Elinympäristömuutosten, suojelutoimien ja lajien välisten vuorovaikutussuhteiden vaikutukset metsähaukkoihin

Human-caused habitat changes have led to declines of many species by impairing their occurrence, reproduction and interactions with other species. In Northern Europe, intensive forestry has transformed boreal forests and worsened conditions of species dependent on old forest, but the mechanisms by which habitat changes affect species are often unknown. In my dissertation, I examined habitat changes, their effects and habitat-associated breeding performances of three declining forest-dwelling hawks, the northern goshawk (Accipiter gentilis), the common buzzard (Buteo buteo) and the honey buzzard (Pernis apivorus). These species can compete for nest sites and goshawks can also predate the buzzards. Raptors may lack nest sites in managed forests which is why their nesting has been supported by constructing artificial nests. I analysed the breeding success of the hawks in artificial nests since their benefits as a conservation measure were not previously analysed. Finally, I studied the conditions when dominant species can exclude subordinate ones in competition for suitable nest sites. According to my results, old forests have decreased and young forests increased throughout southern Finland. These changes are adverse for the goshawk whose breeding success improves when old spruce forests are more abundant and young forests scarce around their nests. Breeding performances of the common buzzard and honey buzzard were not significantly associated with habitats. However, common buzzards were reluctant to re-occupy nests surrounded by a vastness of old forest. The breeding success of the goshawk and common buzzard was lower in artificial nests than in natural ones. Thus, this measure aimed at enabling hawk breeding in managed forests seems to conflict with its conservation objectives. I discuss the possible contributing factors and directions for further investigations. Interspecific interactions with other raptors proved to be important when a subordinate hawk decided on territory occupancy. Common buzzards prefer to occupy safe territories, where threats of goshawk predation and interference competition with other raptors are small. Thus, interspecific raptors that are predators or competitors may exclude subordinate raptors from their territories, and thereby contribute to their occurrence. Adverse interactions with other raptors may even impede a subordinate raptor from fully exploiting the periodic food peaks. My dissertation shows that for each species, it is crucial to identify the most relevant spatiotemporal scales in order to identify, how external disturbances affect them most. Long-term data is of paramount importance to detect these scales.Ihmisen aiheuttamat elinympäristömuutokset ovat monien lajien taantumisen suurin syy, sillä ne vaikuttavat lajien esiintymiseen, lisääntymiseen sekä lajienvälisiin vuorovaikutuksiin. Pohjois-Euroopassa tehometsätalous on muokannut boreaalisia metsiä ja heikentänyt erityisesti vanhojen metsien lajien elinoloja. Elinympäristömuutosten vaikutusmekanismeja ei kuitenkaan aina tunneta. Tutkin väitöskirjassani kolmen vähentyneen metsäpetolinnun, kanahaukan (Accipiter gentilis), hiirihaukan (Buteo buteo) ja mehiläishaukan (Pernis apivorus), elinympäristön muutoksia, muutosten vaikutuksia sekä pesimistulokseen vaikuttavia elinympäristötekijöitä. Lajit voivat kilpailla pesäpaikoista, mutta kanahaukka voi myös saalistaa hiiri- ja mehiläishaukkoja. Talousmetsissä haukoille sopivia pesäpaikkoja on niukasti, joten pesintää on avustettu rakentamalla tekopesiä. Tutkin haukkojen pesimistulosta tekopesissä, joiden hyötyjä suojelutoimenpiteenä ei ole tarkasteltu. Lisäksi tutkin, missä oloissa vahvemmat lajit voivat syrjäyttää alisteiset lajit sopivilta pesäpaikoilta. Tulosteni mukaan vanhat metsät vähentyivät haukkojen reviireillä ja Etelä-Suomessa, kun taas nuorten metsien osuus kasvoi. Nämä muutokset ovat haitallisia etenkin kanahaukalle, jonka pesimismenestys kasvaa vanhan kuusimetsän osuuden kasvaessa ja nuoren metsän osuuden vähentyessä reviirillä. Hiiri- ja mehiläishaukalla ei havaittu merkitsevää yhteyttä elinympäristön ja pesimistuloksen välillä. Hiirihaukat eivät kuitenkaan mielellään asuttaneet uudestaan pesiään, joiden ympärillä oli paljon vanhaa metsää. Kanahaukan ja hiirihaukan pesimismenestys oli alhaisempi tekopesissä kuin haukkojen omissa pesissä. Haukkojen avuksi ajateltu suojelukeino vaikuttaa siten olevan ristiriidassa suojelutavoitteidensa kanssa. Tarkastelen tähän mahdollisesti vaikuttavia tekijöitä sekä tarvittavia lisäselvityksiä. Vuorovaikutussuhteet muiden petolintulajien kanssa osoittautuivat tärkeiksi alisteisen petolintulajin päättäessä asettumisesta reviirille. Hiirihaukka suosii turvallisia reviirejä, joilla uhat kanahaukan saalistuksesta ja muiden petolintulajien häirinnästä ovat pieniä. Hallitsevat petolintulajit voivat siten syrjäyttää alisteisen petolintulajin reviiriltä ja vaikuttaa sen esiintymiseen ja kannankokoon. Epäedulliset vuorovaikutukset muiden petolintulajien kanssa voivat jopa estää alisteista petolintulajia hyödyntämästä täysimääräisesti saalislajiensa ajoittaisia huippuvaiheita. Väitöskirjani osoittaa, että on tärkeää tunnistaa kullekin lajille oleelliset alueelliset ja ajalliset mittakaavat, jotta tiedetään, millä tavalla ulkoiset häiriöt vaikuttavat lajiin eniten. Lajien pitkäaikaisaineistot ovat ensiarvoisen tärkeitä näiden mittakaavojen selvittämiseksi

Petolintujen kannankehitykset Suomessa

Peer reviewe

Predicting valuable forest habitats using an indicator species for biodiversity

Intensive management of boreal forests impairs forest biodiversity and species of old-growth forest. Effective measures to support biodiversity require detection of locations valuable for conservation. We applied species distribution models (SDMs) to a species of mature forest, the northern goshawk (Accipiter gentilis, goshawk), that is often associated with hotspots of forest biodiversity. We located optimal sites for the goshawk on a landscape scale, assessed their state under intensified logging operations and identified characteristics of goshawks' nesting sites in boreal forests. Optimal sites for the goshawk covered only 3.4% of the boreal landscape and were mostly located outside protected areas, which highlights the importance of conservation actions in privately-owned forests. Furthermore, optimal sites for the goshawk and associated biodiversity were under threat. Half of them were logged to some extent and 10% were already lost or notably deteriorated due to logging shortly after 2015 for which our models were calibrated. Habitat suitability for the goshawk increased with increasing volume of Norway spruce (Picea abies) peaking at 220 m(3) ha(-1), and with small quantities of birches (Betula spp.) and other broad-leaved trees. Threats to biodiversity of mature spruce forests are likely to accelerate in the future with increasing logging pressures and shorter rotation periods. Logging should be directed less to forests with high biodiversity. Continuous supply of mature spruce forests in the landscape should be secured with a denser network of protected areas and measures that aid in sparing large entities of mature forest on privately-owned land.peerReviewe

Habitat effects on the breeding performance of three forest-dwelling hawks

PLoS ONE 10(9): e0137877Habitat loss causes population declines, but the mechanisms are rarely known. In the European Boreal Zone, loss of old forest due to intensive forestry is suspected to cause declines in forest-dwelling raptors by reducing their breeding performance. We studied the boreal breeding habitat and habitat-associated breeding performance of the northern goshawk (Accipiter gentilis), common buzzard (Buteo buteo) and European honey buzzard (Pernis apivorus). We combined long-term Finnish bird-of-prey data with multi-source national forest inventory data at various distances (100–4000 m) around the hawk nests. We found that breeding success of the goshawk was best explained by the habitat within a 2000-m radius around the nests; breeding was more successful with increasing proportions of old spruce forest and water, and decreasing proportions of young thinning forest. None of the habitat variables affected significantly the breeding success of the common buzzard or the honey buzzard, or the brood size of any of the species. The amount of old spruce forest decreased both around goshawk and common buzzard nests and throughout southern Finland in 1992–2010. In contrast, the area of young forest increased in southern Finland but not around hawk nests. We emphasize the importance of studying habitats at several spatial and temporal scales to determine the relevant species-specific scale and to detect environmental changes. Further effort is needed to reconcile the socioeconomic and ecological functions of forests and habitat requirements of old forest specialists.Peer reviewe