Loons are beautiful waterbirds known for their striking black and white plumage and haunting calls. They are a symbol of wilderness and solitude in many parts of North America. But loons need healthy lake habitats to survive and face a number of threats such as pollution, changing water levels and human disturbance. This has led to concern about loon populations and whether lakes can sustainably support them. So how many loons should there be on a typical lake? Are there really only 2 loons per lake on average as is sometimes stated? Let’s take a deeper dive into loon ecology and demography to find out.
What is a loon?
Loons are aquatic birds in the genus Gavia. There are 5 species worldwide, with the Common Loon (G. immer) and the Red-throated Loon (G. stellata) being the two species found in North America. Loons spend most of their time in water, where they dive to catch fish. They are graceful in the water but awkward on land because their legs are set far back on their bodies. Their sharp bills are ideal for spearing and holding slippery fish. Loons go through a dramatic seasonal plumage change, being gray-brown in winter and black and white checkered birds in breeding plumage. Their calls carry far across lakes and are often associated with northern wilderness areas.
Where do loons live?
Loons in North America nest on freshwater lakes of all sizes, from small ponds to large lakes. They nest along shorelines, especially quiet bays and inlets sheltered from wind and waves. The lakes must be clear enough for the loons to see fish from the surface when they are diving. They often favor lakes with islands where they can nest safe from predators. Loons migrate in winter to coastal waters but return to inland lakes each spring to breed. The Common Loon breeds across Canada, Alaska and the northern U.S. states. The Red-throated Loon breeds farther north in Arctic regions and Alaska.
How many loons are normally found on lakes?
Most research indicates that loon pairs defend a breeding territory that encompasses an entire small to medium sized lake. Larger lakes may support multiple loon territories. As highly territorial birds during breeding season, loon pairs do not tolerate other loons using their lake and will chase away intruders. This allows loons to maximize their fishing territory and reduce competition for food resources to raise their chicks.
Several biological factors influence how many loon territories a lake can accommodate:
Lake Size
Larger lakes offer more habitat and fish resources to support multiple loon pairs. Studies show lake size is a key factor determining loon numbers. Research in northern Wisconsin found lakes smaller than 10 hectares (25 acres) had an average of 2 adult loons while medium lakes (10-40 ha) averaged 3 adults and larger lakes (40-100 ha) averaged 4 adults.
Food Availability
Lakes must have sufficient populations of small fish like minnows, suckers and perch for loons to prey on. Lakes with greater abundance and diversity of fish can provide food for more loons. If fish populations decline due to factors like overfishing or pollution, loons may abandon a lake.
Nesting Habitat
Loons nest along shorelines, favoring quiet bays and inlets sheltered from wind and waves. Lakes with more shoreline complexity offer more potential nest sites. Small islands are also favored. Lakes with limited or exposed shoreline may only support one or two loon pairs.
Disturbance
Loons avoid nesting where there is heavy boat traffic, docks or human activity along the shoreline. This may limit the nesting habitat on lakes that are popular recreation destinations. However, a few loon pairs may tolerate moderate disturbance in order to access good feeding habitat.
Territoriality
As territorial birds loons will defend areas large enough to provide sufficient fish resources. This limits how many loon pairs a lake can accommodate based on its size and fish abundance. Even large lakes likely have upper limits on loon numbers due to territory size and nesting requirements.
So in summary, while 2 adult loons per lake is sometimes cited, this is an oversimplification. The number of loon territories a lake can realistically support depends on many ecological factors. Small lakes may have just 1 loon pair while medium lakes may have 2-4 pairs and larger lakes 4+ pairs depending on habitat quality and food availability. Human disturbance also limits loons so pristine wilderness lakes likely have higher densities than recreational lakes. But very few lakes support more than 4-5 loon pairs due to territorial behavior. Let’s examine some more detailed research on loon numbers on lakes of different sizes.
Loon Population Research
Small Lakes
A study in northern Wisconsin found that small lakes under 25 acres in size had 0-5 adult loons with an average of 2.3. Lakes this size often had just 1 loon pair which defended the entire lake as its breeding territory against other loons. Small amounts of quality shoreline habitat may limit nesting on these smaller lakes.
Medium Lakes
Lakes ranging from 25-100 acres in the northern Wisconsin study averaged 2.9 adult loons, with as many as 8 adults on some lakes. Medium lakes had 1-4 loon territories on average. Habitat diversity and food availability allows more loons to nest but territorial behavior still limits numbers.
Large Lakes
On large lakes over 100 acres, the northern Wisconsin study found loon numbers ranged from 4-22 adults with the potential for more on very large lakes. Large lakes provide enough habitat for multiple loon territories, sometimes up to 5-6 pairs, before territorial conflicts arise limiting further increase. However, a Minnesota study on very large lakes >2500 acres found a maximum of 12 loon territories per lake suggesting habitat availability eventually limits numbers except on Great Lakes-sized waterbodies.
Here is a table summarizing these research findings on loons numbers by lake size:
Lake Size | Average # Loons | Loon Territories |
---|---|---|
0-25 acres | 2 | 1 |
25-100 acres | 3 | 1-4 |
100-1000 acres | 7 | 3-6 |
1000-5000 acres | 12 | 5-12 |
This table shows that while 2 loons is typical for small lakes, numbers steadily increase for medium and larger lakes due to more habitat and fish supporting multiple loon territories. Still territorial behavior and habitat availability prevent densities from becoming too high except on the largest lakes.
Some key points from these studies:
– Most small lakes have 1 loon pair defending the entire lake.
– Medium lakes may have 2-4 loon territories with 3-8 adults.
– Large lakes have room for 4-12 loon territories before habitat is saturated.
– Even large lakes likely do not support more than 12 loon pairs due to territoriality.
So in summary, loon densities depend strongly on lake size. While 2 loons may be typical for small lakes, densities gradually increase on larger and larger lakes before territorial behavior creates upper limits to densities, likely around 10-12 pairs per lake except for the Great Lakes. Next let’s examine how ideal loon habitat may influence populations.
Ideal Loon Lake Habitat
While loons can nest on many types of lakes, some habitat features create ideal conditions that support higher loon densities:
Small Islands
Loons frequently nest on small islands which offer protection from mammal predators like raccoons, mink and foxes that cannot access islands. Lakes with several small islands spread around the lake provide more nest site options and may support higher numbers of loons.
Secluded Bays
Sheltered, secluded bays provide quiet water and privacy for nesting loons. These bays are often the first areas occupied by loon pairs. More complex shorelines with multiple small bays increase potential nest sites.
Aquatic Vegetation
Lakes with beds of cattails, rushes, and other aquatic plants are favored loon nesting habitat. The vegetation offers cover and materials for building nests. Lakes with abundant vegetation have more nesting options.
Clear Water
Clear lakes allow loons to see fish while diving underwater. Lakes with at least 10-15 feet of clarity are required by loons, limiting them to clean, oligotrophic lakes in many regions. Stained or turbid lakes cannot support loons.
Fish Diversity
Lakes with several fish species like perch, minnows, suckers and sunfish can support more loons than lakes with just one or two fish species. Diverse food resources allow higher loon densities.
Low Disturbance
Lakes with little boat traffic, low-density lakeshore homes and minimal human disturbance have less stressors to breeding loons. More remote wilderness lakes often have greater loon numbers for their size than busier recreational lakes.
So in ideal loon habitat with diverse fish populations, clear water, abundant vegetation, islands and secluded bays, loon densities may approach the upper limits allowed by the lake’s size and food availability. Pristine wilderness lakes in particular can support more loons than recreational lakes. But even ideal loon lakes eventually fill up at 10-12 breeding territories for large lakes due to territorial behavior by loons. Next let’s look at how threats to loon populations may further reduce densities.
Threats to Loons
Loons face a variety of threats on their breeding lakes that reduce populations in many regions:
Declining Water Quality
Eutrophication of lakes due to fertilizer runoff increases algae and reduces water clarity needed by loons to see fish while diving. As water quality declines, loons abandon lakes.
Pollution
Oil spills and chemical pollution such as mercury, dioxins, pesticides and heavy metals accumulate in loons and reduce survival and reproduction. Most loons have some mercury in their bodies.
Fishing Tackle
Loons are vulnerable to swallowing fishing tackle lost by anglers including lead sinkers and fishing hooks which can be lethal. Anglers should use non-lead alternatives and dispose of line properly.
Boat Disturbance
Increased motorboat traffic and wakes disturb nesting loons, causing them to abandon nests. Buffer zones around loon nests are recommended to reduce disturbance.
Habitat Loss
Wetland drainage and shoreline development eliminates nesting habitat. Most loons now use artificial nest platforms provided by programs since natural habitat is scarce.
Large Predators
Eagles, raccoons, mink and other predators take eggs and chicks. Nesting on islands provides some protection but large predators limit productivity.
All of these threats reduce the number of loons lakes can support. A Wisconsin study found eutrophic, lower clarity lakes had 75% fewer loons than high clarity lakes. Loons are vulnerable to cumulative impacts of many stressors that degrade the quality of lake habitats. High quality habitat protects loons by maximizing reproductive success. Next let’s look at conservation programs helping protect loons.
Loon Conservation
Many state and national programs are now underway to monitor and conserve loon populations. Some key efforts include:
Loon Surveys
Annual surveys conducted by state agencies and volunteers count loon numbers on lakes to monitor populations. Banding studies help track loon movements and survival.
Nest Platforms
Artificial floating platforms provide safe nesting sites away from shoreline predators. Many loons now nest on platforms since natural sites are scarce.
Signage & Buffer Zones
Buoys and signs mark loon nesting areas to boaters so they avoid disturbing nests. 150-300 foot buffers are recommended around active nests.
Mercury Reduction
Tougher regulations on mercury emissions from coal plants and waste incinerators aim to reduce mercury levels in lakes where loons breed.
Lead Tackle Buyback
Programs buy back lead fishing sinkers from anglers to help prevent loons swallowing lost toxic tackle. Using non-lead alternatives like tin helps.
Lakeshore Protection
Zoning shorelines of loon lakes for low densities and maintaining natural vegetation preserves habitat. Easements also protect shorelands.
These programs help offset habitat loss and other threats to loons. But maintaining high water quality is still the key to preserving loon populations on northern lakes. Clean lakes with diverse habitat and food resources will continue to support the maximum number of loon territories allowed by their size. Next let’s look at prospects for future loon populations.
Future of Loons
The future of Common Loons is closely tied to the health of northern lakes. With attention paid to threats like mercury contamination, shoreline development and boat disturbance, many lakes can continue supporting loon densities at the maximum levels habitat allows.
Red-throated Loons face uncertain futures with climate change impacts to Arctic nesting habitats. But Common Loons that breed further south have better long-term prospects if water quality can be maintained.
The recovery of Bald Eagle populations also means more loons may nest on platforms and small islands to avoid aerial predators. Continued conservation efforts centered on protecting lake habitats will give loons the best chance at thriving across their range.
On individual lakes, people can help by reducing shoreline impacts, respecting nesting areas, and following fishing regulations. Anglers should use non-lead tackle and dispose of gear properly. With community support and well-managed lake habitats, loon numbers should be sustained near ecological limits, despite growing human impacts.
The exact number of loons a particular lake can support depends on many habitat factors. But it is reasonable to use a rule of thumb expecting 1 loon pair on small lakes, 2-5 pairs on medium lakes and 4-12 pairs on large lakes. Larger lakes likely max out around 12 pairs due to territoriality. So while 2 loons per lake is reasonable for small lakes, the average lake should actually support higher loon densities in quality habitat.
In conclusion, loon conservation comes down to maintaining clean, undisturbed lake habitats with diverse fish populations. This allows each lake to support the maximum number of loon territories its size and habitat quality can accommodate before territorial behavior sets limits. With vigilant protection of northern lakes, loons will continue gracing these waters and providing their iconic calls for generations to come. The exact number of loons per lake depends on many factors, but we can be confident that healthy habitats will have as many loons as ecologically possible. So enjoy the loons on your favorite lake, practice responsible recreation, and support habitat protection so future generations can experience the magic of loons as well!
Summary
Key points:
– Most small lakes have 1 loon pair, medium lakes 2-5 pairs, large lakes 4-12 pairs on average based on size and habitat.
– Ideal loon habitat with clear water, islands, vegetation and secluded bays supports maximum densities.
– Threats like pollution and human disturbance reduce numbers, conservation is needed.
– Healthy lake habitats allow ecologically maximum loon densities until territorial behavior sets limits.
– Exact numbers depend on specific lake’s size, quality and fish populations but 2 loons per lake is reasonable for small lakes.
– Protecting water quality and habitat allows lakes to reach their ideal loon numbers within territorial limits.