Effects of changes of land use on some animal populations

Abstract

Two examples are considered: (1) The effects-of organotin agricultural fungicides on soil Acarina; (2) The effects of reclamation of intertidal land on overwintering shorebirds at Seal Sands, Teesmouth, The effect of triphenyltin acetate and triphenyltin hydroxide was examined by field experiments and the results are discussed in relation to the dose level, regime and season of treatment. Numbers of soil Acarina were reduced by both clianicals when applied in autumn at recctmended doses. The Mesostigmata and an abundant Prostigmatid, Ttarsonemus floricolus. were particularly affected and the magnitude of reductions was related to the quantity of chemical applied. Not all species of mites were affected and treatment of half the recommended dose resulted in an increase in seme families, of Prostigmata, Seasonal changes in the abundance of mites are described and compared with the results of studies elsewhere in Britain, Suitable laboratory culturing techniques were devised for small Prostigmatid mites. Reclamation of Seal Sands between 1972-74 resulted in a loss of feeding area and reduced feeding time. The effects of reclamation are considered in relation to the overwintering numbers of five waders: Grey Plover (Pluvialis squatarola), Curlew (Numenius arauata). Godwit (Limosa lapponica). Redshank (Trinqa tetanus) and Dunlin (Calidris alpina) and to the Shelduck (Tadorna tadorna). Monthly counts of each species are described and compared with counts in previous winters. Changes in numbers are discussed in relation to progressive reclamation. The relative importance of the reduction in feeding area and feeding time in determining the overwintering numbers after reclamation is considered by examination of: (a) the time spent feeding, and (b) the foraging behaviour and diet. The waders overwintered in lower numbers than previously but Shelduck numbers were unchanged. To satisfy their food requirements. Grey Plovers adapted by feeding at night while the other waders fed on adjacent fields in mid-winter. Shorebirds did not change their diet or foraging behaviour. Reduction in numbers was related to the reduced feeding area and food resources available, but for Dunlins loss in feeding tine was more important.