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This report provides methods, results, discussion, and recommendations for a study of California Gnatcatcher (Polioptila californica) natal dispersal at a 200 acre (80-hectare) area of open space divided by an interstate highway, in the Lakeside area of San Diego County, California. The study area lies 23 miles east of the Pacific Ocean at the inland edge of a coastal plain and has a relatively warm, dry Mediterranean-type climate. Topography consists predominantly of moderate slopes on either site of Interstate-8 (I-8) with the more southerly parcel of steeper grade. Elevation ranges from about 700 to 1100 feet. The primary goal of the study was to evaluate whether California Gnatcatcher movement across I-8 occurs at the study area and thus shed light on whether this area serves as a functional corridor - at least for the California Gnatcatcher - as assumed in the MSCP Subarea Plan. Field work was conducted during dry conditions, and simple nest success (that is, the number of nests that produced fledged young) of the subject species was less than 50%. We found and monitored seven pairs of California Gnatcatchers in our study area. We found a total of 11 nests during the study period, an average of about 1.6 nests per pair of California Gnatcatchers; however only six of the pairs constructed nests. Of the 11 found nests, four were successful, that is, they produced young that fledged; five were abandoned prior to egg deposition; and two were destroyed by causes unknown. We banded young at the nest, or we captured juvenile California Gnatcatchers soon after fledging by strategically placing mist nets within natal territories at locations past which we expected family groups to move. We determined the banding strategy based on our assessment of whether approaching a nest would have a high or low likelihood of affecting the nest outcome. We banded all seven successfully fledged young from the site with no mortality (Table 1). Six of these were banded as fledglings; one was banded as a nestling. On 23 July 2002 Kylie Fischer documented the occurrence in the Pembroke parcel of a juvenile (left leg white; right leg silver USGS) that had been banded on 11 June 2002 in Territory C-01b-02 of the CalTrans parcel, that is, north of I-8. This bird had been observed on the CalTrans parcel during the previous week (15 July). On 13 September 2002 William Haas detected a banded juvenile (left leg purple; right leg silver USGS) on the Gatlin parcel. This bird

Monitoring of nesting sites in 2000 resulted in an estimate of 4521 to 4790 breeding pairs of California least terns establishing 5301 nests at 37 locations. This represents a 31 percent increase in the minimum estimated number of breeding pairs from 1999. An estimated 3710 to 4013 fledglings were produced, or 0.77 to 0.89 fledglings per pair. This represents a 453 percent increase over productivity of the 1999 season, and 38 percent over that of 1998. Depredation was the primary limiting factor to reproductive success. Other reported causes of mortality included a heat wave in the San Francisco Bay area, nest abandonment, and human activity, including loss of chicks to vehicles. The nesting colony at Camp Pendleton continues to be the largest in the state, accounting for 22.8 percent of breeding pairs and producing 27.6 percent of this season's fledglings. Other colonies numbering over 200 nests included Alameda Point, Point Mugu, Venice Beach, L.A. Harbor, Huntington State Beach, Mariner's Point, Naval Amphibious Base Coronado North Delta Beach and ocean beach, and Tijuana Estuary. The nesting site first documented in 1998 at Tulare Lake bed evaporation ponds outside of Kettleman City in Kings County was used again in 2000, and newly created Caltrans mitigation islands in Albany in Alameda County were colonized and produced at least one fledgling.

Using observations of reported traffic incidents and carcasses the Road Ecology Center estimates the total annual cost of wildlife-vehicle conflict (WVC) in California to be at least $276 million, up 20% from the year before. This report includes maps of WVC hotspots, discusses impacts to wildlife and people from WVC, and ranks highways in each Caltrans District for financial cost of WVC (spoiler, I-280 in District 4 is the costliest). Projects to reduce WVC can be the most effective of any safety project, with effectiveness often >90%. In addition, only 1- 2% of California’s transportation budget, including the new Senate Bill 1 funds, would be required to carry out these safety projects. This report provides an overview of wildlife-vehicle conflict (WVC) hotspots on California highways in 2015 and 2016, based on a combination of traffic incidents involving wildlife that were recorded by the California Highway Patrol (CHP) and carcass observations reported to the California Roadkill Observation System (http://wildlifecrossing.net/california). Because Caltrans does not systematically record where they pick up the tens of thousands of wildlife carcasses per year they dispose of from state highways, these data are not included. Analytical details are available from Fraser Shilling (fmshilling@ucdavis.edu) upon request.