Nesting habitat overlap between the Common Buzzard Buteo buteo and the Lesser Spotted Eagle Clanga pomarina for conservation planning in Natura 2000 sites

Figures & data

Figure 1. Location of Biržai Forest in the region, and distribution of Common Buzzard and Lesser Spotted Eagle nests.

Table 1. Explanatory variables used to characterize Common Buzzard and Lesser Spotted Eagle nest sites.

Variable	Description	Source
Nest platform
Placement in tree	Three categories: trunk fork, side branches, top branches (Drobelis 2004)	Fieldwork
Height from ground, m	Measured using a Suunto height meter (PM-5/1520)	Fieldwork
Nest tree
Tree species	Tree species supporting nest platforms	Fieldwork
Trunk diameter	Diameter of tree trunk at 1.3 m	Fieldwork
Nest stand
Forest edge	Shortest distance to the forest edge	Map LTDBK50000-V
Stand age	Age of the stand according to dominant tree species in the first layer	State Forest Cadaster
Proportion of spruce	Proportion of spruce in the first layer of trees	State Forest Cadaster
Proportion of birch	Proportion of birch in the first layer of trees	State Forest Cadaster
Proportion of bl. alder	Proportion of black alder in the first layer of trees	State Forest Cadaster
Proportion of aspen	Proportion of aspen in the first layer of trees	State Forest Cadaster
Fertility	1, 2, 3, 4 scores: higher score, lower fertility	State Forest Cadaster
Humidity	1, 2, 3, 4, 5 scores: higher score, higher soil humidity	State Forest Cadaster
Competition
NND between buzzard/eagle nest sites	Distance from the Common Buzzard/Lesser Spotted Eagle nest to the nearest nest of a conspecific neighbour	ArcGIS 10.0 environment
NND between buzzard and eagle nest sites	Distance from the Common Buzzard nest to the nearest nest of a Lesser Spotted Eagle	ArcGIS 10.0 environment
NND between control stands and eagle nest sites	Distance from the control point to the nearest nest of a Lesser Spotted Eagle	ArcGIS 10.0 environment

Table 2. Descriptive statistics for the nest sites of the Lesser Spotted Eagle and the Common Buzzard in the Biržai Forest Special Protection Area.

	Lesser Spotted Eagle				Common Buzzard
Variable	Mean ± sd	Range		n	Mean ± sd	Range		n
Nest platform
Proportion of placement in tree	Trunk fork	Side branch	Top branch	24	Trunk fork	Side branch	Top branch
	79%	17%	4%		77%	17%	6%	52
Nest platform height from ground, m	16.6 ± 3.2	9–22		24	17.2 ± 2.4	13–24		52
Nest tree
Nest tree diameter at 1.3 m height, cm	47 ± 10	30–72		24	50 ± 15	25–101		52
Nest stand
Stand age, years	78 ± 20	30–120		26	82 ± 23	15–135		53
Soil humidity	2.73 ± 0.96	1–4		26	2.49 ± 0.80	1–4		53
Soil fertility	1.85 ± 1.12	1–4		26	1.91 ± 1.15	1–4		53
Proportion of tree in stand, %
Spruce	25 ± 25	0–90		26	23 ± 24	0–80		53
Birch	27 ± 25	0–80		26	33 ± 25	0–100		53
Aspen	13 ± 16	0–60		26	9 ± 15	0–80		53
Black alder	19 ± 26	0–80		26	26 ± 28	0–80		53
Forest edge, m	193 ± 126	19–512		26	754 ± 644	28–2435		53

Figure 2. Proportion of nest tree species used by the Common Buzzard (white bars) and the Lesser Spotted Eagle (black bars).

Figure 3. Distance to forest edge from the nest stands of the Common Buzzard (n = 53) and the Lesser Spotted Eagle (n = 26). The hollow square shows the median, the grey box gives the 25–75% range and the lines indicate the non-outlier range.

Table 3. Summary of supported models (GLMs) used to compare nest stands between species and with control stands. W – AICc model weights calculated for models ΔAICc ≤ 2. Negative estimates - decrease in values of explanatory variables in Lesser Spotted Eagle nest stands compared with the Common Buzzard nest stand, in the nest stand of the Common Buzzard compared to the control stands, and in the nest stand of the Lesser Spotted Eagle compared to the control stands. RIV – relative importance values estimated for variables after supported models averaging. Explanatory variables used: Fr.edge – distance to forest edge, St.age – stand age, Humid. – humidity of stand soil, Fertil. – fertility of stand soil, Bl.alder – proportion of Black Alder in stand composition, Aspen, Silver Birch, Norway Spruce – proportion of these tree species in stand composition.

	Explanatory variables
Model no.	Fr.edge	St.age	Humid.	Fertil.	Aspen	Bl.alder	Birch	Spruce	R^2	ΔAICc	W
Common Buzzard vs. Lesser Spotted Eagle
1	−0.01		0.68						0.34	0.00	0.20
2	−0.01		0.77				−1.64		0.36	0.25	0.18
3	−0.01		0.96			−1.61	−1.89		0.37	1.36	0.10
4	−0.01		0.81		1.80				0.35	1.39	0.10
5	−0.01		0.79					1.17	0.35	1.46	0.10
6	−0.01		0.81			−1.13			0.35	1.58	0.09
7	−0.01		0.90		1.83		−1.66		0.36	1.69	0.09
8	−0.01	−0.01	0.70				−2.05		0.36	1.92	0.08
9	−0.01								0.31	2.00	0.07
RIV	1.00	0.08	0.93	0.00	0.19	0.19	0.44	0.10
Common Buzzard vs. control stand
1		0.04	−0.62			2.72			0.31	0.00	0.19
2		0.04			2.99	2.18			0.30	0.83	0.13
3		0.04	−0.52		2.26	2.85			0.32	0.83	0.13
4		0.05	−0.60	−0.27		2.46			0.32	0.96	0.12
5		0.05	−0.70			3.12	0.92		0.32	1.11	0.11
6		0.04				1.76			0.29	1.27	0.10
7		0.05	−0.59		2.54	3.33	1.09		0.33	1.67	0.08
8		0.05		−0.29		1.52			0.30	1.87	0.08
9		0.05	−0.64			2.56		−0.57	0.31	1.89	0.07
RIV	0.00	1.00	0.70	0.19	0.33	1.00	0.19	0.07
Lesser Spotted Eagle vs. control stand
1	−0.01	0.03			4.76\				0.42	0.00	0.13
2	−0.01	0.03							0.40	0.24	0.12
3	−0.01	0.03			5.59		−1.55		0.43	0.48	0.11
4	−0.01	0.02			5.55		−2.89	−2.17	0.45	1.05	0.08
5	−0.01	0.03					−1.3		0.41	1.07	0.08
6	−0.01	0.03					−2.67	−2.27	0.43	1.24	0.07
7	−0.01				6.45		−3.44	−2.57	0.43	1.27	0.07
8	−0.01	0.02	0.44		7.01		−1.87		0.44	1.51	0.06
9	−0.01	0.03	0.31		5.59				0.43	1.55	0.06
10	−0.01	0.03			5.81	1.17			0.43	1.65	0.06
11	−0.01	0.03		−0.42			−1.9		0.42	1.88	0.05
12	−0.01	0.03		−0.34	5.26		−2.05		0.44	1.92	0.05
13	−0.01				6.74		−1.83		0.41	1.95	0.05
RIV	1.00	0.88	0.13	0.10	0.68	0.06	0.63	0.22

Drobelis, E. 2004. Lietuvos miškų plėšrieji paukščiai [ Birds of Prey of Lithuanian Forests]. Ministry of the Environment of the Republic of Lithuania, Vilnius.

 Google Scholar