. Ecological and behavioural evidence for the systematic status of New Zealand oystercatchers : (Charadriiformes: Haematopodidae) . Fig. _jâ¢Iâ 1â Iâ I 4 3 2 1 LW 12 3 4 TIME BEFORE AND AFTER LOW WATER IN HOURS 3. Comparative feeding rates of mainland New Zealand oystercatchers at Jackson Bay. 1. Pied and intermediate phase H. unicolor: 2. H. ostralegiis finschi; 3. Black phase H. unicolor. demonstrated some factors other than external surface area that operate in determining heat loss. Thus Kendeigh (op. cit.) formulated an equation for calculating the existence energy (energy metabolized to
. Ecological and behavioural evidence for the systematic status of New Zealand oystercatchers : (Charadriiformes: Haematopodidae) . Fig. _jâ¢Iâ 1â Iâ I 4 3 2 1 LW 12 3 4 TIME BEFORE AND AFTER LOW WATER IN HOURS 3. Comparative feeding rates of mainland New Zealand oystercatchers at Jackson Bay. 1. Pied and intermediate phase H. unicolor: 2. H. ostralegiis finschi; 3. Black phase H. unicolor. demonstrated some factors other than external surface area that operate in determining heat loss. Thus Kendeigh (op. cit.) formulated an equation for calculating the existence energy (energy metabolized to maintain constant weight in captive conditions) directly from body weight in non-passerine species at 30°C, as follows: M = WO'^'545 or log M = + log W where M =- existence metabolism in Kcal/Bird-day and W = body weight in grams. Taking the mean weights of South Island Pied and Variable Oyster- catchers as 568 g and 692 g respectively (sexes combined, winter adults) = Kcal/Bird-day ^Variable = Kcal/Bird-day The larger Variable Oystercatcher therefore needs to ingest more food to maintain existence energy than does its smaller South Island congener. Since both species took similar amounts of food at Jackson Bay, it is apparent that H. unicolor is at a considerable competitive disadvantage to H. o. finschi in habitats with soft substrates, especially where food resources are limited. When feeding on rocky substrates at Kaikoura Peninsula in July 1967, Variable Oystercatchers ate an average of g dry weight of limpets per day, which was equivalent to of their body weight (N = 46 observations). Since the calorific values of limpets and tua-tuas are similar ( and Kcals/g respectively). Variable Oystercatchers feeding on 15
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