BIJLSMA RB (1977) The occurrence and ecology of Anthus spinoletta spinoletta and Anthus spinoletta littoralis in the forelands of the river Rhine near Wageningen. LIMOSA 50 (3): 127-136.

This paper deals with (a) the occurrence of Anthus spino/etta spino/etta and A.s. littoralis in the forelands of the river Rhine near Wageningen in the period 1 September 1975-20 May 1976 and (b) the occupation of feeding areas and roosts by both subspecies. The greater part of the forelands is characterized by the vegetationtype Arrhenaterion, but the most important areas can be described as Phragmition + Magnocaricion (Fig. 1). A.s. spino/etta was recorded in the period 11 September-13 May (n=2197). Three peaks of occurence can be seen from Fig. 2. The first refers to the fall migration (end-October), the last to the spring migration (midMarch). The midwinterpeak was considered to be the result ofthe beginning of a severe frost period. The first moulting birds were seen in mid-March. The pre-nuptial moult was finished in mid-April, by which time all remaining birds were in full summer plumage. Throughout the spring the birds showed a kind of display in which the birds approached each other with drooping wings and throat-showing. A.s. littoralis had a synchronous occurrence, but differed from A.s. spino/etta by the absence of a spring peak (n = 835). The few observations on the feeding areas produced the following results (Table 2). Firstly, approximately half of allA.s. spino/etta and A.s. littoralis did not feed in the forelands. Secondly, A.s. spino/etta seemed to prefer the wet marshes to feed on, whereas A.s. littoralis was found mainly alongside the banks of the river Rhine on the groynes. This segregation in habitat-use was nearly complete. In the situation of overlap, A.s. spino/etta preferred the wetter parts and probably took different food with a different feeding behaviour. In fact, the situation at the roosts (Table 3) was the same as on the feeding areas. A.s. spino/etta preferred the marshes and A.s. littoralis the groynes of the Rhine. In very few cases co-occupation of the same marsh occurred, by which A.s. spino/etta remained solely on the wet parts and A.s. littora/is on the dry. It is suggested, that co-occupation of the same habitat was possible without competition by means of a different use of the habitat. In cases of overlap (as well as on the feeding areas as at the roosts) A.s. spino/etta avoided competition by making use of the wet parts and A.s. littoralis of the dry. This tactic of ecological isolation is called coexistence mechanisms. Rock Pipit Anthus petrosus = Anthus spinoletta littoralis Water Pipit Anthus spinoletta

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