornithological Society - Aves Symfony.



Podunajská nížina

Piešťany

Trnava

Hlohovec

Figure 1: Rook nesting in the Podunajská nížina
The monitored area is located in the western part of Slovakia in disctrict of Trnava. It belongs to a warm climate region, where is the number of summer days more than 50. Average annual temperature is 8 - 10 °C; the average daily temperature in July is 20 °C. The average annual rainfall is 550 - 750 mm. In monitored area are dominant sandy - loamy and loamy soils (moderate), followed by clayey - loamy and clayey (hard) and partly sandy soils and loamy - sandy soils (light). From soil types there are the most advanced black soils, fluvisols and brown soils. Studied area is characteristic by maize growing region with a relatively long growing season providing appropriate environmental conditions for all thermophilic crops planting (Čeman et al., 2007; Líška et al., 2008).

Trnava is situated between the river Váh and the mountain Malé Karpaty in Podunajská nížina, at an altitude of 146 m above sea level. Agricultural soils around the city occupies about three-quarters of the total area (5300 ha, i.e. 74 %) while arable soils have absolute majority (4940 ha, i.e. 69 %). Representation of permanent grassland is low (only 83 ha, i.e. 1 %). More represented are permanent cultures, especially gardens, orchards and vineyards, occupying total 277 ha, i.e. 4 % of the area (Čeman et al., 2007). The most important breeding locality in Trnava is Park Janka Kráľa, less important locality is areal of Mestská vodáreň.

Hlohovec is situated at an altitude of 156 m above sea level, imposed between mountain Považský Inovec and Nitrianska pahorkatina. A significant part of the city lies in Podunajská nížina. An important role in the development of the city had river Váh - the longest river of Slovakia (Urminský, 2009). Of the city cadastre (6412 ha) agricultural soils represents 3821 ha (with arable land predominance), forests 155 ha and 295 ha water areas (Čeman et al., 2007). The most important and single rookery in Hlohovec is situated in the Zámocký park.

The worldwide known spa city Piešťany is located next to river Váh, in Podunajská nížina, between mountain Malé Karpaty and Považský Inovec (Šimo et al., 2003). Monitored area occupied 4420 ha, at an altitude of 162 m above sea level. In this area is relatively well developed crop and animal production what is very important for rook existence (Brenchley, 2009). The most widespread soil types of area provide suitable conditions for growing a wide range of crops, especially for cereals, sugar beet, maize, alfalfa, pulses, oilseeds, industrial crops and other (Šembera et al., 2007). The most important rookery in city is situated in the Mestský park.


Results And Discussions

In 2010 was in Podunajská nížina overall recorded 26 breeding localities, where was totally noticed 2416 nests. In 3 localities we found extinct rookeries. In 2011 was recorded 32 nesting localities and extinct 6, with total number of nests 2323. In 2012 it was 30 nesting localities, of which 4 were extinct and the total number of nests was 2454. In 2013 we found noticeable rise in total number of nesting localities and nests; totally was recorded 42 breeding localities, including 8 extinct, with total number of nests 2656. The monitoring results corresponds to the results given by Vongrej & Szalay (2012), who argue that in 2001 - 2009 total number of nests at the same area ranged in average number 2300 - 2400. The development of rook nests in the monitored area in western part of Slovakia in 2010 - 2013 is shown in Figure 2. During monitoring in whole area of Podunajská nížina we observed rookeries different in size from small rookeries with number of nests 3 - 15 (Piešťany, Hotelová akadémia - 13 nests), to large numbers of nests 200 - 303 (Hlohovec - 200 nests, Trnava - 211 nests). The similar size of rookeries from small number of nests 2 - 5, to rookeries with the number of nests 300, also met Vongrej & Szalay (2012), who argue that in 2001 - 2009 the largest rookery was in Tvrdošovce (344 nests). Our results were consistent with the results of ornithologists from Poland. In 2012 Zbyryt & Polakowski (2012) recorded 42 rookeries with 2329 nests of rook in the Podlaskie województwo, in the cities Białystok, Suwałki and Łomża.



Figure 2: Development of rook nesting abundance in western part of Slovakia in 2010 - 2013

Figure 3: Development of rook nesting abundance in Trnava, Hlohovec and Piešťany in 2010 - 2013

In Trnava rooks nested in two localities, the most important of them was rookery in the Park Janka Kráľa. Newly created colony was located in the area of Mestská vodáreň. In rookery in Park Janka Kráľa was in 2010 recorded 89 nests, in 2011 it was already 181 nests. In 2012 there was a decrease to 160 nests, but in 2013 the number of nests increased to 211 (Figure 3). The results of the years 2011 and 2012 are similar to the results showed by Ilavský & Urban (2010) who claims, that in Poprad was in 2010 located 165 nests. Based on our results we concluded that despite the volatility of nests in individual years, this rookery can be considered as stable. The representation of each species of nesting trees in Park Janka Kráľa in Trnava in 2010 - 2013 shows Figure 4. Rooks occupied mainly trees of the species Pinus sylvestris. Other most representative nesting trees were Acer platanoides and Acer pseudoplatanus. Less represented were for example: Tilia sp., Fraxinus excelsior, Robinia pseudoacacia and others. The representation of each species of nesting trees, as well as the number of nests situated on each species, is shown in Figure 5. The dominant nesting tree species in monitored period was Pinus sylvestris on which the average number of situated nests each year exceeds the value of 69 % of all nests of rookery. The average number of nests situated on other species each year ranged up to 11 %. Similar results were submitted by Vongrej & Szalay (2012). Regardless of tree species, in crown of one tree was one nest located in most cases only.

Figure 4: The average share of nesting trees in Trnava in 2010 – 2013

Figure 5: The average number of nests on nesting trees in Trnava in 2010 – 2013

Zámocký park was the only place where rooks nested in Hlohovec. As from the data shown in Figure 3 is apparent, the number of nests from 2010 until 2012 gradually grew. In 2010 was in rookery recorded 130 nests, in 2011 it was 155 nests, in 2012 was an increase to 200 nests, what was largest number ever for monitored period. In 2013 the number of nests in this rookery declined slightly to 186. Observed numbers of nests in 2010 - 2013 were slightly larger, but similar to the numbers of nests recorded in similar rookeries in the Czech Republic. For example, in the Zámocký park in Prague in 2013 Sládeček & Vlčková (2013) found 130 nests; in the colony in area of Hvězdárna a planetárium České Budějovice in České Budějovice Pakandl (2013) recorded in 2013 165 nests. On the basis of these results may be rookery in Hlohovec regarded as a long-term stable. Ornithologists Vongrej & Szalay (2012) considered this rookery as stable too. We believe that rookery is stable due to location in city at protected area, where rooks not come into the direct contact with farmers and hunters as it often becomes with rookeries located in the agricultural land around small villages. No less important role in the development of rookery were also agricultural soils and open agricultural land which have in Hlohovec vicinity large representation, what as stated Brenchley (2009), rook need for its existence necessary. Rooks nested mainly in Hlohovec on Platanus acerifolia (67 % in average). Our results confirm records of ornithologists Mutkovič (1989), Kaňuščák (2007), Vongrej & Szalay (2012). Second most-represented species was Acer sp., less was represented Querqus robur, Pinus sylvestris and Populus alba. Occupation of individual tree species by rook in Zámocký park in 2010 - 2013 is shown in Figure 6. By the evaluation of the number of nests situated on each tree species (Figure 7) was found, that most of nests were situated on Platanus acerifolia (Figure 10) on which it was placed in an annual average of 89 % of all nests. On other tree species it was only 7 % or less of all nests. In crown of one tree was during monitored period in most cases situated only one nest. However, there was 2 - 3 trees, on which was each year located the majority of nests, from 22 to 78 nests on the same tree.



Figure 7: The average number of nests on nesting trees in Hlohovec in 2010 – 2013


Figure 6: The average share of nesting trees in Hlohovec in 2010 – 2013



The rook most important nesting locality in Piešťany was Mestský park. However, rooks occasionally nested in other localities of the city (Hotelová akedémia Ľ. Wintera; Ulica Andreja Hlinku). The number of active nests in Mestský park in 2010 - 2013 was relatively balanced. In 2010 we found 115 nests, in 2011 it was only 95 nests. In 2012 the number of nests increased to 108 and in 2013 their number increased even up to 127 nests (Figure 3). Our results confirm the records showed by Vongrej & Szalay (2012), who in the Mestský park in Piešťany in 2001 - 2009 recorded a gradual enlargement of nests. In Mestský park in Piešťany was recorded fewer nests than in Trnava and Hlohovec, however this rookery can be considered as stable too. The dominant tree species in 2010 - 2011 was Populus nigra, exceeding an average of 33 % of all nest trees. This is not a strong preference for one nest tree species, such as it was recorded Zámocký park in Hlohovec, where the most abundant nesting tree species (Platanus acerifolia) represented 67 %. Another occcupied tree species was Acer sp. (in 2012 it had the same representation as Populus nigra). In 2013 was Acer sp. the most-represented nest tree. The representation of each nesting tree species in Mestský park in 2010 - 2013 is shown in Figure 8. The results of monitored nests located on individual tree species (Figure 9) shows, that the largest average number of nests was each year situated on Populus nigra (Figure 11), always in the average number of above 73 %. In the crown of one tree were most often situated 2 or 3 nests. However, similar as in Hlohovec, we found 2 - 3 trees, on which was situated the majority of nests forming the whole rookery.

Figure 8: The average share of nesting trees in Piešťany in 2010 – 2013

Figure 9: The average number of nests on nesting trees in Piešťany in 2010 – 2013

In the last decades of the 20th century there was a large decrease of abundance of rooks in Slovakia. However, obtained results of monitoring from years 2010 - 2013 in most important rookeries in western part of Slovakia shows the gradual enlargement of rooks nesting abundance in this area. Given the important role of rook in nature, but especially in agro-ecosystems, in coming years it will be necessary to ensure similar trend of rook nesting abundance in Slovakia. Rook is although often considered as the pest of agro-ecosystems. In the future will by necessary stricter enforcement of laws about rook protection, but in particular awareness among the general public, change not only view about rook, but also try to limit the factors which most threaten rook in Slovakia. These mainly include loss of suitable habitat, hunting, bird crime and agriculture. Only then we will be able to objectively talk about success carrying in the spirit of the increasing of numbers of rooks nesting in the western part of Slovakia.

Figure10: Rook nesting on Platanus acerifolia (Ernst, 2014)

Figure 11: Rook nesting on Populus nigra (Ernst, 2014)


Conclusions

In the most important nesting area of rook in the Slovakia - Podunajská nížina in 2010 - 2013 the number of breeding colonies ranged from 42 of which were active 33 with the total number of nests 2656 (in 2013) to 26, of which 23 were active with the total number of nests 2416 (in 2010). The results indicate a slight population increase of breeding rooks in western part of Slovakia. In monitored area, the oldest and most stable rookeries were located in cities Trnava, Hlohovec and Piešťany.

In Park Janka Kráľa, what is the most important rook nesting locality in Trnava was the smallest number of nests (89) recorded in 2010, the largest - to 211 nests in 2013. In 2011 and 2012, the number of active nests ranged from 160 (in 2012) to 181 (in 2011). The most represented nest tree species in this rookery was Pinus sylvestris, on which it was situated annually on average more than 69 % of all nests in park. In Hlohovec rooks nested especially in the Zámocký park, where in 2010 were located 130 nests, in 2011 it was 155 nests, in 2012 was recorded increase to 200 nests in the park, but in 2013 the number of nests fell to 186. Dominant species of nesting tree was throughout the monitored period Platanus acerifolia. On it were situated each year in average more than 89 % of all nests. In Piešťany the largest rook nesting locality was Mestský park, where in 2010 was recorded 115 nests, in 2011 it was 95 nests. In 2012, the number of nests increased to 108, in 2013 even as to 127. Tree species on which was situated the largest number of nests, around 73 % in average, was Populus nigra. All monitored nesting colonies were located in the immediate vicinity of the intensively used agricultural land, especially close to cultivated fields, where rooks seeks for food. Rooks are not pests of agro-ecosystems because of its diet mainly consist of food of animal origin.
Acknowledgement

The research was conducted under the auspices of the Slovak Ornithological Society - BirdLife Slovakia.


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