![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2016\/06\/alula160622bs2.jpg\")
<\/p>\nIt is fun to discover something on one’s own — even if it is already\u00a0in the literature. Such was the case this morning while I watched\u00a0a hummingbird: I realized it\u00a0lacks alulae.<\/p>\n
Most birds have and make good use of alulae. However, alulae are unseen when a\u00a0bird isn’t flying and only momentarily seen when it is. Consequently, the lack of visible alulae would normally merely be a sign that they aren’t deployed, rather than\u00a0that they don’t exist. Well, that is my excuse for having taking so long to realize\u00a0that hummingbirds lack\u00a0alulae.<\/p>\n
Hummingbirds have a different style of flying than other birds. Most birds only obtain lift when their wings are extended during a\u00a0downstroke, not when wings are somewhat folded\u00a0during an\u00a0upstroke. Hummingbird wings are\u00a0extended during both downstroke and upstroke. During downstroke, most of the lift is obtained, but during upstroke lift is increased by a further third when wings are twisted.\u00a0<\/p>\n
Most birds must have\u00a0a rapid flow of air\u00a0against\u00a0sloping wings to stay airborne. But, when such a bird lands, it must slow. This requires an increase in the slope of the wings (the angle of attack) for it to remain airborne at the lower speed. However, this increases the likelihood of a stall. A solution to this problem is to deploy the alulae which force the airflow back over the wing\u2019s upper surface allowing continued\u00a0lift and control.<\/p>\n
As a hummingbird’s flying style enables it to hover, it does not need to constantly move through the air. It\u00a0has\u00a0no need of alulae to prevent stalling, and being extra baggage, evolution has removed them.<\/p>\n
It was the juxtaposition of watching an osprey deploy its alulae and a hummingbird not do so that finally made me suspect that the latter actually lacks them. A literature search confirmed the insight.<\/p>\n
An Osprey deploys its alulae (the small extra feathers at the bend of the wings) as it lands at its nest.
\n![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2016\/06\/osprey160622bs.jpg\")
<\/p>\n
A hummingbird can hover and so is unconcerned with stalling. It lacks alulae.
\n![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2016\/06\/rufoushummingbird160621s.jpg\")
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Alula: A structure on a bird’s wing occasionally deployed to limit stalling at high angles of attack. It is fun to discover something on one’s own — even if it is already\u00a0in the literature. Such was the case this … Continue reading