Expanded home ranges in a peripheral population: space use by endangered Mt. Graham red squirrels

Abstract

Peripheral populations are often of increased conservation value; however, knowledge of the ecological and evolutionary consequences of a peripheral location is poor. Spatial dynamics are often interpreted as strategies to maximize access to fitness-limiting resources. Red squirrels Tamiasciurus hudsonicus are territorial in western portions of their range and exhibit overlapping home ranges in eastern forests. Endangered Mt. Graham red squirrels T. hudsonicus grahamensis represent the southernmost extension of the species. We used radiotelemetry to assess space use and interindividual overlap of endangered Mt. Graham red squirrels. Squirrels maintained nearly exclusive 50% core areas; however, 95% ranges overlapped considerably, especially between males and females. Home ranges increased in summer for both males and females and may be related to sexspecific reproductive strategies. Ranges of Mt. Graham red squirrels in this peripheral population were nearly 10 times the size of red squirrels from other locations. The space use of this limital population suggests that resource availability may be substantially different than in other portions of the range.

Spacing Behavior of a Non‐Larder‐Hoarding Tamiasciurus: A Study of Mearns's Squirrels in Xeric Coniferous Forests

“…In mesic coniferous forests, red and Douglas's squirrels expand their home ranges during summer and autumn, when both sexes travel greater distances to collect unopened cones for their middens, but males also expand their home ranges further to locate estrous females (Smith ; Koford ; Koprowski et al. ; Lane et al. ).…”

“…Tree squirrels in the genus Tamiasciurus display variation in hoarding behavior with no sexual dimorphism in territory size (Layne ; Smith ; Kemp & Keith ; Koprowski et al. ; Lane et al. ).…”

“…In mesic coniferous forests of western North America, red ( Tamiasciurus hudsonicus ) and Douglas's ( Tamiasciurus douglasii ) squirrels defend food‐based territories maintaining non‐overlapping home ranges (Smith ; Don ; Gurnell ; Gurnell & Anderson ; Koprowski et al. ; Lane et al. ).…”

“…In mesic coniferous forests, red and Douglas's squirrels maintain non‐overlapping home ranges during non‐mating season, whereas during mating season, home ranges between males and males/females overlap but not between females (Smith ; Don ; Gurnell ; Koprowski et al. ; Lane et al. ).…”

Severely insect-damaged forest: A temporary trap for red squirrels?

“…We used a beacon to estimate location error (Millspaugh and Marzluff, 2001). Within insectdamaged forests, steep drainages increased the bearing and linear error associated with biangulation (mean AE S.D., n = 32, bearing error, 8.6 AE 6.28; linear error 42.9 AE 28.7 m) relative to undamaged forests (mean AE S.D., n = 64, bearing error, 5.6 AE 4.58; linear error, 12 AE 6 m; Koprowski et al, 2008). Thus, we increased homing in insect-damaged forests (mean AE S.D., % homing 2004 = 35.9 AE 30.9%, % homing 2005 = 87.6 AE 17.3%) and used biangulation most frequently (mean homing = 28 AE 23% S.D.)…”