George M. Linz

Sperm competition selects beyond relative testes size in birds.

Sperm morphology varies considerably across taxa, and postcopulatory sexual selection is thought to be one of the main forces responsible for this diversity. Several studies have investigated the effects of the variation in sperm design on sperm function, but the consequences of variation in sperm design on testis morphology have been overlooked. Testes size or architecture may determine the size of the sperm they produce, and selection for longer sperm may require concomitant adaptations in the testes. Relative testes size differs greatly between species and is often used as an index of sperm competition, but little is known about whether larger testes have more sperm-producing tissue or produce sperm at a faster rate. Using a comparative approach in New World Blackbirds (Icteridae), we found (1) a strong link between testis histology and sperm length, suggesting selection on testis architecture through selection on sperm size, and (2) that species under intense sperm competition had a greater proportion of sperm-producing tissue within their testes. These results support the prediction that sperm competition fosters adaptations in reproductive organs that extend beyond testes size, and raise questions about the trade-offs influencing reproductive investment.

IMPACT OF BLACKBIRD DAMAGE TO SUNFLOWER BIOENERGETIC AND ECONOMIC MODELS

We constructed bioenergetic and economic models to estimate the potential impact of Red-winged Blackbirds (Agelaius phoeniceus), Common Grackles (Quiscalus quiscula), and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) on production yields of sunflower in the northern Great Plains of North America. The amount of sunflower consumed annually by males and females, after considering field metabolic rates, energy value and moisture content of achenes, and percentage of sunflower in diets was, respec- tively: Red-winged Blackbirds 277 g and 168 g; Common Grackles 267 g and 230 g; and Yellow-headed Blackbirds 248 g and 139 g. The per capita annual economic damage was: male Red-winged Blackbirds

Sperm design and variation in the New World blackbirds (Icteridae)

0.09 (U.S. dollars), females

SURVIVAL OF AVIAN CARCASSES AND PHOTOGRAPHIC EVIDENCE OF PREDATORS AND SCAVENGERS

0.05; male Common Grackles

Escherichia coli, Salmonella, and Mycobacterium avium subsp. paratuberculosis in Wild European Starlings at a Kansas Cattle Feedlot

0.09, females

Evaluation of Bird Shield as a blackbird repellent in ripening rice and sunflower fields

0.07; and male Yellow-headed Blackbirds

LETHAL CONTROL OF RED-WINGED BLACKBIRDS TO MANAGE DAMAGE TO SUNFLOWER: AN ECONOMIC EVALUATION

0.08, females

Association of wild bird density and farm management factors with the prevalence of E. coli O157 in dairy herds in Ohio (2007-2009).

0.05. Annual loss was

Assessment of Bird-management Strategies to Protect Sunflowers

5.4 + 1.3 X 106 for all three species in aggregate, with Red-winged Blackbirds accounting for 52% of the loss. Blackbird damage represented 1.7% of the dollar value of the 1999 sunflower harvest in the northern Great Plains. This loss would be inconsequential if damage were distributed evenly; however, bird damage is often localized around wetlands and can be economically debilitating to individual producers. Although our model was based on regional population estimates, it should perform well at local scales, provided that a local population can be defined, accurately estimated, and remains stable in size over the six-week length of the damage period. Because of the large numbers of blackbirds that congregate in the region during August and September prior to migration, sunflower pro- ducers should expect some crop losses. The solution to the conflict appears to be one that focuses not on eliminating all damage, but on preventing it from exceeding 5% per field.

Laboratory Efficacy of Chemical Repellents for Reducing Blackbird Damage in Rice and Sunflower Crops

Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilising selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed.