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2008 Spatial ecology, habitat use, and survivorship of resident and translocated Red Diamond Rattlesnakes (Crotalus ruber) journal article

Lead author: Tracey Brown
Red Diamond Rattlesnakes (Crotalus ruber) have a very restricted range in the United States and are considered a species of special concern in California. Over a five year period (1999-2004), we used radio-telemetry to collect data on the movement ecology and habitat use of this little-studied species on protected coastal sage scrub land managed by the San Diego Zoo’s Wild Animal Park. During the study we compared the movement patterns and survivorship of “Resident” snakes (N=11; 11,090 radio-days) to several C. ruber relocated by Park staff for safety purposes (“Relocates”; N=6; 3,858 radio-days). Among Resident snakes, activity range sizes varied greatly both between individuals, and between years within individuals. Male Resident activity ranges (minimum convex polygon) were typically triple the size of Resident females (2.80 ha vs. 0.88 non-gravid females or 0.76 ha gravid females), and Resident males moved nearly twice as far during an activity season (1.38 km, Resident males vs. 0.77 km, Resident females). Overall, Resident C. ruber have relatively restricted movements when compared to other similar-sized rattlesnakes, typically never occurring more than 300 m linear distance from their winter dens. Relocates used significantly more land (mean activity range size 5.86 ha), and had greater maximum per move distances and total distances traveled during the first year after relocation than did Residents for the same time period. Activity range sizes, annual distances moved, and mean movement speed decreased over time among short distance Relocates (n=3; translocated 97 to 314 m), yet was similar or increased among long distance Relocates (n=3; translocated 856 to 1090 m). Only short distance Relocates were found near (within 50 m) their original capture site at some point during the study (30 to 364 d). Unlike most previous studies of relocated rattlesnakes, there was no detectable difference in survivorship between Residents and Relocates. If translocation is necessary for nuisance rattlesnakes, we suggest only short-distance relocations; long-distance translocations may be a potential conservation tool for future repatriations of C. ruber. We highly recommend more education and public outreach to minimize the need for snake removal.

2014 A Field Study of Small Vertebrate Use of Wildlife Underpasses in San Diego County, 2014 report

Lead author: Cheryl Brehme
In 2012, the U.S. Geological Survey (USGS) started a small animal connectivity study as part of Connectivity Monitoring Strategic Plan (CMSP) developed by the San Diego Monitoring and Management Program (SDMMP). The plan focused on small animals and their use of 8 underpasses throughout San Diego County. Specialized infrared motion detection cameras were set up at each of the underpasses and monitored from May 15 to October 1, 2102 and from March 19 to September 23, 2012. After the first year, concrete structures were set up along the interior wall at 4 of the underpasses to determine if the addition of structure would enhance the use of wildlife undercrossings by small vertebrates. Over the two year period we collected over 3 million of pictures, developed specialized software and methods for processing images, and documented the following species; Pocket Mouse (Chaetodipus spp.), Kangaroo Rat (Dipodomys spp.), California Vole (Microtus californicus), Woodrats (Neotoma spp.), Grey Shrew (Notiosorex crawfordi), Brush Mouse (Peromyscus boylii), California Mouse (Peromyscus californicus), Deer Mouse (Peromyscus maniculatus), White footed Mouse (Peromyscus spp.), Domestic Rat (Rattus rattus), Orange Throated Lizard (Cnemidophorus hyperythrus), Western Whiptail (Cnemidophorus tigris), Western Fence Lizard (Sceloporus occidentalis), Granite Spiny Lizard (Sceloporus orcutti), Side Blotched, Lizard (Uta stansburia), Red Diamond Rattlesnake (Crotalus ruber)- outside only, Western Rattlesnake (Crotalus viridis), Bobcat (Lynx rufus), Coyote (Canis latrans), Grey Fox (Urocyon cinereoargenteus), Mule Deer (Odocoileus hemionus), Greater Roadrunner (Geococcyx californianus), Opossum (Didelphis marsupialis), Striped Skunk (Mephitis mephitis), Raccoon (Procyon lotor), Spotted Skunk (Spilogale putorius), Jackrabbit (Lepus californicus), Rabbit species (Sylvilagus spp.), California Ground Squirrel (Spermophilus beecheyi), Chipmunk Species (Neotamias merriami). This is the first study, to our knowledge, to show the use of underpasses by a community of small vertebrates. Previous studies have lacked the sensitivity to document mice, lizards and snakes. We have shown that these members of the community can be studied successfully using these passive methods. The results of modeling gave evidence to support the short-term effectiveness of the added structure treatments on small vertebrate use and suggested that these rates changed on the specific side