Documentation of Replacement of Native Western Gray Squirrels by Introduced Eastern Fox Squirrels

Muchlinski, Alan E.; Stewart, Glenn R.; King, Julie L.; Lewis, Suzanne A.

doi:10.3160/0038-3872-108.3.160

Cited by 14 publications

(13 citation statements)

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“…McCleery () suggested that urban fox squirrel populations may grow more rapidly than rural ones (McCleery ). Some urban populations in California are expanding rapidly (King , Krause et al ), and have displaced native western gray squirrels in at least 1 urban park (Muchlinski et al ). The fox squirrels we studied exhibited annual proportions of reproductively active females (0.78) within the range (0.10–0.83) reported for rural populations.…”

Section: Discussionmentioning

confidence: 99%

Efficacy and health effects of a wildlife immunocontraceptive vaccine on fox squirrels

et al. 2013

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Continued range expansion of introduced eastern fox squirrels (Sciurus niger) in the western United States could lead to widespread damage to agricultural crops, facility infrastructures, and displacement of the native western gray squirrel (S. griseus). Because traditional management alternatives may not be feasible in many areas, public interest in the use of immunocontraceptive to control local populations has increased. We evaluated the efficacy of GonaCon™ immunocontraceptive vaccine for controlling eastern fox squirrel reproduction in Davis, California. We administered GonaCon to 33 male and 26 female fox squirrels, and a control substance to 33 males and 24 females. We subsequently compared the reproductive status, health, and serum concentrations of testosterone and progesterone of our treated and control populations. In our treated population, we also measured serum concentrations of antibodies to gonadotropin‐releasing hormone (GnRH). To determine potential side effects of the vaccine, we recorded body weight and body condition of all animals, examined injection sites during each recapture, and observed the treated squirrels in the field for signs of discomfort and impaired mobility. Over 17 months, none of the recaptured GonaCon‐treated females (n = 20) reproduced, compared to 12 of 15 control females. Treated males and females developed sufficient antibodies to GnRH to suppress reproduction, suggesting that GonaCon has the potential to be 100% effective in inhibiting reproduction in both sexes. We also observed a reduction in physical signs of reproductive activity for males (P < 0.001) and in hormone levels of both females (P < 0.001) and males (P < 0.001). Control and GonaCon‐treated animals did not differ in body weight but vaccinated squirrels had poorer body condition scores and exhibited severe injection site abscesses. The abscesses may have been caused by the GnRH conjugate used in GonaCon. In our study, GonaCon was effective in reducing eastern fox squirrel reproduction. Changes in the conjugate or its preparation may reduce the severity of associated injection site reactions. © 2013 The Wildlife Society

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Section: Discussionmentioning

confidence: 99%

Efficacy and health effects of a wildlife immunocontraceptive vaccine on fox squirrels

et al. 2013

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“…The expansion of fox squirrels into natural areas along the coast of California may pose a threat to the western gray squirrel (Sciurus griseus), which is native to California, Oregon, and Washington. Although western gray squirrels are aggressively dominant to eastern fox squirrels (King 2004), the latter have replaced the former in some habitats (Muchlinski et al 2009), although they may coexist for long periods in other habitats (Byrne 1979, Gilman 1986, King 2004. Anecdotal observations suggest that western gray squirrels, never common in Davis, may have disappeared from the city about the time that fox squirrels invaded.…”

Section: Damage Caused Impact On Native Squirrelsmentioning

confidence: 99%

Invasion, Damage, and Control Options for Eastern Fox Squirrels

Sara¹,

Douglas²,

H³

2010

vertebrate_pest_conference

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Fox squirrels are an emerging urban, suburban, and agricultural vertebrate pest in California. They cause a diversity of damage to vegetation and property. Multiple introductions of fox squirrels into California have led to a rapid expansion of their range in the state. Fox squirrels at the University of California, Davis increased from none to an estimated 1,609 between 2001 and 2009. Damage due to the dense population of fox squirrels is increasing. There are several population control options available, but social considerations may limit the viable options to non-lethal methods. This paper provides an overview of the impacts of the introduced fox squirrel in California and on the University of California, Davis campus.

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“…As the eastern fox squirrel continues to expand its distributional range, it is moving into many habitats occupied by the native western gray squirrel (King 2004). Western gray squirrels disappear from some habitats soon after the arrival of the eastern fox squirrel (Muchlinski et al 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Habitat loss and fragmentation cannot be the sole underlying causes for replacement of S. griseus by S. niger. Replacement habitats are located in a variety of areas such as city parks, college campuses, recreational areas, and residential neighborhoods which have not had drastic changes to the structure of the landscape during the time of replacement Muchlinski et al (2009). reported replacement of S. griseus by S. niger in only 1 year at the main quad at California State Polytechnic University, Pomona and within 4 years on a more heavily wooded section of the campus.…”

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confidence: 99%

Eastern Fox Squirrels and Western Gray Squirrels in Southern California

Muchlinski¹,

Gatza²,

Lewis³

et al. 2012

vertebrate_pest_conference

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Eastern fox squirrels have been introduced to many regions within the western United States including areas within California, Idaho, Montana, Oregon, and Washington. In California, fox squirrels have been introduced to San Francisco, Fresno, . The geographic range of the eastern fox squirrel has expanded greatly both through natural dispersal and additional intentional introductions by humans. The fox squirrel has replaced the native western gray squirrel in certain habitats while the two species coexist in other habitats. Western gray squirrels exist by themselves in a third type of habitat even though eastern fox squirrels have occupied adjacent habitat for about 30 years. Habitat Suitability Models (HSMs) have been used to predict the presence and/or abundance of a particular species within a habitat. Analysis of 9 habitat variables using Discriminant Analysis produced a HSM where replacement, coexistence, and exclusion habitats can be identified using only 3 of the 9 habitat variables: average height of ground cover, percent canopy cover, and percent of total trees that are deciduous. A field study underway for over two years at Rancho Santa Ana Botanic Garden in Claremont, CA is testing the validity of the HSM with the study site predicted to be a long-term coexistence habitat. The ratio of western gray squirrels to eastern fox squirrels has gone from 3:1 shortly after the fox squirrel entered the habitat to 1:1, but after 2.5 years of coexistence both species are commonly observed in the study site. The HSM is also being tested through the analysis of additional habitats. Although coexistence of the two species is possible for many decades, the number of western gray squirrels in coexistence habitats is often small, coexistence habitats are geographically isolated from each other, and the probability of extinction of western gray squirrels from these habitats could be high. We are also looking for new habitats which could support western gray squirrels if individuals were moved to these habitats.

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Documentation of Replacement of Native Western Gray Squirrels by Introduced Eastern Fox Squirrels

Cited by 14 publications

References 1 publication

Efficacy and health effects of a wildlife immunocontraceptive vaccine on fox squirrels

Efficacy and health effects of a wildlife immunocontraceptive vaccine on fox squirrels

Invasion, Damage, and Control Options for Eastern Fox Squirrels

Eastern Fox Squirrels and Western Gray Squirrels in Southern California

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