The reproduction process is one of the most taxing procedures in both humans and birds. Post the process, feeding the offspring is tougher. The pressure on birds to feed their offspring is more as they have a larger clutch size.
Bird parents decide who to feed first mostly based on natural instinct or love for a young offspring. The food is mostly provided open to all by the parent and the fittest may get the first bite. Based on experiments, adult female birds were giving preference in feeding the UV-reflecting offspring.
The answer depends on the type of scenario that the offspring are being raised in.
- Scenario 1- Nestlings hatch on a young spring morning in an urban household garden with ample food around, in such a scenario, all the offspring get their share of food.
- Scenario 2- It’s the winter season and food is scarce, in this situation the bird parents have to choose which offspring to feed and they choose the strongest offspring that has the largest chances to survive and carry the genes ahead, thus the weaker ones are left behind.
Each baby bird in the nest does not get an equal amount of food. To get fed, they evolve different signals like begging behavior, vocalizations, and open mouths. Yet, how parents react to this information varies from species to species. For example, Tree swallows feed the chick begging the most unlike the blue-footed booby ignores the begging̣.
5 major ways in which bird parents decide who to feed first
- Sibling Rivalry- In a nest full of chicks that are begging for food; bigger and stronger chicks push the weaker siblings off the nest in competition for food. The stronger chick also shrieks the loudest which is also why they are fed and that’s how they become strong in the first place, it’s a cycle that repeats.
- Availability of resources- While feeding, birds shift to insects as they are richer in proteins. According to research, the availability of food is the biggest determinant of which offspring is to be fed. If resources are available the distribution is equal but in uncertain surroundings, the emphasis lies on strength, and the chick with structured signals is fed. Parents also tend to react less to begging in case of food unavailability because everyone is hungry.
- Survival of the fittest – As mentioned earlier, the cycle of getting fed simply depends on the “survival of the fittest” rule. The stronger the chick, the louder shrieking cry for food which gets them fed more. Additionally, if parents had to choose, they go with the strongest chick that has the largest chance of survival.
- Parental Instinct- Adult birds that feed have a strong memory that reminds them which offspring was fed when and who’s been starving the longest. You can call this a parental instinct or a strong memory but the parents know everything!
- Natural Factors- Environmental predictability determines the clutch size. Birds only produce the number which they will be able to feed and survive.
According to a new study, researchers have come across a unique method through which bird parents decide which offspring to feed.
Ultraviolet reflectance in young birds is also a form of communication that helps the parent decide which offspring to feed. In an experiment conducted, adult female birds were giving preference to UV- reflecting offspring but male birds had no preference. This shows the importance of Ultraviolet reflectance in bird communication patterns.
Researchers have studied these patterns in two species of migratory birds. Alpine Swift and European Starling communicate by modifying their UV (ultraviolet) signal.
- UV light reflected by the body skin of an offspring is proportional to the physiological differences of siblings in a brood.
- Parental bias increases as the season progress.
Another observation that came out of the experiment. Initially in the breeding season parent bird prefer less reflective body skin (UV pale – that is small stature) but in the latter part as conditions deteriorate parents get biased toward an offspring which have more reflective skin (UV bright – that is large body mass and skeletal size )
More complex and intricate signals which parents look for in their offspring other than their begging calls and size are:
- Begging amplitude
- Duration between feeding
- Call structure
- Carotenoid saturation of gape or flange
- Specialized feathers and skin patches
How do baby birds let their parents know they are hungry?
Nestlings are demanding, hungry, and need to be fed constantly. There are subtle signs in their behavior from which a parent can tell when their nestlings need to be fed. These signs vary from species to species but include – making noises, shaking, opening their mouths wide open for the food. Small birdies continue with their sleep between meals when they are not hungry. They are usually fed insects by adult birds for high protein. Adult birds kill the insect and make the food soft and moist to feed.
When a chick is starving it has a specific call voice through which a parent knows the intensity of hunger and how long the nestling has been hungry for.
Research by German and Swiss ornithologists have shown that parent birds can hear the changes in calls of their offsprings. Kenyan researchers have discovered that birds can change their calls. As their stomach rumbles their call frequencies change which indicates the intensity of hunger.
What do birds feed their baby birds?
Different ways parent birds feed their baby birds are as below.
- Protein-rich diet– Young ones need protein-laden food to grow. Insects and worms do the task for birds.
- Some birds feed milk– Birds produce crop milk which is like mammal milk. It gets produced by sloughing of special cells. Pigeon milk is the best in crop milk, both sexes produce it.
- Nocturnal birds– Nocturnal birds like owls and nighthawks hunt insects at night and feed their children.
Communication between the offspring and parent birds make for an interesting read. Researchers continue to dig deeper and understand more about the same. We have already discussed the feeding practices of birds in different environmental contexts. Abundant food leads to fewer conflicts in nestlings. Whereas in uncertain surroundings parents respond to quality rather than need.