Winter diet of Yellowhammers Emberiza citrinella on contemporary farmland: the different contribution of forbs, wild grasses and cereals in semi-natural and agricultural habitats

Figures & data

Table 1. The general winter diet composition (expressed as percentages) of Yellowhammers E. citrinella on lowland farmland in Poland comprised of semi-natural (crop-free) habitats with permanent vegetation and agricultural habitats; the number of sites is given in brackets; managed fields were autumn-seeded set-aside fields with mustard and one ploughed field; unidentified plant material was probably fragments of seeds of unidentified cereals (59.4% in one sample from fallow land) and Polygonum sp. (52.9% in one sample from a grassy margin).

Item (characteristic)	All sites	Semi-natural habitats			Agricultural habitats
		Fallow lands (>2 years not cultivated) (2)	Grasslands, unmanaged (3)	Road verges (9)	Managed fields (2)	Stubble fields (5)	Manure heaps (5)
Seeds of forbs (case fragments)
Polygonum aviculare and other Polygonum taxa	7.1	20.8 (2)	1.7 (3)	15.6 (9)	0.62 (2)	1.1 (4)	0.75 (5)
Chenopodium album	1.6	0.03 (1)	-	5.1 (3)	0.06 (2)	0.14 (1)	0.02 (1)
Amaranthus sp.	0.02	-	-	0.02 (1)	-	0.06 (1)	0.04 (1)
Stellaria media	0.01	-	0.01 (1)	<0.01 (1)	0.02 (1)	<0.01 (1)	-
Capsella bursa-pastoris (whole seed)	<0.01	0.02 (1)	-	0.01 (1)	-	-	-
Leucanthemum vulgare	<0.01	-	-	0.01 (1)	-	-	-
P. aviculare (whole seed)	<0.01	0.01 (1)	-	0.01 (2)	-	-	-
P. aviculare (complete shell)	<0.01	0.01 (1)	-	<0.01 (1)	-	-	-
Compositae	<0.01	-	-	<0.01 (1)	-	-	-
Unidentified species	<0.01	-	-	0.01 (1)	-	-	-
Grains of cereal and wild grasses (case fragments)
Wheat	31.4	5.7 (1)	42.3 (2)	8.8 (5)	97.0 (2)	2.5 (3)	73.2 (5)
Other cereals/Elymus repens	11.1	-	12.1 (2)	19.3 (4)	0.01 (1)	0.32 (1)	14.0 (4)
Poaceae (unidentified)	3.9	4.1 (2)	-	4.3 (2)	-	11.33 (1)	-
Echinochloa crus-galli (whole seed)	<0.01	-	-	-	-	<0.01 (1)	<0.01 (1)
Grass husks (case fragments)
E. crus-galli	17.2	0.03 (2)	-	1.9 (4)	-	72.8 (3)	9.3 (2)
Setaria glauca	8.5	0.79 (1)	31.9 (1)	12.3 (3)	-	9.2 (3)	0.03 (1)
Wheat and straw fragments	2.8	0.45 (2)	8.7 (2)	0.52 (6)	1.7 (2)	0.63 (4)	1.7 (5)
Digitaria sp.	0.40	0.07 (1)	0.01 (1)	0.19 (2)	-	1.7 (1)	-
Setaria viridis	0.24	3.2 (1)	-		-	-	-
Other plant parts (case fragments)
Compositae (pappus hair)	2.9	-	-	9.3 (1)	-	-	-
P. aviculare (sepal fragments)	1.9	10.4 (2)	0.88 (2)	3.4 (7)	0.07 (1)	0.05 (2)	0.14 (3)
Leaves of Poaceae (very young shoots)	1.6	-	-	5.1 (2)	-	-	-
Leaves of dicotyledons	<0.01	-	-	-	0.02 (1)	-	-
Unidentified plant material	9.2	54.3 (2)	2.5 (1)	14.0 (6)	0.26 (1)	0.15 (2)	0.69 (3)
Arthropods (chitin fragments)	0.13	0.17 (2)	0.02 (2)	0.21 (6)	0.27 (2)	0.01 (2)	0.11 (4)
Total number of items	119 303	9089	14 349	37 070	12 068	23 971	22 756

Figure 1. Winter diet of Yellowhammers E. citrinella expressed as the number (average ± 1 se) of the various plant parts of the three groups of plants (forbs, wild grasses and cereals) in six farmland habitats (a), pooled semi-natural and agricultural habitats (b), dietary components of all grasses (=wild species and cereals) and non-grass species (c) and the proportions of cultivated species (cereals) and wild plants (weeds) (d). A detailed list of identified food items is given in Table 1 and the Supplemental data.

Figure 2. Results of the PCA analysis of the winter diet composition of Yellowhammers based on the log-transformed abundance of plant fragments of cereals, wild grasses and forbs in six land-cover/farmland habitat types; semi-natural habitats (white); agricultural habitats (black). Eigenvalues: axis 1 – 6.834, axis 2 – 3.449; cumulative percentage variance: axis 1 – 59.1, axis 2 – 89.0. Statistically significant Spearman rank correlation coefficients between the habitat type and axis 1 were found for stubble fields (r_s = 0.61, P < 0.001), crops (r_s = −0.38, P < 0.01) and manure heaps (r_s = −0.31, P < 0.05); and for axis 2 for road verges (r_s = −0.52, P < 0.001), manure heaps (r_s = 0.48, P < 0.001) and fallow land (r_s = −0.29, P < 0.05). Axis 2 also divided all samples into two distinct groups of semi-natural habitats (r_s = −0.60, P < 0.001) and agricultural ones (r_s = 0.60, P < 0.001).

Figure 3. Comparison of habitat-specific indices of diversity and dominance (=specialization) of the winter diet of the Yellowhammer E. citrinella, based on the complete list of different food items presented in the Supplemental data.

Figure 4. Relationship between the dominance and diversity indices of the winter diet of the Yellowhammer E. citrinella, calculated for 52 faecal samples from various farmland habitats; Berger–Parker's Dominance = 1.037 − 0.442 × Shannon's Diversity.