Vyšlo ve Zprávách MOS 2005 – bez jediné změny oproti původnímu znění… Ve dvou jiných redakcích byl článek totiž odmítnut jako „nepublikovatelný“… Chápu, snobi neradí žijí ve stínu.

The monitoring of extra-breeding movements of the Short-eared owl (Asio flammeus )

Monitoring mimohnízdních pohybů kalouse pustovky (Asio flammeus)

Karel Zvářal , Jiří Sviečka , Petr Pavelčík

Ing. Karel Zvářal, Dukelská 3980, 76001 Zlín, Czech Rep.

Jiří Sviečka, 76341 Biskupice u Luhačovic 158, Czech Rep.

Petr Pavelčík, 68761 Vlčnov 831, Czech Rep.

Abstract

During the period 1997-2002, the occurence of the Short-eared owl was monitored in parts of south and central Moravia, Czech Republic. A total of 582 Short-eared owls were trapped, with the species recorded or confirmed in 31 squares of the designated map grid. 10 local retraps were obtained in the same season. Birds were usually re-trapped after a few days, with the longest period being 74 days. One was found 80 km eastwards after 5 days. There were no local retraps of one year plus, nor were any specimen carrying a foreign ring trapped. In addition, 2721 Long-eared owls were also trapped. The first Short-eared owls were recorded on 29.8., with migration strongest in October and November. During December to February, new wandering birds were trapped. The number of such wandering and migrating birds is many times higher than the so far reported number of wintering owls. No invasive occurence has reported by other ornithologists to date. 3 new foreign recoveries describe an unapredictable nomadic character of Short-eared owls in Moravia.

Introduction

The majority of owls are sedentary within their territory, although some northern spescies wander southwards in years when food is in short supply. The only regularly migration owl species is the warmth-loving Scops owl (Otus scops). Interestingly, the Short-eared owl can turn its southward wandering into a regular migration, which sometimes takes on an invasive character. In this context, several questions arise:

-Is the movement south or southwest caused exclusively by lack of food?

-Does the weather play a role?

-Is there a relationship between Short-eared owl mowements and previous over-wintering sites?

-How long do the birds stay in one locality during winter?

-How many birds do winter (or migrate) in non-irruption years and how much they vary in numbers compared to irruptions?

The aim of this study is to contribute to improved knowledge of the occurence and movements of Short-eared owl in the same (or neighbouring) localities in successive years. Our work is motivated by an insufficiently mapped winter occurence of this owl- it was recorded only in certain squares within Czech Republic (Bejček et al. 1995). Even in the rest of Europe it has a scattered distribution in winter, with none being reported from extensive lowland parts of Poland or the steppe areas of north Africa, for example (Snow @ Perrins 1998).

This study was conducted solely on the basic of a long-term trapping of Short-eared owl, of which there is unfortunatebly no widespread tradition outside the Czech Republic. Wide cooperation across Europe is important for correct interpretation of the results obtained.

Material and methods

In the Czech Republic the Short-eared owl is known as a winter visitor, occuring regularly from autumn until spring (Hudec et al.1983). It breeds irregularly and in small numbers when conditions are favourable (Šimčík in Danko 1989, Dohnal 1998). It is more numerous in peak of vole population (Microtus arvalis), when so-called invasions happen. Rumler (1986) documents at least 6 invasions in the course of 50 years: 1930, 1936-37, 1942-43, 1958-59, 1977-78 and 1981.

H. Matušík trapped Long-eared owls (Asio otus) intensively in the Uherské Hradiště region in the 1980´s (sq.7169). He also described his methods (Matušík 1985). He stimulated an interest among certain Czech and Slovak ornithologists, many of whom only net owls occasionally.

Because both species of eared owls specialize in feeding voles, the chosen trap locality must hold medium to high numbers of these rodents. Despite this fact, we decided to systematicly monitor all chosen main localities, i.e. also in the years of latent vole occurence.

As centres of vole gradation vary over time a lot, we selected suitable localities in the regions of Uherské Hradiště, Hodonín, Břeclav, Znojmo, Zlín, Kroměříž, Přerov, Prostějov and Vyškov. The total of 10 main and 30 alternative localities were chosen. In the year 1997 the vole population in the regions of Uherské Hradiště and Zlín was very low. By contrast, the number of voles was higher in the regions of Znojmo, Břeclav and Hodonín. The number of voles was assessed by line method with accuracy deviation of 100 specimen per hectare: within 200-300 m walk, fresh burrow entrances were counted in 2-4 m wide belt (depending on visibility in the terrain- grasses, lucerne, etc.).However, number of voles was roughly monitored to determine the gradation phase. Trapping locality was usually chosen according to presence of raptors in daytime, absence of tractors, strenght of wind, condition of field roads and the limited time avalaible for investigation. Stuble-fields and meadows in the lowland far from busy roads were prefered as the monitored localities. All main localities were chosen specificly to ring maximum numbers of Short-eared owls.

The individual authors trapped owls , using 2-3 nets or 4-5 if assistant was present. Nylon nets with 1-2 pockets were used, situated 200-500 m from each other. Owls were lured with stuffed, plastic or tatter Eagle owl. Tatter dummies of other birds (Common Buzzard, Short-eared owl) were also successfully used. Owls sometimes attacked dummies spontaneously, althogh usually we had to imitate rodent voices (friction of polystyrene on wet glass). We decided do not to include statistics due to ever changing monitoring conditions (muddy terrain, foggy and windy weather, presence of tractors, lucern fields are usually ploughed after 2 years, different number of nets and various dates of trapping, moon phase, etc.).

The three authors trapped owls many times during the course of monitoring over 6 years. They often clearly confirmed the absence of owls in the locality. As we do not have space to present all of our results here, we have therefore decided to give a summary with the most characteristic examples.

Results

Overall, 582 Short-eared owls, 2721 Long-eared owls and 107 Barn owls (plus 78 controls) were trapped and ringed during the research period, 1997-2002.

There were no retraps of Short-eared owl after one or more years, and no bird with a foreign ring was controlled. Repeated traps during one night proved that even fresh and unpleasant experience does not necessarilly discourage a bird from an instinctive attack on an Eagle owl´s sillhouette. The bird either does not see the fine fibres or simply ignores the net. For example, Short-eared owl D-145434 was trapped three times at Blatnička on 25.11.2000, when a further 11 Short-eared and 19 Long-eared owls were trapped (J.S.). We give this unusual example specificaly because local retraps on the same night are rather uncommon- only about 1-2 % of all trapped birds. This means that almost all ringed birds soon disappear from the locality.

From the total of 582 ringed Short-eared owls, only 10 local retraps were obtained in the same season. They were usually retrapped after a few days, with the longest period being 74 days (Table 1).

Among these retraps there is one very valuable record concerning the movement of Short-eared owl

D-153608 80 km eastward after 5 days. This confirms our visual impression that groups of Short-eared owls can be observed coming from N, NE, E or W at a height of 10 to 20 meters, especially during full moon. This indicates that the origin of our wintering (or, perhaps more accurately, our migratory) population is not necessarilly to the north of the Czech Republic.

A report on Short-eared owl D-155382 is noteworthy. It was photographed and released some 8 km to the west, but retrapped in the original location after 7 days.

Among foreign recoveries Short-eared owl D-146455 is interesting, in both temporal and geographical respects. Despite good feeding and weather conditions in Moravia at that time, this owl was shot 1 month later 1551 km to the south, appr. 150 km off the shores of north Africa. Short-eared owl D-123687 was killed by car exactly 3 years later, 1712 km away from previous wintering ground in central Europe, where there was an increase in vole population and hence a good food supply (Table 2).

Table 3) shows the exchange of owls at Kunovice locality. There were very few local retraps there (1 specimen only). New birds were trapped not only in the autumn, but also during the winter, i.e. when they should be present in their wintering grounds (Snow @ Perrins 1998). Our findings indicate that the majority of Short-eared owls stay in the researched area for several days or weeks. This suggests that Short-eared owl´s wintering grounds are not so restricted as for a sedentary adult Barn owl, for example. These nomadic birds are on their way all winter through.

A strong passage of Short-eared owls was observed at locality of the Novomlýnské reservoirs (Břeclav), both in the years of vole abundance (1999, 2001) and latency (2002). The vicinity of the reservoirs is probably the most attractive area for Short-eared owl in south and central Moravia. Long-eared and Short-eared owls both occur there, and sometimes the Short-eared outnumbers its relative, explaining why it is observed there frequently by other ornithologists (Berka, Horal, Chytil in verb.). The Long-eared owl is much numerous elsewhere in the research area (Table 4)

Discussion

Table 4) shows the relative numbers of owls during the course of autumn and winter months. Long-eared owl is the most numerous trapped owl on agricultural land (agrocenoses), and Short-eared owl is 3times more numerous than Barn owl. Recently many nestboxes have been erected for Barn owls in the Czech Republic and many young are ringed each year. For example, 2217 young in nests and 238 adults were ringed in 2001 (Škopek,J.@Cepák,J.2002).

We checked 27 Barn owls and ringed another 35 in that year (2001) during night trapping. These numbers can help us to roughly estimate the total Barn owl population. The strenght of passage of Short-eared owl can be derived from numbers of Long-eared and Barn owls present in the area. Thus we assume that thousands of Short-eared owls annually migrate through the Czech Republic, with high variations betwen different years: a range of 1000-9000 birds. These numbers represent about 1-10% of the total Europian population (Lockie 1955, Ulfstrand @ Hogstedt 1976, Dementiev @ Gladkov 1951 in Snow @ Perrins 1998) but we cannot exclude the presence of west Siberian birds (Danko 2000). We estimate that we have been ringing appr. 1-3 % of the total of owls that migrate through the Czech Republic (a few retraps in the same season and none after one year or more).

Our knowledge of the low rate of return of Short-eared owls to their former wintering grounds is completed by report on Short-eared owl D-126939, ringed in the Czech Republic on 3.11.1997 and killed by car on 22.5.2000 in Spain (Formánek, Škopek 2001). Its breeding site was found to the west of its former wintering ground. If there is a decrese in the vole population in western Europe, the Short-eared owls breeding there cannot move westwards during the non-breeding season. They can choose a route to the south or east, i.e. to north Africa, southern or eastern Europe. This is supported by the finding a young French bird at Astrachan after 6 years, and by English Short-eared owl found at Vologda (Russia) after 2 years (Cramp 1985).

It is possible to observe groups of Short-eared owls arriving from various directions at Novomlýnské reservoirs (Břeclav). These could just be local birds wandering around, but reverse passage, i.e. eastwards, cannot be excluded. The steppes of Ukraine, Russia and Kazakhstan are shown as breeding areas on the map (Snow @ Perrins 1998), whereas in northern Russia the birds should be sedentary. It seems that colours on the map were mistaken. Based on our observations and cited literature, we assume that the passage of Short-eared owl through Moravia (and therefore Czech Republic) is depend on the abundance of food (Microtus spp.) in steppe and forest-steppe areas of northern and eastern Europe (or western Siberia, as the case may be). Short-eared and Long-eared owls move southwestwards only if there is a lack of food in the north or if the weather rapidly changes to the worse (Rumler 1986)- current (and flexibile) change of wintering ground. Phase of vole population cycle are most probably asynchronous in northeastern and central Europe, as is apparent from changing numbers of Buzzards (Buteo spp.) at trapping localities (own observation). Certain section of the Short-eared owl population probably start to migrate irrespective of food supply and weather (thereby showing an inherent migratory instinct).

Bejček et al.1995 established a population of 200-1000 wintering Short-eared owls during winter mapping in the Czech Republic betwen 1982-85. This data agrees with our knowledge on the number of Short-eared owls present on certain dates. Nevertheless, multiple exchange of Short-eared owls staying in the Czech Republic takes place in the course of autumn migration and winter movements. The fact that no invasion occurence was reported is result of significant changes in agriculture. Nowadays only 8% of arable land is made up of fodder crops, the remainder providing less suitable hunting areas for Short-eared owls. Formerly, the large areas of meadows, pastures, orchards and 25% of farmland containig fodder crops attracted higher numbers of Short-eared owls, which could not be overlooked (Damborský in Bejček et al.1995, Hejl-Mračovský in Rumler 1986). If birds stop at an attractive locality (such as around Novomlýnské reservoirs, Břeclav) they are treated as wintering, although they may be transient birds.

Short-eared owls are largely overlooked in the Czech Republic because of their mostly nocturnal habits (this applies to study area). Thus we assume that the species could also be overlooked in other parts of Europe (Poland) and north Africa (Snow @ Perrins 1998). Recoveries come mainly from western Europe (dense road network, many hunters). For example, the majority of recoveries of northern trushes (Redwing, Fieldfare) come from western Europe, though birds tend to winter closer to their breeding areas if there is sufficient food (Formánek 1980 and author´s observation). We assume that this may also be true of the Short-eared owl situation. The different strenght of the autumn migration and winter movements suggest that part of the population winters to the north and east of the Czech Republic. Other recoveries relate to the distance of current wintering grounds and direction of spring passage, or even to a breeding locality (Škopek @Formánek 1988, Formánek @ Škopek 1991).

Volkov et al.(1998) reports 1,5-2x recent increase from the Moscow area. The near future will show if this is only a local and temporary fluctuation or a long-term trend. It is evident that as nomadic species capable of exploiting a good food supply, the Short-eared owl is able to increase its number quickly. As a ground nester it is, however, vulnerable. Watson (1972) in Cramp (1985) reports on finding of 68 young and 8(!) adults of Short-eared owl in one fox burrow. Possibly the adults were shot and the young subsequently robbed by the fox from the abandonemed nests. If not, then the fox is clearly able to capture adult owls and thus affect their reproductive success.

Conclusion

The Short-eared owl has been ringed much less than other owl species, e.g. Barn owl. Nevertheless, its bionomy from the food strategy point of view seems to be very interesting. We therefore eagerly welcome anyone interested in cooperation, especially from countries where Short-eared owls regularly breed. The nest is not always easy to find, but it is possible to ring freshly fledged young or parents. Recoveries based on such cooperation will be more valuable than waiting for a dead bird found at „traditional“(?) wintering grounds. We assume that the ringing of Short-eared owls in the non-breeding season in other parts of Europe could bring new informations concerning this interesting nomadic owl.

Acknowledgments

We thank M. Hrouzek, A. Maniš, R. Viktora and E. Zajíček for their time and effort spent at our nets. We also thank P. Procházka and K. Fryšták, who kindly lent foreign literature. Our thanks to P. Horák for critical review of this article. Our thanks also to M. Hrouzek and J. Parry for help with translation.

Souhrn

V letech 1997-2002 bylo při monitoringu sov na střední a jižní Moravě odchyceno a označeno 582 pustovek, 2721 kalousů ušatých a 107 sov pálených. Kontrolní odchyt pustovky po roce a více nebyl získán ani jeden a nebyla chycena žádná se zahraničním kroužkem. Kontrolních odchytů v téže sezoně bylo 10, většinou po 3-10 dnech, nejvíce po 74 dnech. Na 10 hlavních a cca 30 alternativních lokalitách bylo dosahováno rozdílných výsledků v závislosti na fázi cyklu hraboší populace u nás a v jiných částech Evropy, sněhových podmínkách tamtéž a svou roli sehrává i atraktivnost odchytové lokality. Sovy byly odchytávány do 1-2 kapsových sítí, u kterých je umístěna atrapa výra nebo káně. První pustovky se u nás objevují koncem srpna (29.8.2000 odchyceny 2 ex.). Podzimní průtah je nejsilnější v říjnu a listopadu. Naším územím protahuje přibližně 1000-9000 pustovek, které se však na lokalitách zdrží povětšinou v řádu dnů až týdnů. Okamžitý stav 200-1000 pustovek na našem území během podzimního tahu a zimních potulek je reálný. Snížená atraktivnost lovišť (8% pícnin oproti cca 25% před 20 lety) je zřejmě příčinou , že u nás nedochází k většímu soustředění pustovek, jak bylo v minulosti pozorováno. Rovněž aplikace rodenticidů snižuje početnost hrabošů, kteří jsou její hlavní potravou. Jednotlivě či v malých skupinkách protahující noční ptáci unikají pozornosti ornitologů. Okolí Novomlýnských nádrží patří mezi nejatraktivnější lokality výskytu pustovek („zimoviště“), kde je možno v době úplňku pozorovat skupinky sov přiletujících z různých směrů, povětšinou však od východu a severovýchodu. Odhadujeme, že naším územím protáhne v průběhu podzimu a zimy asi 1-10% populace evropských a možná i západosibiřských pustovek. Domníváme se, že námi kroužkovaní ptáci představují cca 1-3% protahujících sov. 4 nová zpětná hlášení pustovky vypovídají o různých aspektech bionomie nomádských sov:

- O nepravidelnosti zimovišť: přesně po 3 letech ve Španělsku, přičemž u nás byly dobré potravní podmínky (D-123867)

- O rychlém tahu z míst s dobrou potravní nabídkou a příznivými klimatickými podmínkami do jižního Středozemí, které jako zimoviště je zřejmě málo zmapované (D-146455)

- O zahnízdění (přesídlení ?) pustovky v oblasti zimoviště, přičemž tento pták byl u nás kroužkován v listopadu (D-126939)

- O možném podzimním tahu východním směrem, což by korespondovalo s některými literárními údaji. Pustovka D-153608 byla po 5 dnech kontrolována 80 km východně.

Během našich ochytů jsme zjistili pustovku v 31 kvadrátech: 7070, 7170, 7270, 7069, 7169, 7269, 7068, 7168, 7268, 716, 7066, 7166, 7065, 7165, 7064, 7579, 7578, 6966, 6965, 6669, 6371, 6471, 6571, 6671, 6771, 6470, 6570, 5558, 7468, 6770, 6672.

References

Bejček V., Šťastný K., Hudec K., 1995: The Atlas of Wintering Birds in the Czech Republic, 1982-85: 143-146

Cramp S., (ed.) 1985: The Birds of the Western Palearctic. Vol. IV: 588-600. Oxford University Press, Oxford.

Danko Š., 2000: My own bird-ringing results from eastern Slovakia in 1966-1999. Tichodroma/ Vol.13: 205-226.

Danko Š., 1989: Report of the Group for research and protection of birds of prey and owls in Czechoslovakia. Buteo 4/ 1989. Pardubice.

Dohnal J. @ Dufek A., 1998: Nesting of Short-eared Owls (Asio flammeus) in central Moravia in 1998. Buteo 10: 121-124. Třeboň.

Formánek J., 1980: XX Report of the Bird-ringing Centre of the National museum in Prague and the Czechoslovak ornitological society for 1966-70. Sylvia XX: 61-64.

Formánek J., Škopek J., 1991: 22^nd report of the Ringing Centre of the National museum in Prague and the Czech ornitological society for 1976-80. Sylvia XXVIII: 5-30.

Formánek J., Škopek J., 2001: Remarkable up to date recoveries recorded by the Praha Ringing Centre in 2000 (10). CSO News 52: 22-23.

Formánek J., Škopek J., 2001: Remarcable up to date recoveries recorded by the Praha Bird Ringing Centre (11). CSO News 53: 27-28.

Hudec K., et al. 1983: Fauna ČSSR- Ptáci3/II: 95-109. Academia, Praha.

Matušík H., 1985: Experiences with netting of Long-eared Owls. Report on Activities of the G.R.P.B.P.O. in Czechoslovakia in 1985: 35-39. Pardubice.

Rumler Z., 1986: Zur Problematik der Bedingungen fur Winterinvasion von Asio flammeus auf unserem Gebiet. Sovy 1986: 113-116. Přerov.

Snow D. W. @ Perrins C.M. (Eds.) 1998: The Birds of the Western Palearctic: Concise Edition. Vol.1: Non-Passerines. Oxford, New York.

Škopek J., Cepák J., 2002: List of ringed birds by Praha Ringing Centre in 2001. CSO News 55: 30-33. Praha.

Škopek J., Formánek J., 1988: The choice from the recoveries of raptors, in-coming in the course of 1988. Buteo 3: 35-38. Pardubice.

Volkov S. V. et al., 1998: Current distribution and abundance of the Short-eared owl (Asio flammeus), the Great grey owl (Strix nebulosa) and the Ural owl (Strix uralensis) in the Moscow region. Ornotologija, 28: 92-99.

Apendix

Table 1) Local retraps of the Short-eared owl (Asio flammeus)

Tab. 1) Kontrolní odchyty kalouse pustovky (Asio flammeus)

Table 2) Recoveries of the Short-eared owl (Asio flammeus)

Tab.2) Zpětná hlášení kalouse pustovky (Asio flammeus)

Table 3) The exchange of owls at the locality Kunovice

Tab.3) Obměna sov na lokalitě Kunovice

Table 4) Annually relation between ringed Short-eared owls (Asio flammeus), Long-eared owls (Asio otus) and Barn owls (Tyto alba) (ringed by us/ controlled birds with ring) in some regiones

Tab.4) Poměr mezi kroužkovanými pustovkami (Asio flammeus), kalousy ušatými (Asio otus) a sovami pálenými (Tyto alba) (kroužkované námi/ kontrolní odchyty ) v některých regionech

Region / Year	1997	1998	1999
Břeclav region	74: 47: 0/0	9: 12: 0/0	87: 81: 6/0
Uh. Hradiště reg.	2: 86:2/0	19: 279: 4/3	10: 110: 4/7
Elsewhere-jinde	3: 74: 0/0	1: 73: 1/0	2: 21: 0/0
Whole-celkem	79: 207: 2/0	29: 363: 5/3	99: 212: 10/7
Region / Year	2000	2001	2002
Břeclav region	34: 52: 2/3	50: 55: 6/1	26: 36: 6/1
Uh. Hradiště reg.	104: 537: 30/24	46: 284: 20/13	21: 276: 9/1
Elsewhere-jinde	28: 200: 6/11	63: 324: 9/13	7: 175: 2/1
Whole-celkem	166: 789: 38/38	159: 663: 35/27	54: 487: 17/3