Discrimination between grass species and nitrogen-fertilized vegetation by young Barnacle Geese
An experiment is described which tested the ability of young Barnacle Geese Branta leucopsis to discriminate between grass species and between trays of a single species treated with different levels of Nitrogen fertilizer. The geese showed significant preferences for perennial ryegrass Lolium perenne and red fescue Festuca rubra against bent Agrostis tenuis and meadow grass Poa pratensis, and they significantly preferred fertilized to unfertilized Lolium, although they did not select either species or fertilized trays visually. The preferences were correlated with both the water and nitrogen content of the vegetation, and these were themselves positively correlated. Water content seemed to relate better to the preferences shown than did protein content. It is suggested that geese would ingest more protein by selecting leaves on the basis of their water rather than their protein content. This was because water content was not only correlated with protein content but with the ease with which vegetation was broken up in the gizzard, which in itself controls the availability of nutrients to the bird. Although not conclusive the results of this experiment were consistent with the hypothesis put forward earlier that geese select grass leaves and species on the basis of their mechanical not their visual properties.
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