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HOW, and WHY, IS the GOSHAWK &Lpar;<I>ACCIPITER GENTILIS</I

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HOW, and WHY, IS the GOSHAWK &Lpar;<I>ACCIPITER GENTILIS</I J. RaptorRes. 31 (2):107-113 ¸ 1997 The Raptor ResearchFoundation, Inc. HOW, AND WHY, IS THE GOSHAWK (ACCIPITER GENTILIS) AFFECTED BY MODERN FOREST MANAGEMENT IN FENNOSCANDIA? PER WIDEN Universityof Karlstad,S-651 88 Karlstad,Sweden ABSTRACT.-•TheNorthern Goshawk(Accipiter gentilis) is a common raptor in the boreal forest of Fen- noscandia(Norway, Sweden and Finland), with a presentbreeding density of about 3 pr/100 km2 of forestarea. Severalindependent studies show that goshawkpopulations in Fennoscandiahave declined by 50-60% from the 1950sto the 1980s.This declinecoincides in time with an intensificationof forest management, which has changed the forest landscape.Among other effects, forests are more frag- mented and the proportion of old forestis decreasing.Neither pesticideuse nor persecutioncan explain the goshawkdecline. However, changes in habitatand prey populationsare both importantfactors that are affectedby forestry.Goshawks need only a smallpatch of suitablehabitat for nesting,but for their foraginghome rangescover 2000-6000 ha, and in boreal forestareas they prefer large patchesof mature forest.I suggestthat changesin the borealforest landscape have resulted in a deteriorationof goshawk hunting ranges,making it more difficult for them to secureadequate food for breeding.This factor is more important than a shortageof suitablenest sites.Declining prey densities(e.g., grouse) may be associatedwith forestryand is alsoan important factor that may affect goshawknumbers. KEYWORDS: Accipiter gentilis;Northern Goshawk; forest management;, home range,, breeding; habitat selection; Fennoscandia;Sweden; Norway; Finland. dComo,y Porque, esta el Acdpitergentills afectado por la administracitn forestal moderna en Fenno- scandia? RESUMEN.--EIAccipiter gentilis nortefio es un rapaz comfin en el bosqueboreal de Fennoscandia(No- ruega, Sueciay Finlandia) con una densidadde cria presentecomo 3 pr/100 km2 de /trea bosque, variosestudios independientes ensefian poblaciones de Acdpitergentilis en Fennoscandiaaun reducido por uno 50-60% de los 1950sa los 1980s.Estfi reduccitn coincidecon el tiempo de intensificacitnde administracitn de bosque,que ha cambiadoel paisajedel bosque.Entre otros efectos,bosques est/tn mas fragmentadosy la proporcitn de bosquesviejos se estareduciendo. Ni uso de pesticidani perse- cucitn puede explicarreduccitn del Accipitergentilis. Sin embargo,cambios en el h/tbitaty poblaciones de cazar son las dos importantesfactores que son afectadospor forestales.Accipitergentilis necesitan no mas una parcela chiquita de h•bitat convenientepara hacer nidos, pero susforrajes naturalescubren 2000-6000 ha, yen /treasde bosqueboreal ellos prefieren parcela grandes de bosque maduro. Yo, propongoque cambiosen el paisajede bosquesboreal han resultadoen un empeoramientoen campos de cazardel Accipitergentills, haciendo mas dificil para ellosa proveersuficiente comida para cria. Este factor es mas importante que una falta de nidos conveniente.La reduccitn de densidadde cazados, (por ejemplo, urogallo) puede ser asociadacon forestalesy es tambitn un factor importante que puede afectar la cantidad de Accipitergentilis. [Traducci6n de Rafil De La Garza, Jr.] The forests of Fennoscandia (Norway, Sweden, area is productive forest which is very intensively and Finland) have been used by man for a very managed.About 40% of this area has been clear- long period of time. However,in the 1950s,a major cut since 1950 and is now covered by forest estab- change occurred in forest-managementpractices, lished according to modern methods (Anonymous including intensified methods based on clear-cut- 1989). ting, replanting and thinning. This practice grad- As a result of this intensivemanagement, the bo- ually replaced the traditional wayof harvestingfor- real forest landscape of Fennoscandia is now a estby selectivecutting. In Sweden,58% of the land highly fragmented patchwork of clear-cutsand for- 107 108 WID]•N VOL. 31, NO. 2 Table 1. Population studies showing goshawk density changesin boreal forestsof Fennoscandia. DENSITY CHANGE IN CHANGE BREEDING (pr/100 STUDYAREA PE•OD PAIRS km 2) Central Norwaya 1964-93 8 •) 0 5.7 •) 0 SouthernNorway b 1950-84 13 -• 5 7.2 -• 2.7 Southern Norway• 1950-85 35 -• 20 9 -• 3 Southern Norway• 1985-88 20 -• 26 3 -• 4 North-central Sweden a 1950-76 12 -• 5 2.4 -• 1 Central Sweden" 1950-70 10 -• 5 2 -• 1 Central Sweden f 1960-80 35 -• 15 35 -• 15 Southern Finlandg 1974-81 25 -• 10 5 -• 2 Southern Finland h 1977-84 16 -• 10 5.3 -• 3.3 Tommeraas 1993. Figure 1. Map showing the location of goshawkpopu- Hansen 1985, FrydenlundSteen 1989. lation studies cited in the text. 1. Tommeraas (1993), 2. Selfisunpubl. data. Hansen (1985), Frydenlund Steen (1989), 3. Selfs (pers. Carelius (1978). Bylin (1975). comm.), 4. Carelius (1978), 5. Bylin (1975), 6. Lind (in Ltnd (in Nilsson, 1981). Nilsson 1981), 7. Wikman and Lind6n (1981) and 8. Wtkman and Lind6n (1981). Forsman and Ehrnsten (1985). Forsman and Ehrnsten (1985). 13 600. I judge the two latter estimates to be the est standsin different successionalstages. Less than most reliable and conclude that the Swedishgos- 5% of the Swedishforests are primeval, as com- hawk population is about 7000 breeding pairs, pared to 22% and 60% of the forestsin the U.S. which is equivalent to a breeding density of 1.9 and Canada, respectively(Olsson 1992). pr/100 km2 of land area and 2.9 pr/100 km2 of The Northern Goshawk(Accipiter gentilis) occurs forest area. •n forested areas throughout the Holarctic region The goshawkpopulation in Finland wasestimat- (Brown and Amadon 1968), and is one of the ed at about 6000 breeding pairs by Saurola more numerous birds of prey in Fennoscandia. (1985a), implying a breeding densityof 2.0 pr/100 The object of this paper is to review available in- km2 of land area and 3.0 pr/100 km2 of forestarea. formation about goshawkpopulation status and Thus, although the densityper land area differs trends in the Fennoscandian countries and to dis- between the Fennoscandiancountries, the density cusspossible effects of modern fbrest management per forest area is virtually the same,about 3 breed- on those trends. ing pr/100 km2 of forest. POPULATION STATUS POPULATION TRENDS In Norway,the goshawkpopulation wasestimat- The best way to study long-term population ed to be 2700 breeding pairs (Bergo 1992). This is changesin raptors is to monitor a breeding pop- equivalentto 0.8 breedingpr/100 km2 of land area ulation of a given area for a long period of time. and 3.1 pr/100 km= of forest area. By examining trends in individual populations,we The Swedishgoshawk population wasestimated should be able to make conclusions regarding at 10 000 breedingpairs by Svensson(1979), based trends over larger areas. In Fennoscandia,a num- on a nationwide bird censusingprogram. However, ber of such local, long-term goshawkpopulation Ntisson (1981) suggestedthat there were only 6000 studieshave been reported, and they are summa- breeding pairs after analyzinga number of differ- rized in Table 1. The locations of the studies are ent local studies. Marcstr6m and Kenward (1981), shownin Fig. 1. A paired t-testbetween early and based on capture-recapture estimate of ringed late years show a statisticallysignificant decline (! (banded) birds, calculatedthat the number of gos- = 3.474, df = 8, P = 0.0084). hawk pairs older than two yr wasbetween 3500 and Thus, it is well documented from a number of JUNE1997 GOSHAWKSAND FORESTRY IN FENNOSCANDIA 109 different, independent studiesin all three Fenno- gestsorganochlorines have not been an important scandian countries that goshawkpopulations have factor in their population decline. decreased from around 1950 to around 1980. In Thus, although pesticide use ha•sbeen reported most studies, the decrease has been 50-60%. After as the causeof declinesin goshawkpopulations in that period, the pattern is less clear since most other parts of Europe (Bijlsma 1991), I conclude studies have not continued. However, the nation- that there is no evidence that this has been the wide raptor monitoring scheme in Finland indi- case in the boreal forest region. When the use of catesstable populations after 1989, when the pro- persistentpesticides stopped in the early 1970s, gram started (Haapala et al. 1994), and Selfis(pets. positivegoshawk population trends were reported comm.) reports a temporary,slight increase in one throughout Europe (Bijlsma 1991). In the boreal area of Norway. forest region, this has not occurred and goshawks did not recover when the pesticide situation im- WHY I-IAS THE GOSHAWK DECLINED? proved. In fact, several population studies show To determine the reasons for such a dramatic that goshawksdeclined even after mercury levels decline, we nmst look at all possibleenvironmental dropped. This can be compared to the Sparrow- factors, not only forest management. The factors hawk (Accipiternisus), which decreased drastically most often associatedwith declining raptor popu- in Swedenfrom the 1950s, but recovered markedly lations are pesticides,persecution, declining prey when organochlorines were prohibited in the populationsand habitat degradation or loss (New- 1970s (Wallin 1984). ton 1979). Persecution. Goshawkshave alwaysbeen perse- Pestiddes. Most adult goshawksin the boreal cuted in Europe, especiallyin farmland areas by forests of Fennoscandiaare not migratory and re- hunters wanting to protect small game species main in or close to the boreal forest throughout from predation. In Fennoscandia, this has mainly the year. Further, their most
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