Survival, Experience, and Age in Relation to Breeding Success of Canada Geese

Abstract

Success of individually identifiable giant Canada geese (Branta canadensis maxima) in rearing a brood was analyzed with respect to their age, experience, and survival. Twenty-five percent of 2-yearolds raised broods averaging 2.3 young. Approximately 31% of 3and 4-year-old geese raised broods that averaged 2.9 young, whereas 58% of older geese (4+ to 18 years of age) raised broods averaging 3.7 young. Non-nesting and loss of clutches and broods were responsible for low success of 2-year-olds, whereas loss of broods was the major factor in low success of 3and 4-year-old geese. Older geese (4+) were more than twice as successful in raising at least 1 young to fledging as were younger birds. Regardless of age, individuals that succeeded in rearing a brood were more than twice as likely to be successful in producing young in ensuing years as were those unsuccessful in any particular year. Survival did not vary significantly between successful and unsuccessful breeders within or among age-classes. Geese of 4+ years of age comprised 26% of the potential breeding population, but produced 50% of the young. Aggressive behavior toward conspecifics and predators varied, and was probably related to breeding success. This plasticity in behavior could be related to genetically based behavior types that favor different forms in a fluctuating or patchy environment. These results could also be related to the effects of early experience in relation to complex social organization and importance of family structure in these long-lived animals. J. WILDL. MANAGE. 45(4):817-829 Deferred maturity is common in large, long-lived birds, and is characteristic of geese, which do not nest until they are 2-4 years of age (e.g., Klomp 1970). Initial nesting attempts by geese that have not nested before are characterized by later nest initiation dates, smaller clutches, and, usually, poorer success than obtained by older birds that have nested 1 or more times (Brakhage 1965, Finney and Cooke 1978). Such results are usually interpreted in terms of natural selection theory, leading to the conclusion that physiological regulating factors evolved in these animals to prevent earlier maturity because this enables them to leave more offspring over their lifetime (Lack 1968:297-299). Attempts to breed earlier likely would not succeed because of inefficiency in care of young and competition for food, space, etc., and would expose individuals to greater risk of death than if they did not breed. Thus, reproduction costs something in terms of survival and future opportunities for reproduction (e.g., Stearns 1976); if it did ot, if would be advantageous for younger birds to attempt breeding even if they rar l succeeded. Implicit in this scheme is that experience gained by subadults enhances their chances for success at a later time (Lack 1968:299). Specifically, for geese, individuals failing to nest successfiully in a given year may have a survival advantage over successful birds (Newto 1977) because they do not suffer as large an energy drain as nesters and they molt earlier (Hanson 1962b, Ankney 1977, Ankney and MacInnes 1978, Raveling 1979a). An alternative view that has received little attention is that many reproductive failures could be due to the effects of early social experience. Few data are available on survival of unsuccessful vs. successful breeders. Wooller and Coulson (1977) found that some kittiwakes (Rissa tridactyla) first breeding at 5 years of age. The role of experience (other than generalized as age) in affecting future reproductive perfor. \Vildl. Manage. 45(4):1981 817 This content downloaded from 207.46.13.113 on Thu, 06 Oct 2016 04:06:29 UTC All use subject to http://about.jstor.org/terms 818 CANADA GOOSE BREEDING SUCCESS* Raveling mance of individuals has been particularly difficult to evaluate for wild animals. This paper presents data on the reproductive success of known-aged, individually identifiable giant Canada geese in relation to their prior breeding experience and probability of survival. The results lead to an estimate of relative productivity by different age-classes within the population. Support for this study was provided by the Canadian Wildlife Service (CWS) and the University of California, Davis (UCD), Agricultural Experiment Station. The P. D. Curry and A. J. Vincent families generously made available use of their property, East Meadows Ranch, on which the study was centered. I am grateful to C. C. Dixon, L. Bidlake, and several of their assistants, of the Manitoba Department of Mines, Resources and Environmental Protection; L. King, manager of East Meadows Ranch; R. M. McLandress and M. L. Wege (UCD); R. Halladay, G. Adams, and R. Hutchison (CWS); and R. Osika of the Royal Canadian Mounted Police, who assisted in various phases of banding and data collection. A. Dzubin (CWS) was instrumental in making this study possible. H. A. Hochbaum, Delta Waterfowl Research Station, gave permission to neck-collar geese banded by his station in previous years to enhance the sample of known-aged individuals. K. H. Pollock (UCD) helpfully advised on statistical procedures. D. F. Lott and R. M. McLandress (UCD) commented on the manuscript. METHODS AND STUDY AREA Between 1968 and 1970, individually marked plastic neck collars (Sherwood 1966) were placed on 1,406 giant Canada geese at the Marshy Point Goose Sanctuary along the southeast shore of Lake Manitoba, about 105 km northwest of Winnipeg, Manitoba, Canada (50'30'N, 98'W). All geese were banded during July, August, or September, before the opening of the hunting season. Results reported deal mainly with observations made between the time that geese acquired flight capability in early August and late September when the hunting season opened, in 1970 through 1974. Known-aged 2-year-olds first became available for observation in 1970, and after 1974 all surviving marked geese were 5+ years of age. In 1970, 1973, and 1974, marked geese were observed regularly (2+ times/week) during August and September. In 1971 and 1972, results were restricted to an intensive 1-week observation period in mid-September just before hunting.began. Eggs in nests of some marked geese were taken by Cooper (1978). Data for these individuals were excluded from analyses. Geese were artificially provided with barley at East Meadows Ranch to prevent them from causing damage to crops. Thus, most geese at the Sanctuary (up to 5,000+ in autumn) regularly congregated where they were easily observed. Criteria for determining if marked geese were successful in rearing young were behavioral. These were: unity in local movements, preflight, and flight behavior (Raveling 1968a, 1969a, b, c); acceptance or tolerance by other geese (especially adults, i.e., 2+-year-old birds; Hanson 1962a) in a group; unity in agonistic interactions; and especially the performance of the triumph ceremony (a conspicuous display exhibited by familyrelated birds; see Fischer 1965, Raveling 1970). Immature geese in August and September were easily identified by their plumage, size, and behavior. Adult J. Wildl. Manage. 45(4):1981 This content downloaded from 207.46.13.113 on Thu, 06 Oct 2016 04:06:29 UTC All use subject to http://about.jstor.org/terms CANADA GOOSE BREEDING SUCCESS* Raveling 819 ganders were easily distinguished from adult females by their size and behavior. A few captured geese had been banded between 1954 and 1966. These provided a sample of geese of known, extreme age. Survival is used herein in reference to those geese that were seen from year to year during the study period. These figures do not mean survival in a strict sense, because some geese lost their identifying neck collars and a few dispersed (Raveling 1978). However, I have no evidence that these factors biased data reported here. Details of the fidelity of geese in this flock to their areas of prior experience were reported previously (Raveling 1978, 1979b). Chi-square tests were used to compare data on propor-