Why do we need Artificial Nest Boxes for Cavity-nesting Seabirds?

I have always been fascinated with the nesting process in birds. Nesting is such an obvious limitation to an egg-laying species, and birds have evolved fascinating behaviors and preferences that seem arbitrary and sometimes bone-headed. Many birds make their own nests or just lay their eggs on the ground in the open and sit on them until they hatch. Others depend on natural cavities, and it works great when cavities are plentiful, like for forest birds when dead trees are left standing and hollowed out by woodpeckers.

In landscapes that we have converted and managed for human use, the nest cavities are usually limiting resources. What should be a plentiful resource becomes a bottleneck for populations in altered lanscapes. The Bluebird Nest Box movement in the continental United States is credited with restoring the population. For seabirds, we are hoping to get a similar project going that can have population-level impacts for several species.

Nest boxes provide better nesting sites for White-tailed Tropicbirds in Bermuda
In Bermuda, David Wingate, Jeremy Madeiros, and many others have been installing nests for Bermuda Petrels and White-tailed Tropicibirds. Both species were formerly very common on the mainland of Bermuda, but have been devastated by dogs, cats, pigs, rats, and other invasive mammals. For tens of millions of year, these species nested in cavities on islands devoid of terrestrial predators. They have had a hard time adjusting to this new geological era where people and their commensal mammalian community invaded those islands, and their populations have plummeted.

Here is the case for artificial nests for Tropicbirds. You rarely see this type of data in print. But this paper shows - by a simple Wilcoxon Matched Pairs Signed Ranks Test (W+ = 16, W- = 5, N = 6, p <= 0) - that Tropicbirds that nested in artificial nests from 2006 to 2011 had significantly more fledging success than those in natural cavities . The difference was 75% success in artificial nests to 67% in natural nests. Thus, not only are the artificial nests acceptable to tropicbirds, they increase fledging success by 12% on average.

My First Forays into Nest Building
The fact that cavity-nesting birds are limited by nest sites is easy to demonstrate; just put up nest boxes in a suburban area. As my obsession with birds developed in high school, I began building nest boxes for different birds. The first nest I ever set up - a "bluebird" house - was quickly taken up by a pair of Tufted Titmice at my suburban Atlanta yard. Next, I made my own Screech Owl box. Sure enough, there was a Screech Owl pair using it that same year.

The piece de resistance of my nest-box days was the Barred Owl house. It measured about 3 ft in height, 18 inches in width and 15 inches in depth (something like this). I hope my mother has a picture of this monstrosity. I'll post it if I can find it. I had my good friend JR, who worked for a tree-cutting company, use his harness to climb up into an old red oak in my parents' front yard. He tied the box on the main trunk about 20 feet up the tree. Again, within a year, the box was occupied. Not by Barred Owls, but by their bigger, meaner cousins, a pair of Great Horned Owls.

And 20 years later, the Road Goes on Forever. 

Today, I find myself in possession of 25 nests for cavity-nesting seabirds (see below). About 15 are spoken for so far. Please let me know if you would like to try some in your part of the Caribbean.

All or almost all of the world's Bermuda Petrels currently nest in artificial nest sites, and White-tailed Tropicbirds that use nests provided for them are doing better than those in natural cavities. I've made Audubon's Shearwater nests and tropicbird nests in the Bahamas using cement and had good success, but the fragility and inconsistent nature of such nests makes them less than ideal. These nests are stackable, affordable (about $75 - less than an owl house like the one I made back in 1993), and they can help stop the decline of seabirds in the Caribbean.

Sea Level Rise at 3 mm per year since 1993

This current rate - 3 mm per year - is shocking. Since 1999 when I started studying Audubon's Shearwaters in The Bahamas, global sea level has risen 4.5 cm. I find nests that are right in the spray zone of the high tide, including at least one nest that I started studying in 1999. At Little Tobago, there is a shearwater nest that is below the high tide line by a couple of millimeters. They can nest in the same site for 50 years once established. When that nest originated, potentially hundreds of years ago, it was probably 10-20 cm above the high tide level. Now, it gets swamped in Spring tides and likely fails every year.

I often cynically joke that sea level rise is not a problem we will worry about for seabirds -  not because it won't kill them but because we will be so busy dealing with "natural" disasters in coastal areas that no one will think about the seabirds. But this math is pretty scary. 

Shearwaters prefer coastal nests just above the high tide line. In the image above, you can see the spray zone of Long Cay, which is uninhabitable by shearwaters, as the barren area of eroded rock without vegetation. As the sea rises, the spray zone will encroach on this prime habitat and all the nests within it could become sinks that fail every season as a spring tide or storm surge inundates the nest with saltwater and drowns the chick. 

A high percentage - maybe 10% - of their current nests will be unusable within the next 20 years. Of all the seabirds in the Caribbean, this species might be the most affected by sea level rise. Perhaps the new seabird nest boxes (see previous post) could help provide alternative sites above the tide line.

Nest Boxes for Cavity-Nesting Seabirds are Ready to Order!

Designed by David Wingate of Bermuda, these nest houses for cavity nesting seabirds represent decades of design from the world's expert on saving endangered petrels and tropicbirds.

The devices are ingeniously simple and the pieces stack inside one another. The top is vented and held on with sturdy molded tabs that lock in. They can be buried in sand, covered in rock or cemented in place, and you can install them in any location that will be safe from Dogs, Cats or other predators.

Bermuda Audubon and the Bermuda Department of Conservation Services sells the previous version and has had great success filling cliffs with White-tailed Tropicbirds. Special baffles for the entrance can limit the tunnels to smaller species including Cahows or Audubon's Shearwaters. The first 25 are available for installation in the Caribbean. Just contact me with shipping information and an explanation of when and where you will put them in. The only costs are shipping and an agreement to send pictures and reports on the success of your nest boxes.

The molds were funded by Bermuda Audubon Society, while BirdsCaribbean and the National Fish and Wildlife Federation funded the molding of the first 50 boxes. They can be used anywhere in the world. Contact me for ordering information.