HARVEY & STANLEY ASSOCIATES,INC.

Ecological Consultants

RODENT TRAPPING AT CANALWAYS

SAN RAFAEL, CALIFORNIA

by

HARVEY AND STANLEY ASSOCIATES

H. Thomas Harvey, Ph.D. - - - - Principal in Charge

H.S. Shellhainmer, Ph.D. - - - - Principal Investigator

James Hale, A.B.- - - - Field Investigator

for

David E. Coldoff

61 Monte Vista Ave.

Atherton, California 94025

September 1982

906 Elizabeth Street, Drawer E. Alviso, Ca.95002 (408) 263-1814

INTRODUCTION

The area trapped for rodents is located adjacent tO San Francisco Bay in southeastern San Rafael. Of special concern was the possibility of the presence of the salt marsh harvest mouse (Reithrodontomvs raviventris) an endangered species.

The property was live—trapped for three consecutive nights from September 14th through 17th, 1982 by James Hale. The captured animals were checked by Dr. Howard Shellhammer on September 16th and 17th. Two salt marsh harvest mice, (Reithrodontomvs raviventris) were captured during the 525 trap nights.

Six trap lines of twenty—five traps each (A—F), were placed in the vegetation on the western side of the property during the first two nights of the trapping. Two of those lines were moved to the eastern side of the property on the last night of trapping, because a salt marsh harvest mouse had been captured there on the first night of trapping. One line of 25 traps (Dike 1) was placed in the thin strip of vegetation on the east side of the property on the first two nights while three lines were run on the last night, (Dike 1 and Dike 2, Figure 1). Twenty percent of the trapping sites in each line were assessed for percent cover and height of vegetation. A summary is presented in Table 1.

Figure 1 Position of trap lines at Canalways

Table 1. Plant composition of trap lines in percent and average height of vegetation in centimeters.

Line Pickle- Brass Salt Beard Bare Thatch Fat Average ht.
weed buttons grass grass ground hen in (cm)

A 50 35 — 1 12 2 — 25
B 62 20 — 2 15 1 — 30
C 60 34 — 2 2 2 — 31
D 74 22 — 1 2 — 1 33

E 60 32 — 5 — 1 2 33

F 52 52 42 — 3 — 3 — 23
Dike l 76 — 18.5 — 2 3.5 36 — 36
Dike 2 91 — 3 — 2 4 — 37

Pick1eweed=Salicornia virginica, , Brass buttons = Cotula coronopifolia, salt grass - distichlis spicata, Bear grass - Polypogon monspeliensis, Fat hen = Atriplex patula.

Forty-nine animals were captured; 29 house mice (Mus musculus), 18 meadow mice (Microtus californicus), and 2 salt marsh harvest mice (Reithrodontomys raviventris). They are tabulated by day and line on Table 2.

Table 2. Captures of animals by line and day.

Line Species 9/15/82 9/16/82 9/17/82 Totals

----------------------------------------------------------------------------------------------

A house mice 1 — not run 1

B meadow mice 1 1 2 4

C meadow mice 1 1 — 2

D meadow mice 1 1 1 4

house mice — 1 — 1

E meadow mice — 1 5 6
house mice 1 — 1 2
harvest mice -— — 1 1

F meadow mice 1 2 not run 3

Dike 1 house mice 3 8 9 22
harvest mice 1 — — 1

Dike 2 house mice not run not run 4 4

One salt marsh harvest mouse was trapped in the southern tip of Dike line 1 (the southeast corner of the eastern unit of the property) in 85% pickleweed and 15% salt grass that are ranged 35 cm. in height. It was obviously a salt marsh harvest mouse with no unusual traits. The second salt marsh harvest mouse was trapped in the southern third of the western strip of vegetation (southwest corner of the property) in 55% brass buttons, 40% pickleweed, and 5% beard grass. It had some intermediate traits but Dr. Shellhammer’s professional opinion is that it was definitely a salt marsh harvest mouse. Both are characterized in Table 3.

Table 3. Characteristics of the two salt marsh harvest Captured in this study.

Date of Capture

Trait 9/15/82 9/17/82 Tail scores

Sex male male
Testes descended descended
Tag # 361 362

Tale

Thickness 2.4 mm 2.1 mm 0 , 0

Bicolorness of unicolor near bicolor 0 , 1
tail

Color of

vental hairs brown/tan 1/3 white 0 , 1.5

on tail band

Tail tip intermediate intermediate 1/1 , 1/3.5

Tail/body 100% 100%

ratio

Belly color pectoral—spot pectoral spot

of brown of brown

Behavior docile docile, placid

The characteristics of the mouse captured on 9/15/82 were unmistakable. The mouse captured on 9/17/82 had intermediate tail traits (ha1fway between a salt marsh form and the western harvest mouse (Reithrodontomys megalotis, but the behavior and gestalt of the salt marsh species. Dr. Shellhammer does not have any doubt about either identification.

SUMMARY AND CONCLUSIONS

The site yielded 49 small rodents when trapped in September, 1982. Of the animals caught two were salt marsh harvest mice. The habitat is vegetated by relatively low and somewhat open stands of pickleweed and brass buttons. The latter is considered as being of low value to salt marsh harvest mice. The pickleweed providing the best cover is restricted to a narrow band along the eastern edge of the site. The overall impression of the site is of a moderate to moderately—poor habitat for the salt marsh harvest mouse.

It is Dr. Shellhammer’s professional opinion that on—site mitigation for the salt marsh harvest mouse not be recommended for the site, if the proposed project is approved. This is based on the difficulty of maintaining the population during construction, and finally providing a large enough habitat for long term survival of the species. There are no adjacent marsh areas of sufficient size to which to connect a new marsh.

We recommend off—site mitigation for salt marsh harvest mice where creation or protection of an area contiguous with a relatively larger marsh (10 to 20+ acres) is available.