Ornis Fennica 82:107–116. 2005 Dispersal and migration of female Black Grouse Tetrao tetrix in eastern central Finland Arto Marjakangas* & Satu Kiviniemi Marjakangas, A., Department of Biology, P.O. Box 3000, FI-90014 University of Oulu, Finland. Present address: Savontie 1316, FI-84880 Ylivieska, Finland. arto.marja- [email protected] (* Corresponding author) Kiviniemi, S., Saarijärven Keskuskoulu, Koulutie 4, FI-43100 Saarijärvi, Finland. [email protected] Received 10 January 2005, accepted 20 June 2005 We studied the movement patterns of 209 female Black Grouse radio-marked during 1990–1993 in eastern central Finland. Females were captured for marking in late winter, and the transmitters had a life expectancy of 6–10 months. Adults tended to initiate spring movement to breeding range earlier than yearlings. The median net distance between the marking (winter) site and nest site was 2.6 km for adults and 9.2 km for yearlings, and the maximum distances recorded were 29.6 and 33.2 km, respectively. The spring dispersal directions of yearlings differed from a uniform distribution. Data from radio-tracking, re- capturing and recoveries from the public revealed that females that moved less than the median distance in spring as yearlings tended to show fidelity to their first winter range. In contrast, those individuals that moved more than the median distance, mostly switched to using a new winter range. Females marked as adults tended to show fidelity to their winter range. The longest migratory movement recorded between breeding and winter range was 19 km. We conclude that female Black Grouse possess good dispersal abilities, and had no movement problems in our study area consisting of a managed forest landscape. 1. Introduction the study of fragmentation (Johnson & Gaines 1990, Stenseth & Lidicker 1992, Porter & Dooley Natal dispersal has been defined as the movement 1993, Hanski & Simberloff 1997, Paradis et al. of a young animal from its birth site to the site of its 1998). The human-induced fragmentation of natu- first actual or potential reproduction (Greenwood ral habitats can affect animal populations by three 1980), while migration means round-trip travel- major mechanisms, i.e. edge effects such as preda- ling (Stenseth & Lidicker 1992), typically the sea- tion, and the degradation and isolation of remnant sonal movement between breeding site and winter habitat patches (Cooper & Walters 2002). Edge ef- site. Dispersal is a fundamental life-history trait fects and habitat degradation affect populations by among animals, and understanding dispersal and altering fecundity and survival, while isolation other movements is vital to advances in population may alter dispersal patterns (Cooper & Walters and metapopulation biology, population genetics, 2002). conservation biology, wildlife management, and Finnish populations of forest grouse (sub- 108 ORNIS FENNICA Vol. 82, 2005 family Tetraoninae) have shown cyclic dynamics individual grouse with differential dispersal or mi- with a periodicity of about 6 years and large-scale gration patterns (Herzog & Keppie 1980, Hines synchrony, and dispersal was considered an im- 1986, Beaudette & Keppie 1992, Small et al. portant factor in maintaining this synchrony 1993). (Lindström et al. 1996). However, the cyclicity In Spruce Grouse Dendragapus canadensis seems to have disappeared since 1990s, and one (Herzog & Keppie 1980, Schroeder 1985) and reason for this might be habitat fragmentation due Black Grouse Tetrao tetrix (Willebrand 1988, to modern forestry that might hinder dispersal Caizergues & Ellison 2002, Warren & Baines (Anonymous 1999). The isolation of suitable habi- 2002), natal dispersal is divided into an autumn tat patches (because of fragmentation) may be a se- phase, when a juvenile moves from its natal area to rious problem for resident grouse species with its first winter range, and a spring phase, when an poor dispersal abilities (Swenson 1991). Indeed, individual moves to its first potential breeding there is experimental evidence that habitat frag- range. In Spruce Grouse, subsequent migratory mentation can hinder the movements both of resi- movements retrace the first spring dispersal move- dent and migrant forest birds (Bélisle et al. 2001, ment (Herzog & Keppie 1980, Schroeder 1985). Cooper & Walters 2002). On the other hand, frag- While patterns of dispersal and migration mentation might enhance dispersal due to more among North American grouse are relatively well potential dispersers, although evidence for such known (see literature cited above), data on Eur- effects are scarce. The dispersal distances of Nut- asian boreal forest grouse are scarce (Willebrand hatches Sitta europaea tendedtoincreaseina 1988, Rolstad & Wegge 1989, Swenson 1991). highly fragmented forest landscape (Matthysen et Our aim is here to present data on the timing, dis- al. 1995). tances and directional orientation of dispersal and Grouse are important game for hunters. Small migratory movements among radio-marked fe- et al. (1991) and Smith & Willebrand (1999) sug- male Black Grouse, in order to assess life-time gested that grouse numbers on heavily hunted ar- movement patterns. Especially we test the hypoth- eas are maintained by dispersal from adjacent ar- esis that the migratory movements of adults retrace eas with lower or no hunting mortality. Thus high their first spring dispersal movement made as hunting mortality could drastically decrease the yearlings (Herzog & Keppie 1980, Schroeder density of grouse where dispersal is reduced by 1985). habitat fragmentation (Small et al. 1991). In birds, juvenile females disperse typically longer distances than juvenile males (Greenwood 2. Material and methods 1980, Clarke et al. 1997). This pattern has also been observed in grouse (Dunn & Braun 1985, 2.1. Study area Schroeder 1985, 1986, Hines 1986, Willebrand 1988, Small & Rusch 1989, Giesen & Braun 1993, The study was conducted during 1990–1994 in Caizergues & Ellison 2002, Warren & Baines eastern central Finland (ca. 64°N, 27–28°E). Fe- 2002). In a given grouse population, net distances male Black Grouse were radio-marked in 1990– moved during natal dispersal vary considerably 1993 at 2–4 sites, 5–10 km apart (Fig. 1). Each between individual juveniles, and birds can be marking site was a supplemental winter feeding classified as long- or short-distance dispersers, and station installed on a lekking site on an open bog sometimes also as non-dispersers (Schroeder and supplied with oats for wild Black Grouse. The 1985, Hines 1986, Beaudette & Keppie 1992). lekking sites and, consequently, the marking sites However, the distribution of distances is usually in our study were most likely within the natural skewed to relatively short distances (Schroeder winter range of each local flock. This is because 1985, 1986, Hines 1986, Giesen & Braun 1993). adult males having territories at a given lek are In general, the magnitude of dispersal seems to be highly sedentary throughout the year (Willebrand independent of population density (e.g. Hines 1988), and they are social also during summer 1986, Keppie & Towers 1992), and survival or re- (Koskimies 1957). Alocal winter flock is probably productive success, or both, are mostly similar for formed when birds from adjacent areas join the Marjakangas & Kiviniemi: Movements of female Black Grouse 109 Fig. 1. Location of the study area and the sites (asterisks *) where female Black Grouse were radio- marked. adult male assemblage in autumn (Koskimies laying (Marjakangas & Törmälä 1997), and we be- 1957). The area where nests of radio-marked fe- lieve this period was long enough for the birds to males were located, covered 1,000–1,500 km². adjust with the transmitter. Studies addressing the The elevation of the study area ranges from 125 to possible impact of necklace transmitters on sur- 350 m above sea level, and the major habitat types vival in gallinaceous birds have shown no effect were commercially managed coniferous forests, (for a review, see Caizergues & Ellison 1998). bogs and sapling stands. The major logging Female Black Grouse were located about once method was clear-cutting. Forested bogs had been a week by flushing or by triangulation using porta- mostly drained for forestry (Forest Statistics Infor- ble receivers and yagi-antennas. The bearings for a mation Service 1995). triangulation were mostly taken within 30 min., hence we believe that possible bias in radio fixes caused by movements of birds was small. When 2.2. Capture and radio tracking consecutive locations indicated no movement, we approached birds until they either flushed or their Female Black Grouse were captured in traps remains were found. All locations were marked on baited with oats mostly during February to March. maps of scale 1:20,000. Because we attempted to They were classified as yearlings (hatched the pre- find all radio-marked females, missing birds were vious year) or adults (Helminen 1963). We marked located from an aircraft, with a side-looking an- females with a numbered aluminium leg band and tenna under each wing, during late April to early a coloured plastic band using a given colour each June. First, the approximate locations of females year to be able to identify and recapture females were determined by flying a rectangular search marked during previous years. Females were fitted pattern (Kenward 1987) over an area of 60 × 60 with a 17 g necklace radio-transmitter (1.6–2.2% km. The parallel search transects were 7 (in 1990) of body weight) with a life expectancy of 6–10 or 10 km (1991–93) apart because transmitters months, and released immediately after marking. with a known location were detected from the air- Caizergues & Ellison (1998) found that in the craft at a distance of 5 km or more. During the next French Alps the breeding success of female Black flight each female was located more accurately by Grouse marked with necklace transmitters during circling around its approximate location. or just before laying was lower than that of females Nests were mostly located at the onset of incu- marked several months before laying. In our study bation.