For such a small bird, they sure are vocal. The song – an energetic bubbly burst of music. The call – scolding incessant chatter.
Being small, they are also very apt to escape before we can get them out of the net when banding… or before we have finished gathering data. I’ll bet there are many House Wren records with no number in the body mass column!
This year at Audubon, we tried something a little different with regard to nest boxes. We moved all the boxes with 1.5-inch holes to the middle of the field to attract Tree Swallows and Eastern Bluebirds. Along the edge of the field we placed boxes with 1.25-inch holes – big enough for House Wrens and Black-capped Chickadees – both of whom seem to prefer to be a little closer to the brush and trees. And, to facilitate monitoring and photographing, I asked John to make me boxes with hinged roofs, as well as hinged side doors. (Thanks, John!) House Wrens in particular are difficult to monitor from the front or side because they tend to fill the box so full of sticks. With a hinged roof, I can look in from the top! All aspects of this plan are working very well! I have no House Wrens in the boxes I intended for Tree Swallows and Bluebirds, and they ARE so much easier to monitor!
House Wrens start construction of a nest by laying a foundation of sticks in the bottom of the natural cavity or nest box. The nest will then be lined with softer material before egg-laying begins. The eggs are so tiny – like the Easter malted milk eggs – and there can be 4-8 of them (or more), making you wonder how such tiny birds will feed so many mouths once they hatch.
Mom lays one egg each morning until she has a complete clutch. She will start incubating the eggs when the 2nd or 3rd to last egg is laid – so hatching could happen over the span of 1-4 days. When they hatch, they are pink and featherless with eyes tight shut. Slowly the feathers come in – at first all encased in little shafts, and eventually breaking loose.
Both mom and dad will feed the young for 12-18 days in the nest, and another 12-14 days after fledging. A pair may have 2 or 3 broods in a season. I never open Wren boxes after about day 9 or 10, because the babies are apt to fledge prematurely. (OK, once I did… and I had to scramble to find all the babies and put them back!)
Despite their size, House Wrens are very fierce competitors for nest sites, which is why I tried to provide them their own boxes along the edge of the field. Unfortunately, titmice and chickadees also like the edges of the fields. I know for a fact that at least one Black-Capped Chickadee nest with eggs was removed from a box. I assume this was done by the House Wren, as they are known for this kind of behavior, and because the box was next filled with sticks.
In the field habitat, we pair boxes so that if a Tree Swallow gets one, the other will be open for a Bluebird. I’ve never seen that strategy listed for House Wrens and Chickadees/Titmice. Given the House Wren’s habit of stuffing nearby cavities with sticks, providing paired boxes in shrubby habitat probably would do no good.
Can anybody out there suggest strategies for making sure the Chickadees get a place to nest, too?