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April 22nd, 2004  Cavity Protection I walked around 101 Mile marsh today just as the sun came over the trees and burnt the heavy frost from a cool night. I came to the marsh specifically to see if any tree nesting Ducks were showing interest in a duck box I’d hung the previous week. The hanging was what I call a ‘vandal box’ because it was erected on private property without permission. I didn’t feel particularly vandalistic though, as this marsh is part of a Ducks Unlimited project in which a pond has been fenced away from livestock to create a safe shoreline for nesting waterfowl. Stepping inside a fenced area near the roadside, I glassed the water of the marsh hoping to see a pair of Barrow’s, or Common Goldeneye. Common Goldeneye were present - three males and a female - two of the males moved about looking rather frustrated. The third male virtually cordoned the female away from the other two males with his pre-nuptial antics. He swam in tight circles around the female, while she remained in a pose I call ‘the crawl’ with her chin pressed on the water and body low and flat as possible. Every so often the Goldeneye male threw his head back on his shoulders, pointed his beak skyward and ‘beeped’ - a sound reminiscent of a Nighthawk. This activity looked promising. This was certainly a pair of Goldeneyes with mating on their mind. Across the marsh, on the sunny side, I heard the banter of Tree Swallows as they battled over woodpecker holes in the cottonwoods along the fence. I walked around the margin of the marsh to look at my duck box, and as I neared the spot where the Swallows fought, I saw two Starlings attempt to drive a male Northern Flicker from a cavity nest. Suddenly I saw a bird looking from the duck box. I glassed the hole and saw the face of a female Northern Flicker. Her head poked out then retreated inside. She flew off as I approached. I hoped she wasn’t planning on taking up residence in the box especially since she was capable of making a good cavity nest herself. Seeing the Flicker in the duck box brought back a memory of a clutch of Goldeneye eggs I once found while canoeing. As I paddled in a shallow bay, looking into clear water at the stony bottom, the roundness of some stones caught my attention. They weren’t stones at all but eggs. It took a little work but I managed to bring one to the surface to look at more closely. It was the light green egg of a Barrow’s Goldeneye. There were a total of eight eggs strewn along the lake bottom. They were submerged in four feet of water and about 30 feet from shore. I thought about this discovery for some time. The most plausible scenario I could think of was that a female Goldeneye had found a suitable cavity nest. Then believing that she had secured a place to lay her eggs; initiated mating. Between the time of mating and laying her first egg, something happened to the cavity nest. Perhaps it was destroyed when the tree it was in blew down, or maybe the cavity was taken over by another cavity user. Regardless, the Goldeneye’s eggs were on the way and she had no recourse but to deposit them wherever she could. In this case it was in the water. This is all speculation on my part but I do think the unexpected happens to birds who have designs on, but no way of barring entrance to, the cavity that would be their nest. In spring, over two dozen local bird species are in the market for a suitable cavity. That’s a lot of bird species looking at a very limited number of suitable accommodations. Spring real estate action heats up fast. Luckily, most of the Woodpecker clan doesn’t look for second hand digs. They are home makers rather than home grabbers, so that lets eight cavity users out of the competition. There are exceptions however. A Flicker has no qualms about renovating and reusing a cavity as long as the tree is in viable shape. Others of this species may also re-use, but thankfully many are moved to create a new cavity every year and don’t return. Sapsuckers, bless their little sap-sipping hearts, insist on drilling a new home every year, often in a living poplar tree. This activity makes Woodpeckers - on the hole - the biggest bird house makers of any species, even more than humans. So how does the competition for cavities play out? Let’s start with nest holes that are on the small side. Cavity entrances of about 1.25 inches, drilled perhaps by a Downy Woodpecker, lure Black-capped Chickadee, Mountain Chickadee, and the Red-breasted Nuthatch. The small holes exclude larger birds but this does not preclude squabbling. Chickadees and Nuthatches may at times avoid the hassle of fighting over pre-drilled holes; if they can find a trunk with quite soft, punky wood they drill their own holes. The next hole size, about 1.5 inches, might be created by a Hairy Woodpecker, a Three-toed Woodpecker, or a Sapsucker. This size hole is greatly sought after by the Swallow clan and Bluebirds. Unfortunately the European Starling, a most belligerent species, also wants this size hole. A Pileated Woodpecker, or the ravages of time and repeated use, will widen a small hole to about 3 inches in diameter. Holes of this size are sought after by Ducks and Owls. With at least 6 waterfowl species, Barrow’s and Common Goldeneye, Common and Hooded Merganser, Bufflehead, and Wood Duck, vying for the larger holes, many birds do not find suitable nesting sites and do not breed. It’s a tough world when you can’t lock your door to intruders, or rattle a deed in the face of those who would steal your domicile. But that is the prospect many birds face when they must utilize a tree cavity as a nesting place. No wonder I’m moved to do at least 2 ‘vandal hangings’ of duck boxes each spring. Anything less would be downright insensitive to the plight of the homeless. To e-mail Tom CLICK HERE To look at previous column CLICK HERE |
