Friday, June 3, 2011

Mosaics, Patches and Transition Zones

Here comes the science, but first...

I head down to Portage Bay armed with scientific explanations for one of the nagging observations that I've made during the past three years. I even woke up last night thinking about what I could now articulate.

My first few strokes leads me to a pair of pied billed grebes. One dives while the other seems reluctant to follow suit. I take my camera and turn the canoe quietly to follow their motion. The second grebe dives, but only for a brief moment. Coming to the surface, a tiny head pops up on her back, between the wings. She has a new hatched grebe (and probably more than one) riding on her back. Baby pied billed grebes are amazingly small, not much more than sparrow sized, the smallest that I've seen of the water fowl, so small they are hard to spot, and I don't get a photo.

Pied billed grebe - the babies are on the back under the wings

Mosaics, patches and transitions
Several times I have written about the differences between the wetlands in Portage Bay and those in Union Bay. From my canoe, Portage Bay has always appeared to be a healthy, although much smaller marsh. But, size for size, it never seemed to have enough wildlife, particularly in winter when so many migratory ducks are in Union Bay.

The Portage Bay wetland is a 1/2 mile long strip along the south shore with the rest of the bay choked by houseboats and marinas with some working shipyard areas on the north end. It is rarley wider than 50 to 70 yards, a quick transition from lake to shallows to marsh to trees to mowed grass park land.

Portage Bay transition - lake, marsh, trees, mowed grass park, in 50 yards

Union Bay wetlands are either fairly large areas of cattails and beaver forest or narrow strips of wetland with a large nature area attached. In the south end of Union Bay, the east marsh is over a 1/4 mile E-W and a bit more than that N-S and its west side is a forested island with more marsh on the other side.

Landscape Ecologists view land as a mosaic. You have a patch of farm field, then a patch of forest, a patch of marsh land, a patch of urban area. The patches can be any size or shape, but each of them has a border area - a transition zone. Wildlife have preferences. Many like the transition zones, some like the middle of big patches, and some like transition zones attached to big patches, etc. So, as a patch gets larger, it will have increased diversity of wildlife, up to a point, and it will have numerically more wildlife. If a patch gets too small, it loses its core and all that remains is a transition zone. This is what the Portage Bay wetland is, all transition zone, no core. So, the diversity as well as the numbers are lower than one might expect given the appearance. The large patches and rich transition zones in Union Bay are the reason that almost 200 bird species have been sighted in Union Bay. It is why there are a few thousand ducks there in winter while only a 100 are found in Portage Bay.

So, I pass through the crossing under place, the water route from Portage Bay to Union Bay, because like some wildlife, I prefer to be in the transition zones of larger patches.

As I take out, a woman cruises up to me in a kayak and asks, "are you the guy that looks out for the beaver?" I have to think about this a second, stunned by a reputation that seems to have gone farther than I knew. But, it must be me. M and I have mutual friends and it turns out that M helped with the fine restoration of a strip of public land that leads up to the Big Lodge. She is worried about disturbing the beaver, so we chat a bit and I assure her that they will not mind her presence. I also take a moment to fill her head with lots of beaver facts that will keep here busy on the look out as she returns home. I liked, especially, the way her eyes lit up when I mentioned the musky odor of castoreum...she was already familiar with the scent but did not know where it came from.

Notes - lots of marsh wren activity today. Nesting in action at #2 island, across from #2 island, by the osprey tree, and new nesting in the east marsh at the entrance to the big dead end.

1 comment:

kat said...

I did not know that grebes held their babies on their backs. We get the occasional grebe on the lake, but they are always alone.