Loons are waterbirds that belong to the genus Gavia. There are five living species of loons, all of which breed in North America, Europe, and Asia. Loons build their nests close to the water’s edge and typically have two eggs per clutch. The number of offspring loons produce each year depends on several factors.
How many eggs do loons lay?
Most loon species lay two eggs per clutch. The eggs are olive to brownish in color with dark brown or black spots. Some key facts about loon eggs:
- Clutch size is typically two eggs
- Larger loons tend to lay larger eggs
- Egg laying usually happens in May or June
- Eggs hatch after an incubation period of 24-30 days
While two egg clutches are the norm, there are some exceptions. Some common loon pairs have been observed raising just one chick. In rare cases, loons may lay three or even four eggs per clutch, particularly if environmental conditions are favorable or if the previous nesting attempt failed.
How many chicks do loons fledge?
While loons lay two eggs per clutch, they do not always successfully raise two chicks. Here are some key factors that influence how many chicks a loon pair will fledge each season:
- Infertile eggs – Around 13% of loon eggs fail to hatch due to infertility.
- Predators – Eggs and chicks are vulnerable to predators like foxes, raccoons, gulls, and eagles.
- Food availability – Loon parents may struggle to find enough fish to feed multiple chicks.
- Weather – Severe storms, flooding, or cold temperatures can kill chicks.
- Sibling rivalry – The older, larger chick may kill or outcompete the younger chick.
As a result of these challenges, most loon pairs are only able to fledge one chick per breeding season. Some studies have estimated the average number of chicks fledged per breeding pair is around 0.8 to 1.1 per year.
How many times do loons breed per year?
Loons are single brooded, which means they only attempt to breed once per year. If the first clutch or brood is lost, loons do not re-nest that same season. They may try to breed again the following year. Here are some reasons loons only breed once a year:
- High energy cost of incubating eggs and raising chicks
- Need to migrate long distances to wintering grounds
- Time and energy required to prepare nest and court mate each spring
- Short suitable breeding season at northern latitudes
Attempting a second clutch would be difficult for loons given these high costs and time constraints. Their breeding strategy favors devoting all their resources to successfully fledging one or two chicks each season.
How many years do loons live and breed?
Loons are relatively long-lived waterbirds. Their typical lifespan and breeding period is:
- Average lifespan in the wild: 10 to 15 years
- Age of first breeding attempt: 2 to 7 years old
- May breed every year after initial breeding season
- 10 or more breeding seasons in a lifetime is common
The typical loon lifespan allows for many breeding attempts and dozens of hatched chicks over the course of a loon pair’s lifetime. The oldest known common loon in the wild was at least 25 years old.
Total offspring over a loon’s lifetime
Combining these pieces of information, we can estimate the potential offspring a loon pair can produce over their breeding lifespan:
- Loons breed once per year
- Each clutch contains 2 eggs on average
- Around 1 chick per clutch survives to fledge
- Loons may live 10-15 years and breed for 8+ years
So for a loon breeding for 10 years, with 1 chick fledged per year, the total lifetime offspring would be about 10 chicks. A long-lived loon breeding for 15 years could fledge 15 or more chicks in its lifetime.
How do number of offspring vary between loon species?
The five living loon species show some variation in their breeding output:
Species | Clutch Size | Chicks Fledged |
---|---|---|
Common Loon | 2 eggs | 1-2 per year |
Yellow-billed Loon | 2 eggs | 1 per year |
Red-throated Loon | 2 eggs | 1-2 per year |
Arctic Loon | 2 eggs | 1-2 per year |
Pacific Loon | 2 eggs | 1-2 per year |
The numbers are quite similar across species, with clutch sizes of two and typically one or two chicks fledged per year. Slight differences may reflect habitat quality, food availability, and predation pressures across their breeding ranges.
How do human impacts affect loon breeding?
Human activities can negatively impact loon breeding success and number of offspring produced. Some human impacts on loon productivity include:
- Habitat loss from lake shore development
- Disturbance from boaters and personal watercraft
- Pollution exposure from oil spills, mercury, lead
- Fishing tackle entanglement risk
- Climate change disrupting migration and food sources
Conservation measures like protecting breeding lakes, managing boat traffic, and reducing pollution can help mitigate these impacts. Supporting healthy aquatic habitats will allow loons to successfully breed and raise the next generation.
Conclusion
Loons have an average clutch size of two eggs, of which one or two chicks will typically fledge each year. Loons breed annually, producing dozens of offspring over a lifetime of 10-15 years. Exact productivity varies between loon species and is influenced by habitat quality, food availability, and threats like human disturbance and pollution. Maintaining healthy lakes and wetlands will ensure loons can continue breeding successfully for generations to come.