What Explains Forest Grouse Mortality: Predation Impacts of Raptors, Vole Abundance, or Weather Conditions?

Table 3

Some of the main original data used and calculation performed for estimation of raptor predation impact on juvenile grouse (only mean values are presented).

Weight of black grouse hen, g (𝑊h)	Both raptors		950
Weight of black grouse chick, g (𝑊c)	Both raptors		350
Weight proportion of the black grouse hens and chicks, % (WPhc)	Goshawk	Hens	17.3
		Chicks	7.6
	Buzzard	Hens	8.0
		Chicks	11.8
Grouse body weight utilised by raptors, % (U)	Both raptors		75
			Male	Fem.	Juv.
Daily food requirements of male (m), female (f) and juvenile (j) raborts, g/day (DFRmfj)	Goshawk		130	190	196
	Buzzard		100	126	138
Ratio of the black grouse among grouse chicks in the diet of raptors, % (P)	Goshawk		60
	Buzzard		60
Length of the study period (L)	Goshawk		60
	Buzzard		60
Maximum density of raptor population nests/100 km^2 (D)	Goshawk	SO	10
		Oulu	4.7
	Buzzard	SO	14
Occupancy rate of the territory (Or)	Goshawk, buzzard		56, 33
Productivity chicks/occ. terr. (Prod)	Goshawk, buzzard		2.1, 1.2
Clutch size (Cs)	Black grouse		8
Brood size (Bs)	Black grouse		6
Density of hens in August (𝐷h)	Black grouse		3.2
Density of chicks in August (𝐷c)	Black grouse		10.5
Density of hatchlings 𝐷hatch= (𝐷hCs)	Black grouse		25.4
Loss of chicks (𝐷hatch−𝐷c)	Black grouse		20.5
Consumption of a hawk family	C = DFRm + DFRf + Prod × DFRj
Kill rate of adult hens	KRh = (C × U × 𝑊𝑃h)/𝑊h
Kill rate of chicks	KRc = (C × U × P × 𝑊𝑃c)/𝑊c
Total kill rate of black grouse chicks	TKRc = OrD × (0.5KRhBs+KRc) × L