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New Ways of Measuring the Incubation Period of Birds

1963; Oxford University Press; Volume: 80; Issue: 4 Linguagem: Inglês

10.2307/4082850

1938-4254

S. Charles Kendeigh,

Ecology and Vegetation Dynamics Studies

As pointed out by Swanberg (1950) and Nice (1954) there has in the past been considerable confusion concerning the proper way to measure the length of the incubation period of birds. Of concern here is not the entire length of time that the adult sits on a clutch of eggs, but the minimum length of time required to bring an average, newly laid egg to hatching under normal nest conditions. For practical purposes it is now generally agreed that the incubation period should be considered the time from the laying of the last egg to the hatching of the last young when all eggs in the clutch hatch. The confusion lies in the fact that the first eggs of a clutch may receive some heat and undergo a certain amount of development before the clutch is completed or full incubation begins. The eggs tend as a consequence to hatch in the order laid, but the intervals between hatching of the eggs is shorter than the intervals between their laying so that the time that elapses between laying of an egg and its hatching progressively decreases with each additional egg in the clutch. In those species, relatively few in number, where full incubation begins with the first egg laid, the intervals between hatching are more nearly equivalent to the intervals between their laying. Even when the adult bird is observed sitting on the eggs frequently, or for long periods of time, in the egg-laying period, this does not necessarily mean that the eggs are being subjected to full incubation heat (Swanberg, 1950). This depends on the stage of development of the brood patch which is being formed at this time (Bailey, 1952). Activity records on the adult bird and thermocouples placed in the nest show that in the House Wren, Troglodytes aedon, the species here under consideration, full incubation behavior and temperature are not fully established until about the time that the last egg of the clutch is laid (Kendeigh, 1952). The present study is concerned with the total heat applied to the eggs, as a measure of incubation time, and with the proportional amount of heat applied during the egg-laying, incubating, and hatching periods. The original data were secured between 1934 and 1936 at the Baldwin Bird Research Laboratory, near Cleveland, Ohio. The present analysis was supported by a grant from the National Science Foundation.