Tuesday, June 02, 2009

Passerine migrants response to predation risk


I am back again with more bird migration research. This paper is focused more closely on the predator prey relationships, specifically on the response of prey species to the abundance of predators. This is somewhat related to my research on the related timing of migration between predator species and prey species. I am not sure if I can specifically use this paper as it is more behavioral at an individual level as my work is more focused on population level reactions. It's interesting none the less.

CIMPRICH, D., WOODREY, M., & MOORE, F. (2005). Passerine migrants respond to variation in predation risk during stopover Animal Behaviour, 69 (5), 1173-1179 DOI: 10.1016/j.anbehav.2004.07.021

Predator-prey interactions at migratory stop-over points is interesting for a number of reasons. The prey birds must manage the risk of predation against their need for large quantities of food to support their journey. Complicating the situation is that they are in unknown territory with unknown risks. The shrubs may be different, the food may be different, and even the predators may be different.

The researchers studied two prey species (Blue-grey Gnatcatchers (Polioptila caerulea) and American Redstart (Setophaga ruticilla)) and one predator species (Sharp-shinned Hawk (Accipiter striatus)). The "Sharpie" is definitely one of my study species, but the prey mix will be different for my study due to geographic location. Their study used both observational techniques and manipulative techniques in an interesting way. For the manipulative they created a balsa wood airplane which resembled a sharp-shinned hawk and launched it 4m over the heads of some prey birds under observation. This produced consistent reactions to real sharpies flying low over the foraging area. This allowed the researchers to add to the natural migration rate of Sharpies over the site and measure the response.

The results indicate that both prey species moved deeper into the woods as the number of predators flying over per hour increased. The Blue-grey Gnatcatchers also moved at slower rates during higher volumes of predators. It did not appear that the increased presence of predators decreased their foraging rate significantly. This illustrates that the predators changed how they foraged, but not the rate, answering the question on how they balance the risk with their urgent need to build their fat stores.

While this might to be directly useful in my work, the paper did present a couple of interesting references to other papers which promise to be quite helpful. The continued exposure to field and statistical methods is also helping me get my mind around the daunting task ahead of me.

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Robby said...

Your blog is cool and contains valuable information on many things. I write a blog that encourages people to be kind to wildlife: http://www.snakeadventures.blogspot.com/ I invite you to view my blog and add it to your bloglist. Will you let me know what you think?
Robby in Utah
ps. the name for the rattler from your May 31 post was changed from Crotalus viridis to Crotalus Oreganus in 2002

wolf21m said...

Robby, you do have a cool blog. Those are some amazing snake pictures. I have added it to my reading list.

Thanks for the update on the rattler name. I took the name from the Digital Atlas of Idaho. I guess they are a bit out of date. I will make the change. Thanks for stopping by.