cliff swallow decline

[DAVID A LEATHERMAN]

Last week Peter Ruprecht brought up the issue of Cliff Swallows not being at some of his historical sites locally along the Front Range.  A mini-thread developed and I speculated swallow bugs, which are ectoparasites of swallows, especially nestlings, might be involved in forcing them to relocate.  I contacted Dr. Charles Brown at the University of Tulsa.  He is lead author of the "Birds of the World Cornell" account of Cliff Swallow and has a long-term study site in western Nebraska.  He said the likely culprit for the declines we are seeing is a general decline of flying insects upon which they and many other birds feed.  He said swallow bugs are probably NOT the reason for any declines we are seeing, and that one study demonstrated Cliff Swallows are actually coping with them better than they used to.  

To answer the question a few people asked as to why an insectivore like Cliff Swallows wouldn't just eat the swallow bugs, Dr. Brown reminded me swallow bugs and other species in the family Cimicidae (including bed bugs) have scent glands that render them unpalatable to everything except spiders and ants. 

Dave Leatherman

Fort Collins

[David Suddjian]

On the theme of possible population changes, the North American Breeding Bird Survey analysis for Colorado shows a -1.26%  annual declining trend for Cliff Swallow over the span of 1966-2022, and a significant -2.27% trend for the more recent period of 1993-2022. (2022 is presently the latest year given in these analyses). The data is ranked with the higher of three credibility categories, reflecting "data with at least 14 samples in the long term, of moderate precision, and of moderate abundance on routes."  Here is the graph they present for Colorado: 

David Suddjian

Littleton, CO

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[Kirstin C.]

Well, this was a really depressing start to my day, as I sit here drinking coffee, watching the birds outside my window.  Here in Arvada, pest control services are constantly trolling my neighborhood.  I see a Mosquito Squad truck at least once a week.  Sigh.

Sent from my iPad

On Aug 20, 2025, at 7:26 AM, David Suddjian <dsud...@gmail.com> wrote:



On the theme of possible population changes, the North American Breeding Bird Survey analysis for Colorado shows a -1.26%  annual declining trend for Cliff Swallow over the span of 1966-2022, and a significant -2.27% trend for the more recent period of 1993-2022. (2022 is presently the latest year given in these analyses). The data is ranked with the higher of three credibility categories, reflecting "data with at least 14 samples in the long term, of moderate precision, and of moderate abundance on routes."  Here is the graph they present for Colorado: 

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