If Swainson's Hawks are like other raptors, it probably takes a year or two before they attempt to breed. Rather than considering these flocks as late migrants, it's much more likely that they're subadult non-breeders that are spending their first/second summer on the breeding grounds without trying to breed. I came across a few flocks like these last summer when conducting raptor counts on Meadow Springs Ranch in NE Larimer County.
Walter Wehtje Fort Collins On Saturday, June 3, 2017 at 2:01:18 PM UTC-6, Dave Leatherman wrote: > > Ran the Lamar Breeding Bird Survey (BBS) route yesterday with assistance > from Janeal. The route starts at Prowers MM/13 northeast of town, goes > north to Prowers SS then east and north, ending at Kiowa 61/K several miles > sse of Chivington . Had black rail calling on SS about a mile e of 13, a > first for the route. Other interesting species were dickcissels, good > numbers of Cassin's sparrows, orchard orioles on a few riparian stops, and > this: 168 Swainson's Hawks over the last 22 stops, with 106 of them on one > stop! I do not know how to interpret this. It would seem to be one of two > things: a very late kettle still coming north because of the late spring > storms OR families populated with already-fledged young staging for their > return flight south later this summer. Great, great majority of birds were > immatures. Timing seems odd for either scenario. Maybe analysis of eBird > data would shed light on which it is. The birds were mostly on the ground > in fallow wheat and/or corn fields. There is currently a notable shortage > of grasshoppers on the eastern plains of CO. This may change as the season > progresses but it could be that at present this largely insectivorous buteo > is being forced into habitats mostly free of vegetation in order to make > available prey items (including big tenebrionid beetles) more visible > (similar to what mountain plovers do with their habitat selection). Of > note, we detected zero mountain plovers on the entire route and they are > usually present on 5-6 stops. > > > If anyone has input on the Swainson's hawk phenomenon, I'm all ears. > Please share with the whole group. Thank you. > > > Dave Leatherman > > Fort Collins > -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/968d5825-7ed7-4659-8056-7ba81de1aea6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
