Abundance and habitat selection of two American Kestrel subspecies in north-central Florida

-We censused American Kestrels (Falco sparverius) in the three vegetation communities representative of north-central Florida (pine flatwoods, sandhills, and agriculture/ mixed hardwoods) along 24 16-km roadside transects. The winter kestrel population included resident F. s. paulus and migrant F. s. sparverius. Eighty-four percent of the 1,433 kestrels were sighted in winter, reflecting a significant influx of migrant F. s. sparverius, and were primarily females (65%). Significant (P < 0.05) sexual differences in winter habitat use were attributed to the large numbers of migrants. Males preferred closed habitats and smallersized open areas, and females preferred open habitats and larger open areas. Wintering kestrels were most abundant (P < 0.05) in the agriculture/mixed-hardwoods community (51%) and least abundant in the pine-flatwoods community (13%). Seventy-one percent of the 233 kestrels seen during summer were identified as F. s. paulus. Males and females were observed in approximately equal numbers and exhibited no differences in habitat preference. Falco s. paulus preferred the sandhill community (79%) to the agriculture/mixed hardwoods and pine flatwoods. Within the sandhill community, resident kestrels significantly increased their use of the pine/oak woodlands during summer. Received 9 April 1985, accepted 12 February 1986. Two subspecies of the American Kestrel (Falco sparverius) occur in Florida. The Southeastern American Kestrel (F. s. paulus) is a yearround resident; F. s. sparverius occurs in Florida only in winter (Sprunt 1954). An apparent decline in the resident population (McFarlane 1973, Wiley 1978) led to the classification of the southeastern race as a threatened subspecies in Florida in 1978 (Florida Game and Fresh Water Fish Comm. 1981). Hoffman (1983) subsequently documented a significant historic decline (at least 85%) in the resident kestrel population in two areas of the state. In north-central Florida, loss of nesting habitat was identified as the major factor causing this decline. In south-central Florida, the kestrel population declined due to loss of both foraging and nesting habitat. Little information was available, however, on the distribution and abundance of the southeastern race (Layne 1980) and on the importance of specific habitats in sustaining viable populations. Differential winter habitat use by the sexes of American Kestrels is reported frequently and appears to be geographically widespread. Males occur primarily in partially wooded areas, whereas most females occur in open pastures and fields in northern California (Koplin 1973, Meyer 1980), Ohio (Mills 1975), Arizona (Mills 1976), and coastal Georgia (Stinson et al. 1981). These studies involved only winter migrants. Habitat use of kestrels that occupy an area only during winter may differ from that of a permanent resident population. Our goals were to assess the current habitat use and abundance of the Southeastern American Kestrel population in north-central Florida and to evaluate sexual and subspecific differences in habitat use by resident and migrant kestrels. STUDY AREA AND METHODS Roadside transects (number per county) were established in Alachua (5), Clay (2), Levy (4), Marion (5), Putnam (2), and Union (6) counties (Bohall 1984). The three major vegetation communities represented in northern peninsular Florida are pine flatwoods, sandhills, and mixed hardwoods (Davis 1967, Monk 1968). We use these terms to refer to areas within the study area that originally supported these vegetation communities but now include various man-made habitats. The following community descriptions were summarized from Laessle (1942), Monk (1968), and Hartman (1978). North Florida pine flatwoods are characterized by 557 The Auk 103: 557-563. July 1986 This content downloaded from 157.55.39.130 on Wed, 23 Nov 2016 04:59:52 UTC All use subject to http://about.jstor.org/terms 558 BOHALL-WOOD AND COLLOPY [Auk, Vol. 103 TABLE 1. Percentage availability of habitats along both sides of 24 16-km roadside transects in north-central Florida.