Birds nesting together in the same nest is called a mixed colony or mixed-species colony. This occurs when two or more bird species nest in close proximity to each other, sharing the same tree, building, or colony site. Some level of tolerance is required between the species in order for this to occur successfully. There are a variety of reasons why different bird species may nest together in a mixed colony.
Why do different bird species nest together?
There are several key reasons why different bird species may nest in close proximity to create a mixed colony:
- Safety in numbers: Having more birds together may help deter predators. The presence of other nesting birds can act as additional lookouts to alert the colony of incoming danger.
- Shared resources: Nesting together allows the different species to take advantage of the same food and water sources nearby. They can work cooperatively to find and access resources.
- Cooperative breeding: Some birds may actively help care for the young of other species in the mixed colony. This provides additional support in raising chicks.
- Microclimate benefits: Densely packed nests can help retain heat and create shelter from elements. Birds may nest together to take advantage of these improved conditions.
- Limited nesting sites: If prime real estate for nesting is scarce, different species may tolerate each other’s presence in order to access a good nesting spot.
- Reduced parasite loads: Nests spaced closely together may help reduce parasite burdens for some bird species compared to solitary nesting.
Depending on the species involved, some or all of these benefits may come into play when birds decide to nest together in a mixed colony. The advantages appear to outweigh the disadvantages in many cases where nesting tolerance exists between species.
What types of birds commonly nest together?
Some of the more common pairings of different bird species nesting together include:
- Seabirds: Gulls, terns, alcids, and pelicans often form mixed colonies on islands and coastal cliffs.
- Wading birds: Herons, egrets, ibises, spoonbills, and others may nest in loose aggregations in marshes and trees.
- Raptors: Falcons, eagles, hawks, and owls sometimes nest in close proximity on cliffs and bluffs.
- Songbirds: Swallows, blackbirds, and finches may place nests side-by-side in cavities or shrubs.
- Penguins: Gentoo, chinstrap, and Adélie penguins mix nests together in large colonies in Antarctica.
In these examples, the species involved tend to have somewhat similar nesting habits or habitat requirements that facilitate them tolerating each other’s presence. But there are exceptions, including some unusual parings between highly dissimilar species as well.
Unusual examples of mixed bird colonies
Some more uncommon or surprising examples of mixed colonies of nesting birds include:
- Woodpeckers and ducks: Wood ducks and northern flickers sharing nest cavities in trees.
- Parrots and eagles: Burrowing parrots nesting inside cavities dug into cliff faces by crested caracaras in Central and South America.
- Swifts and swallows: Vaux’s swifts and cliff swallows nesting on vertical sea cliffs and cave walls.
- Wrens and kingfishers: Carolina wrens nesting in abandoned belted kingfisher burrows along river banks.
These unique parings tend to reflect situations where suitable nesting sites may be limited. One species (like the kingfisher) establishes a nesting cavity or burrow that is later used by another opportunistic species (like the wren) after it is vacated.
Do different bird species reuse the same nest?
In most cases, different bird species will build their own nests even when part of a mixed colony. However, sometimes birds will reuse a nest built by another species, including:
- Smaller birds using an old hawk, crow, or raven nest.
- Parasitic cowbirds laying eggs in other species’ nests.
- New occupants renovating an existing nest from prior years.
- Colonial seabirds that maintain and reuse nesting burrows.
Reusing an existing nest saves birds the energy and resources required to build a completely new nest. And in some cases, certain species are dependent on the structures built by others in order to nest successfully.
Do nesting birds get along together?
The level of tolerance between nesting birds in mixed colonies can range from mild aggression to close cooperation:
- High tolerance: Species may synchronously build nests side-by-side with no conflict. Parents may cooperatively care for young of multiple species.
- Moderate tolerance: Nesting birds largely ignore each other and nest independently. Some squabbling may occur but serious fights are rare.
- Low tolerance: Frequent aggressive displays and fighting over nest sites occur. Nests may be spaced widely apart despite being in same colony.
Compatible species tend to have similar spacing between nests, equal footing on the breeding grounds, and non-overlapping food resources. Incompatible species show uneven spacing of nests, dominance by one species, and competition for food. Overall though, most co-nesting species show moderate levels of tolerance and largely leave each other alone.
Do certain birds always nest alone?
Some bird species are more solitary nesters and do not participate in mixed colonies. Birds that always nest alone include:
- Many raptors like the bald eagle and peregrine falcon.
- Some seabirds such as Atlantic puffins and razorbills.
- Most forest-dwelling songbirds like thrushes and flycatchers.
- Many ground-nesting birds like plovers, nightjars, and grouse species.
- Backyard birds like chickadees, nuthatches, and woodpeckers.
Solitary nesting may help reduce competition for food and nesting sites. It can also be a strategy to reduce predation risk and parasites. Birds that nest alone tend to be highly territorial and intolerant of others near the nest.
Can competition lead birds to nest together?
Interestingly, competition between closely related bird species may sometimes actually facilitate mixed colonies. Species that overlap significantly in their habitat, food, and nesting requirements tend to compete strongly for these limited resources. However, forming mixed colonies can be a way to “make the best of a bad situation” when the overlapping species cannot exclude each other from prime habitat.
For example, herring and glaucous-winged gulls often nest alongside each other in mixed colonies along the Pacific coast. These closely related gull species compete intensely for food and nesting sites. Nesting together in a mixed colony may limit direct confrontations and allow the colony to function with moderate success despite the competition.
How do different nesting habits facilitate co-nesting?
Birds with compatible nesting habits are more likely to tolerate each other in mixed colonies. Important factors include:
- Timing: Species should have similar breeding seasons and not differ too drastically in nesting or fledging periods.
- Location: Shared preferences for colony location facilitates co-nesting (e.g. on the ground, in trees, on cliffs).
- Spacing: Compatible personal space requirements reduces conflicts over nest density and location.
- Materials: Birds that use different nesting materials are less likely to compete over limited resources.
- Behavior: Species that quietly attend their own nests are better colony partners than loud, aggressive birds.
Even subtle differences in these factors can make or break a mixed colony. Birds are highly attuned to the specific requirements needed to nest successfully alongside other species.
How are nesting duties divided in a mixed colony?
Most birds in mixed colonies build their own nests and attend only to their own eggs and chicks. However, some cooperative breeding does occur, including:
- Joint nest defense against predators.
- Alert calls when a threat approaches to warn the entire colony.
- Shared incubation duties for pairs that need to leave the nest.
- Provisioning food for chicks of other species by more efficient hunters.
- Communal brooding and sheltering of young at crèches when adults are away.
This type of cooperation and sharing of parental duties helps support the overall success of the mixed colony. It allows each pair to spend more time foraging and less time protecting or incubating. The whole becomes greater than the sum of its parts.
Why don’t more birds nest together?
Given the potential benefits shared by communally nesting birds, why don’t more species nest together in mixed colonies? There are a few key downsides that may limit the strategy:
- Increased competition for food near the colony.
- Higher risk of parasites and diseases spreading between species.
- Difficulty finding compatible nesting partners due to differences in behavior.
- Elevated predation risk if the mixed colony becomes too conspicuous.
- Interference and aggression between incompatible species.
Additionally, many birds simply lack the behavioral flexibility to tolerate other species near their nests. The territorial mindset is strong with some birds! Overall, mixed colonies involve both costs and benefits depending on the species involved.
Can introduced species disrupt native nesting colonies?
In some cases, introduced or invasive birds can threaten native species that nest in mixed colonies. Some examples include:
- European starlings displacing native cavity nesters like bluebirds and woodpeckers.
- House sparrows competing with native swallows and evicting them from nests.
- Monk parakeets taking over nest sites from other colonial birds like herons.
The negative impacts introduced species can have are further compounded when the native birds are already threatened or endangered. Managing and preventing the spread of disruptive invasive species is key to protecting vulnerable mixed colonies.
Are mixed colonies a sign of a healthy bird community?
The presence of diverse and lively mixed colonies is generally considered a positive sign for the overall health of a bird community. Features that support vigorous mixed colonies include:
- An abundance of food resources to sustain multiple species.
- Secure nesting locations free from excessive disturbance.
- Balanced populations of predators and prey.
- A variety of quality habitat types.
- Protection from extreme weather events.
Places with shrinking or collapsing mixed colonies may reflect problems with food availability, nesting sites, habitat loss, predation, disease, or climate factors within the ecosystem. Investigating the cause can help identify solutions.
Conclusion
Mixed bird colonies demonstrate some fascinating inter-species dynamics. The complex factors that facilitate co-nesting reflect how integrated bird communities can be. While not all birds participate in mixed colonies, cooperative nesting provides many potential benefits to those that tolerate sharing space and resources with other species. Studying these interactions continues to reveal new insights into the ecology, behavior, and conservation of birds.