Long-Term Retention of Plastic Collars on Canada Geese

Analysis of retrapped Canada geese (Branta canadensis maxima) at Seney National Refuge showed that only 30 percent of the birds retained flexible plastic collars after 6 years. Retention was higher among females than among males. Fading, brittleness, and loss of the number-letter combination of the collars are discussed. J. WILDL. MANAGE. 37(2):1 7S178 During a study of limiting factors and behavior of Canada geese at the Seney National Wildlife Refuge between 1963 and 1965, 518 geese were marked with flexible plastic collars (Sherwood 1966a). Although the study officially ended in 1965, many of the geese survived long past that date and some of the collars were retained for several more years. The purpose of this paper is to report on the long-term retention rates of these collars and to describe the condition of the collars after up to 6 years of use. The author thanks D. H. Johnson, of the Northern Prairie Wildlife Research Center, for his assistance in the statistical analysis. MATERIALS AND METHODS Sherwood (1966b), who conducted the behavior study, designed the collars; their construction has been described in detail in an earlier paper. Each collar was 2.S inches tall and had a number-letter combination routed into the plastic and painted with black lacquer. Orange collars were used in 1963, white in 1964, and yellow in 1965. Ends of the collars were not bonded with adhesive, so a birds could pull the collar off if it became caught. Determination of retention rates was nlade through the analysis of retrap data 1 Present address: Lacreek National Wildlife Refuge, Martin, South Dakota 57551. for the years 1966-69. When a collared or otherwise color-marked goose was retrapped, the marking was recorded on a field sheet. A check of band numbers of all retrapped geese was made to determine those birds that had originally been lllarked with collars. Retention rates were determined by comparing collars still in place with collars lost for each age-group of collars. Only birds trapped were used in determining the retention rates. This has resulted in a smaller sample, but has eliminated the bias of field observations tovards marked birds. RESULTS AND DISCUSSION During the 4-year period, a total of 194 retraps was made, 105 with the collars in place and 89 with the collars missing. A breakdown of the recoveries by the number of years since collar placement and by sex is given in Table 1. The smaller number of retraps of the 1and 2-year-old collars is because orange collars were already 3 years old and white collars 2 years old during the first year of data collection in 1966. The same is true in the older groups where only orange collars were present in ffie 6-year-old group and orange and white collars in the 5-yearold group. The data in Table 1 were analyzed to determine whether the sex of the bird and nurnber of years after placement had an J. Wildl. Manage. 37(2):1973 176 LONG-TERM RETENTION OF PLASTIC OLLARS ON CANADA GEESE Table 1. Collar retention rates of Canada geese at Seney National Wildlife Refuge. YEARS NUMBER OF RETRAPS AFTER RETENTION COLLAR CO11aIS CO11arS RATE PL XCEMENT Sex On Off ( percent ) M 11 5 69 1 F 15 3 83 Total 26 8 76 M 12 6 67 2 F 19 8 70 Total 31 14 69 M 15 13 54 3 F 14 19 42 Total 29 32 48 M 4 9 31 4 F 7 9 44 Total 11 18 38 M 2 5 29 S F 3 5 38 Total 5 10 33 M 0 3 0 6 F 3 4 43 Total 3 7 30 PLASTIC OLLAR ETENTION ON GEESE * Fjetland 177 both their collars and their service bands would have also been overlooked in this study, but this number of birds is small and would not greatly affect the retention rates. The significantly higher retention of collars by females was supported by field observations of marked birds. Of the 518 collars placed, 262 were on males and 256 (49 percerlt) on females. Observations of 24 collared geese in 1969 revealed that 20 were females and only 4 were males. Similar observations in 1968 revealed that 21 out of 28 collars seen were on females. Part of this unbalance in field observations can be attributed to a higher mortality rate for males than females in the Seney flock. Sherwood ( 1966a ) found that of yearlings and older geese in the Seney flock 43 percent s^7ere males and S7 percent females. He offered evidence that males were being shot more heavily than fenlales as one possible explanation for the unbalanced sex ratio. Dispersal of males to other flocks would also account for some of the difference in field observations. An unbalanced mortality rate and dispersal do not explain the different retention rates by sex in Table 1, however, where the rates are independent of the sex ratio of the flock, of field observations, of mortality rates, and of the nulnber of collars originally placed. Sherwood (1966b) reported two principal causes of collar loss. The first, collars slipping over the smaller heads of goslings, was solved by marking the birds after they were 2 months old. The second, collars pulling off on wire duck traps, 11as largely disappeared. Wire duck traps are still used at Seney Refuge, but only one collar svas found on a trap in 1968 and none in 1969. Those birds that tend to feed under the traps have in large part already lost their