APPENDIX A 

 PROCEDURES FOR USING SAMPLING KETHODS IN DETERMINING NEST DENSITIES 

 POINT-CENTER QUARTER 



1. A line should be selected (randomly, haphazardly, etc.) within the 

 study area and followed using compass orientation or markers along the line at 

 fixed intervals. 



2. At a predetermined constant interval along the line, points are 

 selected. At each point, an imaginary circle is circumscribed with the point 

 at the center. The circle is divided into four quadrats. VJithin each quad- 

 rat, the nearest nest to the point is measured (in feet) and recorded. This 

 is repeated for each point along the line, measuring four distances for each 

 point. 



3. An average nearest nest-to-point distance is then computed by summing 

 all distance measurements and dividing by 4 x no. points used. 



4. This value then is converted into an aerial measure by squaring it. 



5. The squared value, divided into 43,560 (no. ft. /acre), represents 

 the number of nests per acre. To get the total number of nests in the study 

 area, the total area (in acres) needs to be calculated. 



BELT TRANSECTS 



The procedure outlined below was adopted from a study conducted in salt 

 marsh heronries along the north Gulf coast by Portnoy (1977). 



1. A transect line is established along the longest axis of the colony. 



2. Either a 10% or 20% sariple of the colony area is taken, using 2-m 

 wide belts as sampling units (approximately an arm's length on each side of 

 the observer while walking the belt). The sampling transects are run perpen- 

 dicular to the long axis of the colony. To obtain a 10% sample by maintaining 

 a 20 m mean distance between 2-m wide transects, only random numbers between 2 

 and 40 are accepted (rationale: a 100% sample would have a mean inter-transect 

 distance of 50 since the range of random numbers is to 100. Hence, a 20 m 

 distance (40% of the 50 m distance) requires that only 40% of all random 

 numbers should be used.) 



3. At each of the randomly-selected points along the transect line, the 

 observer follows a conipass bearing perpendicular to the line and crosses the 

 entire width of the colony area, counting all nests within 1 m of each side. 

 This can be accomplished expeditiously when several observers are used, since 

 several belts can be sampled siiTiultaneously. Separate counts are kept for 

 each belt transect. 



4. The exact percent sample is determined next by dividing the entire 

 length of the long axis into the cumulative width of all 2m width transects. 

 The total nest estimate of the entire colony then is extrapolated by dividing 

 the total number of nests in all belt transects by the percent sample taken. 



124 



