SAN CLEMENTE LOGGERHEAD SHRIKE HABITAT RESTORATION

Background Information

This proposal describes potential shrike habitat enhancement measures for the 12 proposed San Clemente Island Loggerhead Shrike release sites for year 2001

The precise habitat requirements and preferences of the San Clemente Island loggerhead shrike have not yet been determined, but a number of characteristics have been noted to be held in common by habitat successfully occupied by shrikes. These characteristics have been compiled from scientific literature, as well as research and anecdotal observations by field biologists on San Clemente Island. Scoring methods based on these characteristics have been employed by shrike researchers on San Clemente Island to rate the shrike habitat value. Generally, each characteristic is rated to a value from zero to five, with five being the optimal rating. For example, a site with the optimum number of hunting perches, based on visual observation, would receive a score of five. Exceptions to this range are the values scored for habitat diversity and steepness/space, which are rated to an optimal value of ten.

This proposal will be limited in its scope to those rated habitat characteristics that may be improved by enhancement methods. Habitat enhancement shall be defined herein as modifications to the physical and biological environment that would result in an improvement of the scoring for the defined habitat characteristics. Such improvements would presumably increase the likelihood of a successful shrike release. Each characteristic will be briefly described, specific enhancement measures discussed and a scope of work for each site proposed.

Enhancement measures will include alterations to the environment which may be undertaken immediately and completed in the short-term, and biological alterations and longer term modification such as the planting and maintenance of native shrubs.

Hunting Perches

Shrikes are “sit and wait” predators and typically hunt from perches. Ample perching sites throughout a territory are essential for successful foraging, but natural perching sites are thought to be limited by the reduced shrub cover on San Clemente Island. From territory size requirements and the average flight distance between perchings, researchers have determined the approximate number of perches required for a typical twelve hectare shrike territory to be 140. Shrikes will utilize a variety of artificial perches, and observations suggest that island shrikes prefer artificial hunting perches approximately two meters in height (S. Lynn, personal communication).

Perches will be constructed and installed at each site. To determine the number of perches for each site, we have assumed a linear relationship between the site’s rated value and the number of perches at a site. Thus,

A recently used perch design consists of a two meter length of metal tubing installed vertically with a forty centimeter wooden dowel inserted perpendicularly near the top. Modifications to this design may be made. A prototype of each type of perch to be installed will be constructed and approved by the shrike working group prior to installation.

Impaling and Wedging Stations

Impaling and wedging stations are a necessary component of shrike habitat. These stations serve as cache sites for successful forage attempts and also enable shrikes to dismember and consume larger prey items. Shrikes will utilize various natural and artificial impaling and wedging stations including sharp twigs, branch crotches, cactus spines, fencing and barbed wire.

Natural impaling and wedging stations are relatively abundant, however, release sites with relatively low shrub and cactus cover should be supplemented with artificial stations. Designs for artificial impaling/wedging stations will be created by the working group. A prototype of each type of station will be approved by the working group, prior to installation.

Morning glory

Island morning glory (Calystegia macrostegia ssp. amplissima) is a perennial vine endemic to San Clemente Island. Once considered to be in serious decline, its numbers have greatly increased since the removal of feral goats. This species may be considered an early successional species. Its current expansion may be associated with reduced competition from native shrubs, also impacted by heavy grazing.

Ratings for this habitat characteristic have been based on a qualitatively assessed optimum cover, not a maximum or minimum. The relationship of this species to shrike habitat quality appears to be its value as shelter (and possibly as an attractant) for prey species. It is likely that other native taxa will also provide these functional benefits as successional recruitment and plant community restoration continues.

Specific measures for morning glory will be limited to the reduction of cover at sites for which it is deemed excessive. Morning glory will be removed by the use of hand and power tools. Patches of approximately 1.75 meters² will be cut and cleared of vegetation. This species has a rapid growth rate during the winter and spring, therefore, two maintenance trips will be made to each site during these high growth rate periods to clear new growth from the opened patches.

Bare Ground

Observations of foraging shrikes suggest that they prefer to hunt in areas of open shrub canopy supporting short grasses and bare ground. Grazing by feral herbivores has resulted in a loss of native shrub cover and dense cover of exotic grassland species at many of the release sites.

To improve bare ground characteristics at the release sites several methods will be employed. These measures will be considered accumulative with morning glory reduction which will also create open foraging areas. Temporary mulching with plastic tarps and weed control fabric is an effective method for the short-term reduction of annual plant cover. The combination of shading and elevated soil temperatures reduce vegetation cover by killing or stunting the growth of both seeds and seedlings. Mulch tarps approximately one square meter in size will be installed at sites will a low rating for bare ground. Tarps will be left in place for approximately three months and removed prior to shrike release.

String cutters (weed whackers) will be used where it is desirable to reduce dense exotic annual cover, but which also support valuable native species such as Nassella pulchra. Cutting will be done once in mid-winter to remove exotic plant seedlings and again in late spring to remove any developing inflorescences before they set seed.

Weed control rings will be used with a portion of shrub outplantings to provide bare ground and assist in shrub establishment by reducing competition by exotic species.

Burning is an effective method of clearing vegetation. Under strictly controlled conditions, the use of fire can generate bare ground for shrike foraging with the added benefit of creating favorable conditions for native plant recruitment. Should it be deemed appropriate and feasible within the timeframe of the release program, the limited use of control burning should be considered. A series of low intensity wet weather fires with immediate suppression could be utilized to create a mosaic of burned and unburned vegetation. Such a pattern is considered by shrike observers to be ideal for shrike foraging.

Shelter / Habitat Diversity

Native shrub cover has been severely reduced by historic grazing practices, and many species that likely had much wider distribution on the island have been reduced to isolated remnant populations. The reduction of shrub cover by feral grazers has resulting in a net loss of available shelter for animal species and an overall decline in habitat diversity. Shrikes require shrub cover for nesting and roosting sites and for evasion from predators. It is also expected that a general improvement of native plant diversity would benefit shrikes by providing increased habitat for prey species.

To increase shelter and habitat diversity native shrubs will be planted. Seeds of native island shrub species will be collected and propagated at the San Clemente Island Native Plant Nursery. Outplantings will occur at sites with relatively low shelter and habitat diversity ratings and which are reasonably accessible for post-planting maintenance. It is anticipated that these plantings will require approximately six-months of post-planting maintenance. The palette of species planted will be determined by availability of stock from the nursery, but should include Heteromeles arbutifolia, Rhus integrifolia, Malosma laurina, Encelia californica, Artemisia californica, A. nesiotica, Eriophyllum nevinii and Prunus lyonii.

Scope of Work

Site	Habitat characteristic	Rating	Recommendations
Lemon Tank	Hunting perches	3.0	Install 56 artificial perches.
	Impaling/wedging stations	4.0
	Morning glory	4.0	Clear fifteen patches in morning glory (26 meters^2).
	Bare ground	1.0	Install 75 meters^2 of tarping.
	Shelter	3.0	Plant 350 native shrubs throughout the site.
	Habitat diversity	4.5
Burns Canyon	Hunting perches	3.3	Install 48 artificial perches.
	Impaling/wedging stations	4.0
	Morning glory	2.7
	Bare ground	2.7	Install 70 meters^2 of tarping.
	Shelter	3.7	Plant 200 native shrubs along first terrace.
	Habitat diversity	6.3
Horton Canyon	Hunting perches	3.0	Install 56 artificial perches.
	Impaling/wedging stations	3.7
	Morning glory	2.7
	Bare ground	2.7	Mechanically clear 70 meters^2 of exotic grasses along first terrance.
	Shelter	4.0	Plant 200 native shrubs along first terrace.
	Habitat diversity	6.3
Twin Dams Canyon	Hunting perches	4.5	Install 14 artificial perches.
	Impaling/wedging stations	5.0
	Morning glory	4.0
	Bare ground	3.5	Controlled burn on open slope south of canyon rim. If burning is determined unacceptable, mechanically clear 50 meters^2 of exotic grasses.
	Shelter	5.0
	Habitat diversity	8.0
Warren Canyon	Hunting perches	3.0	Install 56 artificial perches.
	Impaling/wedging stations	3.5
	Morning glory	4.0	Clear 10 patches in morning glory (17 meters^2).
	Bare ground	2.5	Install 25 meters^2 of tarping Mechanically clear 50 meters^2 of exotic grasses.
	Shelter	3.0
	Habitat diversity	5.5

Scope of Work (continued)

Site	Habitat characteristic	Rating	Recommendations
Boulder South	Hunting perches	4.0	Install 28 artificial perches.
	Impaling/wedging stations	4.7
	Morning glory	2.0
	Bare ground	3.3	Install 50 meters^2 of tarping on first terrace.
	Shelter	4.3	Plant 150 native shrubs along first terrace.
	Habitat diversity	6.7
Boulder North	Hunting perches	4.3	Install 20 artificial perches.
	Impaling/wedging stations	5.0
	Morning glory	2.0
	Bare ground	3.0	Install 50 meters^2 of tarping on first terrace.
	Shelter	5.0	Plant 150 native shrubs along first terrace.
	Habitat diversity	7.0
Upper Box Canyon	Hunting perches	3.7	Install 36 artificial perches.
	Impaling/wedging stations	3.3
	Morning glory	5.0
	Bare ground	3.0	Install 50 meters^2 of tarping
	Shelter	3.3
	Habitat diversity	7.7
Upper Middle Box Canyon	Hunting perches	4.0	Install 28 artificial perches.
	Impaling/wedging stations	5.0
	Morning glory	2.5
	Bare ground	4.0	Install 60 meters^2 of tarping.
	Shelter	4.5
	Habitat diversity	8.0
Lower Middle Box Canyon	Hunting perches	4.3	Install 20 artificial perches.
	Impaling/wedging stations	4.7
	Morning glory	3.3
	Bare ground	3.3	Mechanically clear 50 meters^2 of exotic grasses.
	Shelter	4.7
	Habitat diversity	7.7

Scope of Work (continued)

Site	Habitat characteristic	Rating	Recommendations
Box Canyon Caves	Hunting perches	3.5	Install 42 artificial perches.
	Impaling/wedging stations	5.0
	Morning glory	1.5	Clear twenty patches in morning glory (35 meters^2).
	Bare ground	3.5	Mechanically clear 50 meters^2 of exotic grasses.
	Shelter	3.5
	Habitat diversity	6.0
Middle Ranch Canyon	Hunting perches	3.0	Install 56 artificial perches.
	Impaling/wedging stations	3.5
	Morning glory	3.5
	Bare ground	3.0	Mechanically clear 50 meters^2 of exotic grasses.
	Shelter	3.5
	Habitat diversity	6.5

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First Annual Report (February 15, 2002)

Second Annual Report (August 5, 2003)

Third Annual Report (February 22, 2005)

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