Shawanagunk Grasslands Kestrel Density


The Shawangunk Grasslands NWR (SGNWR) outside of Shawangunk, NY. is a gem of open country habitat that is locally and regionally important for many bird species. Most of its 597 acres (~240 hectares for the metric savvy) are grasslands, which is in short supply in the northeastern US. Bobolinks, Grasshopper and Vesper Sparrows are threatened nesters. Upland Sandpipers stop here annually during spring migration. Short-eared Owls and Northern Harriers form impressive winter concentrations. It is simply THE place to go in the immediate area to see Short-eared Owls. The refuge was established in 1999 after conversion from a military airfield and is designated an Important Bird Area by Audubon NY. It is definitely worth a visit.
For more information, see https://www.fws.gov/refuge/shawangunk_grasslands/about.html

This vital patch of habitat was the foundation for the kestrel nest box project. I noticed the boxes on my first visit in November 2015 and learned that the boxes were occupied every year. Past monitoring had been casual, with observations of birds occupying the boxes, delivering prey to the boxes and fledglings popping up in early summer. With my raptor biology background, I saw an opportunity to add a bit of rigor to the monitoring and collect data on nesting phenology (timing), clutch and brood sizes and overall reproductive success. And of course the fun part, to band as many of the birds as possible. While not only fun, this has the potential to shed light on the birds' movements, survival and habitat associations. 

Nest box locations. SGNWR. 

One thing that became immediately apparent was how densely packed in these kestrels are. In 2016, 6 pairs successfully raised broods on the refuge. When one does some simple math, that comes out to 1 nesting pair/acre (6 pairs/square mile or 2.4 pairs/100Ha). The shortest distance between two occupied boxes was 340 meters (SG2 and SG7). This density is unusually high but is explained by a combination of two things - the number of suitable nest sites and an ample prey base.  This makes sense since in a given area, these are the primary limiting factors for any raptor population. While I've noticed plenty of territorial squabbling and attempts to take over boxes by neighbors, the birds tolerate one another well enough to nest successfully. The surrounding agricultural landscape is definitely suitable for kestrels (I am finding kestrels occupying boxes in this area) but it definitely doesn't compare in quality to the SGNWR. Some comparisons of reproductive success between these habitats will be informative. 

I also wonder if some polygamy is happening on the refuge. I did a few counts of all the birds on the refuge at one time and it appeared that all boxes were being used by distinct pairs. Even with such a robust prey base, it would be a tough task for a male to provision more than one family. Though it is unlikely, I am definitely keeping my eyes open for it. Color-bands, like the one on the male below, can help shed light on such phenomena. 

And while the Shakespeare quote is technically not 100% accurate (should be 'she' not 'he') it is fitting. 
 
"Though he be but small, he is fierce" Agreed.
Photo: Ed Frampton






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