Last weekend, I took my Marine Ecology students on a trip to Cobscook Bay.\u00a0 One of our activities was a whale watch off Head Harbour on Campobello Island.\u00a0 Birds were abundant with lots of Northern Gannets, Sooty Shearwaters, a few Manx Shearwaters, Black-legged Kittiwakes, Common Loons, many Bonaparte\u2019s Gulls and even a few Atlantic Puffins.\u00a0 And yes, we saw marine mammals.\u00a0 A couple of Minke Whales and groups of Harbor Porpoises tantalized us by breaking the surface of the water briefly.<\/p>\n
Perhaps you feel a bit frustrated like me watching these marine vertebrates because a good bit of their lives is lived under the water out of our vision.\u00a0 Thanks to underwater cameras, small submersibles and SCUBA equipment, we do have some understanding of life under the water surface for marine birds and mammals.<\/p>\n
It is not surprising that these animals have particular adaptations that permit them to make a living by diving underwater.\u00a0 Some of these adaptations are morphological and others are physiological.\u00a0 Let\u2019s explore some of these adaptations using the Common Loon.<\/p>\n
Common Loons are excellent divers, capable or reaching depths of about 200 feet.\u00a0 A loon can stay under water for as long as 15 minutes.<\/p>\n
Loons swim underwater using only their feet.\u00a0 The wings of loons are relatively short and are held tightly against the body during a dive.<\/p>\n
The legs of a loon are set far back on the body.\u00a0 The legs are splayed out laterally when the bird swims. When a loon is first diving from the surface, it breaks the surface by alternating strokes with the left and right leg.\u00a0 Once underwater, the legs beat synchronously.<\/p>\n
The lateral placement of the legs makes for hydrodynamic efficiency.\u00a0 If the legs were close together, the turbulent eddies created by one leg would interfere with smooth movement through the water of the other leg.\u00a0 The lateral arrangement allows a loon to generate maximum thrust while minimizing hydrodynamic drag.<\/p>\n
The feet of loons are large and webbed.\u00a0 The real power in swimming is generated by the rearward movement of those webbed feet against the water.\u00a0 When the loon moves its feet forward during the recovery stroke, the toes are brought together causing the web to collapse and minimizing the effort needed to get the foot ready for the next power stroke.<\/p>\n
Loons have a peculiar yet elegantly adapted leg.\u00a0 Unlike most birds, the major lower bone (the tibiotarsus or the large drumstick bone on a chicken) of a loon has a prominent extension, called the cnemial crest, that extends well beyond the joint where the upper leg bone (the femur) joins.\u00a0 This cnemial crest provides a broad attachment for the large muscles of the upper leg.\u00a0 The massive thigh muscles generate the huge force that allows loons to dive so deeply and so quickly.<\/p>\n
The long bones of birds are not hollow as seen in most species of birds.\u00a0 These heavier bones make it easier for a loon to dive.\u00a0 Just before a dive, a loon compresses its body, driving out the air trapped within its feathers.\u00a0 Air trapped in the feathers would increase the buoyancy of the loon and make it harder to dive.<\/p>\n
On to a physiological adaptation.\u00a0 Loons, like other diving birds and marine mammals, have the ability to store large quantities of oxygen in their blood.\u00a0 Even so, staying underwater for 15 minutes is no easy task.\u00a0 During diving, a loon undergoes a physiological change called the diving reflex.\u00a0 Oxygen flow to most body parts is greatly reduced except to the heart and nervous system.<\/p>\n
This reflex causes the heart rate to slow, decreasing the amount of oxygen used by the heart.\u00a0 Muscles and other parts of the body have to perform anaerobic (oxygen-free) metabolism until the bird surfaces.<\/p>\n
[First published on October 14, 2012]<\/p>\n\n
Last weekend, I took my Marine Ecology students on a trip to Cobscook Bay.\u00a0 One of our activities was a whale watch off Head Harbour on Campobello Island.\u00a0 Birds were abundant with lots of Northern Gannets, Sooty Shearwaters, a few Manx Shearwaters, Black-legged Kittiwakes, Common Loons, many Bonaparte\u2019s Gulls and even a few Atlantic Puffins.\u00a0 […]<\/p>\n","protected":false},"author":146,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"yes","ngg_post_thumbnail":0,"footnotes":""},"categories":[479,420],"tags":[],"builder_content":"","_links":{"self":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/535"}],"collection":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/users\/146"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/comments?post=535"}],"version-history":[{"count":1,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/535\/revisions"}],"predecessor-version":[{"id":536,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/535\/revisions\/536"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/media?parent=535"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/categories?post=535"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/tags?post=535"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}