Have you ever seen a bird standing with its wings spread open and enjoying the sun? If so, you’re probably wondering why it did so. Was it just enjoying the warmth, or was there another reason?
Birds spread their wings to dry themselves up, thermoregulate, and get rid of parasites. Some may rely on this behavior to show contentment after successful foraging, while others use it to show dominance, balance themselves, and keep their nests in the shade.
If you want to learn more, keep reading! We’ve found some incredible studies on why birds stand with their wings open and shared the results below!
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Why Do Birds Spread Their Wings?
Did you know that scientists call this a spread-winged behavior? It turns out it’s not just a simple movement birds do. It’s correlated and prompted by many other factors, which typically depend on the species. Some people call this behavior sunbathing or wing-drying, but other reasons can explain it as well.
1. Wing-drying/Sunbathing
Most commonly, the spread-wing behavior is done for wing-drying purposes. This is usually seen in cormorants and anhingas.
Since their plumage isn’t fully water-repellent but rather water-absorbing, they spread their wings to let them dry after swimming.
Therefore, cormorants and anhingas sit with their backs to the sun with their wings spread to allow the feathers to absorb the pleasant warmth provided by the sun! Their feathers are fanned open, and the wings typically form a semicircular shape.
A study on cormorant wing-spreading behavior showed that these birds engage in this behavior primarily for wing-drying, as most birds did so when their plumage was wet.
Specialists noticed this behavior in other birds as well. Mousebirds, for instance, often spread their wings after rain or heavy snow to dry themselves up.
2. Thermoregulation
Some birds rely on standing with their wings spread to regulate their body temperatures. Take the anhingas we’ve discussed above. Since their plumage is water-absorbing, anhingas have reduced buoyancy. This makes them extremely efficient at taking prey underwater because it helps them remain almost immobile.
On the other hand, this puts them under thermoregulatory stress, and they have to dry as quickly as possible once they get out of the water and heat themselves by rebuilding the lost layer of air close to the skin.
It has been proven that anhingas spend more time with their wings open than other birds. A study on anhingas shows that only 34% of the birds engaged in this behavior were wet, whereas 49% were dry. This indicates that the primary reason for this behavior is thermoregulation, not wing-drying.
In addition, it has been suggested that this thermoregulatory behavior is highly common in birds with black plumage on their backs and wings, as it absorbs more solar radiation.
As mentioned, cormorants do not typically rely on wing-spreading to thermoregulate. However, some tropical and subtropical species have been observed relying on it in a way similar to anhingas.
Other birds engage in a similar behavior, although it’s probably not as specific as the one seen in anhingas. Many species were seen spreading their wings in the sun after a cool night to warm themselves up.
3. A Sign of Successful Foraging
A study on long-tailed cormorants has shown that these birds often spread their wings immediately after catching prey. This may be their way to show their contentment and fulfillment.
However, other scientists disapprove of this theory, suggesting that the study did not consider other aspects, such as weather variables or other circumstances.
4. To Get Rid of Parasites
Scientists discovered that some birds may spread their wings open in the sun to kill parasites. They’ve come to this conclusion after observing some hooded vultures that stayed in the sun in an odd position with their wings widely spread.
They captured four of them and noticed they were full of hundreds of lice and their eggs. Afterward, they collected 41 lice from their plumage and conducted an experiment. Ten were left in the shade for almost a day, and only one died. The other 31 were placed in direct sunlight for only three minutes. All lice died.
Therefore, since many parasites nest under the wing coverts, spreading the wings in the sun may be an efficient method birds rely on to get rid of them.
5. Preening
During preening, birds use their beaks to position the feathers, clean their plumage, and check for ectoparasites. They also spread throughout the plumage the preen oil produced by their oil glands. While doing so, birds may hold one or both wings out from the body. When the preen-gland oil comes in touch with sunlight, this produces vitamin D which is eventually ingested by the bird.
6. Dominance and Territoriality
Some bird species spread their wings wide to show dominance and defend their territories. This way, they appear bigger and intimidate their rivals.
Some species engaging in this behavior are geese and swans. If they become aggressive, they may start flapping their wings and producing various threatening sounds.
7. Shading their Nests
Many stork species were seen standing in their nests with their wings spread to keep the eggs or the young in the shadow. Species known to engage in this behavior are the white stork, the black stork, the wood stork, and the marabou stork. While shading their nests, these birds may also take advantage of the sunlight to thermoregulate.
8. Balancing
It has been suggested that cormorants and storks hold their wings out from their bodies to balance themselves, especially right after landing or when walking on unstable branches, for example.