Average Count Totals

Average Count Totals for 1999-2001

Species	South	Net	%North
Osprey	1004	895	10
Northern Harrier	685	652	5
Mississippi Kite	31	31	0
Swallow-tailed Kite	9	9	0
Sharp-shinned Hawk	4328	3539	15
Cooper's Hawk	533	423	17
Red-shouldered Hawk	25	15	29
Broad-winged Hawk	3268	1693	33
Swainson's Hawk	95	35	39
Short-tailed Hawk	27	13	34
Bald Eagle	16	10	25
American Kestrel	3666	3489	5
Merlin	646	520	16
Peregrine Falcon	1632	1506	7
Unknown	130	112	77
Grand Total	16094	12942	16

In addition to the heavy southbound migration of raptors each fall through the Florida Keys, we see quite a bit of reverse migration, where birds pass south of the count site, and then return again to the north. Some of this behavior may be related to the reluctance of some species to make large water crossings. Therefore, we watch each migrant carefully as it passes over our site and classify its flight direction as either "southbound" or "northbound." This leads to the creation of several different count "totals." In addition to total southbound and northbound sightings, we calculate totals such as "net" totals (southbound minus northbound sightings), and % northbound totals (northbound/total southbound plus northbound sightings x 100). This can be confusing at first, but in the end, having all of these totals proves very useful to interpret raptor migration in the Keys. The three most useful and interesting totals, which we report here, are southbound, net, and % northbound totals.

Southbound totals include both birds that enter the middle Keys and continue to the south, and birds that later return to the north, perhaps to winter north of the Keys in Florida. This total is probably our closest estimate of the real number of birds that migrate into the Keys. Net totals indicate the number of birds that continue their migration past the Middle Florida Keys, and this total may be a more precise estimate (although a low one) of the true number of individuals that migrate into the Keys for species such as Broad-wings with a high percentage of northbound sightings. In the case of Peregrine Falcons, who have a low percentage of northbound sightings, the difference between southbound and net totals is not large, however for some species with a greater percentage of northbound flights, such as Broad-winged Hawks the difference between southbound and net flights is considerably larger. The true number of individual birds that are counted in the Florida Keys is probably somewhere between the southbound and net totals. Both of these totals are consistent indices of migration through the Keys, which will be useful to look at long-term population trends for several species that are counted at this site.