Effects of interspecific relationships in forested landscapes on breeding success in Eurasian treecreeper

Abstract

Jatkuvat vanhoihin metsiin kohdistuvat metsänhakkuut kaventavat puukiipijöiden ja kekomuurahaisten elinmahdollisuuksia. Havaitsin tämän väitöstyössäni, jonka teemoina olivat puukiipijän ja kekomuurahaisten välinen ravintokilpailu puiden rungoilla ja petojen, lähinnä kärpän, lumikon ja käpytikan vaikutus puukiipijän pesintämenestykseen pesäpönttöpopulaatiossa. Tutkimus on toteutettu Keski-Suomen metsissä Konneveden, Hankasalmen ja Laukaan kunnan alueella vuosina 1990-2003. T

his study is focused on the effects of predation to the breeding success of Eurasian treecreeper and resource competition between red wood ants, Formica rufa -group and treecreepers. One of the most important factors in competition between ants and treecreepers seems to be limited food resources on tree trunks. Treecreeper could consume a significant amount of arthropods on tree trunks near the nest during nesting period. Nests of treecreeper suffer from heavy nest predation from the great spotted woodpecker and from mustelids. Nest defence behaviour of parents is quite mild and composed mostly from high-pitched alarm calls that silence hungry nestlings in the nest. I used a moulted great spotted woodpecker as a predator model. Nest defence was similar between female and male on the first brood, but on the second, later brood male is mostly absent. Treecreepers are sensitive to modern forestry. Parents have to take more risk in their nest defence in smaller forest patches keeping the hungry nestlings quiet. It is more difficult to noisy offspring to hear alarm-calls of parents. The land-use and forest resource data of Landsat within two hundred meter radii around the nest boxes were used in GIS. Breeding success of treecreeper was greater and less variable in mature forest areas and lower in young forest areas. Nest predation rate was higher in territories with high proportion of young sapling stands. The territories of red wood ant were counted and each territory was classified as being either with ants, if the territory contained at least one ant mound or without ants. Treecreepers breeding in territories with ants laid their first clutches later and produced fewer fledglings with lower body mass at the nestling stage compared to the pairs breeding in territories without ants. Comparing the pairs that bred twice in the same territory during the same breeding season, I found that those breeding in territories with ants laid smaller second clutches than pairs in territories without ants. Food abundance was higher during the second broods, but the overall availability of food was lower in territories with ants. Additionally, I found associated evidence that the quality of treecreepers nestlings were affected by amount of red wood ants. Morphological characters of nestlings like body mass were lighter, subcutanous fat contents were thinner and tarsus lengths were shorter when the quantity of red wood ants was higher. The amount of wood ants had no significant effect on morphological characters like wing length and also there was no significant relationship between the wood ant level and nest-box occupancy, fecundity (clutch size) or physiological stress of nestlings. The survival and fecundity of treecreepers’ chicks fledging from ant territories may be further reduced by their low fledging mass.