FISH AND WILDLIFE TECHNICAL REPORT 25 



feeds, usually remaining within a relatively small area; 

 (2) foraging flight is when the bird is moving slowly in 

 a search pattern back and forth over the water or milling 

 above a food source; and (3) traveling flight is when the 

 bird is headed in a straight line, generally at a fast pace, 

 and is not concerned with the waters immediately below 

 it. A sighting is the observation of a single bird or group 

 of two or more birds acting as a unit (e.g., a feeding 

 flock). 



The basic survey technique requires the ship to move 

 along a straight path at a constant speed. For a specified 

 length of time, an observer counts birds observed on one 

 side of the ship out to a specified distance and forward 

 of mid-ship until the end of the transect (Fig. 1). All 

 feeding and foraging birds are counted whenever they are 

 observed within the count zone. Birds in each sighting 

 are counted only once, thus birds in a feeding flock that 

 are outside the count zone when the flock is first sighted 

 cannot be counted later as being within the transect. 

 Traveling birds are counted only during periodic "instan- 

 taneous" counts (see Counting Birds). 



Area Surveyed 



The area surveyed during each transect varies with the 

 ship's speed, the width of the count zone, and the dura- 

 tion of the observations. Different ships have different 

 cruising speeds and unless the ship is dedicating time for 

 bird observations, the observer will not be able to con- 

 trol this speed; thus, transects will have to be taken at 

 many different speeds. The speed at which the observer 

 moves along the transect probably influences survey 

 results, but how it influences the number of seabird detec- 

 tions has never been properly studied or evaluated. At 

 high speeds, the observer has less time available to detect 

 and identify all birds, especially in areas of high density 

 and areas where birds are feeding below the surface. At 

 slow speeds, more birds may move into the counting zone 

 and become associated with the water than at high speeds, 

 thus inflating the count. It has been our experience that 

 10 kn is an average cruising speed and probably the most 

 appropriate speed for pelagic observations. In order to 

 hold data variability within reasonable limits we switch 

 to supplemental techniques (e.g., general observations) 

 at speeds of less than 6 kn and more than 15 kn. 



Our standard transect width is 300 m. This width is 

 essentially a compromise between an appropriate distance 

 for detecting all birds under reasonable observation con- 

 ditions and covering an adequate survey area with limited 

 time and money. Detection of all birds especially the 

 smaller species out to 300 m becomes difficult or even 

 impossible when the seas are rough, or when rain, fog, 



or reflected sunlight reduce visibility. The height of the 

 observer above the water also affects detection distance 

 and a 300 m width may not be practical from a small boat 

 except under ideal conditions. 



Thus, surveys using 300-m widths are not always possi- 

 ble. The problem with narrower transects is that as the 

 ship approaches some birds tend to move away from the 

 ship, leaving the count zone and creating higher densities 

 farther out. When most of the birds cannot be detected 

 out to 300 m, the observer may wish to reduce the transect 

 width to 200 m. If 200 m is too far, then only general 

 observations should be conducted. 



The ability to estimate distances is of major importance 

 in conducting shipboard transects. Distance estimation is 

 principally affected by the height of the observer above 

 the water. An observer 15m above the water often over- 

 estimates the transect width because his line of sight to 

 the distal boundary of the survey zone is longer than that 

 of an observer only 4 or 5 m above the water; the latter 

 tends to underestimate because he or she perceives a 

 foreshortened distance. Choose an observation spot as 

 high as possible, especially on small ships. The flying 

 bridge is usually a good choice if it is available, because 

 it affords an ample view of the count zone. On large ships, 

 the bridge wing may be high enough and more conveni- 

 ent than the flying bridge. It is rarely advisable to con- 

 duct observations from inside the pilot house. 



Many techniques and kinds of equipment are available 

 to aid in determining distances, and a primary objective 

 of the observer when first boarding a ship should be to 

 develop an accurate method of estimating the transect 

 width. Most harbors are very accurately charted. Locate 

 several objects that are known distances from the ship 

 (e.g., 300, 500, and 1,000 m) and spend some time look- 

 ing through your binoculars and getting oriented to these 

 distances. Often you will be able to relate the distance 

 to the sizes of birds. The relative sizes of bird species 

 on the water is quite helpful. Practice in the harbor before 

 leaving on the cruise will help you to use bird sizes in 

 judging distances during a survey. 



Heinemann (1981) developed a range-finder for pelagic 

 bird censusing that can help maintain consistency in deter- 

 mining the border of the count zone during transects. A 

 set of dial or slide calipers can be used as the range finder. 

 The major limitation of this device is that the horizon must 

 be in clear view; thus, it is not usable in bays, fog, or 

 in rough seas. The up and down motion of the ship adds 

 to the difficulty of using the instrument. The range- 

 finder's accuracy is considerably reduced at heights of 

 less than about 8 m because the angle is so slight that 

 minor differences in the setting will greatly affect the 

 estimate. Other considerations in using the device are 



