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!

Monday, August 25, 2008

Nongeographical Migrant Traps

Dave La Puma, over at woodcreeper, had some smart analysis today about local scale movements of migrant passerines, and how that may account for reports of new arrivals even following nights of unfavorable weather. The premise is pretty straightforward; lacking favorable conditions to move on, birds are likely to shift from areas of substandard habitat to prime foraging grounds. Remember that a migrant trap typically works by virtue of its geographic location. The classic example of course is Cape May island, essentially the bottom of the bird funnel that is the state of New Jersey. With thousands of birds packed in to such locations, its only a matter of time before competition, or merely a need to seek more fertile feeding grounds, disperses birds across a wider area. Often the tried and true migrant traps are left desolate. If you don't believe it, goto Sandy Hook after four days of south winds sometime this autumn.

Understanding what makes up prime foraging habitat can make your birding more consistent. No longer do you have to wait for those perfect cold fronts, you can take advantage of "slow days" by visiting sites that concentrate migrants left in the area during the last wave. To follow up on Dave's post, I thought I'd give a quick punch list of the sort of attributes that tend to be common among such locales. Of course these aren't hard and fast rules, but sort of a general set of guidelines.

1. Diverse habitats. Lots of habitat types will provide prime foraging for a greater number of different species. Paulinskill Wildlife Management Area; a locale I like, contains upland forest, open woodlands, meadows, shrubby tangles, a riparian corridor, a freshwater wetland, etc. Equally important are the edges. Its a well accepted pillar of ecology that an edge between two ecosystems tends to be more diverse than the interior of either (the edge effect). A sunlit edge between forest and field is precisely what I think of when asking myself, "where would I find lots of warblers?"

2. Structure. Much like diversity across the landscape, lots of variation in a forest profile can be the difference between poor migrant habitat and a productive birding area. Birders are very familiar with the strong preferences some species have for a specific band in the forest spectrum, such as the Mourning Warbler (almost always associated with dense thickets <5 m above the ground) and the Tennessee Warbler (an infamous source of neck pain). The more strata you take out of the forest, the fewer species you can expect to find. Even for birds with a more generalist approach to the forest profile a diverse structure is beneficial, providing more feeding and roosting opportunities.

3. Oaks. Really any native trees, though Oaks are certainly among the most productive. Such trees are absolutely teeming with insects. Your average oak can support more than five times as many insect larvae than a tree not native to the northeastern United States. Why? Well, I've discussed this at length before. Oaks, by virtue of their evolutionary roots in this region, support a far greater number of different species of insects.

4. Fruit. As the breeding season marches on, fruiting shrubs and trees become incredibly important sources of food for migrant birds. Cold weather snaps may kill off insect food sources before later migrating species, such as Black-throated Blue Warblers, pass into our area. These birds have adapted an ability to switch their diet over to primarily fruit (as opposed to obligated insectivorous species such as Cerulean Warblers, which as a result have to migrate much earlier). Areas with lots of fruiting shrubs and trees can be magnets for migrants. Celtis (Hackberry), Prunus (Cherry), and Cornus (Dogwood) are just a few native genera that are especially favored.
Though it is worth noting that the nativity of the fruit does not matter much. You can certainly see migrants feeding on Ligustrum (Privet), Lonicera (Honeysuckle), Rosa multiflora (Multifloral Rose), and other invasive plants. In fact, passerine migrants likely play a big role in moving invasive species from one region to another. Aralia elata (Japanese Angelica Tree) a newly emerging invasive species in the Midatlantic region, seems to be (based on pure anecdotal evidence only) distributed primarily along major migration routes in New Jersey. If you go to the parking lot of the Chimney Rock hawk-watch in September, you can witness dozens of birds gorging themselves on Aralia berries.

5. Sun. This, for me, was an overlooked ingredient of prime feeding habitat until last fall. Look for the little spots that: (1) get sunny the earliest in the morning and (2) stay sunny latest in the evening. Even a little increase in air temperature will get insects moving and birds from hundreds of yards away will converge on the area.

So thats it, five things to look for when seeking good foraging habitat. Of course this is only a starter list, so if anyone has additional suggestions please leave a comment. Make sure to get out and find some feeding sites, then check them on that next slow day. You may end up pleasantly surprised!

Sunday, August 17, 2008

a few migrants around

There were signs of southbound migration around yesterday, though they were few and far between. A slight increase in the number of singing Peewees around our house in Stockton as well as Bull's Island State Park, a lone female Scarlet Tanager making a brief appearance in the backyard, and a few dozen Chimney Swifts (some of which are probably still the locals) made up the most obvious evidence on a round of casual birding. Friday I saw my first fall Osprey, hunting on the lakes at Duke Farms. That bird was certainly a migrant; we never observe local birds using our lakes during the breeding season.

As a recent Hunterdon County transplant, I haven't yet figured out the local hotspots for migrant passerines. I suspect that the Stockton area, situated on flat land between two small ridges, may be a bit of a dead zone but it'll be great to put that theory to the test. I suppose it will depend on how many birds depart the ridges in favor of moving down the river. A similar effect can make the Delaware river corridor in the Walpack Valley (western Sussex County) excellent under the right conditions. Strong easterly winds would probably push birds off the Sourlands and right into our area as well. Probably the key will be finding the geographical features and prime feeding habitats that will concentrate migrants. I have a few hunches, I'll be sure to post reports as I check them out. In the mean time, suggestions would be appreciated if you're familiar with the area!

Thursday, August 14, 2008

Year in Life

I had my 'its that time of year again' moment this morning, when I spotted a dark juvenile Merlin perched atop a telephone pole on my way to work. Upon arriving, a coworker remarked that two Harriers were coursing our grasslands that morning. The grasslands, last week alive with fledgling Ammodramus sparrows, are silent save for the occasional 'jimp' of a lingering Bobolink or the rattling alarm call of a Meadowlark. Most of these birds have passed on as well. Our fields peaked at nearly 50 Meadowlarks in one day two weeks back and they've been in short supply ever since. Autumn is here.

'Autumn?' you say, 'but its only August!'. That's true, but other species have no regard for the Julian Calendar and a good naturalist must remember that. I count the day I ceased to pay attention to seasons as defined by solstices and equinoxes and instead began to follow the cues of migrants as one of my greatest revelations as a birder. It was then that I realized I was missing more than half of migration!

To me, the greatest joy in naturalism is gaining insight into the sychrony of the landscape and the organisms that use it. The flight of migrant birds does not occur unassisted; it times perfectly with swells in insect populations and the ripening of fall fruit. Predatory birds come along for the ride, dependent on the big concentrations of their small cousins to better chances of obtaining a much needed meal. In a great choreographed dance the whole food chain rolls down the continent, leaving the landscape to sleep behind it, and the animals that remain behind to eke out a living until the whole thing happens again.

You don't have to go far to find something extraordinary about nature. A Black-throated Green Warbler foraging in an Eastern Hemlock will do. Such a scene tells a story; of bird, insect, and tree in a relationship rooted in time and sustained for millenia. A single thread in the tapestry of life that defines a year in nature. Endless delight awaits those who take the time to pay attention to it.

Monday, August 11, 2008


Just a few pictures I snapped this weekend. Most of these were taken around my "pollinator garden". I use the term very loosely; its only three plants. One purple giant hyssop, one anise hyssop, and one narrow-leaved mountain mint.

A spring peeper perched on a hyssop leaf, laying low in the hot part of the day. Do you think it was coincidence that this is where it happened to choose? I doubt it, this plant was teeming with insects. Backyard food chains in action!

This daddy longlegs (thats the scientific name right???) appeared to be nectaring at hyssop flowers. I've always thought this group was strictly detritivorous, so if anyone has any insight I'd love to hear it.

One of about ten species of hymenoptera (bees, wasps, etc) frequenting my plants.

a dog-day cicada