Fig. 8 Identification of food items delivered to nestlings by parental EBs Effects of Population Dynamics and Competition on Parental Investment in Eastern Bluebirds (Sialia sialis) Nickolas Davros, Jennifer LaRoche, and K. Winnett-Murray Fig. 9 Nearest nesting neighboring bird species of paired nest boxes for both active and inactive eastern bluebird nests. Fig. 4 Number of active nests of bird species at our study site from Fig. 10 Feeding rates of 2 different brood sizes Introduction During the middle to late 1970’s the status of Eastern Bluebird’s has declined drastically; as a result, they were classified as a species of special concern in many areas. Since the 1980’s, Eastern Bluebird numbers have been increasing due to public support in erecting next boxes; simultaneously, a lot of research attention has been directed at determining what environmental variables influence the reproductive success of recovering species such as Eastern Bluebirds. For example, studies of parental care in many passerines suggest that male and female parental roles can differ. Differences in sexual roles in birds have often been attributed to sexual behavior characteristics and previous investment strategies by each sex. In this study, we investigated the differences in parental roles that may exist between males and females in relation to bluebird reproductive success. In addition, availability of nesting cavities limits reproductive success. Other species using the nest boxes include Tree Swallows (Tachycineta bicolor) (Fig 1), House Wrens (Troglodytes aedon) (Fig 2), and Black-capped Chickadees (Poecile atricapillus) (Fig 3). We sought to understand how neighboring nestbox competitors may influence reproductive success; this will help to further our knowledge of how interactions among species influence one another’s population dynamics. Abstract The effects of parental investment on the reproductive success in a west Michigan population of Eastern Bluebirds (Sialia sialis), were determined by field observations with simultaneous video recordings. Feeding rate measurements was one way used to gauge the level of parental investment. The primary result was that no difference in male and female investment for feeding rate, food type, and food size was demonstrated, contrary to our hypotheses. However, significantly more food was brought to larger broods (3+ chicks) as compared to smaller broods (1-2 chicks), and parents may alter food type relative to chick age as well. We also examined nesting success of Eastern Bluebirds in relation to bird species occupying the nearest nestbox was done. The results of this study add to our scientific understanding of interspecific interactions, and how ecological factors may impact apportionment of parental care. This information can assist in conservation efforts directed at particular species of concern. Methods Data were collected from 167 nest boxes from May 10 - July at J.H. Campbell complex of Consumer’s Energy in Ottawa County, Michigan (Fig 4). Nest boxes were located in varying human-impacted habitat fragments. During nest monitoring, each nest box was checked at least weekly to determine species, number of eggs/offspring, and other parameters. Relative parental investment was quantified by direct observation and by video recordings of nest visits during which we recorded deliveries of food to boxes containing chicks (Fig 5). Photographic stills were obtained from video recordings and from these, we identified the relative size and type of each food item (Fig 6,7,8). Statistical tests were used to determine if feeding rate, size of food items, and types of food items were dependent on parental sex, chick stage, or brood size either separately or as interactive effects. We also analyzed reproductive success in relation to nearest neighboring bird specie. Acknowledgments Hope College Biology Department and our advisor Dr. Kathy Winnett-Murray Consumers Energy of Port Shelton, MI in particular Dennis McKee (Public Affairs) Funding Provided By Howard Hughes Medical Institute Science Education Scholar Program Award Cronkite Research Award - Hope College Biology Department REU Grant provided by the National Science Foundation Conclusion The main cause of nest failure was predation. Eastern Bluebirds at our study site strongly avoided nesting next to other Eastern Bluebirds, and because of this it is difficult to say whether other Eastern Bluebirds would have significantly influenced the reproductive success of another mated pair by nesting near them. It was found that no significant difference in nestling provisioning existed between males and female Eastern Bluebirds in this particular study. Eastern Bluebirds are providing equal amounts of parental care in terms of number of feeding visits, load size, and arthropod food type. This is particularly interesting because in most sexually dimorphic species, there is often a difference in the roles of males and females, especially with regards to parental care. The main difference usually found is that male partners feed chicks more. Parents fed their chicks at less than half the rate of the previously reported low (5,6). Additional observations by our team suggest that parents were not expending maximal effort maximizing chick feedings, but may have been conserving energy for later possible broods. This would be consistent with the prediction that, when predation rates are extremely high, parents might opt to safeguard their ability to re-nest, should the current nest fail. Results Of the 167 nest boxes monitored, 51 were active Eastern Bluebird nests of which only 17 were successful. Eastern Bluebirds in this population were avoiding nesting next to other Eastern Bluebirds and preferred nesting next to empty boxes. Nearest neighbor did not appear to affect reproductive success of Eastern Bluebirds (X 2 = 0.07, df = 2, P = (Fig 9). There was not a significant difference in the average feeding rates of female and male Eastern Bluebirds (t sex = 1.772, df = 89.4, P = ). The chick stage did not appear to have a significant effect on the average feeding rate (F age = , df = 2,91, P = ) (Fig 10). The most common identifiable food type delivered by adult bluebirds was any larva (Fig 8). There was a significant effect of chick age stage on the type of food (larval versus non-larval) being brought, the younger chicks received more of the larval items (X 2 = , df = 2, P = ) (Fig 11). As was expected, data provided evidence that parents significantly increased average feeding rates for the larger broods (t = 4.212, df = 88.3, P = ). Fig. 1 Tree Swallow Fig. 5 Video Camera Set-up Fig. 6 Male EB with food Fig. 7 Female EB with food Fig. 11 Feeding rate comparison between male and female EBs for chicks of 3 different stages Fig. 3 Black-capped Chickadee Fig. 2 House Wren Biology Department, Hope College