Wednesday, February 26, 2014

Hovering and Landing

I have been reading and re-reading Carrol L Henderson's book, Birds in Flight: The Art and Science of How Birds Fly. The author provides many illustrations and makes reference to several birds. Among these are the brown pelican, great white egret, royal and sandwich terns, laughing gull and osprey, birds that I have photographed many times.

One of my favorite spots to photograph birds is a great white egret and brown pelican rookery located in the Everglades. Accessible only by boat, I come to the rookery several times during the spring and summer months to observe a large community of bird families. I am always awestruck with how easily the brown pelican and great white egret fly in and land on the trees that are heavily populated with adult birds and nests with chicks.

With fascination, I read the book and learned about how these birds are capable of landing with pinpoint precision. As the bird nears its landing point, it changes its posture from a horizontal to a vertical position, increasing the "angle of attack". This slows the air speed and allows the bird to stall or more carefully land. For better control, it often lands into the wind. In the vertical position, wings are outspread and the long broad wings serve as parachutes which gives the look of suspension in mid-air. The tail feathers are outspread and pointed downward, which also provides increased drag. Fine tuning is achieved with the "alulas" which is a portion of the wing located near the birds wrist (about midpoint across the length of the wing) and is similar to a thumb. The alula points out during the landing and by doing so, creates a little lift to prevent premature stalling. So basically, the bird uses several strategies to control its landing.

Landing is similar to hovering in some ways and among my bird list, there are a few hoverers, such as the osprey and royal tern. The osprey hovers when it hunts. It's long wings allow it to stay in flight and to fly slowly for long periods of time as it searches for prey. The hovering maneuver allows the osprey to remain in one place. It can do this by using its primary feathers as propellors that provide lift needed to stay in one place. The tail is outspread and as with the landing strategy described above, the body posture is vertical. The primary feather are spaced apart (like window blinds) to minimize air resistance. The royal tern is similar in this regard.

Where I have seen laughing gulls, sandwich terns and royal terns put their hovering to good use is when attempting to land on a small space, often times occupied by another bird. In these photographs, I capture these birds suspended over their landing site and when there is a conflict with another bird, I will see the hovering behavior carry on for several seconds before one bird gives up and flies away. On occasion, the bird's landing is not perfect (animal blooper alert!).

Capturing birds in flight, when done well, is very rewarding. In my opinion, landing flights are the most beautiful to observe for the obvious reason that the fullness of the bird's wings are seen. Two conditions are important when photographing landing birds; the sun should be behind you and the wind should be to your back. Remember, birds typically land into the wind, so before going out to photograph birds, check the wind directions. With the wind to your back, the bird will be landing toward you. Concerning the sun, an advantage of capturing birds in a vertical position is that the sun can be relatively high and it will hit the underside of those wings in full spread. This is not the case when the bird is flying above you in a horizontal position. So if you are shooting in late morning or early afternoon conditions, look for the landing bird or birds that bank while in flight.

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