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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 4. December 2012 
1982, Thiollay 1989, Panasci and Whitacre 
2002). The extensive spatial overlap of home 
ranges during our study suggests that, while 
Red-tailed Hawk pairs may be highly territorial 
in the immediate area around their nest, 
individuals may move and forage over commu¬ 
nally-shared space. This may be a result of 
reduced competition from the absence of other 
species of similar-sized raptors (i.e., ecological 
release) provided by the isolation of an oceanic 
island setting and the soaring conditions in the 
Luquillo Mountains (McNab 1994, Vilella 
2007). 
Home range size in raptors increases with body 
mass and is influenced by prey composition in the 
diet (Pecry 2000). Moreover, home range size 
may be a function of prey availability, dominance 
status, and territory acquisition. Female Red- 
tailed Hawks in the Luquillo Mountains are 
considerably larger than males averaging 199 g 
more, suggesting they may be dominant during 
interactions. Garcelon (1990) showed larger 
females displaced smaller males during observed 
interactions. Dominance and aggression in raptors 
enhances territory acquisition and access to 
limited resources in temperate regions (Janes 
1994, Shelley et al. 2004). 
Studies on resource availability of Red-tailed 
Hawk prey in El Yunque have not been 
conducted, but previous research suggests diet 
varies with elevation. Santana and Temple (1988) 
reported Red-tailed Hawks in lowland habitats 
outside El Yunque consumed mostly mammals 
such as small Indian mongoose (Herpes,es 
auropunctatue) and rats (Rentus spp.) in contrast 
to the high elevation rain and cloud forests of El 
Yunque where they relied on amphibians, reptiles, 
and birds taken from the canopy. Food delivery 
rates by parents tu nestlings can also be impeded 
by rainfall and fog, contributing to nest failure at 
high elevations (Santana and Temple 1988). 
We documented substantial home range over¬ 
lap among radio-marked hawks during our study 
(Fig. 2). Valdez (2009) reported a slight home 
range overlap among five species of Micros,nr 
forest falcons in the Peruvian Amazon. The Red¬ 
shouldered Hawk (H. lineatus) exhibited limited 
amount of overlap between adjacent home ranges 
in uiban and suburban environments (Dykstra el 
. 2001 ) Alternatively, home ranges of nesting 
Red-ta, ed Hawks in Wisconsin overlapped ex 
tensively (Stout et al. 2006). The extent of spatial 
overlap exhibited by Red-tailed Hawks in the 
Luquillo Mountains may be related to high 
population density, as well as distribution and 
availability of prey (Zwank and Layton 1989. 
Rivera-Milan 1992. Boal et al. 2003, Nimitz 
2005). 
Red-tailed Hawks in the Luquillo Mountains 
moved considerable distances between weekh 
locations, averaging 3.063 m per movement 
(Table 2). Paired females had slightly greater 
weekly movements compared to paired males and 
may have been related to dominance status. 
Unpaired individuals of some raptor species 
exhibit larger home ranges and movement be¬ 
tween weekly locations (Bloom et al. 1993). Male 
juvenile Red-tailed Hawks in our study had larger 
average mean weekly movements than juvenile 
females during the post-fledging dependency 
period. I his could be related to earlier flight 
leather development and active dispersal of 
juvenile males (Hargis et al. 1994. Mar/lulT et 
al. 1997). Radio-marked hawks frequently exhib¬ 
ited long distance flights (4-7 km) within a short- 
time period (<4 min) and readily used areas 
inside and outside El Yunque. This may reflect 
the soaring conditions in the Luquillo Mountains 
and the generalist nature of the species (Snyder et 
al. 1987, Bildslein et al. 1998). We detected shifts 
in core area use lor Red-tailed Hawks within and 
between years (Table 3). Large range use shifts 
have been reported for Northern Goshawk (4. 
i’entiUs) outside the breeding season (Hargis et al. 
1994, Drennan and Beier 2003). Resource de¬ 
pression in core areas and habitat alteration can 
also influence shifts in range use by raptors 
(Jaksic 1988. Rodriguez-Estrella et al. 1998). 
Red-tailed Hawks in El Yunque and surround¬ 
ing lands were associated with roadside habitats. 
Roadside vegetation in the Luquillo Mountains is 
characterized by an open canopy of pioneering 
tree species (e.g., Cecropia peltata) and a sun- 
tolerant understory dominated by early succession 
plants and ferns (Lugo and Gucinski 2000). 
Compared to the surrounding dense forest vege¬ 
tation. openings along riparian forest and roads in 
the contiguous forest of El Yunque and fragment¬ 
ed lowlands may facilitate resource acquisition 
and benefit Red-tailed Hawks (Preston 1990). We 
frequently observed hawks hunting along rivers, 
roads, and in pastures. The Red-tailed Hawk is 
considered a habitat generalist throughout its 
tange; our findings suggest fragmentation of 
contiguous forest outside protected areas may 
benelit Red-tailed Hawks. Additional research on 
