birds respond rapidly to changes in available food. 

 The closure of dumps and improvement of sani- 

 tation at fish-handling facilities resulted in 

 markedlj lower gull numbers. Quite clearly. 

 effective biological control of herring gulls must 

 depend on reduction in the amount of food avail- 

 able at metropolitan dumps, piggeries, sewage 

 outlets, and open-air fish processing sites. 



Seagull -problem, at naval air station n lu ved. — 

 The distress call of an immature herring gull was 

 used by Denver Center personnel to frighten gulls 

 from runways at Mollett Naval Air Station, Moun- 

 tain View, Calif. The call was broadcast from a 

 loudspeaker mounted on top of a truck driven, 

 with sound on, toward cadi group of gulls resting 

 on runways. At the call the gulls quickly arose, 

 circled the truck, and flew away. Some 2,000 to 

 3,000 birds were driven away during a 45-niinute 

 period each morning during the test period of No- 

 vember 16 to 21, clearly demonstrating the effec- 

 tiveness of the method. 



Bird hazard survey at Washington National 

 A irport. — Ornithologists of the Audubon Natural- 

 ist Society of the Central Atlantic States, under 

 contract with the Bureau to study the bird-hazard 

 problem at Washington National Airport, ob- 

 served bird species, numbers, and movements on 

 or near the airport between dawn and dusk about 

 once a week since October 1962. 



At least 143 species of birds were observed on, 

 over, or near the airport. The greatest number 

 was seen during spring and fall migrations. Con- 

 sidered potentially hazardous to aircraft were 23 

 species in the fall, 35 in the spring, and 8 species 

 from May through July. Herring, ring-billed, 

 and laughing gulls were the most abundant and 

 constituted the greatest hazard to aircraft landing 

 and taking off. Of lesser importance were shore- 

 birds, swallows, swifts, crows, starlings, black- 

 birds, pigeons, mourning doves, and horned larks. 

 Evidence was obtained of at least nine bird-plane 

 strikes in 1963. Five of the strikes occurred in 

 April and 1 each in May, June, September, and 

 October. 



System developed for rating chemicals. — There 

 has long been a need for a better method of rating 

 the hundreds of chemicals that are screened an- 

 nually by Bureau laboratories for animal damage 

 control. Both lethal agents and repellents are 

 being sought, but these terms are not well defined 

 and some compounds may qualify in both cate- 

 gories. 



Denver Center biologists recently developed a 

 rating system that more accurately defines the 

 toxic and repellent qualities of chemicals under 

 study. The system incorporates three functions: 

 ( 1 ) The lethal dose of the compound: (2) accept- 

 ance in relation to lethal dose: and (3) mortality 

 in the test species. A rating of 5, 10, and 100, 

 respectively, for the 3 functions — written 5-10- 

 100 — would indicate a highly toxic compound (5 

 mg/kg) that is well accepted (10 times a lethal 

 dose) and extremely effective ( 100 percent mortal- 

 ity). At tin' other extreme, a compound with a 

 rat ing of 1,000-0.05-0 would be one that is practi- 

 cally nontoxic (1,000 mg/kg), poorly accepted 

 ( o.o5 times a lethal dose), and has no lethal effect 

 on test animals (0 mortality). Such a compound 

 would be an excellent repellent. 



Antifertility, agents have promise in predator 

 control. — The first field trial of an antifertility 

 agent in coyote control has been carried out by the 

 Denver Center. In March, 5,000 drop baits con- 

 taining a synthetic estrogen, DRO-629, were used 

 in a 20-township area in southeastern New Mexico. 

 The baits were placed when coyote sign was evi- 

 dent, and were spaced over the area so as to reach 

 as many of the animals as possible. 



An appraisal of the study was determined by 

 collecting female coyotes in April and May. Ex- 

 amination of 27 animals from the treated area and 

 21 from the untreated area indicated that only 

 21 percent of the females on the former would have 

 whelped, and that 100 percent of those on the latter 

 would have reproduced. It can be concluded at 

 least tentatively that in the first comprehensive 

 field test the antifertility agent reduced the coyote 

 crop on the treated area by 80 percent. 



Compound S-6999 shows specificity for com- 

 m* nsal ruts. — Based on toxicological investigations 

 by McNeil Laboratories, Fort Washington, Pa.. 

 compound S 6999 appears to have specific toxicity 

 for commensal rats. Its high toxicity to Norway 

 rats (LD 50 percent 7.4 mg/kg (4.76-11.69) is in 

 contrast to its toxicity for laboratory mice, which 

 is in the range of 2.000 to 3,000 mg/kg. 



Because of the highly specific nature of com- 

 pound S 6999, the Denver Center supervised a 

 total of 134 separate field trials during 1963 to 

 determine the optimum practical concentration, 

 suitable bait ingredients, and pattern of action 

 when exposed for rat control. Trials involved 

 both Norway and roof rats. 



60 



