Red-winged Blackbirds (1988-2000)

    I studied Red-winged Blackbirds from 1988-2000 in both Ithaca, NY and Western Kentucky. Although fieldwork ended in 2000, data analyses still continue (I am reanalyzing some parental care data in 2011 that was collected in 1988!) and I remain fascinated by these birds. During the 13 years of study, my work was funded by two grants from the National Science Foundation. Multiple projects focused on the factors shaping male and female mating tactics, and their consequences for parental behavior and sexual selection. My students, collaborators, and I have concentrated on the following specific questions:

 

(A) How often do females pair with one male but produce young sired by another? My lab used molecular genetic techniques to analyze paternity of nestlings and identify the true sires (see Westneat 1993a, Westneat and Mays 2005).

(B) How do males and females interact over matings? I combine the genetic approaches with detailed observations of sequences of behavior to understand patterns of male persistence and female resistance. Experiments manipulating food resources and male behavior have uncovered some of the ecological factors influencing male mate-guarding behavior (see Westneat 1993b, 1994).

(C) What are the selective consequences of extra-pair matings? Females may be gaining through EPFs, because broods with extra-pair offspring fledge more young, but the exact mechanism is still uncertain. Females also may incur costs, because they resist strongly on occasions, and their resistance to males declines as they approach egg-laying, a time when struggles with males may be most costly (see Westneat 1992).

 

(D) Does paternity influence paternal behavior? I have approached this question both theoretically and empirically. The answers are not simple, and the data suggest some fascinating complexities. Male red-winged blackbirds do not provide food to nestlings in relation to their paternity. The circumstances surrounding the patterns of paternity in the population and the means by which extra-pair copulations occur and lead to fertilizations suggests that red-winged blackbirds fit those situations in which paternity should have relatively little effect on paternal behavior. For more information, see Westneat and Sherman 1993, Westneat 1995, Westneat et al. 1995, Westneat 2001).

 

 

(E) How do extra-pair fertilizations influence sexual selection? The focus of this work is to investigate two aspects of sexual selection in blackbirds:

  1. the influence of male morphological characters on components of reproductive success (including success at EPCs) and,

  2. the types of behavioral interactions between males and females that give rise to variance in success at EPCs.

I have experimentally addressed the following questions:

These data are currently being analyzed and have yet to be written up for publication.

 

(F) Techniques for assessing paternity in natural populations.- One major aspect of my research on red-winged blackbirds has been to develop more efficient techniques for assaying genetic variation in natural populations. We  started out using multilocus minisatellites (results pictured to the left, see Westneat 1993b), but now use PCR amplified microsatellite loci for assessing paternity and maternity, in red-winged blackbirds and in a number of other passerine birds.

 

 

(G) Several undergraduates and I (in collaboration with Tim Birkhead's lab in Sheffield, UK) examined male sperm counts using model females (Westneat et al. 1998). We found that male ejaculate size decreased with multiple copulations in a short period of time, but appeared to recover after a delay of an hour between copulations.

 

(H) Recently, we have surveyed the microbes present in male ejaculates and in the cloacae of males and females. The goal was to uncover the possible importance of sexual transmission of fitness-affecting bacteria (see Westneat and Rambo 2000 or Hupton et al. 2003). We found bacteria in many male ejaculates but no one type predominated, meaning that every male had a unique assemblage of types. This has important implications for understanding the risks of multiple mating for females and for further studies of sexually transmitted microbes.

 

(I) In collaboration with Dennis Hasselquist of Lund University, Sweden, we have used Diphtheria-Tetanus antigens to measure the responses of the male immune system to presumably novel antigens. John Wingfield of the University of Washington analyzed testosterone titer for these birds as well. We found few significant relationships (Westneat et al. 2003), which complicates our understanding of the potential links between advertisements, immunity, and hormones. See  also Westneat and Birkhead 1998 for some background ideas of relevance to this project.

 

Acknowledgments

The red-winged blackbird project has benefited from the efforts of a very large group of people. Funding has been provided by the National Science Foundation, The University of Kentucky, and Cornell University.

Ithaca Study Site

Cornell University Pond Unit, Bob Johnson, Dr. Nelson Hairston, Jr., Dr. Ann Clark and her field crew, and field assistance from Christine Butler, Cathy Corson, Dan Christian, Karin Gastreich, Jennifer Davis, Jeff Dickhaut, and Herman Mays.

Kentucky Study Site

Peabody Mining Co., KY Fish and Wildlife Resources, and field help from Tony Roberts, Zeb Weese, Emily Reed, Maribeth Polhill, Lisa McGraw, Pete Blank, Chad Johnson, Tasha Macilveen, Sarah Laughlin, Jennifer Fraterrigo, Michelle Brant, Nevelyn Russell, Brian Smith, Jamie Moseley, Jessica Brock, and Matthew Shawkey.

Lab

Thanks to Dr. Chip Aquadro at Cornell for his support during the early part of this project. Assisting on the paternity analyses in the lab were Lorna Breen, Greta Crutcher, Tamara Roush, Brent Little, Jana Hawks, Jamie Moseley, Richard Hanschu, and Herman Mays.