[Tweeters] Where Have All the Swallows Gone?

[Thomas Dorrance via Tweeters]

For many years barn swallows have constructed colonies beneath houses and
decks overhanging Lake Washington at about NE 145th Street, Seattle. The
numbers are down in recent years but there are currently about 20,
including the newly fledged. Each year I make sure there's a muddy bank in
my yard for nest building. Not that there's a local shortage of mud - I
just like having them in the yard.
They are harassed on the ground (harmlessly, I believe) by juvenile house
finches and in the air by Anna's. But last year a Sharpie snagged a swallow
and flew off with it alive and screaming. Normally, detection of a predator
brings out the full Swallow Air Force and a virtuosic flying display.
The advent of wakeboard boats, generating waves so big they can slap the
undersides of docks and houses, could spell the end of these otherwise
ideal nesting sites.
We haven't had violet-greens, who used to nest nearby, for at least 10
years.
Tom Dorrance



On Thu, Jul 25, 2024 at 10:54 AM Carol Riddell via Tweeters <
tweeters at u.washington.edu> wrote:


> Hi Tweeters,

>

> In general, I too have noticed a decrease in swallow numbers over the

> years. For about 25 years I have watched swallow numbers decline at Edmonds

> marsh, even though there seem to be plenty of insects. In the late 70s and

> early 80s, Barn Swallows were a summer fixture in my yard. They nested in

> my neighbor’s carport. When that house sold, the new owners eradicated the

> nests. I have not seen a swallow in my neighborhood since then even though

> there have been plenty of insects. This is a July 2014 article at phys.org

> that may be of interest to some of you. It was provided by Dalhousie

> University. Perhaps they were noticing the problem before we were. I would

> suspect that the extensive use of insecticides on commercial farm land has

> a great impact on migrating insectivores.

>

> Carol Riddell

> Edmonds, WA

>

>

> Extinction: the permanent loss of a species. It is deeply troubling—and

> scientists and birdwatchers are ringing the alarm about a bird species that

> only a few decades ago was widespread and very common.

>

> Swallows, along with other birds that feed primarily on flying insects,

> are experiencing the greatest population declines for any group of birds in

> North America, and their declines are particularly pronounced in the

> Maritimes. The Barn Swallow, for example, has seen a 95 per cent drop in

> numbers across North America in the last forty years, placing it on the

> endangered species list in Nova Scotia.

>

> PhD student Tara Imlay and master's student Sarah Saldanha are trying to

> figure out why this is happening—hopefully, a first step in reversing this

> alarming trend.

>

> "This decline is especially concerning because this type of bird used to

> be so widespread and abundant and the decline of a common, widespread

> species hints at a broad scale cause," explains Saldnha. "Although this

> decline may be attributed to changes in North America ecosystems, it may

> also be attributed to changes in the birds' wintering grounds.”

> An ecological mystery

>

> Working for the summer from a busy research station near Sackville, N.B.

> (run by Acadia University and Ducks Unlimited), the two student researchers

> are focused on the decline in Bank, Barn, Cliff and Tree Swallow

> populations in the Maritimes.

>

> "I grew up in Wolfville and I have always been interested in the

> conservation of species in the region," says Imlay, "I heard about the huge

> decline in swallows and the lack of information about the cause so I really

> wanted to investigate this question. Understanding the cause—or causes—of

> declines is vital for determining the right steps to reversing these

> downward population trends.”

>

> There are two leading theories about the decline. The first suggests it's

> driven by a related decline in insect abundance or a mismatch in the timing

> of when insect abundance is highest and swallows are breeding. The second

> theory is connected to the fact that the greatest declines have been in

> birds that migrate long distances to Central and South America. This theory

> suggests that conditions at wintering locations or during migration could

> be impacting these species.

>

> Imlay and Saldanha are examining the first of these theories: the

> relationship between daily insect abundance and the timing of swallow

> breeding. They are closely tracking a multitude of factors in the swallows'

> summer routines, including variable insect populations, the date the first

> eggs are laid, the date eggs hatch, the number of eggs laid and the number

> that hatches, and chick survival rates. This data will allow them to

> determine if insect abundance is limiting population growth.

>

> They're also looking at the foraging habits of Bank Swallows during the

> breeding season, using very small radio transmitters on the birds and

> high-tech receiving towers to monitor the birds' movements.

>

> "This is the first time automated telemetry on is being used on the local

> scale," says Saldanha. "With this technology, I am getting a much better

> understanding of how the birds are traveling and using the habitat in their

> daily lives." The number of daily foraging trips and their distance from

> the breeding colony may suggest clues as to insect abundance.

>

> *Summer field work*

>

> To test the wintering ground theory, they are using a variety of methods,

> including lightweight nets to collect feather samples from adult birds to

> determine where the birds spend the winter and their stress levels during

> the wintering period. This data will allow them to determine whether

> wintering ground conditions are also impacting populations.

>

>

>

>

>

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