Actually you're hardly taking a breath, as normally it's there, right in front of your nose. And it doesn't involve thinking. Only if you do you might get short of it.
For a dolphin this is entirely different. They need to breathe as much as we do, only there were they are most is no air. Therefor they have to go to the surface and that takes a bit of planning. Dusty does take a breath indeed and usually she does this a few times a minute. She can stay under for a quarter of an hour and even longer in case of emergency. Usually she comes to the surface in an arch. By her speed and momentum she continues the arch down again. Try this out in your browser:
http://www.revolutietheorie.be/dolfijnspel.htm
When the water is smooth she can plan her breath precisely. But usually there are waves and sometimes even very big ones. How does she know when to breathe without getting a splash of water into her blowhole? Of course there is a certain steadiness in the waves. When they break you can hear that under water. You can also see them from down under. Would Dusty choose her moment of breathing by the rhythm of the waves?
http://youtu.be/KkeAOMOT59M
Some time before I wrote that at various occasions I saw that before breathing Dusty swims to close under the surface. I then had this theory that she uses her dorsal fin as an inverted dipstick to assess the height of the waves. I still think so. But a few more things have come up. It would be handy when before breathing you would know from which direction the waves come. From her dorsal fin of course she can feel if she lies across that direction or in line with it. The latter is preferable because the regularity of the waves then is most predictable. Moreover, she keeps her momentum. When you swim across or at an angle into the waves you get slowed down.
At times I swim with a dorsal fin myself and I have noticed that in waves I can go faster with it. It can be of course that because of the resistance it gives me I intuitively swim more head on into the waves.
But there is something else. Everything that stands out above the surface is subject to gravity. And it's not only so that the higher a body protrudes the heavier it falls back. Also the weight of the dorsal fin itself makes a difference in the speed in which you dive down again. With Dusty the weight of her dorsal fin is constant, but not with me. Because I made two. The first is made of African Padouk, a bright red species of wood that, exposed to air turns brown and has a specific weight of about 1, so just as heavy as water. The other is made of Surinam Greenheart and has a s.w. of about 1.25. The latter is thereby a quarter of the weight heavier and thus gravity gives an extra push down. I do have to get more mass going, but then also have more momentum.
Furthermore a wooden dorsal fin of course is also pretty decorativeintuïtief and I have often deceived people with it. They thought there were two dolphins swimming.