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Numerical Data on African Birds' Behaviour at the Nest: Hirundo s. smithii Leach, the Wire-tailed Swallow

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Summary.

The data, from three nests at Amani, are derived from a total of 500 hours of observations made in spells of five hours and upwards. The effect of rain on the parent birds' activity is given in detail; rain much heavier than 1 mm. per hour reduced feeding heavily, except when termites were on the wing.

Brooding of eggs and young was done only by the females; their mates helped to bring food, as a rule slightly less than half the total. Incubation period 14 days; fledging 18–21.

The daily percentage of time the eggs were brooded varied from 43 to 66, with no tendency to rise at lower air-temperatures or towards the end of the incubation periods. Frequency distribution curves are given of the duration of (a) individual spells on the eggs and (b) intervals when the eggs were left uncovered. About 70 per cent, of the spells “on” lasted 2–7 minutes and 70 per cent, of the intervals “off” 2–5 minutes. Few intervals uncovered exceeded 15 minutes and none 37. Corresponding data for the fledging period are tabulated. For the first three days the young in all the nests were brooded much as the eggs had been, but after that the amount of brooding varied greatly between the nests.

After a slow rise, comparatively stable feeding rates were attained at each nest during the last week of fledging. Then the average number of feeds brought in 200 minutes varied between 75 and 97 for two young and between 49 and 65 for one. The latter, which received more meals, had the shorter fledging period. There was no well-marked diurnal rhythm in the feeding activity except that it was usually least in the early morning. The frequency distribution of length of intervals between feeds, which naturally changed with the age of the young, is tabulated. Less than 1 per cent, of the intervals exceeded 30 minutes.

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