Pilot whales were sighted in association with fish schools and feeding flocks of 

 birds. Such association allowed detection from greater distances than other solitary 

 animals of comparable sizes. 



Large whales are more easily detected even over long distances. Identification 

 was possible except when a whale was sighted from a distance and sounded prior to the 

 approach of the aircraft. 



The effect of altitude on detection and identification of marine mammals was 

 investigated using the data available. 



Birds 



Marine birds provide problems for aerial censusing which are very different from 

 those of marine mammals and turtles. Birds are much smaller than most marine 

 mammals and turtles. They are also more mobile and may fly to high altitudes above the 

 ocean's surface. In general, conspicuousness is a function of size, color, and behavior. 

 Large birds and white birds are more conspicuous than small and dark birds, and birds 

 that stay near the water surface are less conspicuous than those that fly several meters 

 higher. Identification is affected by these same variables but is mainly a function of 

 taxonomic diversity. The rest of this section is a brief review of the conspicuousness and 

 identification problems of the birds we encountered in the pilot project. 



Shearwaters are easily identified as such by their characteristic shape and manner 

 of flight. The two species seen (Cory's and Audubon's) are easily distinguished from one 

 another by their plumage patterns, but Audubon's may be impossible to distinguish from 

 the air from the very rare Manx shearwater. The shearwaters are dark above and usually 

 stay close to the water, so they are more difficult to detect than pale birds such as terns. 



Storm-petrels are very small, and most are dark colored. Most storm-petrels are 

 probably missed in censuses conducted from 228-m altitude, and they may be missed at 91 

 m. The three species (Wilson's, Leach's, and Harcourt's) likely to occur in the Gulf of 

 Mexico are very similar in plumage and we did not identify many individuals to species. 



Tropicbirds are fairly large and predominately white. They also typically fly at an 

 altitude of at least several meters and are very conspicous. They can be confused only 

 with the larger pale terns; however, their shape and wingbeat are distinctive. 



White and brown pelicans are among the largest and most conspicuous birds in the 

 area and are probably the most easily identified. 



The boobies and gannets are also very conspicuous but masked (blue-faced) boobies 

 can be confused with gannets, particularly as subadults. 



Cormorants are so distinctively shaped that they are easy to identify when on the 

 water or flying, and tend to be conspicuous despite their dark color. In Texas we did not 

 distinguish between the very similar olivaceous and double-crested cormorants. 



Frigatebirds tend to be very conspicuous because of their large size. They also 

 have a unique profile which makes identification very easy. They have a habit of soaring 



19 



