February 28, 2013

Where Did The Roadside Hawk Live Before There Were Roads?

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The Roadside Hawk. Image by Liz Paipay.

Walk or drive along virtually any road in the Amazon and you’ll hear that unique screech of a roadside hawk and look up to see one perched in a tree. On a particular two mile road I used to walk daily I would typically see three to four of these birds of prey acting true to their name- along the side of the road.

But wait- there haven’t always been roads in the Amazon, they were created by humans! I wondered where they are found naturally, in regions without large clearings like roads as the forest used to be. The answer? Typically either along a river, or in the forest, but in fewer numbers. 


Being a visual predator, there is a definite advantage to being in an area like a road- prey are probably easier to see than in the dense rainforest. For some reason, roadside hawks in particular have adapted to this roadside lifestyle more so than other birds of prey, and it seems to have made them more prevalent than ever.


One study compared the roadside hawk nesting activity in an area of untouched rainforest with an area with slash-and-burn farming landscape. The slash-and-burn area likely had roads in it, and at the very least represents a more open landscape for the purposes of our comparison. 


What did they find? In the open farming landscape, there were more nests, more young raised per pair, and a higher portion of breeding vs non-breeding pairs. They’re bringing home the same amount of food for their young, but the open area appears to allow more nesting and predation opportunities in general and is thus able to support a larger population.


This is an example of when a human interference and habitat disturbance can appear to ‘help’ a population. But more numbers doesn’t necessarily mean we are helping these birds. Many animals end up falling ill to disease when they are in an unnatural higher density due to human activity (like high density coyotes in neighborhoods suffering from mange in the United States), and the prey that the birds are feeding on may suffer from an unnaturally high mortality rate. 


While it doesn’t appear to be affecting the birds negatively at this point, it is a strong lesson that as we modify the rainforest, we modify the animals within, as well.


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