counted at approximately the same 

 time each year and in much the 

 same order. 



In making a strip count the crew- 

 is lined up at the most logical start- 

 ing point on the area to be cen- 

 sused. The men are placed about 

 50 feet apart — a convenient width 

 of strip for each counter. The ob- 

 jective is to cover as wide a strip as 

 possible, but the type and density 

 of the vegetation determine this to 

 a large extent, as all muskrat houses 

 and feeding stations must be clearly 

 seen. The two men on the outside 

 lines are responsible for guiding 

 the crew. Each counter moves 

 down a strip and counts from him- 

 self to the man on his left or right, 

 as predetermined, using a hand 

 tally machine. The counters on the 

 outside are responsible for marking 

 the outer limits of the area by heap- 

 ing muskrat-house material into 

 small towers on the larger houses; 

 these temporary mounds are readily 

 discernible from a considerable 

 distance. 



The strip-count method must be 

 modified in areas that are badly 

 eaten out by the muskrats, or that 

 are broken up by numerous ponds, 

 creeks, or guts. If the topography 

 is such that the strip-count method 

 cannot be used, it may be advisable 

 to assign a unit or a marsh to a sin- 

 gle counter. Bank dens occurring 

 along drainage ditches or streams 

 in a strip being censused are in- 

 cluded, but care must be taken to 

 count only the main entrances to 

 the dens. They are usually the 

 larger entrances and have more 

 signs of being used. 



20 



An aerial census provides a 

 quicker and more-economical meth- 

 od of counting houses than does the 

 ground count. Its accuracy can 

 also be checked against photo- 

 graphs made during the flight (fig. 

 25). An aerial observer often 

 covers in a few hours an area that 

 would require a three-man ground 

 crew several days. The strip count 

 is generally employed in an aerial 

 census — the pilot moving back and 

 forth across the area being cen- 

 sused, in much the same manner as 

 in the ground strip count. Bound- 

 ary markers must be clearly visible 

 from the air. On badly eaten areas 

 the muskrat houses stand out 

 clearly, but dense vegetation pre- 

 sents difficulties. With good visi- 

 bility the larger houses can be seen 

 from 800- to 1,000-foot elevations 

 over a %-mile radius. After a 

 snowfall, or when a count of indi- 

 vidual trapping units is desired, 

 lower-level observations at 200 feet 

 or less become necessary. Counts 



Figure 25. — Against the dark water, 

 muskrat houses on this North Carolina 

 coastal marsh appear as numerous 

 white spots from the air. Count of the 

 houses serves as a practical basis for 

 determining the population. 



