Birds feeding other birds that are not their own offspring is a phenomenon that has been observed in various species. However, the frequency and motivations behind this behavior vary between different types of birds. In this article, we will explore whether birds commonly feed birds other than their own young, the potential evolutionary benefits of this behavior, and some examples of bird species that exhibit feeding of non-kin.
Do birds commonly feed other birds that are not their offspring?
While feeding their own offspring is a common and essential behavior for parent birds, regurgitating food for or actively bringing food to unrelated birds is rarer. Some bird species may occasionally feed other individuals, but most research indicates this is not a widespread or frequent behavior in the majority of birds.
That being said, there are some species where feeding non-kin is more habitual. For example, certain types of eagles, vultures, and seabirds have been observed feeding unrelated juvenile birds at the nest. Additionally, species that live in large flocks, such as the house sparrow, may benefit from reciprocal feeding relationships where an individual feeds another with the expectation of being fed in return someday.
Overall the frequency of intentional feeding between adult birds that are not mated appears low but does occasionally occur in certain species or situations.
What are the potential evolutionary benefits of feeding non-kin?
From an evolutionary perspective, there are some possible explanations for why some bird species may feed unrelated birds despite the energy cost:
- Improving the survival of the overall flock or colony. In highly social species, feeding others may help ensure more members survive.
- Gaining future access to resources. By feeding others now, a bird may gain preferential access to food sources later.
- Developing alliances. Unrelated birds may form affiliations through reciprocal feeding.
- Attracting potential mates. In some cases feeding others may signal fitness to potential mates.
- Parenting practice. Juvenile birds may feed others to practice for rearing their own offspring.
The dominant theory is that in most cases, feeding unrelated birds offers some potential for direct or indirect reciprocity through alliances or access to resources. It may strengthen bonds between individuals that provide a future benefit in highly social or colonial species.
Examples of bird species that feed non-kin
Some specific examples of birds that exhibit feeding of unrelated juveniles or adults include:
Eagles and Vultures
Both bald eagles and Egyptian vultures have been documented bringing food to nests that are not their own and feeding unrelated chicks. One theory is that they use these food gifts to investigate potential future nesting sites and assess the quality of territories. Another possibility is establishing early social bonds with potential future mates from nearby territories.
Seabirds
Certain seabirds like the Nazca booby may feed unrelated chicks at their nesting site. This is thought to help maintain the overall robustness of the colony by ensuring offspring survive even if their parents are unsuccessful at finding food.
House Sparrows
Flocks of house sparrows frequently contain unrelated individuals. They have been observed feeding juveniles that are not their kin, potentially helping establish the reciprocal relationships that strengthen the flock. Adult sparrows may also feed one another.
Waxwings
Waxwings live communally and forage in flocks. They frequently share food by passing berries back and forth in what has been described as a “food-relay system”. This may promote information exchange about food sources within the flock.
Ravens
Common ravens engage in food sharing both between mated pairs and with unrelated individuals in the flock. Juveniles frequently offer food to adults, even when not their parents. This helps establish social bonds and status that can provide future benefits.
What factors influence feeding of non-kin in birds?
The likelihood of birds feeding unrelated individuals seems to be influenced by several key factors:
- Social structure – More common in species that live in groups year-round like house sparrows versus solitary species.
- Food type – More likely when food can be easily regurgitated or passed such as berries.
- Kin recognition – Species with abilities to recognize kin may focus feeding on relatives only.
- Age – Juveniles are more likely to feed non-kin as they learn to become parents.
- Personality – Individual propensity for reciprocal behavior varies within species.
The evolutionary mechanisms driving non-kin feeding behavior are still debated. But factors like social structure, food type, kin recognition ability and age all seem to play a role in whether birds will provide food for unrelated individuals.
Conclusion
While feeding non-offspring is certainly not ubiquitous among all bird species, it does regularly occur in some highly social species and situations. Certain eagles, seabirds, waxwings, and other flocking birds exhibit this behavior most frequently. Evolutionary drivers likely relate to strengthening overall flock success, establishing affiliations, gaining territory information, and social bonding. But feeding of unrelated birds comes with energy costs, meaning it is an investment in potential future benefits. Overall, the feeding of non-kin by birds appears strategic and complex, varying across different types of species.
