Image of the Day: Tree Casualties In Animals' Hunt For Food

By Bruce G. Marcot, Ecology Picture of the Week:

Three trees.  With the bark stripped.  And cavities.  Where are we?  And who made these?

We are looking at what can be termed the results of functional vicariates -- that is, very similar ecological roles ("key ecological functions") played by very different animals in different ecosystems.  

On the left is a Douglas-fir tree (Pseudotsuga menziesii) in a state park in Oregon, USA.  The cavities and wood chip pile were made by a foraging Pileated Woodpecker (Dryocopus pileatus), the largest woodpecker of the region.  Pileated Woodpeckers serve as a primary cavity excavator, creating tree hollows for feeding and nesting, in which many other species (secondary cavity users) can take residence.  The bark and wood chip pile at the base of the tree is used by other species including clouded salamanders, snakes, lizards, and invertebrate prey.

In the center is a Rockingham candlenut tree (Aleurites rockinghamensis) in a semi-deciduous forest near Wongabel, northern Queensland, Australia.  The cavities and wood chip pile were made not by a bird (there are no woodpeckers in Australia) but by a Striped Possum (Dactylopsila trivirgata), an uncommon marsupial locally endemic to the rainforests and woodlands of the region.   It excavated this tree in search of wood-boring grubs to eat.  The cavities can be inhabited by parrots and other birds of the area.  The bark and wood chip pile here has been further scraped into a nest mound by an Australian Brush-turkey (Alectura lathami), which is not a true turkey but rather one of the species of megapode.  

On the right is an Oregon white oak (Quercus garryana) along the Columbia River Gorge east of the crest of the Cascade Mountains in eastern Oregon.  The bark has been chewed and fragmented by foraging Black-tailed Deer (Odocoileus hemionus).  The loose bark on the tree can be used as roosting sites by bats, salamanders, snakes, and other species, and the bark chip pile can hide reptiles and amphibians.  

So here we see three different forest ecosystems with vastly different species each performing the same key ecological function of cavity excavation and bark-pile formation, with different sets of other wildlife species that secondarily use the cavities, loose bark, and bark and chip piles.  There are many other species in other forests of the world that also perform these primary key ecological functions.  It is very interesting to focus on the functions and see how different ecosystems can be so similar! 

--Bruce G. Marcot

Image and text © Bruce G. Marcot, Ph.D. Research Wildlife Ecologist,
who produces the Ecology Picture of the Week website.