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Basket Cases

2013 May 28
by Seth Inman

What strange growths protrude from this tree? Photo by Seth Inman.

There are birds around the world that use strands of different materials to craft marvelous woven nests that hang from tree branches — if you’re lucky enough to see them! Of course, in some circumstances it is not hard to find these pendent, or hanging, nests, as with many species of caciques and oropendolas in Central and South America (birds related to our North American blackbirds, orioles, and cowbirds). That’s right, the photo above isn’t of some weird fruit tree, but a tree-wide colony of oropendolas at Las Isletas, in Nicaragua!

Yellow-rumped Cacique in Avian Architecture by Peter Goodfellow © Princeton University Press 2011. p95

Diagram of pensile nest in Avian Architecture by Peter Goodfellow © Princeton University Press 2011. p97

Caciques, close relatives of Oropendolas, often nest beside wasp nests; orioles, only slightly more distant relatives, frequently nest near Eastern Kingbirds and Great Kiskadees. Wasps and these large flycatchers all help defend against nest predators. Yellow-rumped Caciques like the one pictured on the right start their nest building with a loop in a tangled mass of fibers that surrounds the end of a branch. The female sits in this loop and weaves new strands into a sleeve flowing downwards from the branch, often working upside-down inside the sleeve. She only leaves her construction through the original top loop, probably to tighten her weave through the stress of stretching, and to not compromise the looser new strands at the bottom of the sleeve.

The Montezuma Oropendola, which ranges from Mexico to Panama, mostly uses banana leaves for its pendent nests, supplemented by palm fronds and vines. The female finds a large banana leaf with a tear in the strong supporting rib or stem, and pulls off strands as long as two feet (60cm) long, making trips back and forth to her chosen nesting location with a few of these streamers trailing behind her. The nests take an average of ten days to complete, and are between three and four feet (90-120cm) long and seven to nine inches (18-23cm) in diameter near the bottom. The interior is lined with dead leaves, which help incubate the eggs with their heat and also shelters them from violent rocking during high winds. Below are some examples of loops and weaves that have been found in nests around the world. In the case of the birds mentioned here, females instinctively know how to weave their nests, though they do appear to grow more experienced over time.

1a. Loop tuck, 2b. Simple loop. 3c. Interlocking loop, 1. Spiral coil, 2. Simple weave, 3. Alternately reversed winding. In Avian Architecture by Peter Goodfellow © Princeton University Press 2011. p101

Orioles, such as the Baltimore and Bullock’s, use materials like horse hair, bits of cloth, and string in addition to the more usual long and flexible fibers from stems and leaves. These two species make pouches or shallow cups that can hang up to eight inches (20cm) long, and if there is Spanish moss in the area you’ll probably see it camouflaging the exterior of their nest. The interior is lined with down from plants, wool from sheep, and other fine materials. Although male Orchard and Baltimore Orioles have been reported to help in nest building, almost always it is the female who weaves the close to ten thousand stitches in a typical nest.

Representation of the process of Baltimore Oriole nest construction in Avian Architecture by Peter Goodfellow © Princeton University Press 2011. p103

My nest post will include a slideshow of many woven nests, particularly of our North American orioles, so stay tuned!

Focal Species Close-up: Barn Swallows

2013 May 7
by Seth Inman

The Barn Swallow’s nesting and habitat preferences have made it the most abundant and widely distributed swallow species in the world. The species adapted to using human structures as nest-bases from their previous preference of nesting in caves (although a single population on California’s Channel Islands still chooses to nest in its ancestral cave-grounds), and today you can find Barn Swallows nesting nearly anywhere in the US, even ranging as far afield as southern Alaska.

Since they nest on man-made structures so often (hence their common name, as well as their species name rustica in the genus Hirundo), they make for frequent subjects of our Funky Nests in Funky Places challenge, and are a great focal species in general for Celebrate Urban Birds given that their habitat of choice can coincide with rural, suburban, and urban landscapes that include buildings, open areas, and water, especially bodies of which provide a source of mud. As you can see in the photos above and below, mud is the main building material for their nests, as it is for Cliff Swallows, a few of which are featured in these slideshows!

In the slideshow above, you can see Barn Swallows gathering mud from the shore of some body of water (it can be anything from a river to a lake, although preferably there is grass or straw near or mixed into the mud so that the birds can more easily create the pellets that will be the building blocks for their nest). Both parents build the nest after having explored several potential nesting sites; once they’ve chosen one, they start construction by creating a small shelf that they can sit on and add the sides of the nest to. The pair can either build a semicircular cup plastered to a wall, or a full cup perched on top of a horizontal surface like a roof beam or other objects, as you can see in these slideshows.

When the main body of the nest is complete, the interior of the cup is lined with grass and feathers, and as in other swallow species (especially Tree Swallows) colonial groups might experience severe nest-lining theft — in these areas, if you take a handful of feathers and throw them in the air or leave them outside, you might see swallows swooping in to engage in a free-for-all to retrieve the precious bed-lining. Sometimes Barn Swallows reuse old nests, as long as they seem clean and free enough of parasites, and when they do so they throw out any old feathers and replace them. They also add new mud to the rim of the nest, which might explain some of the striation of mud colors in many of these photos.

So if you find a nest stuck to your walls or rafters and you see that there’s a pretty significant amount of mud in it, chances are it’s a Barn Swallow’s nest! If instead of mud there seems to be a bunch of greenish moss in the construction, it is more likely a phoebe’s nest. Barn Swallows generally lay 3-7 eggs per brood, and their eggs are a pinkish/creamy white, spotted with brown or gray.

To learn more about how to differentiate Barn Swallows from similar species, click here!

Funky Hummingbird Nests

2013 April 26
by Seth Inman

I’d like to correct a gross understatement I included in my post Silky Nests in Funky Places. I mentioned, based on what I knew at the time, that over the past few years of the Funky Nests challenge we had received “photos of over a dozen hummingbird nests,” upon which Karen pointed out that we had in fact been sent “a lot, lot more.” So, in part to correct my previous miscalculation and mostly to share fantastic contributions by previous participants that display most or all of the nest traits I laid out in my first post, I’ve compiled the majority of our received hummingbird photos that haven’t already been shown recently on the blog.