New hypothesis links dinosaur feather displays to modern bird hunting strategy

What are the origins of wings and tails in birds? This is one of the key questions in the evolution of animals. It has long been accepted that their evolution began in feathered dinosaurs.

Some of these dinosaurs had feathers on the tails and small wing-like feathers on their forelimbs. These small wing-like structures called ‘proto-wings’ are composed of special feathers known as pennaceous feathers—the stiff feathers found in the wings and tails of birds.

The ancient form of these feathers first emerged in dinosaurs during the Jurassic Period, and these dinosaurs, called Pennaraptorans, had proto-wings made of pennaceous feathers. However, it has been known that these proto-wings were too small for powered flight. Because we cannot time-travel to observe their behavior, what dinosaurs did and how they behaved remains unanswered.

Various functions of proto-wings and tail feathers in the ancestors of birds have been considered since John Harold Ostrom proposed the first idea 50 years ago that proto-wings were used to knock down insect prey by small predatory dinosaurs living on the ground and following their prey. However, how the small ‘proto-wings’ and feathered tails helped the dinosaurian ancestors of birds in their lives has not been resolved.

A new scientific collaboration involving a team of field-biologists and integrative ecologists (Piotr G. Jablonski, Sang-im Lee, Jinseok Park, Sang Yun Bang, and Jungmoon Ha), paleontologists (Yuong-Nam Lee and Minyoung Son), and roboticists (Hyungpil Moon and Jeongyeol Park), has proposed a new idea: the ‘flush-pursue hypothesis.’ Their paper was published in Scientific Reports.

This movie illustrates three different ways in which dinosaurs with proto-wings might have flushed their prey by visual displays to subsequently pursue them. First, the grasshopper jumps/flies away in response to expanding Robotperyx’s forelimbs with protowings. Second, the grasshopper jumps/flies away in response to the folding of forelimbs with protowings. Third, the grasshopper escapes in response to upward movements of the tail. Credit: Movie by Jinseok Park, Minyoung Son, Jeongyeol Park, SangYun Bang, Jungmoon Ha, Hyungpil Moon, Yuong‑Nam Lee, Sang‑im Lee, Piotr G. Jablonski. Fragments of supplementary movie to the paper “Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs” by the above Authors in Scientific Reports DOI: 10.1038/s41598-023-50225-x

The name of the hypothesis provides a clue to its content. Some birds employ a ‘flush-pursue’ foraging strategy, using wings and/or tail displays to visually flush out hiding prey and pursue the flushed prey (e.g., Northern Mockingbird, Linzy’s Vids). The hypothesis suggests that small dinosaurs with proto-wings use a similar strategy.

The hypothesis is rooted in years of detailed field-ornithological studies on several species of insectivorous birds conducted by a co-author of the current study, Piotr Jablonski and collaborators, as well as by Ron Mumme and collaborators [for example, the Painted redstart, the Slate-throated whitestart, the Spectacled Whitestart, and the Hooded warbler].

Studies on these birds have revealed that displaying contrasting plumage (often with black-and-white patches) on the wings and tails triggers the escapes of their prey and thus increases bird foraging efficiency because the escaping prey is pursued and caught by the birds.

Neurobiology behind this relationship was also studied. It has been proposed by Piotr Jablonski and Nicholas Strausfeld, a leading expert in arthropod’s nervous system, that special neurons in insects are activated by simple properties of flush displays by insectivorous flush-pursuing birds.

Robopteryx startles grasshoppers to flee in response to visual stimulation from the folding and spreading of forelimbs equipped with protowings, and in response to tail movements. The video shows the robot’s movements slowed down 12 times. Credit: Movie by: Jinseok Park, Minyoung Son, Jeongyeol Park, SangYun Bang, Jungmoon Ha, Hyungpil Moon, Yuong‑Nam Lee, Sang‑im Lee & Piotr G. Jablonski—authors of the paper “Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs” published in Scientific Reports: DOI: 10.1038/s41598-023-50225-x

Piotr Jablonski with collaborators first mentioned the flush-pursue hypothesis at the 2005 Gordon Research Conference on ‘Neuroethology: Behavior, Evolution and Neurobiology’ chaired by N. Strausfeld. Since then, the idea was developed and presented at 2018 International Ornithological Congress, and at the Society for Integrative Biology Annual Meeting 2023.

Source: Seoul National University

Leave a Comment