Effect of plot type, age and date on seed depletion and bird use of Wild Bird Seed Mixtures in England

Figures & data

Figure 1. Locations of seed mixture plots surveyed.

Figure 2. Mean predicted densities (+/− se) of buntings and finches in seed mixture plots in relation to survey.

Table 1. Results of GLMM analyses relating bunting and finch densities to features of seed mixture plots recorded during surveys. Significant terms highlighted in bold.

		Buntings		Finches
		Birds/ha	P-value	Birds/ha	P-value
Region	East Anglia	3.12	0.44	8.60	0.07
	Oxfordshire	2.15		20.54
Plot type	EF2	3.10	0.83	16.89	0.70
	HF2	2.16		10.91
	HF12	2.60		12.73
Plot age	First-year	3.89	0.22	17.15	0.39
	Second-year	1.73		10.30
Survey	Nov/Dec	4.04	<0.0001	24.40	<0.0001
	Jan/Feb	1.66		7.24
Presence of predators	Y	2.32	0.43	11.07	0.30
	N	2.90		15.95
No. of non-target species			0.75		0.95
Plot type × survey			0.43		0.08
Plot age × survey			0.47		0.96
Plot type × plot age			0.65		0.09

Non-significant interaction terms were removed from the model.

An individual-level random effects approach was taken for the model of finch counts to aid convergence.

Figure 3. Mean predicted densities of cereal and non-cereal seed samples from seed mixture plots in relation to (a) survey and (b) plot age.

Table 2. Results of GLMM analyses relating vegetation attributes in relation to features of seed mixture plots. Significant terms highlighted in bold.

		Veg. Height (cm)	P-value	% Bare ground	P-value	% Cereal cover	P-value	% Non-cereal cover	P-value	Mass of cereal seed (g)	P-value	Mass of non-cereal seed (g)	P-value
Plot type	EF2	62	0.90	15	0.54	12	0.70	23	0.80	0.04	0.07	0.06	0.24
	HF2	64		15		7		25		0.01		0.11
	HF12	60		11		9		24		0.04		0.11
Plot age	First-year	65	0.52	20	0.0001	17	0.0026	37	0.027	0.09	0.027	0.24	0.068
	Second-year	59		8		1		11		0.01		0.03
Survey	Nov/Dec	na	na	na	na	na	na	na	na	0.04	0.04	0.16	0.016
	Jan/Feb									0.01		0.05

All two-way interaction terms were included in original models; non-significant interaction terms were removed from the model.

Table 3. Results of GLMM analyses relating vegetation attributes of seed mixture plots to densities of buntings and finches. Estimates shown on modelled log scale. Significant terms highlighted in bold.

	Buntings		Finches
	Estimate (se)	P-value	Estimate (se)	P-value
Vegetation height	−0.03 (0.01)	F 1, 104 = 9.41	0.01 (0.01)	F 1,104 = 2.39
		P = 0.0027		P = 0.12
% Bare ground	−0.08 (0.04)	F 1,92 = 3.93	0.06 (0.05)	F 1,101 = 1.45
		P = 0.050		P = 0.23
Mass of cereal seed	0.62 (0.14)	F 1,90 = 18.87	0.12 (0.18)	F 1, 104 = 0.45
		P < 0.0001		P = 0.51
Mass of non-cereal seed	−0.43 (0.23)	F 1,71 = 3.41	0.66 (0.17)	F 1,103 = 15.43
		P = 0.069		P = 0.0002

Table 4. Results of GLM analyses relating mass of seed in January/February 2011 to numbers of buntings, finches and non-target species in November/December 2010. Significant terms highlighted in bold.

	Mass of cereal seed Jan/Feb	Mass of non-cereal seed Jan/Feb
	P-value	P-value
Density of non-target species in Nov/Dec
	P = 0.24	P = 0.25
Plot type
	P = 0.20	P = 0.40
Density of non-target species in Nov/Dec × plot type
	P = 0.27	P = 0.08