3. Results
3.1 Sampling completeness
Plant DNA was successfully amplified from 262 faecal samples. We identified 49 plant zOTUs of which 86% could be identified to species and 100% to genus (Table S1). The most common taxa detected were beech (38.5% of samples), sunflower seed (Helianthus sp., Linnaeus), provided ad libitum throughout the year at all feed sites, (30.5% of samples) and hornbeam (16.0% of samples). At the genus level, 30 genera were detected in Hawfinch diet. Across the study sites, 78.7% of the available dietary diversity at genus level was detected, where the total extrapolated estimated genera diversity (Chao estimate) was 38.1 ± 8.2 (Figure 3). Invertebrate DNA was extracted successfully from 120 faecal samples. Of the 90 invertebrate zOTUs identified, 92% were identified to species level and 100% to genus (Table S2). The most common taxa detected were the winter moth (Operophtera brumata , Linnaeus) (26.7% of samples), mottled umber (Erannis defoliaria , Clerck) (22.5% of samples) and tree slug (Lehmannia marginata , O.F.Müller) (22.5% of samples). At the genus level, 74 genera were detected in Hawfinch diet, with 62.4% of the available dietary diversity detected across the sampling regions. The extrapolated total estimated genera diversity (Chao estimate) was 118.6 ± 22.6 (Figure 5). A Wilcoxon matched-pairs test revealed a significant difference between plant and invertebrate taxonomic richness within the diet of Hawfinch (V= 1436, p = < 0.001) (Figure 2). The mean number per faecal sample of plant genera detected in Hawfinch diet was 2.3, while the mean number of invertebrate taxa was 3.3.
3.2 Dietary differences
Herbivorous dietary composition differed between sampling regions (R2 = 0.05, MGLM: LRT = 266.8, p = < 0.001). Univariate analysis revealed six genera were associated with regional differences: Betula sp. (LRT = 21.3, p = 0.002),Carpinus sp. (LRT = 36, p = 0.001), Fagus sp. (LRT =56.4, p = 0.001), Helianthus sp. (LRT = 51.6, p = 0.001), Quercus sp. (LRT = 19.2, p = 0.002) andUlmus sp. (LRT = 30.5, p = 0.001) (Table S3). Specifically, Fagus sp. and Ulmus sp. were detected with the highest frequency in the Wye Valley (62.1% and 16.4% respectively), with birds sampled from north Wales showing the highest frequency for Helianthus sp. (50.9%). Quercus sp. were detected at the highest frequency in Hawfinches sampled within the New Forest (57.9%). The nMDS visualises the patterns of genus level consumption revealed from the manyglm model (Figure 4). All sampling regions show some degree of dietary overlap, while the diets of Hawfinches sampled from the regions of north Cardiff and the Wye Valley appear the most similar to each other. Pairwise comparisons revealed significant genus level dietary composition differences between all site comparisons except the Wye Valley and north Cardiff (p = 0.323) (Table S4). Invertebrate dietary composition differed between sexes (R2 = 0.07, LRT = 109.7, p = 0.003), however no specific invertebrate genera were associated with the dietary differences detected. The nMDS visualises the patterns of genus level consumption revealed from the manyglm model (Figure 6).