the horizontal furnace-pipe boxes and none of 

 the horizontal roofing-paper boxes. Wood ducks 

 used 28 percent of b"> available vertical boxes, 25 

 percent of the ~>2 furnace-pipe boxes, and 15 per- 

 cent of '■'>'■* roofing-paper boxes. 



Management of aquatic plants. - Eurasian 

 watermilfoil has spread rapidly over many of the 

 more protected parts of Chesapeake Bay and now 

 occupies more than loo.OOO acres. It has also been 

 found in Alabama. California, Indiana, New Jer- 

 sey, New York, North Carolina, Ohio, Pennsyl- 

 vania, Tennessee, and Wisconsin. This exotic 

 milfoil grows in medium to hard water and in 

 saline situations up to about 28 percent of sea 

 strength, and it can exist in salinities as high as 

 13 percent of sea strength. 



In the Chesapeake Bay area, the effectiveness of 

 •_M-D treatment at 20 and 30 pounds acid equiva- 

 lent per acre was best when the water temperature 

 was above 18° C, the vegetation thick enough to 

 contain the treatment, and before the period of 

 flowering. Preliminary studies with new com- 

 pounds reveal that diquat, a mixture of endothal, 

 and the potassium salt of silvex, showed promise 

 in tidal situations. The sodium salt of fenac was 

 not effective in tidal areas in controlling Eurasian 

 watermilfoil. 



Alligatorweed is another exotic plant that de- 

 tracts from waterfowl habitat in southeastern 

 United States by crowding out food plants and 

 blocking waterways. In cooperation with U.S. 



^'\ - 



A typical 12-acre pond on the Yellowknife area. Mackenzie 

 District. Northwest Territories. Lesser scaup commonly 

 nest in the sedges bordering such ponds. In the Far 

 Xorth. water tables are still relatively stable. (Photo 

 by II. W. Murdy) 



Army Engineers, biologists from Patuxent tested 

 several methods of control. They found that the 

 iso-octyl ester of silvex is effective for a longer 

 period of time than the potassium salt of silvex. 

 Both formulations are effective in controlling 

 rooted alligatorweed at rates of 20-pound acid 

 equivalent per acre. Elicit ivc methods of control- 

 ling floating mats have not yet been found. 



1 mprovement in North Dakota waterfowl 

 habitat. — Most potholes in three study areas in 

 North Dakota were in good condition in the spring 

 of 190;}, owing to an excellent winter carryover of 

 water from the previous fall and fairly good 

 spring snow melt. During mid-April, water levels 

 in potholes of the more permanent type were much 

 higher than during the corresponding periods in 

 1961 and 1962. Water levels of temporary or sea- 

 sonal types also were considerably improved, with 

 the exception of a few potholes on higher eleva- 

 tions. Date spring and summer rainfall in 1963 

 was not sufficient to maintain levels and potholes 

 dried increasingly as the season progressed. On 

 October 15, at the end of the growing season, only 

 19 out of 137 ponds still contained water. Com- 

 parable figures for 1961 and 1962 were and 109. 



Transient waterfowl concentrated on the study 

 areas in much larger numbers last April and May 

 than in 1961 and 1962. Diving ducks, including 

 redheads,' canvasbacks, and lesser scaup, were 

 especially abundant. Unusually large populations 

 of waterfowl were resident during late spring and 



Many potholes in Stutsman County. N. Dak., even large 

 ones like this, became completely dry during the summer 

 of 1961. In years of average precipitation, this is one of 

 the better duck-nesting areas in the prairie pothole coun- 

 try. Waterfowl reproduction is seriously affected as 

 drought becomes severe. (Photo by R. E. Stewart) 



19 



