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CHAPTER 2: NEW TERRITORY FORMATION IN THE COOPERATIVELY BREEDING RED-COCKADED WOODPECKER
ABSTRACT
In species exhibiting cooperative breeding behavior, emphasis is placed on constraints on acquiring a suitable breeding position and queuing in the form of helping or floating to obtain a breeding vacancy. However, despite this driving force that underlies cooperative breeding social systems, few studies have described territory creation events and factors that induce new territory formation. I used 20 years of demographic data collected as part of a long-term monitoring study of Red-cockaded woodpeckers (Picoides borealis) to investigate mechanisms that stimulate territory creation in this cooperatively breeding species. Because the Red-cockaded woodpecker is an endangered species, I sought to determine how to naturally increase populations, as well as contribute greater understanding to cooperative breeding systems. I determined that young male helpers and affiliated floaters bud, while young male unaffiliated floaters and solitary males pioneer. Intensified competition, measured as an increased proportion of nonbreeding males in the population, was positively associated with new territory formation.This study also revealed the large role that floaters play in territory creation events in this system.
INTRODUCTION
Cooperative breeding systems have stimulated much research regarding demographics of individual species, the evolutionary basis of helping behavior, and the causes underlying the evolution of this social system. Theories about the latter such as ecological constraints and benefits of philopatry (Emlen 1984; Stacey and Ligon 1987, 1991) focus on limitations to acquiring suitable breeding positions. A characteristic of the most common types of cooperative breeding systems is the predominance of turnover on existing territories, as opposed to creation of new territories, in acquiring breeding positions, but new territory formation does occur. Given the emphasis placed on attainment of breeding positions as a driver in the evolution of this social system, it is surprising that few studies mention the creation of new territories, and even fewer have investigated mechanisms promoting territory creation activities such as budding and pioneering (but see Woolfenden and Fitzpatrick 1978, 1990; and Komdeur and Edelaar 2001ab) that are alternatives to helping. Territorial budding (sensu Woolfenden and Fitzpatrick 1978)divides one territory into two, while pioneering creates a new territory in formerly unoccupied habitat. Pioneering may not be an option in species constrained by absolute habitat saturation,but budding may be widespread and understudied among cooperative breeders. My objective was to investigate factors that trigger budding and pioneering in the Red-cockaded woodpecker (Picoides borealis).The Red-cockaded woodpecker is a federally endangered species, endemic to open, mature pine forests of the southeastern United States. It is unique among North American cavity nesters because it constructs roost and nest cavities in live pine trees (USFWS 2003). Cavity excavation may take several years due to the difficulty of construction in live pines (Jackson et al. 1979; Harding and Walters 2002, 2004), which has caused cavities to be a critical resource that appears to have promoted the evolution of cooperative breeding in this species (Walters et al. 1992). Rather than construct cavities in unoccupied habitat, Red-cockaded woodpeckers compete intensely for territories with existing cavities (Walters 1991, Walters et al. 1992), with the natural creation of new territories being rare (Hooper 1983, Walters 1990). Red-cockaded woodpecker groups typically contain a breeding pair and 0-4 nonbreeding helpers, usually male offspring from prior breeding attempts (Lennartz et al. 1987, Walters et al. 1988, Walters 1990). Helpers assist in incubation and provisioning nestlings and fledglings, as well as territory defense. However, helpers do not engage in extra-pair copulations even if the opposite sex breeder is unrelated, and thus gain fitness benefits from helping mostly indirectly through assisting kin (Haig et al. 1994, Khan and Walters 2000). Male helpers inherit the natal territory upon death of the breeding male and will pair with the widowed female if she is unrelated to him. If she is a relative, the female leaves and the male attracts a new female.Helpers may also disperse short distances to fill vacancies on nearby territories. Red-cockaded woodpecker population size, as measured by the number of groups, is not greatly affected by natality or mortality because male helpers act as a buffer between these processes and number of breeders (Walters et al. 2002b, USFWS 2003). Individuals rapidly occupy breeding vacancies when mortality outweighs reproduction, while helper class numbers grow when births exceed deaths (Walters 1991, Heppell et al. 1994). Thus, the number of breeding pairs varies little across years. Conversely, because cavities are a limiting resource and an essential component of high quality territories, cavity tree dynamics have a substantial impact on population demography (Walters et al. 1992). Therefore, population dynamics are driven primarily by the availability of suitable territories – i.e. habitat containing cavity trees.
Abstract
Dedication
Acknowledgements
List of Tables
List of Figures
CHAPTER 1: EFFECTS OF MILITARY TRAINING ACTIVITY ON RED-COCKADED WOODPECKER DEMOGRAPHY AND BEHAVIOR
ABSTRACT
INTRODUCTION
STUDY AREA
METHODS
RESULTS
DISCUSSION
MANAGEMENT RECOMMENDATIONS
LITERATURE CITED
CHAPTER 2: NEW TERRITORY FORMATION IN THE COOPERATIVELY BREEDING RED-COCKADED WOODPECKER
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
LITERATURE CITED
