Sunday, September 14, 2008

Broadwings are coming!

Northerly flow will drive winds across New Jersey beginning, according to weather underground, tomorrow afternoon and continuing through until next weekend. Such weather in mid-September surely means we will see our largest push of migrant Broadwing hawks of the fall this week. Depending on wind patterns and conditions, single hawkwatches in New Jersey could see single days of 5,000 or more birds. It is truly a spectacular sight!

Taking a look at birdhawk archives, you can see that hawkwatches to our north were reporting modest totals late last week; between 800-1000 birds. Hawk Mountain in PA already had a one day total of 1100, the vanguard flight if you will, but Broadwings have yet to build up in the Northeast in large numbers. I suspect that between Monday and Wednesday they will, as the remnants of Ike take an exit and a cold front sweeps across the region. This would set things up perfectly for NJ to see a big push Thu or Fri. There's a few weather hiccups between now and then, so keep an eye on the forecast, but this entire week should be great hawk watching.

Looking ahead, with the exception of tomorrow winds will range from N-ENE. Wind direction is important to bear in mind when deciding where to catch the big Broadwing push. Broadwing hawks are buteos, a group of raptors adapted for sustained, low energy soaring. The drawback to such morphology is a greater reliance on winds and conditions to stay aloft. The result is a strong tendency to go with the flow, so to speak. With winds primarily from the Northeast, more inland hawkwatches will be favored, particularly those along the hawk super highway that is the Appalachian ridge. Raccoon Ridge and Hawk Mountain could be excellent. Scott's mountain could also be very good. Watches further east, such as Chimney Rock at the south western terminus of the Watchung range, may see smaller numbers as broadwings have the wind at their backs along less risky, more inland routes. This of course could change as the week goes on, and a substantial shift to the NW would make Chimney Rock, or Montclair at the other end of the Watchungs, the place to be.

Thursday, September 11, 2008

kestrels, nighthawks, and ...friendly invaders?

This is the time of year where migration is evident, even if you aren't really trying.

Duke Farms set a new one day total for stop-over Kestrels, with fifteen(!) working our grasslands this afternoon. We didn't even cover the entire area.

From center bridge in Stockton this evening, I counted sixty two Common Nighthawks.

oh, and somewhere along the way single Nashville and Yellow warblers.

Lastly, in case you didn't catch Tuesday's New York Times this article, titled "Friendly Invaders" is worth a read. As is often the case with the NYT, their bias on invasion science comes out, but it does raise some interesting points.

I'm not going to fly off the handle on this one, but as you read it consider the following:

1. Biodiversity alone is not a good barometer of ecosystem health. So all of these native species of New Zealand are still there, but at what kind of populations? How isolated are they? How have the insects that depend on them been affected? You get the point. There's more to consider than a species list.

2. Biological invasions, especially on large bodies of land, rarely act alone. There is almost always some underlying anthropomorphic disturbance helping to drive the invader's spread. In the Mid-Atlantic, for example, its white-tailed deer and a four hundred year history of screwing up the soil (agricultural land use). I think this idea of strong interactions (such as predation) versus weak interactions (competition) is interesting. I also think its well demonstrated that in an ideal, healthy ecosystem invaders that have to out-compete natives for space either fail to introduce themselves entirely, or manage to assimilate into the ecosystem in some innocuous way. However, disturbed ecosystems are a totally different ball game, and probably better represent reality for most invasion scenarios. Lets face it, there are few places left on earth where we haven't made our mark. Certainly none in New Jersey and I doubt there's very many in New Zealand.

3. These ideas about native snakes rapidly evolving to eat cane toads and the like that Dr. Sax raises throughout this article are hard for me to swallow. There are many excellent scientists who downplay the role of evolutionary history during biological invasions. It is difficult for me to imagine that non-native flora can provide the same value to all of the same species as the plants it replaces. There is two opposing ideas about ecosystems at work here: the ecosystem as the complicated, meticulously constructed natural order that will collapse if disturbed and the ecosystem as the living dynamic thing that will take whatever we can throw at it. Personally, I think its probably somewhere in the middle. The former idea is a little too "Scala Naturae" and the latter stinks of human hubris.

4. Thinking of invasions as a symptom of global change. I think this is a great notion. Species are spreading around the world in unprecedented ways. Dismissing it as another great migration misses the point entirely. We are also exporting nutrients around the world. Nitrogen and Phosphorous are showing up in high concentrations where there should be hardly any at all, largely the result of modern agricultural practices. Of course we are all familiar with the huge net export of Carbon we are putting into the atmosphere, largely as the greenhouse gas Carbon Dioxide. With the science behind these symptoms of global change now universally accepted, does it really make sense to downplay the drastic changes we're seeing in plant and animal communities all over the world? These two elements, the abiotic (non-living) ecosystems components and the biota, are inexorably linked. Change in one will invariably drive change in the other.

Anyway, if you read the article, post a comment and let me know what you think!

Monday, September 8, 2008

rare flies?

apparently someone keeps track!

We found this monstrous insect at Duke Farms a few weeks back (photo by Mike Van Clef):



Its a robber-fly (family Asilidae). It was later identified (not by me) as Promachus vertebratus, a species for which only two previous NJ records exist! There is nothing for scale in that photo, but this thing was huge; 2-2 1/2 inches from head to tail. According to the first site I pulled up on google by searching Asilidae, these guys are top predators in the insect world. Wikipedia tell me they capture prey using their legs and then inject a mixture of neurotoxin and digestive enzymes directly into the body using their piercing mouthparts.

Man, why do I bother with plants and birds? I'm going to become a Dipterist!