Effects on Habitat Integrity

Effects on Use by Predators

Increased recreational use of intertidal areas has several consequences although these may be minor for intertidal sand and mudflats. Greatest visitor pressure occurs on recreational beaches, for example the impact of beach cleaning which removes organic inputs and affects the cohesiveness of sediment (Pearce, 1998).

Human disturbance changes bird behaviour in accessible areas such as intertidal sand and mudflats (Smit & Visser, 1993). Disturbances to waterfowl in estuaries and nearshore areas includes movements by people, dogs and horses, helicopters and light aircraft, and from water sports such as windsurfing, sand yachting and boating. The intensity of disturbance is related to the species of bird and the speed and duration of the stressor and the direction in relation to bird flocks (Smit & Visser, 1993). For example, aircraft cause widespread and long lasting disturbance and, on tidal flats, moving people and dogs generally create greater disturbance than stationary ones. Furthermore, the impact of human disturbance requires to be assessed in relation to other activities such as land-claim. Industrial and urban development may restrict the adjacent areas suitable receiving displaced birds.

The impact of disturbance has been quantified although this differs according to species, type and scale. For example, for some shy species such as the curlew as few as twenty evenly distributed people could prevent birds from feeding on over 1,000 ha of estuary, an area of tidal flats equivalent to estuaries such as Hamford Water or Southampton Water (Goss-Custard & Verboven, 1993).

Even the same species of bird can react in different ways at different times and at different areas - for example, sometimes by habituating to repeated disturbance and at others becoming increasingly nervous. Species such as the brent goose, redshank, bar-tailed godwit and curlew are more ‘nervous’ than others such as oystercatcher, turnstone and dunlin. One person on a tidal flat can create a large disturbance in which birds stop feeding or fly off, affecting approximately 5 ha for gulls and 13 ha for dunlin up to 50 ha for curlew (Smit & Visser, 1993). In some cases, for example wigeon on parts of the Exe Estuary, a single disturbance incident at the wrong time can deter birds from feeding until the next tidal cycle (Fox et al, 1993).

Disturbance will cause birds to fly away and in response they could either (i) increase their energy intake at their present (disturbed) feeding sites when undisturbed, or ii) move to an alternative feeding site. Such a response will affect energy budgets and thus survival, with particular consequences for overwintering wading birds (Davidson & Rothwell, 1993). There may be little overlap of use by overwintering birds as recreational activities occur mainly in the summer and early autumn. However, in late summer/early autumn, (and sometimes spring) when most recreational activities take place, intensity of use is greatest, and waterfowl are more vulnerable. This period coincides with the latter part of the breeding period for some species and the arrival and moulting of the more northerly breeding populations.

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