{"id":66093,"date":"2018-11-23T05:40:48","date_gmt":"2018-11-23T12:40:48","guid":{"rendered":"http:\/\/www.featheredphotography.com\/blog\/?p=66093"},"modified":"2018-11-23T07:17:07","modified_gmt":"2018-11-23T14:17:07","slug":"cormorant-landing-on-water-a-related-physics-question","status":"publish","type":"post","link":"https:\/\/featheredphotography.com\/blog\/2018\/11\/23\/cormorant-landing-on-water-a-related-physics-question\/","title":{"rendered":"Cormorant Landing On Water (+ a related physics question)"},"content":{"rendered":"

Sometimes I observe this phenomenon when birds land on water and other times I don’t. I believe it depends on the landing style of the bird\u00a0but I’m trying to figure out how and why\u00a0it happens.<\/p>\n

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\"\"1\/3200, f\/6.3, ISO 640, Canon 7D Mark II, Canon EF 500mm f\/4L IS II USM + EF 1.4 III Extender, not baited, set up or called in<\/em><\/p>\n

I photographed this juvenile Double-crested Cormorant five days ago as it was landing on a local pond. I think photos of birds landing on water can be\u00a0quite dramatic, in part because of the water splash they create, so I have to pay particular\u00a0attention to\u00a0that splash or “plume” when I’m cropping the image to get the composition I like best.<\/p>\n

But with cormorants and a few other water birds I’ve noticed\u00a0something intriguing about the water disturbance they make.\u00a0That disturbance\u00a0often extends far out in front of the bird\u00a0where I wouldn’t expect it to be, especially because I’m quite sure it isn’t water thrown forward by the feet. Both when I see it with my naked eye and when I photograph it that water seems to come almost straight up from the surface of the water far in front of the feet.<\/p>\n

If so, and I’m quite confident it is, how\u00a0can that be? And what makes it happen?<\/p>\n

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It doesn’t happen with many species, only some. American White Pelicans for example don’t cause water to rise far\u00a0in front of their feet when landing on water. Instead they appear to keep their webbed feet nearly flat on the surface and simply “water ski” on the\u00a0water until their slowing speed won’t support their weight and they sink into the water, much like the floats of a landing seaplane.<\/p>\n

I have several photo sequences of pelicans landing on water and that’s what happens every time and in every photo in the sequence.<\/p>\n

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\"\"But in my experience cormorants don’t keep their webbed\u00a0feet nearly\u00a0flat – instead they’re at a steeper angle to the water\u00a0(the angle of one foot can be seen here in the same photo as the\u00a0first one)\u00a0so they appear to use their feet more as brakes\u00a0than as water skis and as a result\u00a0they\u00a0sink into the water more quickly.\u00a0And that might make the casual observer assume that the water in front of the bird is thrown forward by the angled\u00a0feet but I don’t think so. I’m convinced it comes almost straight up out of the water far in front of the feet. If so, how and why does\u00a0that happen?<\/p>\n

Well, I have a theory. Keep in mind this old biology teacher only took one college physics course and that was 49 years ago so my limited knowledge of the subject is rusty at best.<\/p>\n

Unlike highly compressible gases, liquids like water cannot be compressed (see first note below). The cormorant’s feet at\u00a0this steep angle and speed are pushing water molecules forward and those molecules are pushing on other water molecules in front of them. Since water cannot be compressed it must almost be like pushing a near-solid through the water and those pushed molecules in front of the bird\u00a0have to go somewhere – if they didn’t they would stop the bird like it had hit a brick wall. So where do they go? They take the path of least resistance and go almost straight up with a little forward motion and that’s what we’re seeing here far\u00a0in front of the cormorant’s feet (if they went down or sideways they’d just hit more dense water).<\/p>\n

Well, there you have it – my theory for what it’s worth. I’d love to know for sure, one way or another, so any thoughts on the subject would be appreciated.<\/p>\n

That’s assuming of course that you’ve had the stamina and fortitude to wade all the way through this\u00a0nerdy\u00a0post. Apologies to those who may not be intrigued by stuff\u00a0like this but it’s been gnawing at me\u00a0on and off for years now so I finally decided to just throw it out there and see what might come of it.<\/p>\n

And yes, I’m prepared to be wrong but I had to start the ball rolling. If I am it won’t be the first time and after all, that’s what theories are all about.<\/p>\n

Ron<\/p>\n

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Notes: <\/em><\/p>\n