Efficiency of Aerial and Ground Methods 



Since inventories were conducted by both fixed-wing and rotary-wing 

 aircraft as well as by ground (boat, foot) methods, the opportunity arose to 

 compare the efficiency of the three methods. During the spring of 1976, 

 colonies in Massachusetts and eastern Rhode Island were censused using all 

 three methods. Accurate records of time and travel expenses were kept, allow- 

 ing relative costs of each method to be determined. The census accuracy could 

 not be statistically compared because the three methods could not be conducted 

 simultaneously and independently for obvious logistical reasons. 



The results of the cost comparison are shown in Table 22. Fixed-wing 

 aircraft provide a fast, inexpensive method of censusing while ground methods 

 dre the most costly because of the time required (nearly 3 weeks). Helicopters 

 are the most expensive per day, but the time saving renders them more effi- 

 cient than ground methods. 



Despite the low cost of the fixed-wing methods, there were a number of 

 drawbacks: (1) Federal aviation regulations prohibit flying censuses near 

 metropolitan airports; (2) the high airspeed, restricted vision, and often 

 dense vegetation resulted in missing colonies of the smaller birds such as 

 least terns or cryptic herons; (3) "ground-truthing" by nest counting in 

 sample areas is usually not possible because of landing limitations. 



Helicopters provide efficiency and flexibility by combining the time- 

 saving advantages of aerial methods with the ability to land and make ground 

 counts for improved census accuracy. Usually one hour of "free" ground time 

 is allowed for each "air hour" so that the two methods can be combined without 

 added cost. 



Surveys are best performed for most species by helicopters. When con- 

 ducting ground surveys, there is a tendency to restrict one's coverage to 

 areas where previous nesting occurred because of the time involved in travers- 

 ing large expanses of beach, marsh, and water. With helicopters, all rocks, 

 points, and beach areas can be examined in a brief time. Low-flying helicop- 

 ters may be the only way to flush and locate the more cryptic herons when they 

 nest in dense, inaccessible swamp, marsh, or mangrove colonies (Buckley and 

 Buckley 1976). 



Other advantages in using heli 

 can be taken from a variety ^^ "'' 

 conditions can limit boat 

 landing can be achieved eas 



jsing helicopters are (1) good quality photographs 

 ety of altitudes and angles; (2) weather and sea 

 use to islands much more than helicopters; (3) 

 i ly in a small (ca. 15 m^ ) area. 



One of the major unknowns in census methodology is the relative degree of 

 disturbance involved. There are few good, controlled field studies of distur- 

 bance effects on breeding colonies (Kury and Gochfeld 1975, Robert and Ralph 

 1975). Results are often equivocal. Of the human activities at an oil well 

 drilling site in Canada, helicopters were felt to be the most disturbing 

 factor, but the results were qualitative (Barry and Spencer 1976). There are 

 probably regional differences based on the history of disturbance factors at 

 the colony. Least terns on Long Island remain on nests when a helicopter 

 hovers less than 30 m above (M. Gochfeld pers. comm. ) but in Florida, least 

 terns seem to be more sensitive because of less exposure to air traffic (E. J. 

 Fisk pers. comm.). In general, the more remote the observer, the less distur- 

 bance will result. 



40 



