Common nighthawks are my "Spark Bird," the species that turned me into a birder.
Nighthawks are due back in Pittsburgh soon but their population has declined precipitously in this century. Fifteen years ago I used to see flocks of 20 to 30 nighthawks swooping over our neighborhood ballpark. Now I'm lucky to see just one.
This week I learned that chimney swifts and bank swallows are declining, too. Most of it happened in this century. Trouble everywhere. And so I wonder: Do these species share a trait that's causing their mutual decline?
Is it a problem with their nesting sites? The answer is mixed.
- In cities nighthawks nest on gravel roofs but gravel has been replaced by rubber. City nest sites have declined so the answer for nighthawks is Yes.
- Chimney swifts nest in chimneys. Some reports say the number of chimneys has gone down. (This has spawned projects to provide artificial chimneys.) Other reports say the chimney count is OK. I've not seen a decline in Pittsburgh chimneys. Answer for chimney swifts: Maybe.
- Bank swallows nest colonially in holes that they dig in the banks of lakes and rivers. These sites seem to be stable. Answer for bank swallows: Probably No.
Is it a problem where they spend the winter? Do they all go to the same place? Not exactly.
- Nighthawks spend the winter from eastern Ecuador, eastern Peru and southern Brazil to Argentina.
- Chimney swifts winter in western Peru and the upper Amazon basin.
- Bank swallows spend the winter in nearly all of South America.
Do they eat similar food? Yes! All of them eat flying insects!
There's a common thread. Recent studies have shown that around the world invertebrates including insects have declined 45% in the last 40 years and in Germany insect biomass has declined 81% from 1989 to 2014. Though insect decline has happened across the spectrum, it's not something that's made headline news except for two species not eaten by these birds: monarch butterflies and honeybees.
With such a massive drop in flying insects it's no wonder that the birds who eat them have declined. And there's another interesting side effect. The fish that eat flying insects are declining as well. Discovered in the U.K. in 2003, this problem threatens the fly fishing industry.
A massive decline in flying insects and the birds and fish that eat them indicates we have a large and widespread problem. My hunch is that it's something in the environment and it's caused by us.
We humans are ignoring it at our peril.
Here are resources for learning more:
- Where have all the insects gone? Science Magazine, AAAS, 10 May 2017
- What’s Causing the Sharp Decline in Insects, and Why It Matters: Yale Environment 360, 6 July 2016
- Empty Skies: Insect-eating birds that feed on the wing are vanishing: National Wildlife Federation, 2009
- Declines of Aerial Insectivores in North America Follow a Geographic Gradient: Avian Conservation and Ecology, Canada, 2010
- Insect-eating birds on the decline in Connecticut: Connecticut Audubon Society, 2013
- End of the Line for Fly Fishing: The Independent UK, 2003
(drawing of common nighthawk by Bob Hines, US Fish and Wildlife, in the public domain via Wikimedia Commons. Click on the image to see the original)