First PhD Paper is live in Journal of Experimental Biology!

Three years ago was my first field season working with Calliope hummingbirds, where I began exploring the nagging questions I had about competition among hummingbirds. The fights are fierce, and individuals defend flowers and feeders all day long; how could this make sense for a bird with a massive mass-adjusted metabolic rate?

Fast forward to year 5 of my PhD, and I still have so many questions. But one thing I observed with collaborators in that first year, and in (nearly) every agonistic hummingbird encounter since, is the use of tail flaring in hummingbirds during competition. Males do it, females do it, juveniles do it. The behavior is directed to conspecifics, heterospecifics, and even predators (such as preying mantises)!

Not only did we see this tail flaring in Calliope Hummingbirds, we saw it in seven species present in the autumn in Southeastern Arizona.

I compared tail flaring across different behavioral contexts. This began with using 3D videography to define the angle of tail flaring in relation to the body width, as shown by green arrows in some body posture examples here.

Using this method, I was able to quantify tail angles in solitary, small maneuvers: take-offs and landings from the perches. I then compared these angles to those seen during dyadic trials of male calliope hummingbirds. We found a large difference between tail flaring when in the presence of a competitor. Further, individuals who won contests regularly had larger flare angles in their tails.

Hummingbirds also demonstrated some unique 3D movements during these competitions, what we termed a 'waggle'. This flight includes movement in both body yaw and roll, while maintaining an upright body pitch and, of course, a flared tail. Together, we propose that this could serve as a looming stimulus to a competitor.

Projected area of the combined body and tail increased when birds flared their tails and was further augmented by ‘waggle’ body movement. Three phases of a display performed by a male calliope hummingbird (S. calliope) in flight while approaching and intimidating a perched bird. (A) Tail not flared, (B) tail flared and (C) during a ‘waggle’ where tail flaring was paired with linear translations and body rotations. Positions in A–C sampled every 200 ms. Dashed lines represent body outline at end of display. Solid black lines, beak; green, plane of tail; filled circles, head and center of anterior spine, with shading intensity increasing with time during the display. (D) Angles of yaw, pitch and roll during the waggle shown in C (continuously sampled at 2000 Hz).

What does it all mean? We're still hoping to understand how this tail flaring serves a communication role. The behavior and use of the tail morphology is consistent with what animal contest literature would call a signal. How it communicates something about individual quality is still a question I hope to understand more during my PhD.

This chapter is published, with lots of ideas about signaling, flight consequences, and some future directions. Check it out here in the Journal of Experimental Biology!