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Avian clutch size should be proportional to breeding season resource productivity per breeding pair of birds. [10] This relationship has been found in a series of studies from Alaska and Costa Rica. [10] According to Ashmole's Hypothesis, the clutch size of resident birds is proportional to the level of competition with migrant birds. [11]
Clutch size variation can also reflect variation in optimal reproduction effort. In birds, clutch size can vary within a species due to various features (age and health of laying female, ability of male to supply food, and abundance of prey), while some species are determinant layers, laying a species-specific number of eggs.
Lack's principle, proposed by the British ornithologist David Lack in 1954, states that "the clutch size of each species of bird has been adapted by natural selection to correspond with the largest number of young for which the parents can, on average, provide enough food". [1]
Clutch size varies with location: Northern Hemisphere birds lay more eggs than those in the Southern Hemisphere, and birds at higher latitudes have larger clutches than those closer to the equator. In central and northern Europe and Asia the clutch size is around 12, whereas it is around four in the tropics and seven in the subtropics.
The clutch size is influenced by latitude, with clutch sizes of northern populations being higher on average than southern populations. [69] The eggs are 20 mm × 14 mm (3 ⁄ 4 in × 1 ⁄ 2 in) in size, and weigh 1.9 grams (29 grains), of which 5% is shell.
A species' average litter size is generally equal to one half of the number of teats and the maximum litter size generally matches the number of teats. Not all species abide by this rule, however.
Clutch size varies with location: Northern Hemisphere birds lay more eggs than those in the Southern Hemisphere, and birds at higher latitudes have larger clutches than those closer to the equator. In central and northern Europe and Asia the clutch size is around 12, whereas it is around four in the tropics and seven in the subtropics.
Clutch size differs greatly between species, sometimes even within the same genus. It may also differ intraspecies due to many factors including habitat, health, nutrition, predation pressures and time of year. [106] Average clutch size ranges from one (as in northern gannet [107]) to about 17 (as in grey partridge [108]). A rooster with a ...