What does "clutches" mean in relation to birds?

What does “clutches” mean in relation to birds?

The term “clutch” refers to the number of eggs a bird lays in each brood. Many birds have more than one brood each year. But the term “clutch” always refers to how many eggs were laid by a single female or breeding pair per brood.

What Is The Average Size Of A Clutch?

The clutch size varies from bird type to bird type for instance;

Bird TypeAverage Clutch Size 
Petrels, Albatross & Shearwaters1 Egg
Auks & Vultures1 to 2 Eggs
Gulls & Terns2 to 3 Eggs
Shorebirds3 to 4 Eggs
Songbirds & Hawks2 to 5 Eggs
Ptarmigan & Grouse5 to 12 Eggs
Ducks7 to 12 Eggs
Partridge & Pheasants8 to 18 Eggs

The size of the clutch is also affected by certain circumstances which is why all of the above are only averages.

What Can Affect The Size Of The Clutch?


There are a number of factors that can affect the amount of eggs laid in each clutch which include;

The Health Of The Female

If the female of the pair isn’t in good health, the number of eggs laid could be reduced. It takes a great deal of energy to produce each egg so her health is of the utmost importance.

The Age Of The Female

The age of the female can also affect the number of eggs per clutch with older birds tending to produce more eggs than younger females.

The Availability Of Food

If there is a good source of constant food, you can expect more eggs per clutch. For instance areas that have a high level of available food in Spring and Summer often support larger clutches than those in colder less food intense areas.

Whereas areas not affected by seasonal variations like tropical rainforests tend to have smaller clutch sizes because the availability of food is relatively constant.

The Size Of The Bird Colony


It has been noted that females tend to lay fewer eggs per clutch when breeding in colonies with a high density of population.

The Average Temperature

Birds tend to lay less eggs during periods of unseasonal cold weather than in warmer conditions.

The Time Of The Season

Clutches laid at the beginning of the breeding season tend to contain more eggs than those laid towards the end of the season.

Proximity Of Nest Predators

If the female is aware of nest predators she is likely to produce fewer eggs per clutch as this makes them less likely to be spotted by predators. A larger clutch would be harder to disguise from any would-be predators.

Type Of Nest

Bird Nest with Eggs

The type of nest the bird uses to lay her eggs also determines the size of the clutch. For instance those birds that use a scrape nest which is just a small depression in the ground, lay less eggs per clutch than birds that nest in enclosed areas like tree stumps etc.

Then there are those birds that invest a lot of time and effort into building their nests like woodpeckers for example. As it takes them such a long time to build a safe and secure nest, they lay more eggs per clutch.


When comparisons have been done within single bird species, it has been noted that egg clutches tend to be smaller when laid in areas of lower or higher latitudes. This is because those areas are subjected to greater seasonal variations in temperature and food supply.


The size of many bird’s clutches are also influenced by the length of daylight. With many birds producing larger clutches during those periods when daylight is at its longest. 

This is because a longer day means more time is available for food gathering which allows more nestlings to survive.

SEE ALSO: Where is the Supercilium?

Frequently Asked Questions

What does “clutches” mean in relation to birds?

The clutch size is the number of eggs laid in a single brood by a nesting pair of birds.

How many birds are in a clutch?

The amount of eggs (potential birds) in a clutch depends on the type of bird as well as many other circumstances. For instance; shearwaters only lay one egg whereas partridges tend to lay 8 to 18 eggs per clutch. Other factors include; the health of the female, the availability of food, the time of the season, the amount of daylight and seasonal variations.

What is the clutch of Magpies?

The average size of a clutch laid by a female magpie is around 5 to 8 eggs but can vary between 2 to 10 eggs if the conditions are right.

How many clutches do blackbirds have?

Blackbirds tend to have 2 or 3 clutches during the breeding season with an average of 3 to 5 eggs per clutch.