EPOW - Ecology Picture of the Week

A Tale of Two Scrapes

Left:  Ngorongoro Crater, Tanzania
Right:  Oregon Oak Woodland, Columbia River Gorge, Oregon USA

Explanation:  What in the world (literally) does a boulder in a pit in Africa have to do with bare dirt in an oak woodland in the U.S.?  

We are looking at two types of scrapes, which are marks left by large mammals for different purposes.

The left image above -- from Ngorongoro Crater in Tanzania -- shows one of many isolated basaltic boulders found in this grassland environment.  The Crater itself is a massive volcanic caldera.  The boulder is used as a scratching or rubbing post by many ungulate species including warthog, Burchell's zebra, blue wildebeest, African buffalo, and others.  This action creates a bare-ground dirt patch that is secondarily used as a dust bath by these and other species including birds for ridding ectoparasites, dust mites, and other nasties.  This is an example of at least a commensal or symbiotic key ecological function, that is, use of the site for one purpose (rubbing) that creates another function (dusting).  

The right image above -- from an Oregon oak woodland along the Columbia River Gorge in western Oregon, USA -- shows a scrape made by a blacktail deer, possibly a doe with young, with their hoofs.  Deer typically bed down in such spots where they can lay low -- literally -- and escape detection by nocturnal predators such as mountain lions.  The deer often mark their spot, such as the tree here, with pheromones from a scent gland on the tops of their head.  Sometimes deer scrapes are further marked with urine and droppings as a way for dominant males to assert their presence.  

So there you have it ... just a simple patch of bare ground can tell a lot about the presence, behavior, and ecology of the mammals that passed this way!  

The stone and dirt patch that tell the tales of volcanic origins
and ungulates needing a good scratch and a good dust bath!