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April 11, 2015

Female Barn Owl “Spottiness” Signals Genetic Quality

by Bryce W. Robinson

To begin, I should have illustrated the frontside of this Barn Owl to illustrate the concept I’m about to present. I did not, however, have “spottiness” in mind when I began the illustration, so I decided to illustrate the backside. I find the back patterning mesmerizing.

So, for the concept you’ll just have to imagine the frontside of this bird, being spotted throughout.

Ornamentation in birds is generally considered a male’s way to communicate their quality to females. A more ornamented, vibrant, decorated, etc. male is generally considered higher quality, thus driving selection for particular traits (Peacock is an easy example, but think about birds like the Greater Sage-grouse as well).

Studies supporting this theory have generally focused on males, and for good reason. Males tend to be the showier sex. But, what about species where females exhibit unique markings?

Barn Owls are one species where the female shows more markings (spots) than males. Additionally, studies support that female Barn Owls are not the choosers in breeding, as per usual. Because of these reasons, Roulin et al. (2000) decided to test the theory that heavier spotted females were of higher quality (tease out the mechanisms of spottiness). They hypothesized that females with more spots also had higher levels of specific antibodies important for parasite resistance.

Their study looked into immunocompetence of offspring. They found support for the idea that heavier spottiness communicates immunocompetence, but also may be a “heritable signal of parasite resistance”. This is important for Barn Owls, as they nest in cavities and tight spaces. I remember a few weeks ago I went with a peer, Tempe, to check on a Barn Owl nest for her Master’s Project. The box held four owls (lower than normal), and was full of feces and dead animal remains. In such situations, parasites and all sorts of things may run rampant. Having higher resistance then becomes advantageous, and ways of communicating such resistance will then be selected for and prevail. Makes sense (eureka?).

Literature Referenced:

Roulin, A, T. W. Jungi, H. Pfister, and C. Dijkstra. 2000. Female Barn Owls (Tyto alba) Advertise Good Genes. Proceedings of the Royal Society B-Biological Sciences 267 pp. 937-941

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February 22, 2015

Tail Pumping Behavior in the Black Phoebe

by Bryce W. Robinson

Black Phoebe – Sayornis nigricans. 14 x 17″ prismacolor on bristol board. Image copyright Bryce W. Robinson

The Black Phoebe – Sayornis nigricans in it’s simple suit of black and white, catches the eye of anyone remotely keen on the goings on of the natural world. This phoebe demands attention, even in a guild of flashy desert denizens. In doing so it provides some quality behavior birding that never disappoints.

One behavior I have noted while watching the bird forage is the methodic tail flick, not uncommon in the family Tyrannidae, but somehow unique in the Black Phoebe. I’ve wondered about the habit, but never sought to satisfy the wonder until now. The illustration above came about in preparation for the coming San Diego Bird Festival that I will be attending. In practice, I decided to couple the illustration with looking into any insights in the literature regarding the tail pumping habits of the Black Phoebe.

In little time I found a paper (Avellis 2011). The study addressed four hypotheses explaining the behavior, the Balance Hypothesis where the phoebe tail pumps to maintain balance atop unstable perches, the Foraging Enhancement Hypothesis where tail pumping increases foraging success, the Signal to Territorial Intruders Hypothesis where the tail pumping signals conspecifics of the birds fitness and establishment on a territory, and the Signal to Predators Hypothesis where the tail pumps exhibit the birds vigilance amidst predators.

The results of the study indicated the following:

Balance Hypothesis – Not supported

Foraging Enhancement Hypothesis – Not supported

Signal to Territorial Intruders Hypothesis – Not supported

Signal to Predators Hypothesis – Supported

The paper reports that the Black Phoebe increased tail pumping rates significantly when a predator was detected either visually or audibly. The suggested purpose of tail pumping then is to advertise the birds awareness to the predators presence. Tail pumping communicates the phoebe’s health, and that it in turn will be a more difficult prey to capture.

So, when asked why the Black Phoebe pumps its tail, I’ll answer that the behavior is to exhibit the birds vigilance, acting as a deterrent for predators looking for the path of least resistance for procuring food. Another day, another bit of knowledge gained.

Referenced Literature:

Avellis, G. F. 2011. Tail Pumping by the Black Phoebe. The Wilson Journal of Ornithology 123:766-771

5 Comments

February 8, 2015

Thoughts on the Past, Present, and Future of the Snowy Plover in North America

by Bryce W. Robinson

Snowy Plover – Charadrius nivosus. 11 x 14 ” prismacolor on bristol. Image copyright Bryce W. Robinson 2015

I’m becoming increasingly fascinated with how our changing world may impact the distribution of a given species, either shifting or fragmenting breeding ranges. I have a particular affinity for the family Charadridae , and I’ve found myself paying closer attention to one species in particular, the Snowy Plover – Charadrius nivosus. The Snowy plover occupies a widespread but disjunct breeding range in its western North American population(Figure 1). This range is likely a result of the bird’s need for specific (in turn limited) habitat for breeding.

Figure 1. Range of Snowy Plover – Charadrius nivosus in North and Central America. Image taken from Birds of North America Online (see referenced information)

The Snowy Plover is a species that has faced many challenges with the ever increasing human presence. Throughout the bird’s North American breeding range (Figure 1), human impacts have caused a multitude of threats to its ability to reproduce. These threats include but are not limited to environmental contaminants, an increase in nest predators such as Raccoon, Common Raven, Coyote, and Red Fox, all of which have experienced a human-subsidized boost in population numbers in recent decades, and recreation on beaches causing both disturbance and nest destruction. A great discussion of all factors impacting Snowy Plover populations can be found on the Birds of North America species account under the Conservation and Management section.

Multiple organizations are working with state and federal wildlife authorities to augment the negative impacts humanity and its residuals are having on Snowy Plover populations. These organizations include Point Blue Conservation Science, Friends of the Dunes, the National Audubon Society, and many others. The effort is impressive and has seen some success. Still, there is a looming threat on the horizon, the impacts of human induced climatic changes.

What the threats of climate change mean for the Snowy Plover in western North America and across the rest of its range in S. America are still to be determined, but I’d like to emphasize the need to determine and augment these threats as they are occurring. I’ve become aware of a population level analysis that is meant to track the distributional patterns of a given species throughout its yearly cycle (Ruegg et al. 2014). The idea is to identify population structures during the major life events of a species through genetic analysis of individuals at each location; breeding, migration, and non-breeding. Understanding where individuals spend each part of the year holds the power of identifying where negative impacts are occurring that are driving population declines. This is the big idea behind the banding effort, but this technique provides larger sample size and more power for determining population structures. It’s a huge step in the right direction.

My point is, wouldn’t this be a great tool for assessing changes in populations of the Snowy Plover over its disjunct range as the impacts of climate change become more visible and severe? The answer is yes, and we ought to begin the effort…

Referenced Information:

Page, Gary W., Lynne E. Stenzel, G. W. Page, J. S. Warriner, J. C. Warriner and P. W. Paton. 2009. Snowy Plover (Charadrius nivosus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/154

Accessed 7 February 2015

Ruegg, K. C., E. C. Anderson, K. L. Paxton, V. Apkenas, S. Lao, R. B. Siegel, D. F. Desante, F. Moore, T. B. Smith. 2014. Mapping migration in a songbird using high-resolution genetic markers. Molecular Ecology 23:5726-5739

September 4, 2014

Molting Gyrfalcon in Flight

by Bryce W. Robinson

While in Alaska this past summer conducting research on nesting Gyrfalcons – Falco rusticolus, I made many notes and observations concerning the stage of molt for each adult bird that I encountered. I’d like to share a few things that I noticed. I’m still a young student of ornithology, so none of this is new information, just a few interesting things that I noted and count as important information to retain.

First, I was interested to note the difference in stages of molt between male and female Gyrfalcons during the incubation period. The bird I have illustrated above portrays the stage at which most females molt had reached in early to mid May. Males on the other hand had either not initiated molt yet, or had just started. Needless to say, the general trend was that females were farther ahead of males and in some cases were even more advanced than what I have drawn.

Another interesting thing I noted was that this difference in molt stage by sex changed. Once the female began provisioning for nestlings, the females molt slowed as the males caught up.

I set out to illustrate a Gyrfalcon in flight to show some of my observations on molting Gyrfalcons, however creating the digital image of the illustration did not transfer some of the aspects I had hoped it would. One thing I noted concerning the body molt was that the rump was the first to be replaced. All birds in early summer had nice contrasting rumps consisting of fresh feathers. The mantle and scapulars as well as the upper wing coverts had yet to be replaced.

The Gyrfalcons in May were growing in feathers at their initiation points. In Falcons, this is P4 or 5, S4 and 5, the inner tertials, and in the tail the central deck feathers T1. This beginning stage is important for understanding the difference between hawks and falcons, and is another reason I wanted to illustrate a molting falcon

I love studying molt, and in the largest of the falcons it interests me to a great degree. Molt is costly, energetically. When you consider a large species that lives in a harsh climate such as the Arctic, it is remarkable that they complete an entire molt a year, save perhaps a few underwing coverts. Other large avian predators of the region like the Rough-legged Hawk and Golden Eagle do not do this, a fact that makes my respect for the Gyrfalcon grow evermore.

I enjoyed the exercise of drawing this falcon in flight, and adding the aspect of molt to tell a story. I plan to make this a goal of my illustration, to combine creative imagery with context that communicates ideas and facts about the chosen subject. Of course my ability to do so is still a work in progress itself, but as with learning, the process is ultimately satisfying and something I look forward to for the remainder of my life.

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Tag: research

by Bryce W. Robinson

by Bryce W. Robinson

by Bryce W. Robinson

by Bryce W. Robinson