Jennifer L. Newbrey, Ph.D. Current affiliation Department of Biological Sciences University of Alberta Edmonton, Alberta, T6G 2E9 Canada E-mail:  jennifer.newbrey@ualberta.ca Education Ph.D. 2007. Zoology. Department of Biological Sciences North Dakota State University M.S. 2002. Natural Resources. University of Wisconsin at Stevens Point B.S. 1997. Wildlife and Biology. University of Wisconsin at Stevens Point

Dissertation Research

Dissertation Research Summary
My dissertation research has focused on the interaction between female condition and the allocation of carotenoid pigments into sexual signals and reproductive success. Carotenoids are biologically-active, lipid-soluble yellow and red pigments synthesized by plants and photosynthetic microorganisms, which birds obtain from their diet. In the egg, yolk carotenoids protect embryonic tissues against metabolic free radicals, which can damage lipids, proteins, and DNA. As powerful antioxidants and immunostimulants, carotenoids are also incorporated into the sexual signals of many birds and are thought to honestly reflect phenotypic and genetic quality. It is believed that carotenoids are scarce in nature, which leads to tradeoffs between the use of carotenoids for physiological functions, the expression of sexual signals, and reproduction. While working on my main dissertation objectives, I have also studied the effects of nest contents on female broodiness, the relationship between maternal condition and avian reproductive success, and I captured and tested a variety of blackbird species for West Nile virus (WNV) antibodies.

Laying Sequence Variation in Yolk Carotenoid Concentrations in Yellow-headed Blackbird Eggs
I quantified intraclutch variation in the concentrations of four carotenoids, β-carotene, β-cryptoxanthin, lutein, and zeaxanthin, in Yellow-headed Blackbird (Xanthocephalus xanthocephalus) eggs collected from five free-living breeding colonies in central North Dakota. To my knowledge this research project was not only the first report of yolk carotenoids in a North American passerine species it was also the first report of yolk carotenoids within the blackbird family, Icteridae. I also investigated the relationship between egg metrics (i.e., egg mass, yolk mass, and yolk water content) and carotenoid allocation to eggs. Concentrations of the four yolk carotenoids were significantly related to egg laying order, but there were differences in their patterns. The concentration of lutein decreased from first to last-laid eggs, whereas the concentrations of β-carotene, β-cryptoxanthin, and zeaxanthin increased from first to last-laid eggs. The differences in carotenoid-concentration patterns I observed across Yellow-headed Blackbird clutches suggest that the carotenoids may be differentially available in the diets of females during egg production, they may compete with each other during absorption, and they may be of different value to the developing embryo due to differences in antioxidant function. Carotenoid concentrations were not significantly related to any of the egg metrics measured despite previous research that has found an effect of egg size on carotenoid allocation to eggs in other bird species. Most studies of laying sequence variation in carotenoid concentrations have focused on either one representative carotenoid or total carotenoids, but based on my results I caution that using one representative carotenoid to study laying sequence variation in carotenoid allocation to eggs may provide misleading results.

Effect of Female Condition on Yellow-headed Blackbird Reproduction
To explore the relationship between maternal condition and avian reproductive success, I studied the effect of female physical condition on reproduction in the Yellow-headed Blackbird. I examined the effects of female body condition, heterophil to lymphocyte ratio, and packed red blood cell volume on egg metrics, number of eggs hatched, number of chicks fledged, and fledgling mass. Female Yellow-headed Blackbird body condition was positively correlated with yolk and fledging mass and female heterophil to lymphocyte ratios were positively correlated with egg size. This suggests that females in better condition were able to allocate more energy and resources into reproduction than females in poor condition, which allowed them to produce larger eggs and fledglings. There were no significant relationships between female physical condition and hatching or fledging success, but many factors irrespective of female condition such as predation and weather, could have influenced these aspects of reproduction. All of the female Yellow-headed Blackbirds included in this study had high levels of packed red blood cells and were healthy enough to initiate a reproductive attempt, indicating that stress was not a limiting factor for reproduction.

Effects of Nest Contents on Female Yellow-headed Blackbird Broodiness
While collecting data for my dissertation research, I also studied the effects of nest contents (i.e., eggs or nestlings) on the broodiness of female Yellow-headed Blackbirds. Specifically, I quantified the amount of time required for 77 flushed females to resume incubation or brooding behavior after a trap was placed over their nests. Developing avian embryos and nestlings have different self thermoregulatory abilities, which could influence the broodiness of parental birds. In my study, female Yellow-headed Blackbirds incubating eggs entered the trap in less than half the amount of time required by females with nestlings only. My results suggest that female Yellow-headed Blackbirds are more broody when their offspring are at greatest risk of exposure due to offspring age and threat of Marsh Wren (Cistothorus palustris) predation. Marsh Wrens are common nest predators of Yellow-headed Blackbirds that destroy eggs and young nestlings in an attempt to reduce potential competition for resources on a wetland.

West Nile Virus Antibodies in Breeding North Dakota Icterids:
West Nile virus (WNV) is an exotic disease that was introduced into North America in 1999 and has resulted in the deaths of tens of thousands of birds. In light of concerns regarding the status of North American bird populations, I captured and tested 170 free-living icterids for WNV specific antibodies to determine if antibody positive blackbirds were present in central North Dakota during the early summer breeding seasons in 2003 and 2004. A small blood sample was collected from all captured individuals and I tested the plasma for WNV antibodies using competitive enzyme-linked immunoabsorbent assay. During the 2004 breeding season, I also trapped and tested female Culex tarsalis (n = 291), a known WNV vector in North Dakota, for WNV RNA. Four blackbirds were positive for WNV antibodies, including two adult Yellow-headed Blackbirds (see picture), an adult Common Grackle (Quiscalus quiscula), and an adult Red-winged Blackbird (Agelaius phoeniceus). In contrast, all C. tarsalis were negative for WNV RNA. The low numbers of blackbirds expressing WNV antibodies in my study area during the 2003 and 2004 breeding seasons (i.e., 1.9 and 2.6% respectively) suggest that WNV antibody positive birds were rare in the breeding population. However, difficulty in capturing infected individuals and virus-induced lethality could influence detection of WNV antibody positive birds in free-living populations.

Yellow-headed Blackbird fledgling.	Banded female Yellow-headed Blackbird.

Great Blue Heron on Allequash Lake, Wisconsin.	Common Loon on Katherine Lake, Wisconsin.
Osprey on North Nokomis Lake, Wisconsin.	Female Common Mergansers on Loon Lake, Michigan.