Communal night roosts are reported for some species of diurnal North American raptors, e.g., White-tailed Kite (Elanus leucurus; Dunk 1995, The birds of North America, No. 178. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.), Northern Harriers (Circus cyaneus hudsonius; MacWhirter and Bildstein 1996, The birds of North America, No. 210. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.), Bald Eagles (Haliaaetus leucocephalus; Buehler 2000, The birds of North America, No. 506. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.), and Rough-legged Hawks (Buteo lagopus; Bechard and Swem 2002, The birds of North America, No. 641. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.). I could find no records of such night roosts for Merlins (Falco columbarius) in North America (e.g., Sodhi et al. 1993, The birds of North America, No. 44. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.) but did find records of Merlin roosts in Europe (Cramp and Simmons 1980, The birds of the western Palearctic, Vol. 2. Oxford University Press, Oxford; Clarke 1993, pages 178–184 in M.K. Nicholls and R. Clarke (Eds.), Biology and conservation of small falcons. Hawk and Owl Trust, London). I had observed a winter night roost of more than 50 Merlins in northern Israel in the mid-1980s. Several of the above accounts from North America mention other species sharing the night roost; in all cases the other species were congeners or owls (which presumably used the roost at a different time).
Kelly and Thorpe (1993, British Birds 86:49–52) report a mixed species night roost of five to nine Peregrine Falcons (Falco peregrinus), up to five Common Kestrels (F. tinnunculus), four to six Eurasian Sparrowhawks (Accipiter nisus), and two Merlins together in a grove of conifers on the Isle of Man off the Scottish coast. Van Duin et al. (1984, Limosa 57:97–103) reported a mixed species night roost of up to 25 Eurasian Sparrowhawks, up to 10 Hen Harriers (Circus cyaneus cyaneus), and up to 10 Merlins in an area of reeds and willows in Holland. A large roost count from India consisted of three species of harriers (Clarke et al. 1998, Forktail 14:70–71).
Thus, it was of great interest that I and my colleagues observed a night roost of White-tailed Kites, Merlins, and Northern Harriers together in the same sugarcane field. The field was located approximately 7 km north of Harlingen, Cameron County, Texas (26°15.5′N, 97°38.3′W) and measured approximately 500 m by 200 m, with a paved road running along one side. Clark and Wheeler (1989, J. Raptor Res. 23:116–117) had previously reported a White-tailed Kite roost in a sugarcane field. The adjacent fields of cane had been recently harvested, but similar fields of standing sugarcane were plentiful in the area. A similarly-sized field approximately 0.5 km ESE was not used by raptors for roosting.
We counted the number of each species arriving at dusk to the roost on six evenings in December 2004 from 1.5 hr before sunset until it was too dark to see. But our counts of kites were always fewer than what we counted when the kites boiled up and flew around just as it became dark.
The count of kites varied from 27–97 on six count evenings. Counts of Merlins varied between 6 and 13, and harriers between 7 and 12. We also saw from 5–10 American Kestrels (Falco sparverius) gathered on the telephone wire that ran along one side of the field. Some were seen to fly into the sugarcane as it became dark. One juvenile White-tailed Hawk (Buteo albicaudatus) and one juvenile Crested Caracara (Caracara cheriway) were observed dropping into the sugarcane field on different nights, apparently to roost with the other raptors.
All three species were seen to pre-roost on the bare ground of adjacent harvested fields. Relatively few kites did this, more harriers did, and almost all of the Merlins did so. None of these species were regularly seen to hunt the recently-harvested sugarcane fields. It was not clear whether the kites roosted for the night on the ground or on the sugarcane stalks, some of which were bent horizontal, or both; they have been reported to do both (Dunk 1995, The birds of North America, No. 178. The Academy of Natural Sciences, Philadelphia, PA U.S.A. and the American Ornithologists' Union, Washington DC U.S.A.). Harriers usually roost on the ground, but Merlins usually roost in trees, as did the ones I observed in Israel. Also, we were unable to determine whether or not the raptors roosted in species clusters or were spread out over the rather large field.
Given their different foraging habits, I believe that the species were not roosting together for interspecific information gathering as per the Information Center Hypothesis (Ward and Zahavi, 1973. Ibis 115:517–534). Rather, the three species found this a suitable roosting area and, through communal use of this area, might have experienced reduced predation pressure.
This is the first record of communal night roost of Merlins in North America, and the first North American record of three species of diurnal raptors from two families of Falconiformes roosting together, although both have been reported from Europe.
I thank Pat Wade for spotting and calling my attention to the kites coming to roost. Roger Clarke, Jeff Dunk, and Ian Warkentin made comments on earlier drafts.