Birds of lowland arable farmland: The importance and identification of invertebrate diversity in the diet of chicks.

Abstract

Farmland birds, as the name implies, have evolved to co-exist with agriculture, relying on the farmland habitat to provide food and nesting sites. Within the last few decades, however, farming practices and advances in mechanisation have started to alter radically the balance that had evolved between birds and man's use of the land. Between 1970 and 1990, 86% of the 28 species classified as farmland birds (Gibbons et al., 1993; Fuller et al., 1995) have declined, and of the 40 listed by Campbell et al. (1997), 78% have reduced breeding areas. Reduced food availability may be the major reason for many of these declines, with insects being a vital component in the chick diet of most species of farmland bird, as well as being important in the adult diet (Table 2.1). Adults can alter their feeding behaviour in response to changes in food availability, e.g. due to changes in cropping practices, and movement between suitable feeding areas usually posing no significant problems (O'Connor & Shrubb, 1986). However, when they have young to feed, any changes that affect the availability of food for the chicks can become critical (Potts, 1986). A good supply of insects in the diet is often vital for good chick survival, with research over 60 years ago highlighting the need for insect food (Ford et aI., 1938). Insects provide a high and easily assimilated source of protein, and are essential to chicks and nestlings as these lack the necessary gut flora for breaking down cellulose, are not able to utilise high fibre roughage as an energy source, and require ready formed amino acids. Protein is also important for muscle development and feather growth, which are important for the early development of flying ability, which is essential for anti-predator avoidance (Potts, 1986). Insects can contain four times as much protein as plant food, with the protein digestibility being 70-90% compared to that of 20-80% in plant foods (Savory, 1989). Even the young of many vegetarian birds are known to require a good proportion of animal protein in their diet (Newton, 1967).