January 25 2017
Birds are the members of class Aves. They are the homeothermic organisms that imply they can regulate the inner temperature. Birds lay eggs, are toothless and have the four-chamber heart. Almost all the bird’s species are capable of flight whereas some species of bird cannot fly.
It was commonly believed that the ancestors of the birds are the Archaeopteryx. The Archaeopteryx was the primitive dinosaurs capable of flight and was believed to be carnivorous. Recently, studies are suggesting the ancestors of the birds be omnivorous (1).
Clutch size refers to the number of eggs laid by the birds in the nest during the reproductive season. There are various factors governing the clutch size and intensive research has been done in determine the precise mechanism that governs the clutch size of the birds. David Lack an ornithologist did an intensive study on the clutch size in relation to latitude (2).
None of the hypothesis can precisely predict the mechanism that governs the clutch size. Every hypothesis has the flaws and needs to be refined.
1. Food limitation
David lack the world renounced ornithologist found that the clutch size increase with the increase in the Latitude. Due to the longer time for the storage in food in colder climate food availability increases, therefore, increases the clutch size. Although some birds species do not show the increase in clutch size while increasing the latitude.
2. Nest predator’s hypothesis
This hypothesis states that the Predator is higher in the tropical area and low in temperate place. Small clutch size is not easily noticed by the predators thus increases the survival of offspring.
3. Photoperiodism
Availability of the daylight is vital to governing the clutch size. This is based on the assumption that diurnal bird can invest more time in foraging food to feed the offspring. Able to feed the offspring increase the survival.
4. Ashmole’s hypothesis
This is the interesting hypothesis on the clutch size. It predicts that the clutch size depends on the resource availability in the breeding season. Assuming every other thing to be normal. The clutch size decreases when the resource is abundant in the non-breeding season.
5. Environmental sustainability
This hypothesis emphasises the larger clutch size in harsh condition is due to the high mortality rate of the parents during harsh condition. It is mainly due to lack of food resource during the adverse climatic condition. The larger clutch size in the colder place is the compensation of the loss that occurs during harsh condition.
Image source:
https://pixabay.com/en/bird-baby-nest-hungry-oriole-1969650
https://pixabay.com/en/bird-blackbird-nest-hatching-boy-793914
References:
1. Luiggi, Christina (July 2011). "On the Origin of Birds". The Scientist. Retrieved on 20 January 2017.
2. Bell, C. (1996). "The relationship between geographic variation in clutch size and migration pattern in the Yellow Wagtail". Bird Study. 43: 345–345.
