Farmland bird diets

ChiffchaffThe populations of farmland birds have declined sharply in recent decades as a consequence of agricultural intensification. In 2005, a new agri-environment scheme (Environmental Stewardship) was introduced and one of the aims was to reverse the declines in farmland wildlife that includes farmland birds.

Many of the options within the different schemes are targeted at farmland birds and aim to create appropriate foraging, breeding or overwintering habitat. Some are designed to specifically provide food resources. These include the wild bird cover option in which plants are cultivated to produce copious amounts seed over the winter and Conservation Headlands in which invertebrate rich cover is generated at the edge of cereal fields.

Autoecological studies have helped to identify the causes behind the decline of some farmland bird species, such as those conducted on grey partridge, corn bunting and yellowhammer. These revealed a strong relationship between invertebrate food availability during breeding and breeding success and this was consequently linked to population change.

The majority of other farmland birds also feed their chicks invertebrates because they provide the necessary protein for growth and the energy to resist chilling. Supplies of food overwinter and prior to breeding may also be a factor contributing to population declines. The decline of farmland birds that feed on seeds in winter has been much greater (39%) than for other farmland birds (26%) that occur predominantly on farmland.

In order to help develop better foraging habitats for farmland birds, we conducted a review in which we identified and compared their key dietary components. The reviewed the scientific literature for 22 farmland bird species and determined the relative value of different weed and crop seeds and invertebrates in their diet. The importance of the plant and invertebrate taxa was also ranked based upon the number of bird species for which they are important. Each of these was conducted for adults in the breeding and non-breeding season and for their young.

The most important plant families overall were Poaceae, Polygonaceae, Caryophyllaceae, Cruciferae, Compositae, Chenopodiaceae and Labiatae, although the latter two were unimportant for chicks (Table 1). At lower taxonomic levels for adults in the breeding season Stellaria, especially S. media (chickweed) and Polygonum spp., especially P. aviculare (knotgrass) and P.  persicaria (redshank). In addition, highly ranked taxa for non-breeding adults were Chenopodium album (fat hen) and Poa spp. (meadow grasses), while for chicks they included Sinapsis (e.g. charlock) and Poa.

Similarities in dietary preferences were observed among Fringillidae (finches) and members of the Columbidae (doves and pigeons). Fringillidae and Carduelis cannabina (linnet) were associated with plants which occur in semi-natural habitats, while Emberiza citrinella (yellowhammer), Phasianidae (partridges), Columbidae were shown to be more closely associated with agricultural environments.

Table 1: Rankings of weeds

Rank Adults - breeding season No spp. Adults non-breeding No spp. Nestlings No spp.
1 Caryophyllaceae 9 Polygonaceae 11 Poaceae 5
2 Polygonaceae 7 Poaceae 9 Cruciferae 4
3 Poaceae 6 Chenopodiceae 7 Caryophyllaceae 3
4 Cruciferae 5 Cruciferae 7 Polygonaceae 3
5 Asteraceae 4 Amaranthaceae 4 Violaceae 2
6 Chenopodiceae 2 Caryophyllaceae 4 Asteraceae 2
7 Lamiceae 2 Fabaceae 4 Euphorbiaceae 2
8 Rosaceae 2 Asteraceae 4 Ulmaceae 2
9 Fabaceae 2 Rosaceae 3 Fumariaceae 1
10 Boraginaceae 1 Lamiceae 2 Ranunculaceae 1

 

The most important invertebrate Orders overall were Coleoptera adults, Hemiptera adults, Arachnida, Lepidoptera larvae/pupae, Diptera adults, Lepidoptera adults, Diptera larvae/pupae, and Hymenoptera adults (Table 2).

However, Lepidoptera adults, Hymenoptera adults, and Arachnida were not important food items during the non-breeding season, when a smaller number of invertebrate taxa were important (only 11 taxa, c.f. up to 28 taxa in the breeding season). For adults in the breeding season there were ten families of invertebrate that were important for four or more bird species (Aphididae, Carabidae, Curculionidae, Elateridae, Formicidae, Scarabeidae and Tipulidae).

For chick the following families were important: Aphididae, Carabidae, Chrysomelidae, Curculionidae, Formicidae, Staphylinidae, Tenthredinidae, and Tipulidae. In the non-breeding season, Curculionidae and Lumbricidae were important in the diet of three species. A few species showed some strong preferences for particular invertebrates. Similarities in dietary composition were observed among closely related bird species, while that of chick and adults sometimes differed.

The most important invertebrate Orders overall were Coleoptera adults, Hemiptera adults, Arachnida, Lepidoptera larvae/pupae, Diptera adults, Lepidoptera adults, Diptera larvae/pupae, and Hymenoptera adults (Table 2).

However, Lepidoptera adults, Hymenoptera adults, and Arachnida were not important food items during the non-breeding season, when a smaller number of invertebrate taxa were important (only 11 taxa, c.f. up to 28 taxa in the breeding season). For adults in the breeding season there were ten families of invertebrate that were important for four or more bird species (Aphididae, Carabidae, Curculionidae, Elateridae, Formicidae, Scarabeidae and Tipulidae).

For chick the following families were important: Aphididae, Carabidae, Chrysomelidae, Curculionidae, Formicidae, Staphylinidae, Tenthredinidae, and Tipulidae. In the non-breeding season, Curculionidae and Lumbricidae were important in the diet of three species. A few species showed some strong preferences for particular invertebrates. Similarities in dietary composition were observed among closely related bird species, while that of chick and adults sometimes differed.

Table 2: Rankings of invertebrates

  Adults breeding   Adults non-breeding   Nestlings
Rank Order - stage eaten No spp. Order - stage eaten No spp. Order - stage eaten No spp.
1 Coleoptera - A 9 Coleoptera - A 4 Diptera - A 14
2 Hemiptera - A 6 Hemiptera - A 2 Coleoptera - A 14
3 Lepidoptera - L/P 6 Lepidoptera - L/P 2 Araneae/Opilliones 11
4 Diptera - A 5 Lumbricidae 2 Lepidoptera - L/P 10
5 Lepidoptera - A 5 Coleoptera - L/P 2 Hemiptera - A 9
6 Araneae/Opilliones 5 Diptera - L/P 2 Lepidoptera - A 7
7 Hymenoptera1 - A 5 Diptera - A 1 Diptera - L/P 7
8 Diptera - L/P 3 Symphyta - L 1 Hymenoptera1 6
9 Lumbricidae 2 Hymenoptera1 - P 1 Orthoptera 5
10 Coleoptera - L/P 2 Orthoptera 1 Symphyta - L 5

 

Click here to download a PDF of chick food favourites.

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