Ants are one of the most abundant insects on earth, with over 12,000 known species. They can be found on every continent except Antarctica and occupy a wide range of habitats from deserts to rainforests. Birds also occupy diverse habitats worldwide and rely on insects, including ants, as a food source. But are ants helpful or harmful to birds? The answer is complex and depends on the species of ant, the species of bird, and the context of their interaction.
Ways ants may be harmful to birds
There are a few ways ants might be harmful to birds:
- Stinging/biting – Some ants have painful stings or bites as a defense. Stinging ants like fire ants or bullet ants can harm birds that come into contact with them while foraging.
- Competition – Ants compete with birds for food resources like seeds, nectar, fruits or other insects. Dominant, aggressive ant species can temporarily displace birds from feeding areas.
- Nest takeovers – A few tropical ant species conduct raids on bird nests to take over the nest for their own colonies. Army ants are notorious for this behavior, sometimes killing nestling birds in occupied nests.
- Parasitism – Ants are not typical bird parasites but a few rare cases exist of ants parasitizing nestling birds. For example, Formica ants have been documented parasitizing young cliff swallows in North America.
So in limited contexts, certain ant behaviors or characteristics can directly or indirectly harm bird individuals or populations. However, most bird-ant interactions do not clearly fall into harmful categories.
Ways ants may be helpful to birds
Ants provide a number of ecological services that benefit birds in most cases:
- Prey – Ants are a nutritious food source for many omnivorous or insectivorous bird species. Ants contain proteins, carbohydrates, lipids and other nutrients birds need.
- Pest control – Ants prey on or compete with various arthropod pests that harm bird nests, eggs or hatchlings. Birds indirectly benefit from ant pest control.
- Soil aeration – Ant burrowing activity helps aerate soils which benefits plants and contributes to productive bird habitats.
- Seed dispersal – Some plant species rely partially on ants to collect and move seeds, which aids vegetation growth and food availability for seed-eating birds.
- Pollination – Ants are frequent flower visitors and effective pollinators for many plant species that provide nectar, fruit or shelter for birds.
Through these and other ecological services, ants help maintain healthy bird habitats and food webs. Even when competing with birds, ants rarely force long-term exclusion or displacement of bird populations from optimal habitats.
Specific bird-ant relationships
Context is very important in evaluating if ants are harmful or helpful to certain bird species. Here are some examples of how the interaction plays out in certain species:
Woodpeckers
Woodpeckers like acorn woodpeckers, red-headed woodpeckers and red-bellied woodpeckers regularly feed on ants from ant mounds they drill into with their beaks. Carpenter ants and other tree-dwelling ants are an important protein source for these primary cavity nesting birds. Woodpeckers may help limit ant populations but are not generally displaced by dominant ant species.
Antbirds
Antbirds such as antwrens, antshrikes and antvireos have specialized behaviors and morphologies for following army ant swarms or raids to prey on insects and other arthropods flushed by the ants. Antbird diversity and abundance benefits from this association with army ants in neotropical forests.
Hornbills
Large forest hornbills in Africa and Asia regularly consume ants and show preferences for certain species. Suitable ant abundance and biomass contributes to habitat quality and hornbill foraging success. Hornbills are important ant predators but ants do not generally displace hornbills from optimal habitat when present in moderation.
Hummingbirds
Tropical hummingbirds obtain substantial amounts of nutrients by visiting flowers also frequented by ants. Ant body surface chemicals appear to enhance nectar quality and increase sugar secretion in some plant species. This extra-floral nectar benefits hummingbirds. Ants and hummingbirds peacefully coexist in these nectar-based food webs.
Antpipits
The antpipits are ground-dwelling songbirds specializing in preying upon ants and other small insects. Genera like Corythopis and Rhinomyias thrive in tropical forests with abundant leaf litter and rotting wood that sustain their ant prey. Competition between ants and antpipits for invertebrate prey is likely minimal.
Do bird diets rely heavily on ants?
Most bird species do not rely exclusively or even primarily on ants or other insects for sustenance. However some groups like antbirds, antpipits and some woodpeckers are highly specialized ant-eaters. The proportion of ants in bird diets also varies by habitat and ecological contexts such as seasonality.
According to dietary studies, ants generally comprise the following proportion of prey biomass for various bird groups:
- Hummingbirds – 6-31% of prey biomass
- Woodpeckers – 3-69% of prey biomass
- Antbirds – 55-94% of prey biomass
- Tyrant flycatchers – 0-12% of prey biomass
- Sparrows – 0-8% of prey biomass
- Tanagers – 2-20% of prey biomass
- Wrens – 0-31% of prey biomass
- Warblers – 0-13% of prey biomass
These proportions help explain why some groups like antbirds are so strongly associated with ants in terms of ecological adaptations and behaviors. However for most birds ants are just one of many prey options.
How do ants affect bird reproduction?
Ants can influence bird reproductive success in various ways:
- Nest predation – Some ants prey on bird eggs and nestlings, reducing reproductive output.
- Nest parasitism – Ant nests near bird nests can parasitize incubating birds, lowering parenting investment.
- Nest protection – Birds often choose nest sites with ant colonies nearby since ants deter nest predators.
- Nesting material – Birds frequently use small pieces of ant nests as nest insulation material which aids incubation.
- Extra-floral nectar – Birds benefit reproductively from nesting near extra-floral nectar producing plants frequently visited by ants.
Overall ants are occasionally nest predators but more frequently benefit bird reproduction through protective effects or providing useful nesting materials. Optimal bird reproduction relies on finding a balance between ant density and protective effects.
Conclusion
In most cases ants appear helpful rather than harmful to bird populations and individual birds. Ant predation, competition and parasitism on birds is ecologically insignificant compared to the benefits ants provide as prey, ecosystem engineers, pest regulators and pollination facilitators. A moderate level of ants contributes to habitat quality and food web complexity that supports thriving bird communities. Exceptions exist when invasive ants displace native ants and birds, or certain army ants raid bird nests. But on the whole, birds have adapted well to living alongside ants, and some specialist bird groups actually rely heavily on ants to persist.