Monitoring Tree Swallow Nests

Nature Notes for June 24, 2011

Over the past two weeks, I have been spending a lot of time with Tree Swallows. For about 15 years, I have been monitoring their nest boxes and banding the young.

Tree Swallows females are quite synchronous in their egg laying. That is, all females in an area will lay their eggs at almost the same time and start incubating at the same time. That means that I am very busy in mid-June. This year, chicks were ready to band starting on June 8 and almost all have been banded as I write. Many young birds have fledged already. There are only a few nests that still have nestlings in them.

One of six species of swallow that nest locally, Tree Swallows are cavity nesters. Prior to European settlement, they used old woodpecker holes, often in dead snags around beaver ponds. However, like the bluebird, they nest readily in man made nest boxes. This has made them a good species to study, since the nests can be found easily and Tree Swallows are quite tolerant of disturbance.

Tree Swallows nest throughout most of North America. They winter from the Gulf coast to Central America. They can winter further north than most swallows since they are not completely dependent on flying insects for food. They can digest the berries of the wax myrtle, a common coastal shrub.

The plumage of adult Tree Swallows is iridescent blue/green above and white underneath. They have a slightly forked tail, but not the long tail streamers of a Barn Swallow. Female Tree Swallows take two years to acquire their iridescent plumage. This is unusual for female songbirds. In their first breeding year, they are primarily brown above, with sometimes a few scattered green feathers.

Nests of Tree Swallows are made of a neat cup of grass lined with finer grasses. If pine needles are available, they may make a nest of them instead of grass. They also always contain feathers which act as insulation for the chicks. I have found body feathers of ducks, gulls, Ruffed Grouse, Wild Turkey and domestic chicken lining Tree Swallow nests.

Tree Swallows lay small white eggs, typically five or six to a clutch. When the female is laying, she lays one egg per day until the clutch is complete. Only then does she start incubating. Sometimes incubation does not start immediately. Incubation can be delayed for up to two weeks and the eggs will still be viable.

Incubation typically takes about 14 days, with the entire clutch hatching on the same day. Newly hatched chicks are naked and helpless. They seem all mouth and stomach with very truncated wings and legs. It hardly seems possible that in three weeks they will grow enough to have feathers and be able to fly. “Eating like a bird” takes on a whole new meaning when you see how quickly they grow. It takes a lot of flying insects to fuel that growth.

Although at the beginning of the nestling period, the adults remove the fecal sacs from the nest, as the chicks grow, they stop doing this. The result is that by the time the chicks fledge, the nest is a matted mess which needs to be scraped from the box. Successful Tree Swallow nests, that is chicks survived to leave the nest, are disgustingly filthy.

Although there are a few exceptions, most Tree Swallows have only one brood per year.

So far this year, I have captured 3 previously banded adult females. One was banded as a chick in 2007, one as a chick in 2008, and the third as an adult in 2008. The third bird is at least 5 years old, although she could be older. The oldest known Tree Swallow on record is a male which hatched on a long-term study site at Long Point on Lake Erie. This bird was a little over 12 years old when last captured, alive and well and at an active nest on Long Point.

The last Breeding Bird Atlas for Ontario reported a significant population decline in Tree Swallows since the preceding Atlas, as with all aerial foragers. The reasons for this decline are probably many and include habitat loss, drainage of wetlands, changes in farming practices, competition with other species for nest cavities and pesticide use which reduces their food source.

Since this species is quite tolerant of humans, it is really unfortunate that human activity is the main cause of its decline.

16th Northumberland Summer Bird Count

Nature Notes for June 10, 2011

On Saturday, June 4, I awoke to gentle rain. This was not good news, since this was the first day of the 16th Northumberland Summer Bird Count. I ate breakfast and drove to my assigned area near Castleton in the rain. By the time I arrived, the rain had stopped but the skies were still very gray.

Even without rain, the weather was going to be a problem. On a bird count at this season, observers find birds mostly by sound – songs and calls. Overcast skies tend to suppress bird song, so birds can be very difficult to detect.

I donned my rain gear and started down the road allowance. This is a very interesting route, since there are treed hedgerows along both sides of the road. Part of the length has forest on one side and open agricultural fields and pasture on the other.

The variety in habitats houses a good variety of landbirds. In the hedgerows were such species as Indigo Bunting, Brown Thrasher and Chestnut-sided Warbler. The forest held Veery, Ovenbird and Rose-breasted Grosbeak. In the open fields, I could hear Eastern Meadowlark, Bobolink, Grasshopper Sparrow and Savannah Sparrow.

There is one wet field with a small pond. Here I encountered swarms of mosquitoes. In an area that is generally high and dry, I am assigned the “buggiest” walk. Thanks goodness for the rain gear!

I returned to my car and drove slowly up Jakobi Road, stopping from time to time to get out and count the birds I was hearing. Next stop was another unmaintained road allowance, where I startled a group of people checking the transformer for their solar collectors. I’m sure they thought I was a bit odd when I told them I was doing a bird count. Who would walk into that valley with thunder rumbling from increasingly dark clouds?

This time, I used the environmentally friendly bug spray that I had purchased at Port Hope’s Living Green Fair. I also donned my mesh bug shirt. As I ventured down the road, light rain began to fall. By the time I had walked to the river bottom and back to my car, it was raining hard.

This seemed a good time to have some lunch and wait for the storm to pass. It didn’t. The rain fell even harder. I decided to drive slowly with the car window open along several secondary roads to see if I might hear or see any other birds. I learned that not only robins sing in the rain, but so do Baltimore Orioles. Since the rain seemed to have settled in, I ended my day at 11:45 and headed for home.

On Sunday,  I had a friend birding with me. I picked Katsu up and drove to our starting place, this time in fog. There was intermittent sun and cloud, so the birds were singing more. Our first walk was another buggy walk (for which Katsu wasn’t prepared) along a different road allowance to Piper Creek. This walk yielded Mourning Warbler, Alder Flycatcher, Black-throated Green Warbler, Black-and-white Warbler, Blackburnian Warbler, Northern Waterthrush, Yellow Warbler, Common Yellowthroat, and Swamp Sparrow, as well as other species.

On a drive in an agricultural area we found Horned Lark, more Bobolinks, Savannah Sparrows, Grasshopper Sparrows and a pair of Northern Harriers. These were the first raptors I had seen. They don’t like to hunt in the rain.

Next was a walk through a pine plantation in search of Red-breasted Nuthatch (success) and Red Crossbills (no joy), but we did find Blue-headed Vireo. Then another walk along a wooded trail through the forest. This walk added Scarlet Tanager, seen as well as heard.

The last bird of the day was a Ruby-throated Hummingbird.

Why do we do these counts? It is mainly to monitor breeding bird population trends. Data from this count has been used by the Nature Conservancy of Canada in their conservation work on the Rice Lake Plains and is available to other agencies.

This count is organized by Willow Beach Field Naturalists. The data from past counts is posted on the WBFN web site, www.willowbeachfieldnaturalists.org. The 2011 data will be added when it has been compiled.

Let’s hope for dry weather in 2012. We’re due. It also rained on the 2010 count.