She's Going In and Out, But Is She Nest Building?
Ok, I have a confession to make. I’ve been getting quite impatient waiting for the Tree Swallows at the Salmon Creek nest box grid to start nest building for real. After all, swallows have been here nearly seven weeks now, and pairs began forming six weeks ago, but aside from a few bits of dead grasses there’s nothing in any of the eight boxes remotely resembling a nest. So, to see if my impatience was justified I decided to review records from the past nine years to determine if nest building truly is abnormally late this year.
This Is the Most "Advanced" Nest as of 4/29/12
First, let me explain how I define the start of nest building. As we’ve seen, female Tree Swallow often bring a few bits of vegetation into their nest cavities early in the season. These have been termed “claim grasses”, but if they are meant to claim a cavity the claim certainly isn’t honored by other swallows. A pair must often spend weeks repelling other Tree Swallows who would like to kick the original owners out, claim grass or no claim grass. Personally, I believe these early bits of vegetation signal a brief post-migration transition into the nesting season, a slight tweaking in the female’s hormonal balance, nothing more. The shift to nest building comes several to many weeks after arrival when, like a motor that sputters and sputters before it catches, the females rather suddenly start bringing large amounts of vegetation into their boxes. It really is like an internal switch has been thrown.
When, in checking boxes, I find a substantial ring of vegetation around the outside of a box’s floor, a ring that wasn’t there the previous day, I label that day the start of nest building in that box. And when the female has covered the box bottom with vegetation and formed the cup that will hold her eggs, I note in my records that her nest building is complete as of that date. I do not include feather-gathering by males or females in this formula, since feathers may continue to be added for many more weeks.
So, here’s some statistics. We had 86 nestings at Salmon Creek between 2003 and 2011. Four of these had takeovers that interrupted nest building, and 16 were late nestings in boxes added in May to reduce competition. But of the remaining 66 nestings where nest building began “normally”, 50 of them, or 76%, began during the eleven day period between 4/29 and 5/9. In other words 2012 could still easily fall in the normal range if most of our females begin to build in the next ten days. And actually there were some encouraging hints today that nest building is about to start in earnest. As I sat with the swallows at Box 2 the female began gathering dried grasses vegetation from the ground, and she went right into high gear, bringing piece after piece into the box. For the half hour I watched she stopped only to help the male ward off floaters or to dash away in response to raptor alarms. Box checks later revealed some additions of vegetation in Boxes 1 and 3 since yesterday also. I think the female Tree Swallows of Salmon Creek are on the verge of an intense bout of nest building and, if so, they’ll be right on time after all.
Yes, She Is Bringing Nest Grasses
Did nest box checks today and most boxes have claim grass with a lesser number having claim feathers. Additionally, this claim grass was “fronted” – the grass was in an observable pattern at the front of the nest box – maybe this is due to wind moving material around in the box or perhaps nest building starts in a certain spot of a nest box and proceeds from there? I checked records and from the time this “fronted” pattern is observed until actual nest building starts is around 6-10 days.
At almost every one of these boxes, there were two, then three/four Tree Swallows in the general area. Alarm calls were sounded by one of the birds, and on some occasions you could observe some fighting between birds.
There were also on a three occasions Barn Swallows that flew over to the general area of a nest box, perhaps alerted due to the alarm calls, but they then swooped low for ostensibly feeding on insects.
No dead Tree Swallows were found in nest boxes, although there were three boxes that had substantial droppings which suggests communal roosting was occurring the last 4-6 days.
Hi Tom,
Today, 5/1, three of my eight boxes had a situation similar to the one you describe: an assemblage of grasses concentrated at the front of the box floors beneath the entrance holes. For some reason tree swallow females tend to build this way, with the nest cup usually ending up being situated along the back wall or in a back corner rather than being centered. I’ve no good explanation for this except that they may be instinctively trying to get their eggs and young as far from the entrance, and predators, as possible.
How did your killdeer nest make out during the snow and cold?
Chris
Your explanation seems reasonable to me on nest building. We’ll check tomorrow to see what one of the nest box trails yields.
The Killdeer nest is active. On last Monday, there was 3-4″ of snow and the driveway had snow on it. The Killdeer must have sat through that. When I went out for a walk two days later, an adult spied me from a distance and walked around a bit – no injury feigning behavior as was probably not perceived as a threat based on my distance from the nest.
I should have given these birds more credit. They have adapted to survive and have gotten to the point where nests are laid that allow them to hide in plain sight, a point I’ll keep in mind!