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Indexed under : Life Sciences / Zoology

Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

Avian clutch sizes and latitude

Avian clutch size - the average number of eggs found in a particular (or comparable) bird species nest - often correlates with latitude.

The effect was discovered in the 1940s, and has been extensively researched since then. In general, comparable bird species near the equator lay approximately half as many eggs as those in northern temperate habitats.

There are at least seven theories - including :

  • The 'Food Limitation Hypothesis'
  • The 'Nest Predation Hypothesis'
  • 'Skutch’s Hypothesis'
  • 'Ashmole’s Hypothesis'
  • 'Environmental seasonality'
  • 'Day length'
  • The 'Egg-viability hypothesis'.

See: Wikipedia for details.

To date, none of the theories has sufficient supporting field-evidence to be accepted as a definitive explanation.


Also see :Tropical coloufulnessplugin-autotooltip__plain plugin-autotooltip_bigTropical coloufulness

As far back as the 19th century, biologists pointed out an apparent anomaly in the extra 'colourfulness' of birds and insects in tropical regions.

The reasons for the differences remain unproven, but Alfred Wallace and others suggested that they …


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