ACORN DISPERSAL BY CALIFORNIA SCRUB-JAYS IN URBAN SACRAMENTO, CALIFORNIA DANIEL A. AIROLA, Conservation Research and Planning, 114 Merritt Way, Sac- ramento, California 95864; [email protected] ABSTRACT: California Scrub-Jays (Aphelocoma californica) harvest and cache acorns as a fall and winter food resource. In 2017 and 2018, I studied acorn caching by urban scrub-jays in Sacramento, California, to characterize oak and acorn resources, distances jays transport acorns, caching’s effects on the jay’s territoriality, numbers of jays using acorn sources, and numbers of acorns distributed by jays. Within four study areas, oak canopy cover was <1%, and only 19% of 126 oak trees, 92% of which were coast live oaks (Quercus agrifolia), produced acorns. Jays transported acorns for ≥117 days. Complete (28%) and partially recorded (72%) flights from acorn sources to caching sites averaged 160 m and ranged up to 670 m. Acorn- transporting jays passed at tree-top level above other jays’ territories without eliciting defense. At least 20 scrub-jays used one acorn source in one 17.5-ha area, and ≥13 jays used another 4.7-ha area. Jays cached an estimated 6800 and 11,000 acorns at two study sites (mean 340 and 840 acorns per jay, respectively), a rate much lower than reported in California oak woodlands, where harvest and caching are confined within territories. The lower urban caching rate may result from a scarcity of acorns, the time required for transporting longer distances, and the availability of alternative urban foods. Oaks originating from acorns planted by jays benefit diverse wildlife and augment the urban forest. The California Scrub-Jay (Aphelocoma californica) is common in oak woodlands and residential areas in the Pacific states (Beedy and Pandolfino 2013, Curry et al. 2017). In central California, the species declined during the mid-2000s as a result of West Nile virus (Airola et al. 2007, Wheeler et al. 2009), but it appears to have recovered (Pandolfino 2017). Despite its abundance, the California Scrub-Jay has attracted fewer ecological stud- ies than have its more threatened sister species, the Florida Scrub-Jay (A. coerulescens; Woolfenden and Fitzpatrick 1996) and Island Scrub-Jay (A. insularis; Curry and Delaney 2002, Caldwell et al. 2013). The primary ecological study of the California Scrub-Jay took place in a coastal California oak woodland (Carmen 2004). The California Scrub-Jay’s acorn-caching behavior is widely known, noted as early as the late 1800s in Mark Twain’s fanciful Jim Baker’s Bluejay Yarn (Clemens 1875). In California oak woodlands, individual scrub- jays cache approximately 7000 acorns per year, which serve as a critical food resource during fall and winter (Carmen 2004). The species’ social organization there consists of territorial pairs and nonterritorial floaters. In areas with an adequate supply of acorns, Carmen (2004) reported territory sizes varying from 0.7 to 6.5 ha and averaging 2.2–2.5 ha. Territorial birds harvest and cache acorns almost entirely within the territories they occupy year round, unless the acorn crop fails, when some territories are abandoned (Carmen 2004). The importance of oaks to the various scrub-jay species, and jays’ im- portant ecosystem roles in dispersing and caching acorns, have long been recognized (Grinnell 1936, Griffin 1971, DeGange et al. 1989, Carmen Western Birds 50:243–254, 2019; doi 10.21199/WB50.4.3 243 ACORN DISPERSAL BY CALIFORNIA SCRUB-JAYS IN URBAN SACRAMENTO 2004, Curry et al. 2017). For example, Morrison et al. (2011) and Pesen- dorfer et al. (2016b) have shown that seed dispersal by the Island Scrub-Jay has a key role in restoring oak and pine woodlands on Santa Cruz Island. Ecological information on urban California Scrub-Jays is limited. Blair (1996) reported the jays to be more abundant in suburbs with a low density of buildings than in natural oak woodland. Many urban areas in the species’ range are dominated by non-native ornamental trees that may include few or no acorn-producing oaks (McPherson 1998, Whipple et al. 2010, Peper et al. 2011, Greco and Airola 2018). Given the importance of oaks to scrub- jays in natural settings, a scarcity of acorns in urban areas could alter the jay’s social organization . For example, Webber (1984) anecdotally reported jays moving beyond territorial boundaries to harvest and cache acorns at an urban–wildland interface in southern California. As urban habitats expand at the expense of native habitats and agriculture in the Central Valley and elsewhere (Thompson 2007), more information is needed on how wildlife uses urban habitats, what determines species’ occur- rence and abundance, and how these areas can be designed and managed to support a greater diversity of wildlife (Marzluff et al. 2001, Warren and Lepczyk 2012, Airola and Greco 2019). In urban Sacramento, I have long observed scrub-jays flying considerable distances with acorns during the fall and winter. In the fall and winter of 2017–18, I characterized these movements to help understand the impor- tance of oaks and jays to each other in this area. Specifically, I sought to quantify the resources of oaks and acorns, to evaluate the extent of urban jays’ use of acorns, to quantify the distances the jays traveled to harvest and transport acorns, to quantify the numbers of acorns dispersed, to assess the effect of the sparseness of acorns on the jay’s social behavior (especially territoriality), and to identify implications for urban forest management. STUDY AREA AND METHODS The study grew from an initial observation of jays transporting acorns to a broader assessment of the phenomenon over the course of the season. As a result, my methods were somewhat more opportunistic than systematic, as new insights led to my adding further components to the study. Study Sites I studied scrub-jays at four sites within three neighborhoods in urban Sac- ramento: Midtown, Curtis Park, and East Sacramento (Figure 1; www.cityof sacramento.org/-/media/Corporate/Files/GIS/Maps/Neighborhoods_E. pdf?la=en). The urban forest in these areas consists mostly of a rather dense canopy of older non-native ornamental trees including hybrid London plane (Platanus ×acerifolia), American elm (Ulmus americana), deodar cedar (Cedrus deodara), and many other species (McPherson 1998, Peper et al. 2011). Two California native oak species, the local valley oak (Quercus lo- bata) and coast live oak (Q. agrifolia), make up most of the small component of oak canopy in urban Sacramento (Sacramento Tree Foundation 2007, Greco and Airola 2018). The coast live oak is native to the Coast Ranges just west of Sacramento (Griffin and Critchfield 1972) but occurs in the city 244 ACORN DISPERSAL BY CALIFORNIA SCRUB-JAYS IN URBAN SACRAMENTO J St. SACRAMENTO Capitol McKinley A ve. Park BUS 80 H St. MIDTOWN 46th St. P St. J St. Folsom EAST SACRAMENTO Blvd. 19th St. EAST LAWN Alhambra Blvd. 50 BUS 80 Broadway Stockton Blvd. 50 T St. 34th St. 2nd Ave. CURTIS BRET HARTE PARK SCHOOL OAK PARK Broadway 99 KEY Rd. Acorn Source Sutterville Franklin Blvd. Caching Area WILLIAM CURTIS PARK NORTH 0 0.5 MLK Jr. Blvd. Miles Figure 1. Acorn sources and areas within which California Scrub-Jays were observed to transport and cache acorns at four study sites in urban Sacramento, California. primarily as a planted cultivar and, in undeveloped areas, as volunteer trees likely established by acorns planted by jays and other acorn dispersers such as the native western gray squirrel (Sciurus griseus) and non-native fox squirrel (S. niger) and eastern gray squirrel (S. carolinensis). I distinguished oaks as human- or animal-planted trees from their location, in highly landscaped and maintained areas or in undeveloped, unmaintained areas, respectively. Midtown. Most surveys and observations were made within this 54-ha 245 ACORN DISPERSAL BY CALIFORNIA SCRUB-JAYS IN URBAN SACRAMENTO older neighborhood (originally built in the mid-to-late 1800s). The area includes mixed commercial and residential buildings and Sutter’s Fort, a 3.3-ha historical park that supports a higher density of valley and coast live oaks than the surrounding neighborhood. Bret Harte School. In its northwest corner, the yard of Bret Harte School in the Curtis Park neighborhood has several large coast live oaks that were likely established from plantings by jays or squirrels. The surrounding area consists of homes constructed from the 1880s to the 1920s (Murphy 2005) and a dense urban forest dominated by London plane but including a variety of other non-native ornamental trees (Peper et al. 2011, Greco and Airola 2018) and a few oaks (see Results). William Curtis Park. This area includes the southern portion of William Curtis Park and the adjacent neighborhoods of Curtis Park and North City Farms. The park is planted mainly with non-native trees, but valley and coast live oaks are concentrated near Sutterville Road. Adjacent areas include older houses and a dense canopy of non-native trees with few oaks. East Lawn. East Lawn Cemetery in the East Sacramento neighborhood was established in 1904, and now supports a canopy of tall ornamental trees, especially conifers, and several coast live oaks. Data Quantification Oak Characterization. For each study area I identified the total number of oak trees and, for acorn-bearing trees, the number of each oak species and canopy cover (in hectares, measured horizontally with the ruler/polygon tool in Google Earth Pro). I also calculated the absolute percent canopy cover of bearing oaks by dividing their area by the total area of each study area. Jay Numbers and Acorn Transport. Throughout the four study areas, I mapped and quantified the jays’ movements and the duration of their acorn use. In the Midtown and Bret Harte School neighborhoods, I also plotted jay territories and estimated the numbers of acorns transported by jays.