Western Burrowing Owl Workshop August 14, 2015 Western Burrowing Owl Workshop Topics Workshop � Distribution � Identification � Life History � Habitat Requirements � Status & Threats � Habitat Enhancement Methods Dr. Lynne Trulio � Reestablishing Owls on Sites ltrulio@earthlink.net Steve Thurman � Management for Population Persistence August 14-15, 2015 Athene cunicularia An Odd Bird Burrowing Owl or “Little Miner” � Does not hoot � Active day and night � Only owl that lives and nests underground � Life revolves around the burrow � Lines burrows with dung, collects burrow decorations � Juveniles do a great rattlesnake mimic! Entire Species Range - US Subspecies of Burrowing Owls ~20 subspecies � Two subspecies in the US: � Western burrowing owl ( A. cunicularia hypugaea ) � Florida burrowing owl ( A. cunicularia floridana ) � Very similar in appearance/behavior Martin Meyers 1 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 Range of the Western Migration Burrowing Owl � Year-round residents � Migrants – coastal, bay edges, hill sides � Breed in more interior, flat areas � Focus is on the breeding season… � …but the winter season is also vital Wilkinson and Siegel, 2010 Identification - Adults Identification - Adults Male and female not sexually dimorphic, but � Ht ~7.5-9.5 inches male is slightly larger & paler in summer; � Wt ~5-6 ounces behavioral differences. � Wing span ~22 inches � Long legs, few feathers � Mottled brown and cream Garrit Vyn � Designed for camouflage! � Bright lemon yellow eyes � No ear tufts � Active day and night � On ground or low perch Steve Thurman Steve Thurman Steve Thurman Identification - Chicks Chicks over the Season � May – September in CA � Smaller than adults until about July � Buffy breast, whiter eye-brow, darker collar Steve Thurman Pete Bloom Steve Thurman 2 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 Life History Characteristics � Inhabits open grasslands; short scrub habitat Calls � A raptor – although a small one � Many predators � No typical owl “hoots” � Migratory in much of range, but in temperate � Males: “coo – coo” territorial/mating call areas some resident and some migrant � All birds: “chatter” alarm call � Semi-colonial, esp. with sciurids � Females & Juveniles: “rasp” food call � Semi-fossorial – inhabits burrows year round � Monogamous during the breeding season � Nestlings & Juveniles: defensive call � Sexually mature at 1 year � Listen to the calls: � Lays 2-12 eggs; one clutch per year http://www.allaboutbirds.org/guide/burrowing_owl/s ounds � Lives ~3-5 years, but up to ~8 years Bird of Open Grasslands: Habitat Types - Statewide in CA (Wilkerson & Siegel, 2010) Prairies, Ag Lands, Bases, Golf Courses, Open Fields – Natural Grasslands and Urban Sites ~10%=urban ~30%=irrigation canals ~ 8%=pasture ~16%=natural grassland ~ 6%=brushland ~10%=idle/fallow field ~ 3%=grain/row ~10%=field crop But in Nevada, Nesting Habitat Requirements for example… Flexible requirements…within limits � 44% in sagebrush � 22% in grasslands � 21% in salt desert scrub � 9% in agriculture (Great Basin Bird Observatory. 2010. Nevada Comprehensive Bird Conservation Plan at http://www.gbbo.org/bird_cons ervation_plan.html) 3 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 Nesting owls are found… Predators? Just about everything! � At lower elevations in much of California � Primary: hawks, larger owls, skunks, (often <200 ft) foxes, coyotes, snakes � In open areas, typically with few trees � Others: crows, dogs, cats, badgers � Short grass (<6”) around burrows � Structural heterogeneity elsewhere - long grass, shrubs, rock + brush piles � Associated with ground squirrels � With some level of disturbance, esp. from ground squirrels Gil Miller Scott Thurman Burrows are key, California Ground Squirrels natural and artificial Many burrows are needed: * Per pair: primary + satellite Artificial * Overall: prefer high-burrow density areas burrow with lots of debris out front 4 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 Wintering Season in CA: Breeding Season Many resident birds but… Territory & Home Range � Saskatchewan Study � Site tenacity – during season using geolocators showed: � Some site fidelity – 32%-57% � 9/10 females to CA � 10/15 males to OR/WA � 80% of foraging within 600m of burrow, but as far as 2 miles away � CA = important winter � Home range size varies widely, habitat for birds depending on prey availability and � Males nearer breeding quality sites than females http://usfwspacific.tumblr.com/post/54113535534/wintering-habits-of-burrowing-owls-come-as-a-surprise …shows amazing Current migratory research using travels ! satellite telemetry conducted by a number of researchers Bend, Oregon (Conroy, to Johnston, Holroyd, Salinas, California Trefry) … Birds pair up starting in February Aggressive/Defensive Typically seen when defending burrow 5 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 Chicks emerge in May – stay with Females lay up to 12 eggs parents all summer Chicks stay below ground for several weeks By September: Year-round Timeline * juveniles molt and disperse to seek their own burrows * adults migrate or move to other local Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec burrows for the winter Pair & Lay Eggs Chicks Hatch Chicks Adults Move & Chicks at Nest Migrants Leave & Emerge Disperse Migrants Arrive with adults Non -Breeding Season Feb 1 – Sept 1 : Breeding Season (legally-designated) (legally-designated) Opportunistic predators Burrowing Owls In Action! * insects and small rodents dominate the diet * also eat amphibians, reptiles, crustaceans, birds � Adults at nest burrow: � http://www.arkive.org/burrowing-owl/athene- cunicularia/video-00.html � Parents and Chicks: http://www.arkive.org/burrowing-owl/athene- cunicularia/video-03a.html � http://www.arkive.org/burrowing-owl/athene- cunicularia/video-09.html 6 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
Western Burrowing Owl Workshop August 14, 2015 5 Study Sites: Total ~1450 ha Diet in Santa Clara County, CA (Site sizes: 62 to 722 ha) Shoreline Park Tasman Dr. Moffett Field Mission College Trulio, L. and P. Higgins. 2012. The diet of western burrowing owls in an urban landscape. Western North American Naturalist 72:348-356. Sunnyvale Park Compared to other habitats? Results—As a Whole Similar to other ag and more natural habitats � 3092 pellets from 92 burrows Percent Frequency in Diets � 54 burrows associated w/specific owls 100 90 80 70 60 Invertebrates 50 % Frequency - 94:6 (inverts to verts) Vertebrates 40 % Biomass: 30:70 (inverts to verts) 30 Dermaptera 20 (earwigs) 10 Coleoptera 0 (beetles) Grassland (Colorado) Prairie (Montana) Shrub-steppe (Oregon) Shrub-steppe (Washington) Shrub-steppe (Idaho) Shrub-steppe (Oregon) Shrub-steppe-grass (Idaho) Agriculture (Idaho) Urban grasslands (SF Bay) Agriculture (CA) Orthoptera Invertebrates (grasshoppers) Vertebrates Rodentia Other Verts Landscape as a Factor in Key Findings Habitat Quality � Year-round prey - rodents and insects � Composition and species, especially insect taxa, similar to other habitats � ����������������������������������� - do well in urban settings Patches – yes - but enough foraging habitat in the landscape is needed to support long-term populations Avg. mass = 53 g Avg. mass = 155 g 7 Lynne Trulio, Presenter Elkhorn Slough Coastal Training, Sponsor
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