[Tweeters] Swallow Status

Carol Riddell cariddellwa at gmail.com
Mon Aug 20 13:24:34 PDT 2018


Hi Tweets,

I have been reading with interest the thread on the apparent lack of swallows. Anecdotally, I notice lots and lots of insects, from dragon flies to much smaller, around my home turf of Edmonds and wonder why a seemingly abundant supply of insects does not support more avian activity. I have taken a look at Birds of North America Online and have found the following comments. I certainly do not discount the impact of chemicals on bird populations, but it appears that House Sparrows may be more problematic, at least for Cliff and Violet-green Swallow populations. I am also aware of homeowners who have told me that House Sparrows have destroyed Tree Swallow nests or killed the nestlings.

At the Edmonds marsh we installed five nest boxes with the goal of inducing Tree Swallows to nest. Three boxes have been used by Tree Swallow pairs and only one has been in use by a pair of Violet-green Swallows. During the couple of months that Violet-greens are in residence, there are far more than the one pair using the nest box. I have not been able to locate other nest sites, although they must exist and perhaps other birders know where they are. There is a very small House Sparrow population near the marsh so I keep on eye on the nest boxes for signs of sparrow activity. So far, I have not seen any.

BNA Online is a subscription service, but one that can be accessed for free as part of many library subscriptions. It is available after log in on the Seattle Public Library and Sno-Isle Libraries web sites. It is worth investigating access at the online research portal of your local library web site. It provides much more detailed information than the Cornell Lab information that comes up for free when you put a species name in your internet search field.

Barn Swallow

Effects of Human Activity
On balance, human activity has had strongly positive effects on this species: construction of artificial structures has provided abundant nesting sites, leading to population size that is probably several orders of magnitude greater than before European settlement of North America. Barn Swallows are popular with people, and farmers often protect (rarely persecute) the birds on their property. The species seems to have adapted well to nesting in human-altered habitats in North America and worldwide.


Cliff Swallow

Effects of Human Activity
On balance, probably positive. Breeding habitat has been enhanced by the widespread construction of bridges, culverts, and buildings that provide alternative nesting sites and have probably led to a range-wide population expansion. Cliff Swallows are extremely tolerant of humans, frequently occupy colony sites in close proximity to people, and do not seem negatively affected by researcher activity in and around their colonies.

. . .

Measures Proposed And Taken
House Sparrow control seems to be the most effective means of increasing Cliff Swallow numbers locally and probably regionally (Samuel 1969b <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF32696>, Krapu 1986 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF41668>, Silver 1993 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF41679>). Trapping and shooting House Sparrows at colony sites varies in effectiveness but eventually eliminates most individuals. Knocking down all old Cliff Swallow nests after the breeding season also controls House Sparrows, by removing places for them to roost during the winter and preventing them from becoming established in the existing nests at a colony site before Cliff Swallows return in the spring. A colony in Wisconsin grew from 1 nest to over 2,000 nests over a 38-yr period, primarily through House Sparrow control and annual removal of old nests during the winter (Buss 1942 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF41657>). Nest removal also reduces buildups of ectoparasites from year to year. Fumigation of nests with the insecticide Dibrom is effective in eliminating parasites (Brown and Brown 1986 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF41652>, Brown and Brown 1996 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/cliswa/references#REF7281>) but has not been used specifically for management to date.


Violet-green Swallow

Effects of Human Activity
No documentation of effects on numbers. This species' domesticity and ability to nest both in remote cliffs and near human habitation may have saved it from harmful human impact (Erskine 1979 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/vigswa/references#REF21782>). Introduction of House Sparrows and European Starlings (Sturnus vulgaris), however, may have negatively influenced populations in s. Canada, particularly in urban areas (Erskine 1979 <https://birdsna-org.access-proxy.sno-isle.org/Species-Account/bna/species/vigswa/references#REF21782>).

Management
Little information. Nest boxes have clearly helped this species in some regions, but extent of nesting in boxes remains poorly documented. Comparisons of breeding numbers and success in boxes and in nearby natural sites would be helpful data to have.


Carol Riddell
Edmonds, WA
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