Instead of song, most woodpeckers use a mechanical drumming sound as their audio advertising display. It’s easy to tell when you hear a woodpecker, harder to tell which species. Nevertheless there are distinct differences between species, and with practice most drumming sounds can be recognized with a high level of confidence.
I’m comparing just Downy and Hairy woodpeckers here, but these happen to be two of the most easily distinguished drums, and the differences are clearly evident in the sonagrams shown below, as well as in the linked audio recordings. ((Pitch of woodpecker drumming depends mostly on the thing being drummed – a hollow log, rotten branch, or metal gutter all make very different sounds – so I’ve cropped these sonagram snippets to match each other, and left off the y-axis scale of pitch.))
|Example of Hairy Woodpecker drumming, from Arizona
|Example of Downy Woodpecker drumming, from Arkansas
I was particularly interested to check for geographic variation in drumming sounds of these two species. With evidence that other forest birds like Brown Creeper and White-breasted Nuthatch have diverged significantly in three or four regions, and a similar result in a recent DNA study of Hairy Woodpecker, it is plausible that Hairy and Downy Woodpecker could be hiding some cryptic species. As you can see from the sonagrams above, however, there is little or no regional variation in their drums. The species-specific differences described above apply across the entire North American continent.
Jackson and Ouellet (2002) summarize several studies on variation in Downy Woodpecker drumming. Both males and females drum, and no consistent sexual, seasonal, or regional difference in drumming has been found.
One potential regional variation involves the length of the drum. The two California samples each diverge from the normal duration for the species: Hairy Woodpecker shorter than elsewhere, Downy Woodpecker longer. This is a sample size of one, and given that much more extensive studies (see preceding paragraph) could not find any regional difference this almost certainly is not meaningful. Observers in California and nearby should listen to see if the drum of local Downy Woodpeckers is consistently longer than the drum of Hairy, that could offer an extra clue to distinguish the two species there.
Jackson, Jerome A. and Henri R. Ouellet. 2002. Downy Woodpecker (Picoides pubescens), 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/613