Each Spring, the Broad-Winged Hawk Project has begun the same way: scrambling to locate nests to ensure we have sufficient birds to study. The prime window of opportunity is short and the hawks unpredictable. Though inconspicuous for most of their breeding cycle, Broadwings ease into the reclusive portion of their lives gradually, their return to northern territories punctuated by shrill whistles. Bordering on boisterous, courting pairs can be very loud, frequently exchanging vocalizations from both perch and sky. Because courtship rituals continue for several weeks, it is relatively easy, during this time to identify an established territory. Pinpointing the location of a nest however, almost always presents a bigger challenge. Noisy as they may be, flight affords them the ability to cover much ground quickly and quietly making them difficult to trace as they navigate their grounds.
The most reliable way to locate a nest is to follow an
individual with building material back to a home tree, the catch being that
birds will not so easily give up such a secret in the presence of a perceived
threat. I believe the saying goes, a watched Broadwing never boils... Usually if
you meet, they will be spooked enough to either take their find elsewhere or
drop it altogether before retreating. It is possible to circumvent this
trepidation by sitting tight in a well
concealed location and hope that a bird comes within your field of view. Whether
they can be tracked or not, a bird carrying materials is a great sign that a structure
is nearby. Comparably suggestive, though only sometimes exhibited, are the more
confrontational responses to an intrusion into a nesting space. This can range
from agitated vocalizations from a number of alternating perches and defensive
circling overhead to repeated warning
dives. Aggressive swooping is atypical, but when they do resort to this,
looking skyward will likely yield a nest.
Spotting something so telling this early on is uncommon, so
the best course of action is to first amass a bank of observations and plot
them on a map to isolate an area of high activity and manageable size. If prior
year's sites are known, it is the best place to start. Instances of pair
interactions can be weighed on heavily, since it can loosely be said that most pair
bonding occurs near to the nest site.
Thanks to powered flight, our near is
slightly askew from theirs, so this can still comprise an area of a few hundred
meters square. Nests can be rather nondescript so all reasonable stick heavy structures
should be noted and monitored to check for new material and promising examples
can be staked out from a distance to identify the owner. They can vary
dramatically in size and orientation but fresh greenery at nests edge is a
solid cue to follow, as live sprigs are added regularly throughout the season.
By the time females lay their clutch and begin incubating, a
veil of foliage is falling on the forest uppers further obscuring the treetops.
Broadwings retreat below canopy and all but cease vocalizations except for the
brief exchanges preceding prey deliveries from male to female. These transfers
usually occur at a few locations closely surrounding the nest, and after
hatching at the nest itself, increasing in frequency as the young grow older. Now,
these occurrences may be the only indicators of nest presence apart from a
direct view of a female on site, who despite a near constant presence, may be
invisible when hunkered down low. A month later, nestlings will have emerged, and
soon whitewash around the base of the tree will become an additional sign of
occupancy.
Looking back, the very first nest that I found on the job
represented a bit of an anomaly and proved to be a very misleading introduction
into the world of nest searching. On my second visit to a study site I was
greeted, at my parking space no less, by both halves of a pair, each with
sticks grasped in their beaks. After conveniently shuttling them to their final
destination in a nearby oak, they were off to fetch more, this time comically
large just in case I missed it the first time. That was a freebie for me never
repeated. The vast majority of cases involve patiently gathering pieces of a
puzzle until you have a complete picture. Often whether or not you are in the
right place at the right time to see the important parts is squarely in the
hands of luck. Our quarry is unpredictable and the birds can appear to be
everywhere at once or nowhere at all. I have passed, oblivious, beneath more
nests than I care to admit, and have been fooled more than a few times by the
work of squirrels, crows, and cooper's hawks alike. Despite the challenges, and
perhaps because of them, I think I can speak for everyone involved when I say
that finding an active nest is an incredibly satisfying experience because it
translates into so much more. Each confirmed nest opens the doors to a wealth
of knowledge and the potential answers to many questions formerly so far out of
reach. It represents a rare look into nesting behavior and habitat, as well as
a chance to remotely monitor movements across continents, into the southern
expanse.
Early this week, Rosalie, our tagged female on the Sanctuary
showed up at the cabin property where I live currently. It just so happens that
she and I share a territory and I have seen her and her mate meander through
here regularly since their April return. A bit maddening during the weeks it
took to locate their nest, but now a pleasant reminder of what that effort became.
A bird with an antenna is a very curious thing. Her backpack tracker looked
secure, everything exactly where it should be. I watched her lazily from the
hammock feeling glad that there would be no need to chase her today, excited by
what this marriage of technology and nature will tell us, content to have the
satellites take on the legwork for a little while.
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| Zach holding Rosalie, female from the River of Rocks nest on Hawk Mountain Sanctuary |
Blog post and photos by Broadwing Project Field Assistant Zach Bordner- July 2016
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