Animal Behavior-The Effects of Grassland Restoration on Avian Mating Patterns

Introduction A central tenet of mating system theory is that habitat structure and composition affect the distribution of individuals in time and space, which in turn affect patterns of mating within a population (Emlen & Oring 1977, Westneat et al. 1990). For example, resource defense polygyny occurs when males defend resources attractive to females In habitats where resources are unevenly distributed, males that defend more of the resource may acquire more mates than other males. If resources are evenly distributed, they are less easily monopolized, and males tend to mate monogamously (Emlen and Oring 1977). Similarly, extra-pair paternity (EPP) may be influenced by habitat. In areas where resources are clumped, density may be high, which can increase encounter rates between individuals on different territories, thereby increasing EPP (Birkhead 1978, Westneat and Sherman 1997). Habitat structure and distribution can also affect the trade-offs with mate-guarding, thereby affecting EPP (Westneat et al. 1990, Mays and Ritchison 2006). Habitat structure is often greatly influenced by human activity. While the negative effects of habitat destruction are well known, a common response to such negative impacts is to use management techniques to restore or maintain habitat. It is becoming more apparent that these practices can also affect the reproduction and viability of target species in more subtle, but no less important ways. For example, the initial attempt to rescue the wood duck (ALt sponsa) was to mount nest boxes in highly visible groups that were easily found and quickly occupied by females. However, this arrangement significantly increased intraspecific brood parasitism and decreased egg hatchability (Semel et al. 1988). Careful study revealed that natural tendencies to parasitize nest sites were adapted to the natural condition of dispersed and hidden nest sites (Semel et al. 1988). In the same way, management practices that affect abundance can also affect the mating system and mate choice dynamics of animals in ways that can severely impact reproductive success, sexual selection, gene flow and population dynamics. I intend to investigate the effects of fire, as used to manage tallgrass prairie grasslands, on the mating system of an obligate grassland breeding bird, the dickcissel (Spiza americana). Specifically, I intend to compare the rate of polygyny, EPP, and nesting success of this bird in sites with burn intervals of one, two, four, and twenty years. Tallgrass prairie is an early successional ecosystem dependent on fire to prevent the incursion of trees and other woody plants. The time between fires (fire interval) affects the structural complexity and composition of prairie vegetation, with short intervals producing simple, grass dominated structures and longer intervals promoting a structurally complex mix of grass, forbs, and woody shrubs. Historically, fires are thought to have occurred every 2-10 years (Hulbert 1973, Rowe 1969, Wright and Bailey 1982). Current management practices favor annual burns that maximize primary productivity. While it is known that annual burns decrease the abundance of certain grassland birds, their effects on the reproduction and mating system of these birds is unknown.