Helping birds build nests in my yard

Inside view of the house wren's dummy nest. I love the wren-shaped hollow in the middle!

For the second spring in a row, a male house wren used my window birdhouse to hold one of the dummy nests he showed his mate. House wrens apparently make several dummy nests for the female to choose from. Just like last year, though, she chose a different location to actually lay her eggs. Phooey! So that started me wondering whether there was anything I could do to improve the chances she might actually use my birdhouse next year. Would she prefer a different location? Or should I make better materials available for the male to use?
 

Outside view of the nest. Both years, twigs or grass stems stuck out of the entrance. I'm not sure if this is typical for the species, or just my individual bird.

As I researched house wrens’ nest preferences, I realized I could also explore other neighborhood birds’ nesting requirements. If I added more possible nest sites to my yard, like birdhouses and large bushes, and provided appropriate nesting materials, maybe I could convince even more species to nest in or near my wild back yard!

Cornell Lab of Ornithology has lots of information on birds, from how to ID them to their habitat and life histories. I looked for the species I know visit my yard in the summertime, figuring they’d be my likeliest nesters.

Anyway, my backyard birds are either cavity nesters, or branch nesters. Birdhouses can attract cavity nesters, since they look close enough to the tree holes the birds normally use. On the other hand, birds that normally build their nest on open branches aren’t likely to use a bird house. But of course birds don’t always go by the book. An ornithologist friend of mine discovered a house wren pair that was raising their young not in a cavity nest, but in an open cup nest built on some branches! Weirdos.

In doing my research, I also found that www.Nestwatch.org has downloadable plans to make birdboxes for various species too. I’m definitely adding "building birdhouses" to my project list. Maybe something to work on this winter? Nestwatch also lists helpful features of good birdhouses to guide aspiring nest hosts like me.

Cavity Nesters

A lot of birds like to nest in the hollows of dead or dying trees. Whether they add materials to the cavity, or just use the soft decayed wood that’s already there, varies by species. These birds are one of the main reasons for leaving dead trees standing in your yard when possible, rather than cutting them all the way to the ground. But if you don't have any dead or hollow trees in your yard, birdhouses make a reasonable alternative!

·       Carolina Chickadee—moss, bark strips, and hair

·       Tufted Titmouse—leaves, moss, grasses, bark strips, soft fur and hair

·       White-breasted Nuthatch—fur, bark strips or shreds, grass, feathers

·       Downy Woodpecker—wood chips

·       Red-bellied Woodpecker—wood chips

·       House Wren—twigs, feathers, grasses, hair, snakeskin

·       Carolina Wren—bark strips, grasses, leaves, pine needles, hair, straw, feathers, shed snakeskin

·       

Branch Nesters

Other birds prefer to build nests on the branches of trees or shrubs, or even under the overhang of building eaves and bridges. While you wouldn’t build a birdhouse for these species, you can still provide materials for them to use. On winter hikes, I enjoy spotting the empty nests that had been hidden during the summer.

·       Northern Cardinal—branch fork in a shrub. Uses twigs, leaves, bark, grasses.

·       Blue Jay—branch fork in a tree. Uses twigs, grass.

·       Mourning Dove—branch, also frequently nests in gutters, eaves, flowerpots. Uses twigs, grass, and pine needles.

·       House Finch—tree branch, also structures like hanging flowerpots, vents, & streetlamps. Uses fine stems, leaves, twigs, and feathers.

·       Eastern Goldfinch—branches in a shrub. Uses spider silk, plant fibers, and fluff from seeds like dandelion and thistle.

·       Eastern Phoebe—under the overhang of building eaves or under bridges, especially near running water. Uses mud, moss, leaves, grass, and animal hair.

·       Northern Mockingbird—Shrubs. Uses twigs, grasses, rootlets, and leaves.

·       American Robin—horizontal tree branch, or on/under structures like eaves, gutters, and light fixtures. Uses twigs, grass, feathers, and mud.

You might have seen suggestions to provide bits of string and yarn or even dryer lint for nesting birds. When I was a kid, we often draped scraps of yarn on bushes outside, in hopes that birds would weave them into their nests. But it turns out string and lint aren't actually safe or useful for the birds. Dryer lint turns hard and crumbly once it’s gotten wet, rather than staying soft or helping hold the nest together. And even short bits of yarn can tangle around baby birds’ feet and toes. I don't want to hurt or endanger the baby birds in my yard, so I won't be using yard scraps for my nest material kits.

Some of the nest materials I listed are already available in my yard, like the drifts of dry leaves that collect in corners. Others I will tuck into clean, empty suet feeders to make little supply stations for inquisitive birds, as described here. I don't put out suet in the summertime, so the suet cages are available for use. Fat can go rancid in the Maryland heat, and softened fat could also foul a bird's feathers. So next spring, I'll stuff the cleaned cages with materials like bark strips, dry grasses, plant fluff and odd feathers. I have lots of milkweed plants in my yard, and plan to collect some of their seed fluff when the pods ripen this fall.

In the long term, I also want to add more shrubs and bushes to my property. I have a back yard that's mostly underutilized in terms of gardening-- it has a few trees that were already there when I moved in, but I haven't changed things very much beyond adding the log pile. The back is partly to mostly shady, so isn't conducive to most pollinator plantings. But birds don't need the sun quite as much as bees and butterflies and flowers do. So I might focus my back yard landscaping on bird habitat. Stay tuned! 

Do you have any birds nesting nearby this year? Have you discovered birds nesting in odd places? I'd love to hear about them in the comments!

The wren mostly used twigs this year, but also some tall grasses complete with seeds. Handy snacks, perhaps?

Could Raising Captive Monarchs Mess Up Migration?

A late-season male Monarch butterfly nectars on my New York Asters

As you may have heard, alarming new research about raising Monarch butterflies was published recently, by Ayşe Tenger-Trolander, Wei Lu, Michelle Noyes, and Marcus R. Kronforst. Their study found that indoor-reared fifth-generation Monarch butterflies did not display southward flight in tests, which means they wouldn't migrate properly. Uh-oh!

I haven't been able to access the entire article yet, just the abstract linked above, and a write-up in Science. But even those limited sources give me concern about my techniques in raising Monarchs. The researchers raised both commercially-bred monarch caterpillars and wild-caught. Although they used the caterpillar generation that's supposed to migrate, both groups  had neither the elongated wings of migratory individuals, nor showed predominantly southward flight under test conditions. (They attached the mature butterflies to poles in the experiment, so they could observe which directions each butterfly would head. Previous research has shown that in these conditions, migratory monarchs reliably try to fly southward.) The scientists even raised some wild individuals outdoors until the point of pupation, and found that if those individuals eclosed indoors, they too seemed to have lost the tendency to migrate!

Two of my Monarch chrysalids last year, raised indoors & then released after eclosing.

Not unexpectedly, this has thrown the butterfly-raising community into a bit of a tither. Are we actually exacerbating the threats to monarch migration as we try to help? When our efforts include raising the caterpillars indoors, especially the migratory generation, it looks like maybe so.

From what I'm seeing on various email groups, Twitter, and Facebook, many caterpillar hobbyists and citizen scientists are distraught. Should we change our habits and maybe abandon the hobby of raising monarchs?

Honestly, I've already been somewhat concerned about my butterfly raising. This isn't the first study to indicate we might be doing more harm than good, for one thing. I had thought, though, that the main problem was using captive-bred caterpillars, like classrooms might when they mail-order caterpillars from who knows where in order to have them on time for the lesson plan. Since I only raise wild-caught individuals (whether starting as egg or already-hatched caterpillar), I hoped I wasn't doing too much damage.

But another effect of captive-raising caterpillars can be to allow weak genes to survive and get passed along. Since I'm protecting the caterpillars from natural stresses, a trait that would have made an individual less likely to survive isn't actually a problem, and may end up expressed in the next generation too. Especially if I raise every monarch caterpillar I can find, I might still be making my local population less fit. Now this new research just adds more support to reconsidering my actions.

This Monarch caterpillar lived its entire life outdoors at Brookside Gardens, where I found it getting ready to pupate.

I can't speak to what anybody else will or should do, of course, but here are ways I'm planning to change my caterpillar husbandry:

• In general, I will collect and rear no more than 50% of the eggs and/or caterpillars that I find in my garden, of each species. The rest I'll leave wild and unbothered, to fend for themselves. (This also means I'm not reducing the amount of available food for hungry birds!)
• For monarchs in particular, I will rear no more than two caterpillars per generation for the first four generations each year.
• Once the migratory generation's eggs are laid, starting around August in my area, I won't raise any monarchs. 

I also considered trying to create an outdoor setup for raising monarch caterpillars, rather than keeping them in my office indoors. That will take quite a bit more planning, however, so stay tuned.

Another idea was to raise monarchs indoors until they look ready to pupate. Then I could move them outside while they pupate and later eclose. Although I'm not sure exactly what the pupa get from being outdoors, the new research does indicate it's a crucial factor in triggering migration: "In fact, merely eclosing indoors after an otherwise complete lifecycle outdoors was enough to disrupt southern orientation."

I'm not changing how I raise Black Swallowtail caterpillars, or other non-migratory species, as much as I'm changing my treatment of monarchs. I'm definitely reducing how many I raise, going by the 50% rule above. Also, if I find a single egg or caterpillar on any day, I won't bring that in at all. I know I still might be changing something essential in these butterflies by raising them in the protected environment of my office. However, I do call them "pets" sometimes because I know they may not be the same as totally wild individuals. I guess they're kind of half-wild; I do release them as soon as they eclose. I always hope they make my local population larger, going on to mate and lay more eggs that lead to more caterpillars. This summer I'll keep thinking about whether I feel comfortable bringing them inside any more.

As much as I love watching the caterpillars up close, am I being selfish by bringing them inside?

Do you raise butterflies indoors, or have you ever? What do you think about this new research? I'd love to hear your thoughts, whether you plan to stop raising butterflies at all or keep on caring for them like you always have.  Perhaps you even have a totally different method of raising caterpillars than I do. Whatever the case, please leave a comment below to keep the conversation going!