Anna’s Hummingbird belongs to the genus Calypte, which also includes the species Costa’s Hummingbird. Both C. anna and C. costa display courtship behaviour that includes diving displays. The courtship behaviour of these hummingbirds has been researched extensively as it is incredibly interesting!

Observations done by Stiles¹ & Clark² defined these activities. It was noticed that there is an initial contact made by the female in which she will fly into the male’s territory and try to feed.¹ While the female is in the males territory she will evaluate its quality. She will then be approached by the male whereby he will proceed to sing to her with his gorget flared, perform a “shuttle” display, and then partake in a series of outstanding diving displays.³ These performances may result in copulation if the male is lucky!  The “shuttle” display is described as a back-and-forth motion above the female, while producing a high-intensity song.¹ This display is said to be the most crucial part of courtship! The diving display consists of the male rising approximately 30 m and then carrying out a high-speed swooping dive over the female.³

Overall C. anna can produce a variety of noises, such as a chip note, a chatter, a song, and a sonation from diving. The chip note is described as a low-intensity “short, sharp, dry, ‘tzin’”¹ which represents basic interaction amongst all members. The chatter resembles buzzy, harsh, high-intensity notes to signify aggression¹, often given by territorial males or females guarding their nest. The song produced by C. anna is highly complex and structured. Males rely heavily on their song in breeding territories.¹

The chip, chatter and song all rely on vocal mechanisms from the syrinx. It was once thought that the sound created from the dive display was vocal as well, however through multiple studies^2,3 with the use of high-speed video it has been proven the sound is a mechanism of the outermost tail feathers.² The dive was analyzed extensively and split into 5 stages.² The first stage begins with the hummingbird diving with a trajectory towards the sun. The diving male will propel himself downwards with wings flapping at a frequency of approximately 55.5 ± 1.72 Hz. In stage 2 the male ceases the flapping and tucks in his wings. In stage 3 the wings are spread to glide, transitioning into stage 4 in which the male reaches the bottom of the dive and will swiftly spread his tail, achieving the diving sonation. The final stage of the dive involves the male flapping his wings once and shutting the tail.

By comparing the sound produced with the event of the tail opening, it was determined that the tail does in fact produce the sound.² Specifically, it is the result of air flowing over the R5 outermost feather causing fluttering of the trailing vane. A study² was conducted whereby the R5 feathers were removed or trimmed and the birds performed the dive display. Removing the R5 feather resulted in the elimination of the dive sound. It was also evident in this study that faint changes in the shape of the feather can tune the frequency of sound generated when the tail is spread.

Watch this video to hear the sound the tail feathers make when diving! [Link]

It’s been shown that C. anna can vocally produce a sound of the nearly the same frequency of their diving sonation.² So why do these birds produce sound through their tail when they could produce an acoustically similar sound vocally? Phylogenetic reconstruction studies⁴ suggests that the diving sonation is ancestral and vocal song form evolved to mimic the dive-sounds. However, the function of the dive beyond impressing females is unclear, as is the chirping mechanism that results.

In performing this dive displays, hummingbirds reach an average maximum velocity of 27.3 ms^-1, which is highest length-specific velocity performed by any vertebrate.² It’s been hypothesized by Clark² that hummingbirds reach these extreme speeds as a element of courtship display. The females sexual selection for high motor skills is the likely reasoning for hummingbirds executing these dives at their maximum performance limit.⁵ Another explanation suggests that an increase in dive speed results may be correlated to the sound amplitude produced by the tail feathers, and that females are likely selected to be able to discern these slight differences.⁵

Another factor that comes into play in mate selection by females is the territory quality of the males, as mentioned previously. The female comes into the males territory to feed, and male earns his territory by successfully competing for a high quality area with other males. A study⁶ shows that the females demonstrate their preference for higher quality territories as the males possessing them encounter more females than males on impoverished territories.

 

Overall, hummingbirds truly have some unique adaptations, from their courtship displays, to their hovering flight. I hope you enjoyed reading about them today!

 

Literature cited:

1. Stiles, F. G. Aggressive and Courtship Displays of the Male Anna’s Hummingbird. Condor. [Online] 1982, 84 (2), 208 http://www.jstor.org/stable/1367674?seq=1#page_scan_tab_contents (accessed Oct 12, 2017).

2. Clark, C. J. Courtship Dives of Anna’s Hummingbird Offer Insights into Flight Performance Limits. P. R. SOC. B.[Online] 2009, 276 (1670), 3047-3052 http://rspb.royalsocietypublishing.org/content/early/2009/06/05/rspb.2009.0508.short (accessed Oct 12, 2017).

3. Clark, C. J.; Feo, T. J. The Anna’s Hummingbird Chirps with its Tail: A New Mechanism of Sonation in Birds. P. R. SOC. B. [Online] 2008, 275 (1637), 955-962 http://rspb.royalsocietypublishing.org/content/275/1637/955.short (accessed Oct 12, 2017).

4. Clark, C. J.; Feo, T. J. Why do Calypte Hummingbirds “Sing” with Both Their Tail and Their Syrinx? An Apparent Example of Sexual Sensory Bias. The American Naturalist [Online] 2009, 175 (1), 27-37 http://www.jstor.org.ezproxy.viu.ca/stable/pdf/10.1086/648560.pdf?refreqid=excelsior%3Ae14adb349bb8d821471e197033863e35 (accessed Oct 12, 2017).

5. Byers, J.; Hebets, E.; Podos, J. Female Mate Choice Based Upon Male Motor Performance. Animal Behaviour. [Online] 2010, 79 (4), 771-778 http://www.sciencedirect.com.ezproxy.viu.ca/science/article/pii/S0003347210000308 (accessed Oct 12, 2017).

6. Tamm, S.; Armstrong, D. P.; Tooze, Z. J. Display Behavior of Male Calliope Hummingbirds During the Breeding Season. Condor. [Online] 1989, 91 (2), 272 http://www.jstor.org/stable/1368304?seq=1#page_scan_tab_contents (accessed Oct 12, 2017).