A wader perspective to Boreal Baltic coastal grasslands: from habitat availability to breeding site selection and nest survival
Kuupäev
2022-04-25
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Rannaniidud on liigirikkad kooslused, mis pärast aastakümneid kestnud hääbumist on taastamistööde ja karjatamise tulemusena teinud nüüdseks läbi positiivse muutuse. Ometi ei ole sellest elupaigast sõltuvate ohustatud maaspesitsevate lindude – kahlajate – asurkonnad madalseisust taastunud. Doktoritöö keskendub eelkõige praktilise looduskaitse küsimustele eesmärgiga parandada killustunud rannaniitudel pesitsevate kahlajate seisundit. Töö põhitähelepanu on elupaiga ulatuse hindamisel, olulistel elupaiga tunnustel ning pesade ellujäämusel. Tulemustest nähtub, et rannaniitude hooldajatele makstav keskkonnatoetus mõjutab positiivselt kahlajatele sobiva rohustu kõrgusega alade laienemist. Elupaiganõudluse uuring näitas, et kahlajate pesitsusterritooriumid asuvad lompidele ja avatud rannajoonele lähemal ning metsast kaugemal kui võiks juhuslikult eeldada. Tõenäoline metsaserva vältimise põhjus on sealne kõrgem pesarüüste – metsa serva lähistel koorub hinnanguliselt vaid 7% pesadest. Madala koorumisedukuse taga on rebase suurem tihedus ja pesarüüste metsa servas. Enim ohustab kahlajapesi just rebane, kellele järgnevad šaakal, ronk ja mäger. Šaakali puudumine Hiiumaal andis võimaluse võrdlevalt mandriga selgitada selle liigi mõju pesade koorumisele, mis osutus kompenseerivaks – kuigi šaakal rüüstab pesi, tundub ta vähendavat rebase arvukust. Viimase, metoodilise uuringu, tulemusena selgus, et tehispesad ei ole sobiv alternatiiv kahlajapesade koorumisedukuse uurimisel rannaniitudel.
Kuigi doktoritöö käsitleb Läänemere-äärseid rannaniite, võib tulemusi üldistada ka teistele killustunud märgadele rohumaadele. Enamus töösse kaasatud uuringutest käsitlevad kogu niidukahlajate kooslust. Selline harvakasutatav lähenemine aitab mõista mitmete koosesinevate liikide elupaiganõudlust ning näitab, et rannaniitude killustatus ja kõrge pesarüüste mõjutavad eri liike sarnaselt. Töö tulemuste põhjal tõstatub küsimus, kas rannaniitudel pesitsevad kahlajad võivad hetkel elada väljasuremisvõlas. Doktoritöö annab siiski lootust, et elupaiga edasise taastamise ja majandamise ning röövluskontrolliga on võimalik kahlajapopulatsioonide käekäiku parandada.
Semi-natural grasslands, where low-intensity agricultural activities that imitate natural disturbances have created ecosystems for millennia, are a prime example of the rare positive anthropogenic effect on biodiversity. However, as these habitats are usually marginally productive, they are currently endangered by either intensified or ceased management. A species group often dependent on semi-natural grasslands is waders – threatened ground-breeding birds adapted to breed in open landscapes. Primarily as a result of habitat loss and low reproduction rates, they are going through substantial population declines both in Europe and globally, making them one of the most threatened groups of birds. This thesis focuses on a semi-natural wet grassland– the Boreal Baltic coastal grassland – which in Estonia hosts protected plant species, amphibians, and birds, including waders. Similarly to other types of semi-natural grasslands, ca. 90% of the coastal grassland habitat was lost in Estonia during the last century, mostly as a result of land abandonment. However, since the 1990s steps towards improving the coastal grassland habitat have been taken, including an active restoration programme and continuous agri-environment scheme-supported management. Nevertheless, the threatened wader populations dependent on this habitat have not recovered, raising the concern whether the currently fragmented landscape still holds suitable conditions for breeding waders. The issues faced by the breeding wader community on Boreal Baltic coastal grasslands were investigated in this thesis, concentrating on habitat availability, important habitat features, nest survival, and predator community. For the first time, it is shown that the agri-environment scheme applied on coastal grasslands increases the availability of suitable habitat for breeding waders in terms of vegetation height. Waders need access to wet features and as open habitat specialists prefer wide intact areas, while avoiding forest edge. The probable reason behind the avoidance of forest is driven by the higher nest predation rates by the red fox at the proximity of woodland. However, nest survival rates remain low even furthest from the forest, questioning the viability of the wader community breeding on coastal grasslands. While nest predation is a serious issue, a novel predator with a quickly expanding range, the golden jackal, does not seem to add pressure on wader nest survival in this habitat. Lastly, as a methodological finding, it is shown that artificial nests are not an adequate alternative to wader nests when studying nest survival in this habitat. The results of this thesis inform nature conservation actions that have the potential to improve the state of breeding wader populations in the coastal grassland habitat.
Semi-natural grasslands, where low-intensity agricultural activities that imitate natural disturbances have created ecosystems for millennia, are a prime example of the rare positive anthropogenic effect on biodiversity. However, as these habitats are usually marginally productive, they are currently endangered by either intensified or ceased management. A species group often dependent on semi-natural grasslands is waders – threatened ground-breeding birds adapted to breed in open landscapes. Primarily as a result of habitat loss and low reproduction rates, they are going through substantial population declines both in Europe and globally, making them one of the most threatened groups of birds. This thesis focuses on a semi-natural wet grassland– the Boreal Baltic coastal grassland – which in Estonia hosts protected plant species, amphibians, and birds, including waders. Similarly to other types of semi-natural grasslands, ca. 90% of the coastal grassland habitat was lost in Estonia during the last century, mostly as a result of land abandonment. However, since the 1990s steps towards improving the coastal grassland habitat have been taken, including an active restoration programme and continuous agri-environment scheme-supported management. Nevertheless, the threatened wader populations dependent on this habitat have not recovered, raising the concern whether the currently fragmented landscape still holds suitable conditions for breeding waders. The issues faced by the breeding wader community on Boreal Baltic coastal grasslands were investigated in this thesis, concentrating on habitat availability, important habitat features, nest survival, and predator community. For the first time, it is shown that the agri-environment scheme applied on coastal grasslands increases the availability of suitable habitat for breeding waders in terms of vegetation height. Waders need access to wet features and as open habitat specialists prefer wide intact areas, while avoiding forest edge. The probable reason behind the avoidance of forest is driven by the higher nest predation rates by the red fox at the proximity of woodland. However, nest survival rates remain low even furthest from the forest, questioning the viability of the wader community breeding on coastal grasslands. While nest predation is a serious issue, a novel predator with a quickly expanding range, the golden jackal, does not seem to add pressure on wader nest survival in this habitat. Lastly, as a methodological finding, it is shown that artificial nests are not an adequate alternative to wader nests when studying nest survival in this habitat. The results of this thesis inform nature conservation actions that have the potential to improve the state of breeding wader populations in the coastal grassland habitat.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
waders, habitats, habitat choice, nest, survival, coastal meadows