Abstract
BackgroundNesting trees and habitat represent the key factor underpinning stand selection by forest-dwelling birds. While two large European species – the black stork (Ciconia nigra L.) and white-tailed eagle (Haliaaetus albicilla L.) – are known to require old, large trees for nesting, we sought to investigate further by comparing species requirements at the levels of the nesting tree, nesting stand, and landscape. This entailed a detailed examination of forest features within circles of radius 15 m surrounding 16 and 19 trees holding the nests of storks and eagles respectively. The same parameters were also checked in the vicinity of 50 randomly-selected mature trees.ResultsOur results indicate different nesting preferences, with the eagles entirely confining themselves to Scots pine (Pinus sylvestris L.) – a species also chosen by black storks, which nevertheless regularly favour pedunculate oak (Quercus robur L.). Both species select trees of greater girth than the random ones, but white-tailed eagles choose to nest in the vicinity of patches of mature old stands with a loose canopy, to the extent that nesting trees and surrounding trees are of similar ages. In contrast, black storks prefer “veteran” trees with low-set crowns that are much older than any others in their vicinity. Nesting trees of the eagles are away from roads and close to lakes, while black storks do not avoid roads.ConclusionsAs the ages of nesting trees of both species are greater than ages at final cutting in this region’s managed forest, silvicultural measures will need to be adjusted, with small patches of forest spared, or larger areas as “islands” of old-growth. Likewise, as tending and thinning are engaged in, certain trees with horizontal branches will need to remain, with relict trees also left untouched. As it happens, all of these recommendations are anyway key elements of close-to nature silviculture and multifunctional forestry.
Highlights
Nesting trees and habitat represent the key factor underpinning stand selection by forest-dwelling birds
A number of endangered species are associated with old, mature forests, and stand age as related to diversity of structure is known to be especially important for certain kinds of raptors and owls, as well as for the black stork (Ciconia nigra L.) (Lõhmus 2003; Rosenvald and Lõhmus 2003; Treinys et al 2009a, b; Mikusiński et al 2018)
Oaks were only noted as neighbouring trees in the cases of 2 eagle trees, 3 stork trees and 5 random trees
Summary
Nesting trees and habitat represent the key factor underpinning stand selection by forest-dwelling birds. A number of endangered species are associated with old, mature forests, and stand age as related to diversity of structure is known to be especially important for certain kinds of raptors and owls, as well as for the black stork (Ciconia nigra L.) (Lõhmus 2003; Rosenvald and Lõhmus 2003; Treinys et al 2009a, b; Mikusiński et al 2018). A key element of breeding habitat for birds is the presence of nest sites (Zawadzki and Zawadzka 2017), while the lack of suitable places to nest is associated with lower populations of certain bird species in managed forest This seems especially true of large birds in need of large trees if they are to nest (Lõhmus and Sellis 2003; Zuberogoitia and Martinez 2011). The protection zones provided for in law do not protect potential breeding sites and trees, only existing, occupied nests
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