Carolina were used by wnterfowl, according to 

 food-habits studies. Alligatorweed was replaced 

 in treated plots by valuable waterfowl food plants, 

 including southern cutgrass, ari-owhead, and 

 smartweeds. 



Eurasian watermilfoil. — Continued investiga- 

 tions on Eurasian watermilfoil revealed that, in 

 addition to its previously known range from New 

 York to Alabama, this important pest plant also 

 occurs in Ohio, Indiana, and California. Control 

 in the Chesapeake Bay area with granular formula- 

 tions of 2,4-D is limited to a very short period in 

 late May and early June. 



Salinity and aquatic plant growth. — A severe 

 storm in March poured ocean water into Back Bay 

 and Currituck Sound, raising the average salinity 

 for most of the remainder of the year to about 11 

 percent of sea strength. This influx caused a clar- 

 ification of the water and an increase of over one- 

 third in the production of submerged vegetation, 

 particularly wigeongrass, sago pondweed, and 

 claspingleaf pondweed. Southern naiad was the 

 only important plant to become less common. 

 There was also a marked increase in production 

 of sago pondweed seed and tubers. Some species 

 of invertebrates increased : others decreased. A 

 spectacular rise in the numbers of a brackish- water 

 clam occurred. Overall abundance of invertebrate 

 food organisms was about the same after the stoiTn 

 as before. All indications were that the salt-water 

 intrusion did not harm the fishing of the area, and 

 that it led to considerably improved food condi- 

 tions for waterfowl. Waterfowl utilization of 

 the area during the fall and early winter of 1962 

 was higher than during any of the 4 previous years 

 despite severe ice conditions in December. 



Water bird ft on mosquito-control impound- 

 ments. — Contract studies were continued by the 

 Florida State Board of Health on the effects of 

 mosquito-control impoundments on wildlife. 

 These have revealed some of the reasons for the 

 consistently greater use by water birds of im- 

 pounded areas than of unimpounded areas. Rais- 

 ing and stablizing water levels increased the 

 amount and availability of submerged aquatic 

 plants and of certain fish and invertebrates that 

 serve as food for aquatic birds. Impoundments 

 with stabilized levels also provided attractive rest- 

 ing areas. Ducks, coots, grebes, and cormorants 

 were most abundant in areas with the greatest 

 amount of open water, wiiereas the reverse was 

 true for herons and related birds. Areas flooded 



continuously with water of low salinity became 

 choked with cattails and showed decreased use by 

 birds. Impoundments generally decreased the 

 number of clapper rails and killdeers. 



Hydrafed lime on goose pastures. — Fertilization 

 experiments at the Patuxent AVildlife Research 

 Center have shown that goose pastures treated 

 with hydrated lime produce over twice as much 

 clover 1 year later than pastures treated with the 

 cheaper ground limestone. There was a limited 

 gain in production during the second year after 

 the pastures had been treated with ground lime- 

 stone. 



Waterfowl nesting structures. — A new type of 

 shallow-water nesting structure for Canada geese 

 has been developed. It consists of a basket con- 

 stmcted of wire netting and steel rod mounted on 

 four steel fenceposts. Straw is added for nest 

 material. Geese readily accept this structure and 

 are able to defend it successfully against swimming 

 predators. 



A simple guard has been developed at the 

 Patuxent Center for excluding raccoons and other 

 climbing predators from duck-nesting boxes 

 mounted on steel fenceposts. It consists of a piece 

 of thin sheet aluminum with the free edges fast- 

 ened together to form a panel 9 inches wide and 

 38 inches long. The panel is constructed so that 

 it encloses, lengthwise, a fencepost in sandwich 

 fashion. 



OTHER MIGRATORY BIRD STUDIES 



Mourning dove studies. — It was found in an 

 Arizona Unit investigation that male doves tend 

 to call less often when their nests were successftil 

 than when their nests were broken up. IVIales of 

 active nests called very little or not at all, but, in 

 contrast, males known to be unmated or to have 

 lost a mate called 7 to 16 times more frequently. 



In a Missouri Unit project, cooing behavior of 

 wild mourning doves was studied during two 

 breeding seasons. Unmated wild birds cooed an 

 average of 13 times more per 3-minute listening 

 period than mated birds. The probability of hear- 

 ing an unmated dove call in any 3-minute period 

 is at least 3 to 6 times greater than the maximum 

 probability of hearing a mated dove call. 



Preliminai-y analysis of nesting data ol)tained 

 by the Colorado I^nit during the suunner of 106'2 

 disclosed great variability in dove iirodiidion by 

 liabitat types in the north-central part of t he State. 



20 



