Parker research

Pattern and process in sexual selection in birds

Much of my research has invovled the role of sexual dimorphic 'ornaments' in the interactions between individual animals. In particular, most of this work was done in the context of determining whether sexual ornaments are signals of individual condition and how ornaments influence the behaviors of competitors and potential mates.

Some completed projects:

1. With David Ligon, my PhD supervisor at the University of New Mexico, I demonstrated the central role played by social interactions in determining steriod hormone levels and the expression of sexual signals in red junglefowl (Gallus gallus).

2. In collaboration with Dany Garant, I identified and quantified heritability of comb size in red junglefowl and its strong genetic correlation with a body condition index, as predicted by the hypothesis of capture of genetic variance in condition by sexually-selected signals.

3. I demonstrated that female red junglefowl adjust maternal investment in response to experimentally manipulated mate appearance by laying larger clutches of eggs for more attractive males.

4. I found that the the area of melanin-pigmented black plumage on the cap of Kentucky Warblers (Oporornis formosus) was greater in older males and in heavier males (controlling for body size), and that males with more black on their caps were more likely to attract a mate.

5. As my portion of a collaborative effort with Simon Griffith and Valerie Olson, I used meta-analysis to demonstrate that melanin-pigmented and carotenoid-pigmented plumage ornaments in birds did not differ in their susceptability to experimental manipulations of condition. Further I found evidence of a bias against the publication of results that failed to support predictions of condition-dependent signaling.

6. Iain Barr and I, in collaboration with Simon Griffith showed that a number of song variables previously identified as condition signals in the blue tit (Cyanistes caeruleus) do not show consistent relationships to condition across studies, and that the limited set of song variables which may signal condition do so only weakly.

Some ongoing projects

1. I am currently continuing my collaboration with Simon Griffith, Iain Barr, and others to investigate the striking UV-blue and yellow plumage patches of Blue Tits. This work is based on several years of data collection on many thousands of individual birds. Among other things, we are attempting to determine whether male color influences female reproductive success after controlling for the strong effects of local environmental variation and the females' own quality.

Patch area and edge effects on the occurrence patterns of forest songbirds

In 2002 I worked closely with Brooke Stansberry, an MS student I supervised at Kansas State University, studying forest-nesting, migrant birds. The most important part of this work ended up being a meta-analysis of published studies to determine edge and small-patch avoidance patterns across a large number of migrant forest bird species in Eastern North America. See my publication list for a link to the appendices to our Conservation Biology paper on this topic. A major results included our observations that in forest dominated landscapes, almost no forest-nesting bird species appear to avoid edges, but in landscapes not dominated by forests, many forest-nesting bird species appear to avoid smaller forest patches and/or edges.

Several alternative explanations exist for this result. One hypothesis we proposed is that larger forest patches end up with higher densities of forest birds through the process of conspecific attraction - preferential recruitment into already occupied locations. Since the publication of our paper, empirical support for this mechanism as a link between patch area and bird density has been growing.

Nest abandonment by Bell's Vireos: an adaptation to brood parastism?

When conducting my MS thesis work I observed that Bell's Vireo (Vireo bellii) nests were frequently abandoned when brood-parasitic Brown-headed Cowbird (Molothrus ater) eggs were present. If a cowbird egg hatches in a vireo nest, the vireo chicks are outcompeted, and typically all starve to death. Thus I first thought that the vireos were abandoning parasitized nests in response to this strong selection pressure. However, the number of cowbird eggs laid in a nest was not a good predictor of abandonment. Instead, the number of vireo eggs remaining in the nest (cowbirds often remove host eggs) predicted abandonment, suggesting that vireo behavior might best be explained as a response to egg loss. Vireos typically failed to abandon parasitized nests, and thus resigned themselves to tending a doomed nest, unless the cowbirds removed a sufficient proportion of the clutch. Because abandonment in response to egg loss is a standard behavior across bird species, this suggests that Bell's vireos have not evolved a unique response to cowbird parasitism.

In 2005-2006 I collaborated with Karl Kosciuch, whose dissertation focussed on this system, and Karl's PhD supervisor Brett Sandercock. Karl's large correlative data set supported my original observations, and experiments we designed and implemented in spring 2005 supported the conclusion that Bell's Vireos do not recognize or respond to cowbird eggs, but instead abandon their nests when a sufficient proportion of the clutch is removed by cowbirds. In fact, nearly all the variation in abandonment of parasitized nests within and among pairs was explained by loss of host eggs. This raises the interesting question of why a species that pays such a high cost of being parasitized by cowbirds, and has presumably co-existed with cowbirds for a long time, has not evolved behaviors that would more effectively reduce the costs of cowbird parasitism.

Geographic patterns of song sharing in dickcissels

In many bird species, distinct vocal neighborhoods develop in which neighbors closely resemble each other in song types. We know that social learning is sufficient to promote the development of this phenomenon, but there has been almost no empirical exploration of the habitat or population processes that lead to the strikingly different patterns and scales of song sharing among, and even within, species.

Since 2005, Bill Jensen and I, along with a series of undergraduate students, have been exploring song sharing in the dickcissel, a Neotropical migrant songbird and one of the most common grassland birds breeding in the central United States. The students who have worked on this project, Perry Williams, Derek Schook, Anthony Dalisio, Amy Strauss, and Cory Castro, have all been supported by an REU grant to Kansas State University. Thanks to their hard work, we have started to develop a more sophisticated understanding of geographic variation in dickcissel song. Within an area of continuous habitat (Konza Prairie Biological Station) adjacent dickcissel males sing nearly identical songs, but there is a steady decline in similarity with distance such that males several km apart have many differences in their songs. These differences are both qualitative, in the form of different elements, and quantitative, in the form of changes in note frequency and duration within elements. Furthermore, we found dramatically different patterns of song sharing in different landscapes with different patterns of habitat.

We are continuing to investigate song sharing in dickcissels. Our current questions in this system include:

-How do different habitat patterns influence dickcissel population processes potentially relevent to song learning, and how does this lead to different patterns of song sharing among landscapes?

-How does vocal culture change over time as a function of habitat effects on population processes such as site fidelity and territory connectivity?

-What is the benefit of conforming to the neighborhood dialect?

-What is the timing of song learning?

-How has the tendency to readily colonize often ephemeral habitat patches influenced the evolution of song learning and the developoment of dialect patterns?