Nest-site selection by the white-tailed eagle and black stork–implications for conservation practice

Background:Nesting 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.Results:Our 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.Conclusions:As 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.

Mature stand developmental stage has ceased to constitute the most suitable habitat for the capercaillie in the Augustow Forest,Poland

Background:Forest management affects the habitat conditions for many forest-dwelling species.Among them,the capercaillie(Tetrao urogallus)is a rare forest grouse inhabiting old,mature forests.We compared the structure of forest habitat among 9 active and 9 abandoned leks in the Augustow Forest(North-Eastern Poland),within a radius of 1 km of the leks,defined as the Key Areas for the capercaillie in lowland temperate forest.Habitat measurements were conducted on 1779 circular plots.Assessments made on all plots related to 13 habitat variables measured or noted in the field,including stand structure,canopy closure,stand developmental stage,percentage of Scots pine(Pinus sylvestris),soil fertility and soil moisture,the share of undergrowth,the cover of shrubs,the cover of bilberry(Vaccinium sp.),and the presence of certain habitat elements important to the capercaillie.Results:To compare the still-occupied and the abandoned KAs for the capercaillie,a logistic regression model was developed.The variables best explaining differences between these two categories were:the occurrence of undergrowth layers,canopy closure in the second canopy layer,and stand age.According to the model,with the increase of the shrub-layer cover as well as the density of trees,the probability of the presence of the capercaillie decreased.The capercaillie in the area of the Augustow Forest occupy mainly dry and poor,middle-aged,pinedominated forests,with a moderate extent of stand canopy closure and only weakly-developed layers of undergrowth.Conclusions:The filling-in of mature stands with sub-canopy trees and shrubs(the process which is stimulated by climate change and site eutrophication)causes structural changes,which are unfavourable to the capercaillie.This might explain why in the course of the recent decades the capercaillie has abandoned the oldest stands,distinguished by the presence of bigger shares of undergrowth.The capercaillie has shifted to younger stands,which reveal a lesser extent of canopy closure and a more limited development of understorey vegetation.