A Pacific parrotlet about to land on a natural perch. Image credit: Roderick, Chin et al. (CC BY 4.0)
Most of the flying vehicles designed by humans need to land on smooth, standardized surfaces such as runways. A bird, on the other hand, can use structures that vary widely in diameter and texture, from phone lines to branches to statues. Yet, few studies have focused on how these animals transition from the air to a perch, and especially on how they adapt to different surfaces.
To fill this gap, Roderick, Chin et al. recorded how Pacific parrotlets landed on nine natural and man-made perches that varied in diameter and texture, ranging from smooth Teflon to rough sandpaper. High-speed cameras tracked each of the landings while sensors measured how hard the birds landed on and squeezed the perches.
The experiments revealed that the first landing phase was the same regardless of the nature of the perch. The birds used their wings to slow down, unfurled their feet and claws in preparation for touchdown and then allowed their legs to absorb the landing impact.
Once the feet had made contact with the surface, however, the birds used their toes and claws to adapt to different perches. First, they steadied their grasp by tightly squeezing the perches. Then, the parrotlets dragged their claws on the surface of the perches to find minuscule bumps and dips that allowed better stabilization. These movements could be remarkably fast – in the range of one to two milliseconds. The birds also curled their claws more on perches that were harder to grasp. Once secured on the branch, they relaxed their grip.
The results by Roderick, Chin et al. will help biologists understand how birds, insects and even large tree-dwelling creatures can grab perches in various environments. This knowledge will also be relevant for engineers who are trying to create robots that can climb or land on diverse surfaces.
