Check out these articles:
http://www.nytimes.com/2007/02/13/world/americas/13dolphin.html?_r=0
http://www.naturalhistorymag.com/features/201414/how-now-little-cow
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1076&context=usdeptcommercepub
http://eebweb.arizona.edu/courses/Ecol406R_506R/DAgrosaetal2000.pdf