Foraging in a landscape mosaic : diet selection and performance of free-ranging cattle in heathland and riverine grassland

This thesis focuses on two main questions regarding the relation between a large herbivore, Bos taurus, and habitat quality: a) how do differences in habitat quality relate to nutrition and herbivore performance? and b) is herbivore foraging behaviour affected by habitat differences and can it be explained by optimal foraging theory? The study was carried out in the Netherlands using free- ranging steers in an experimental set-up with four combinations of two habitats of contrasting soil fertility: heathland and riverine grassland.

A hand-plucking method was developed to estimate forage quality and intake; calibration was carried out using oesophageally fistulated steers. Cattle performance was significantly affected by habitat quality. On heathland animals showed relatively low weight gains and slow fat accumulation coupled to high weight loss over winter. These impairments were caused by deficiencies in sodium and phosphorus which led to a reduced energy retention, bone resorption and pica behaviour. Animals on riverine grassland demonstrated a performance close to their growth potential. The treatments with combinations of habitats emphasized these differences.

Foraging selectivity increased with differences in forage quality and quantity and with spatial scale. Selectivity between short, tall and stemmy patches within two grassland communities was low but significant. Short and tall patches were preferred over stemmy patches. The preference for short patches was consistent with a daily intake maximization of digestible organic matter but not in agreement with instantaneous maximization. It is suggested that cognitive limitations reduce selectivity of cattle at lower spatial scales. At a higher scale level selection between landscape types was distinct and broadly agreed with model predictions assuming daily maximization for the intake of digestible organic matter, sodium and phosphorus.

Implications of the relation between habitat quality and herbivore performance are discussed with regard to nature conservation. Breed differences in cattle are of little consequence in mild climates. Fragmentation and uniformity of habitats are of much greater importance. It is argued that the habitat requirements of large herbivores should be used to develop guidelines for basic conditions to the design of nature reserves. Experiments using free-ranging domestic herbivores can elucidate these habitat requirements.