The kiwi is a unique and fascinating bird native to New Zealand. When a female kiwi is ready to lay an egg, an intricate process begins that sets the kiwi apart from other birds. Kiwis go through physiological and behavioral changes leading up to egg laying, followed by the egg development and brooding process.
When does a female kiwi lay eggs?
Kiwis are seasonal breeders, meaning they only lay eggs at certain times of the year. The breeding season for most kiwi species is between June and March. Some key things happen leading up to the breeding season for a female kiwi:
- In April or May, the female kiwi’s ovaries start to enlarge with egg yolks as she prepares for breeding season.
- Egg white starts being added to the yolks around June or July.
- By August, the female’s ovaries can weigh up to 1/3 of her total body weight.
- Egg laying starts in late June and goes through March, with most eggs laid between August and January.
Kiwi eggs develop very quickly before being laid – the egg white and shell are added just 24-48 hours before the egg is laid. The speed of this development is unique amongst birds.
How often do kiwis lay eggs?
Female kiwis generally lay 1-2 eggs per breeding season. The eggs are laid every 1-3 days. Because the egg development happens so quickly, almost immediately after laying an egg the female kiwi will develop another egg for laying.
Some key facts about kiwi egg laying frequency:
- North Island brown kiwi females lay about 2 eggs per season
- Great spotted kiwi females lay 1 egg per season
- Little spotted kiwi females lay 1 egg every 2-3 seasons
- Rowi kiwi females lay only 1 egg every 3-4 years
So egg laying frequency depends on the species, with larger kiwi species tending to lay more often than smaller species. The egg laying process puts significant physiological strain on the female’s body, so smaller kiwis are not able to lay as often.
Where do kiwis lay their eggs?
Kiwis are unique in that they lay their eggs directly into underground nests. The nests are dug into soil, under tree roots, or into hollow fallen logs. Kiwi pairs often return to and maintain the same nest sites year after year.
Key facts about kiwi nest sites:
- Nests are dug by both the female and male kiwi using their long claws and strong legs.
- Nest depth can range from 10 cm to over 1 meter deep.
- Nest size ranges from 15 cm wide by 30 cm long for smaller kiwi, to over 1 meter wide and long for larger kiwi species.
- Nests are usually well-hidden in vegetation or other cover for protection.
The most common nest sites are in forest areas with soft soil or rotted logs that the kiwis can easily excavate. Using underground nests helps conceal and protect the eggs.
What is the egg laying process?
When the female kiwi is ready to lay an egg, the process takes place deep inside the underground nest. Here are the steps:
- Up to 20 hours before laying, the female starts contracting muscles to position the egg. This may cause her to grimace and squeal.
- In the final hours before laying, the female kiwi puffs up her feathers, trembles, and may emit loud grumbling noises.
- During the actual egg laying the female will strain while standing over the nest. This can take over 10 minutes for large eggs.
- The egg emerges blunt end first. The female sometimes assists by rolling the egg along with her beak.
- Once laid, the egg sits blunt end up. The female then covers the egg with nest material.
The egg laying process takes a physical toll on the female and requires intake of extra calcium. Females lose significant weight after laying eggs – some species losing over 20% of their body weight.
How are kiwi eggs unique?
Kiwi eggs have several unique properties that set them apart from other bird eggs:
- Kiwi eggs are very large relative to the size of the bird. For example, the little spotted kiwi is about the size of a bantam chicken, but lays an egg that is about 15% of its own body weight – proportionally one of the largest eggs of any bird.
- The eggs are elliptical or pear-shaped rather than oval. They have a very thick and strong shell.
- Kiwi eggs have a relatively small yolk compared to overall egg size. The yolk provides nutrition for the chick.
- They contain very large amounts of albumen (egg white) which provides hydration. Kiwi chicks hatch fully hydrated and can survive without water for the first several days.
- The albumen makes up over 60% of the total egg volume.
The giant size and unique shape of kiwi eggs is likely an adaptation to provide maximum nutrition and hydration needed for the chick to survive once hatched.
Kiwi egg size comparison
Here is a table comparing different kiwi species and the size of their eggs:
Kiwi species | Female weight | Egg size | Egg weight relative to female |
---|---|---|---|
Little spotted kiwi | 1.3 kg | 15 x 30 cm | 15% |
Rowi kiwi | 3.2 kg | 20 x 45 cm | 25% |
Great spotted kiwi | 3.3 kg | 17 x 45 cm | 20% |
North Island brown kiwi | 2.8 kg | 17 x 30 cm | 12% |
This helps illustrate the large size of kiwi eggs compared to the weight of the female bird that lays them.
How do kiwis incubate and raise their chicks?
Kiwis have an unusual breeding system where it is the male who incubates the eggs and raises the chicks. This is different than most bird species where females do the majority of nesting duties. Here is what happens after the female kiwi lays an egg:
- The male kiwi takes over the egg incubating duties, only leaving the nest for short periods to feed.
- Incubation takes around 75-85 days. The male turns the egg regularly to ensure even warmth.
- When the chick hatches, it digs its way out of the egg and nest. The male kiwi then guides the chick above ground.
- For the first 2-3 weeks, the male protects and broods the chick while teaching it how to find food.
- The chick remains with the male for around 5-10 months until it can survive independently.
This breeding system allows the female kiwi to conserve resources after egg laying and quickly develop new eggs. The male takes over parenting duties and provides long-term care to raise the chick.
Kiwi chick growth and development
Kiwi chicks grow and develop rapidly under the male’s care. Here is an overview of kiwi chick growth:
Age | Development milestones |
---|---|
1 week | Chick weight doubles |
3 weeks | Eyes fully open, starts exploring outside nest |
1 month | Nearly full size, starts trying solid food |
2 months | Able to probe soil and find insects/worms |
5 months | Fully weaned off male, forages independently |
With the male kiwi’s constant brooding and protection, kiwi chicks grow rapidly and gain independence several months after hatching.
Threats kiwi eggs face
Kiwi eggs and chicks are vulnerable to many predators introduced to New Zealand. Some key threats include:
- Stoats – Carnivorous mustelids that kill and eat adult kiwi, eggs, and chicks.
- Possums – Omnivores that raid nests and eat eggs.
- Feral cats – Skilled kiwi nest hunters that consume eggs.
- Dogs – Roaming and uncontrolled dogs sometimes find and dig up nests.
Other hazards like floods or landslides can also destroy eggs and nest sites. Conservation programs monitor and protect wild kiwi nests from threats to increase egg and chick survival rates.
Kiwi egg incubation in captivity
Many kiwi conservation programs include captive incubation of eggs collected from the wild. Reasons for this include:
- Removing eggs from risk of predators in the wild
- Carefully controlling incubation temperature and humidity
- Boosting overall kiwi chick survival rates
- Monitoring chick health and development
Captive incubation provides optimum conditions for fragile kiwi eggs. The chicks can be reared in a predator-proof environment until ready for release back into the wild population.
Conclusion
The kiwi’s egg laying and breeding process is unique among birds. Their large eggs, underground nests, and reversed parental roles allow kiwi to successfully raise chicks against the odds in New Zealand’s environment. While threats remain, active conservation efforts centered on meticulous egg incubation and predator control continue to boost wild kiwi numbers and demonstrate the success of science-based species management.