Browsing by discipline "Metsäekologia (riistaeläintiede)"

Suomenselän keskiosissa elävän metsäpeuraosakannan kehitystä on seurattu muutaman vuoden välein toistuvilla talvisilla helikopterilaskennoilla. Menetelmällä saadaan tarkka arvio osakannan yksilömäärästä sekä ikä- ja sukupuolijakaumasta. Lentolaskenta on kuitenkin kallis, eikä sitä voida tehdä vähälumisina talvina. Tietoa kannan tilasta ei saada laskentojen välisinä vuosina. Näiden syiden vuoksi seurantamenetelmiä on tarpeen kehittää ja monipuolistaa. Peurapopulaation ikä- ja sukupuolirakennetta voidaan arvioida keräämällä havaintoja eläimistä sellaisena aikana jolloin kaikki ikäluokat liikkuvat samoilla alueilla. Vasaosuuden perusteella voidaan arvioida kannan lisääntymismenestystä ja suurpetojen saalistuksen vaikutuksia. Sukupuolijakauma puolestaan kertoo esimerkiksi väärin kohdennetun pyynnin vaikutuksista. Suomenselän alueen metsästäjät keräsivät maastohavaintoaineiston peuraosakannan ikä- ja sukupuolijakaumasta 11.10.–16.12.2007. Peuralaumoja valokuvattiin samassa yhteydessä havaintojen tarkentamiseksi. Kevättalvella 2008 tehtiin helikopterilaskenta. Menetelmien antamia ikä- ja sukupuolijakaumia vertailtiin, ja syitä poikkeamiin pohdittiin. Sekä maastohavaintojen että lento- ja maastolaskennan kuva-aineistojen perusteella arvioidut metsäpeuran vasaosuudet olivat yhdenmukaiset. Yksittäisten laskijoiden havaintojen vasaosuuksissa oli vaihtelua, joka johtui ensisijaisesti peurojen elintavoista. Laskennan ajankohta, havaitun lauman koko ja laskijan taidot vaikuttivat tulokseen vain vähän. Hirvas- ja vaadinosuuksissa oli hajontaa. Maastolaskennassa naaraiden osuus oli aliarvio, lentolaskennassa puolestaan hirvasosuus. Tulosten perusteella maastolaskenta sopii erinomaisesti metsäpeurakannan vasaosuuden seurantaan, ja ns. ”early warning” -järjestelmäksi ilmaisemaan muutoksista kantaa säätelevissä tekijöissä. Aikuiskannan rakennetta voidaan seurata parhaiten valokuvaamalla tai videoimalla peuralaumoja silloin kun laumakoko on suurimmillaan.

Osprey Pandion haliaetus has been under a strict surveillance of the nature conservationists and a conservation icon since the early 70’s. At that time the accumulation of persistent environmental toxins and pollutants lowered the populations of many birds of prey to low levels, threatening the survival of entire species. Nowadays osprey is one of the successful models of endangered species protection. Because of its status osprey is very thoroughly studied raptor. Due to environmental toxins many birds of prey suffered from eggshell thinning and lost clutches till the end of 1970’s. Eggshell thinning has later stopped and is now reverting, but after the start of intense studying of the birds other threats have been observed to reduce reproductive success. Many earlier studies have suggested that extreme weather conditions may have an effect on the nesting success of diurnal birds of prey. In osprey´s case many researchers have examined the effects of different weather patterns to foraging success and food delivery, but a specific review over their effects on the nesting success hasn’t been conducted so far. In this study I focus on the effects of different weather factors and their contemporary nesting success. I study a nature conservation based supplementary feeding pond‘s effect to the local osprey population’s reproductive success, combined with the weather variables and the density of nesting pairs. Osprey is recorded to fly approximately 3–15 km on its foraging trips. At their longest these fishing trips can be over 40 km long one-way. The Osprey Center, working in Pohtiolampi at Kangasala (61° 26.876' N, 24° 7.705' E), in Southern Finland, feeds the local ospreys with living rainbow trout from an old fish farm pool. In theory, the birds nesting or living near the supplementary feeding pond benefit from this in a form of easy sustenance. The fish move near the water surface and are thus available all the time. Especially during bad weather conditions the pond is frequently visited by nesting ospreys. In this study I examine 1) does supplementary feeding have an effect on the nesting success of the local osprey population, 2) what is the role of weather factors affecting the breeding success and 3) does supplementary feeding have an effect on nesting density? I used 16 years of weather and breeding data (1997–2012) and evaluated the individual and combined weather variables and their possible effects on nesting success and brood production, comparing study and control area. I set my study area in a shape of a circle with 30 km radius. Pohtiolampi feeding pond was placed in the center of the study area, surrounded by a vast labyrinthine lake area. For the control area’s and study area's ecosystems to be as much alike as possible, I established the control area, also in a form of a circle and continuing the next 30 km, to start where the study area ended (see: Map 1.). I calculated the covariance and Akaike weights of different weather variables and annual nesting success with R (2.15.0) statistical calculation program. Collinearity was assessed with variance inflation factors (VIF). Generalized linear mixed models (GLM), to asses simultaneously the role of weather variables and the nesting success of both study and control area, were used. Finally the scenarios were arranged in significance order by their AICc values (Akaike information criterion adjusted for finite sample size). After the comparing analysis, I repeated the calculations also without the division to study and control area, gaining information about the effects of weather variables in general. I also calculated the proportional effects of different land use types to the nesting density of the local osprey population by using ArcGIS mapping tool and compared the results between study and control area. My results indicate that supplementary feeding does not influence the nesting success. Same annual average of young fledged the nests each year, regardless of the area. Weather variables, however, showed some effect on the nesting success when viewing the entire population. The assembled weather data shows examples of weaker nesting success in summers with prolonged storms, rainy weather or low average temperature. However, levels of significance, derived from the data, are still too low to be used as generalizations. Only three day long storms had a better AIC weight than the null model. I presume that the good fishing waters, wind shelter and shoreline forests are possible explanations to this trend. Most harmful weather to the osprey nestlings was a prolonged storm (? 7 m/s wind) and rainy summers. The nesting density of osprey was recorded to be significantly higher in the study area than in the control area, when viewing the total land acreage. Moreover, I recorded that the density in the study area grew up to almost four times the number of control area, when studying the acreage of potential nesting areas. When viewing the area of foraging waters the difference was reduced to 1.5 fold. I conclude that the local osprey population benefits from the supplementary feeding area by nesting more densely near the abundant food source and thus producing more young per km².