Most birds sense when their clutch is complete via tactile stimulation of their brood patch, the featherless area on their bellies that warms the eggs. But there is evidence that some species count their eggs by sight.
American coots (pictured above), for example, are rather good at spotting (and removing) eggs left sneakily in their nests by neighbours during the laying period. If the parasitic egg is a very close match to their own, however, not only do they fail to spot it, but they apparently lay one less egg, suggesting that they are deciding how many eggs to lay based on the total number in the nest.
The theory is controversial, though – its possible that the parasitic eggs are added once the laying period is drawing to a close.
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How Do Birds Lay Eggs?
Female birds ovulate (small swellings that burst) on a regular basis from their ovaries, just like women do. They do this independently of males. Female birds do not menstruate, although ovulation causes women to do so. As an alternative, their ova, also known as ovulated follicles, pass through their bodies and emerge as the well-known hard-shelled eggs.
Although wild female birds ovulate year-round, they typically increase their reproductive activity in response to environmental cues, such as longer days and warmer temperatures in the spring, in order to get ready to lay eggs and raise young. Because they are typically not exposed to these variations in light and temperature, pet birds living in our homes may ovulate and lay eggs year-round.
For example, American coots (shown above) are quite adept at identifying (and removing) eggs that their neighbors covertly deposit in their nests during the laying season. However, if the parasitic egg closely resembles their own, they not only don’t recognize it but also appear to lay one fewer egg, indicating that they are choosing how many eggs to lay in accordance with the total number within the nest.
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It’s possible that the parasitic eggs are added as the laying period is coming to an end, although this theory is debatable.
The featherless area on their bellies that warms the eggs is called the brood patch, and most birds use tactile stimulation to determine when their clutch is complete. However, there is proof that some species use sight to count their eggs.
How Does an Egg Develop?
As embryos, birds have two ovaries. With the exception of certain raptor species and Australia’s brown kiwi, most birds regress their right ovary as they mature, leaving only their left ovary to develop.
The developing follicle on the surface of the ovary ruptures to release the egg, or ovum, which then enters the funnel-shaped end of the oviduct, which resembles a woman’s fallopian tube. This tiny bundle of cells travels down the oviduct with a coating of yolk around it, which, should the egg be fertilized, serves as the “food” source for the growing embryo. After that, the membranes inside the egg, the shell, and another layer of albumen, or “white,” are applied to the ovum inside the yolk.
The hard shell, which is the last to be added while the egg is still in the uterus and right before it exits the bird’s body through the cloaca, contains calcium and other minerals. This common chamber of the cloaca is where the reproductive tract, urogenital (reproductive and urinary) tract, and gastrointestinal tract empty.
Through the vent opening, birds transfer their eggs from inside their cloacas to the exterior of their bodies. This is also the exit point for both urine and stool (the white, solid, chalky part of the urine and the clear liquid urine).
For the egg to properly deflate and not become stuck, its pointed end needs to be facing the vent. In the event that it is not, or if the egg is large, birds may experience difficulties laying, become “egg-bound,” and need veterinary assistance in order to lay the egg.
The majority of parrots require up to two days for the egg to exit the ovary, travel through the oviduct, and exit the vent. Therefore, female parrots can typically lay an egg every other day!
FAQ
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