Hummingbirds: Elaborate Trappings Of The Nectar Eater

During the 1990s I had untold opportunities to witness the full exuberance of nature’s rich offerings. My parents’ house on the southwestern edge of Ecuador’s capital Quito was set in a prime location for observing all manner of wildlife. And most memorable of all were the hummingbirds that frequented our garden attracted as they were to the blooming plants that had been strategically potted next to the outside walls of our living room. These veritable masters of flight, the smallest of warm blooded creatures on our planet, arrived with the sole purpose of extracting sweet nectar from the flowers we had laid before them. Their hovering maneuverability was their most striking attribute.

To date over 330 different species of hummingbird have been identified across the expanse of the American continent (1–3). And the mechanisms behind their supreme agility are being dissected out by the likes of UC Riverside biologist Doug Altshuler (1,4). Using revolving feeders filled with nectar and cameras that record minute positional adjustments relative to feeder rotation, Altshuler has uncovered one of the secrets behind these birds’ exquisite capabilities: flexible rotating shoulder bones that allow them to hover while maintaining their bills firmly inside flowers (1,2). With little to no opportunity to perch during feeding, their wing anatomy is indispensable for survival (1). On average ‘hummers’ consume more than half their body weight in nectar extracted from as many as 1000 flowers each day (1). To sustain this extraordinary rate of consumption their berry-sized hearts must beat 600 times a minute during rest and almost double that during flight (1).  This totals up to 4.5 billion times during their 12-17 year lifespan (4).  A continuous feeding binge supplies them with the energy they need to beat their tiny wings a staggering 80-200 times per second (1,2).    

In the mountain forests of Ecuador, not far from where my parents lived, there exists a species of hummer whose popular name, the swordbill, accurately describes the appearance of its feeding accoutrement (1,5).  With its four inch beak the swordbill is able to feed on the nectar of the Datura plant (1,5).  And it turns out that it is uniquely equipped for the job. Because Datura blossoms hang straight down, a four inch bill is what it takes to gorge on the effusions coming out of nectaries at the very base of the flower. But there is a trade-off. As the bird feeds, it is dusted with pollen that it carries to its next port of call (1). 

Although hummers are built to feed on nectar, they cannot sustain themselves on sugar alone. They depend heavily on insects as a primary source of protein (3). It is little wonder then that bugs form ¼ of their daily diets (1). With deadly accuracy hummers can pick out their prey mid-flight by opening their flexible bills to the widest capture position possible (1). And that is not the only way their bills are so refined for the functions they perform.  Today eight thousand plant species depend on the hummer for pollination. Like a lock and key, each bill fits into a limited set of blossoms. The Purple-throated Carib even exhibits marked gender differences in bill length tailored as they are to feed on different species of the colorful Heliconia plant (1).  

At nighttime hummers thwart the clutches of starvation by fluffing up their feathers to conserve heat and entering into a low energy sleep state called Torpor (3).  By lowering their heart rates to a sluggish 36 beats per minute and their body temperatures from a comfortable 105 degrees Fahrenheit to the ‘hypothermic threshold’ of life, they barely manage to stay alive (1,3).  The process is easily reversed however.  And when day breaks, vital signs ramp up to normal in 20 minutes or less in readiness for another day of high cost flying (3).

Flight behaviors amongst hummers challenge even our most optimistic preconceptions of avian aerobatics.  UC-Berkeley biologist-engineer Chris Clark has captured the steep death-defying 60 miles/h dive of the male Anna’s on camera as they perform a carefully choreographed mating display (6).  By taking high definition shots at 500 frames per second Clark estimates that g forces in the Anna’s dive match those at which military fighter pilots black out (1). Males descend at such an angle and speed that their tail feathers vibrate at the appropriate acoustic frequency to woo female onlookers (6). When it comes to heroic feats, most hummer votaries will wax lyrical over the seasonal migrations of their feathered icons.  Licensed ‘banders’ devote much time to the study of feeding and migration habits by crimping tiny uniquely-coded metal rings onto the hummers’ toothpick-sized legs (7,8).  And their work has brought the hummers’ continent-wide peregrinations into sharp focus. Some fly as many as 6000 miles between North and Central America breeding in the temperate zones of the north and wintering in the warmer climes of the south (3).  One species, the Ruby Throat, even endures an 18 hour, 500 mile long trek across the open waters of the Gulf of Mexico with no place to stop or feed, by storing the extra 2-3 grams of fat it needs to make it across (3).

The hummer story tells of irreducible complexity at key levels of functionality.  Anatomically these birds require not only a unique hovering system and long beaks but also a heart that can keep up with their voracious appetites.  And the exacting nature of their specific behaviors leaves little room for evolution’s undirected mutational ‘potshots’.  Species like the Ruby Throat, for example, need to binge on the grub that will get them through their sea-crossing expedition.  But their food quota must be carefully regulated.  Too little nourishment means not enough energy to make it across. Too much nourishment and they risk over-weighting themselves and plunging into the unrelenting waters below.

There is one hummer that is indelibly etched into my wish list of nature’s must-sees- the Peruvian Spatuletail (9). The furious waving of its long tail feathers during courtship has recently been captured on camera (9).  And like everything else in the hummer, these movements are made at neck-breaking speed (9). The Spatuletail waves the spoon-shaped spatules at the ends of its feathers while hopping on a twig 14 times a second (10). Awakened by such feats, my parents and I indulged in a little ecotourism by traveling down to the Maquipucuña nature reserve about 50 miles to the north of Quito in Ecuador (9).  Even though we knew little about the birds that graced the hills of this unspoiled paradise, we were able to appreciate the numerous hummers as they flaunted their iridescent colors. The setting could not have been more visually arresting. And while we never made it down to Peru what we saw more than made up for that particular missed opportunity.

Further Reading

1. Hummingbirds: Magic In The Air, See PBS Nature Special at http://www.pbs.org/wnet/nature/episodes/hummingbirds-magic-in-the-air/introduction/5424/
2. Mike Klesius (2007) Hummingbirds: Flight Of Fancy,  National Geographic, January 2007, See http://ngm.nationalgeographic.com/2007/01/hummingbirds/klesius-text/1
3. How do Hummingbirds survive cold nights? Hummingbirds and Torpor, See http://scienceblogs.com/grrlscientist/2006/04/hummingbirds_and_torpor.php
4. Biologist’s Lab at UC Riverside Is a Hummingbird Health Spa, See http://newsroom.ucr.edu/news_item.html?action=page&id=2233
5. Mary O’Leary (2009) Local filmmaker captures hummingbirds for PBS, New Haven Register, December 27^th, 2009, See http://www.nhregister.com/articles/2009/12/27/news/new_haven/doc4b36ce70697f1930415349.txt
6. Robert Sanders (2008) Anna’s hummingbird chirps with its tail, http://berkeley.edu/news/media/releases/2008/01/30_hummingbird.shtml
7. Like Banding A Toothpick! Talking With Sarah Driver, Hummingbird Bander, See http://www.learner.org/jnorth/tm/humm/HumBander_Sarah.html
8. Hummer/Bird Banding Research Collaborative (HBBRC) http://www.hbrcnet.org/index.htm
9. The Maquipucuña Reserve: http://maqui.myweb.uga.edu/
10. Matt Walker (2009) A Marvelous Hummingbird Display, BBC Earth News, 3^rd November, 2009, http://news.bbc.co.uk/earth/hi/earth_news/newsid_8338000/8338728.stm