11

C h a p t e r E l e v e n Bir ds & Mam m a l s

James T. Harvey, Sarah Connors

he diversity of habitats within the Elkhorn Slo u g h gr ove of pines and eucalyptus in the Elkhorn Slough Nat i o n a l watershed largely explains the vast number of bird and Estuarine Res e a r ch Res e r ve (ESNERR); Caspian Terns nest T mammal species that use this region as yea r - r ound res - on man-made islands on the ESNERR; and threa t e n e d idents or seasonal visitors. One may encounter denizens of Sno wy Plo vers nest at the salt ponds and on beaches. channel waters, coastal dunes and beaches, intertidal mudflats, salt marsh, oak woodlands, and grasslands. The moderate cen- Fifty-nine species of mammals are believed to occur in the tral coast climate allows for a diverse assemblage of species Elkhorn Slough watershed, five of which are marine (Schafer th r oughout the yea r . 1986; appendix 11.2). The sea otter (Enhydra lutris) ret u r n e d to its historic range in the slough in the early 1980s, and the Elkhorn Slough is rec o g n i z ed as a Globally Imp o r tant Bir d number using the slough has increased gradually since then. Ar ea by the American Bir d Conservan c y . Mor e than 265 bird Harbor seal (Phoca vitulina) populations have also increased in species (73% of the California total) have been rec o r ded in the recent years. California sea lion (Zalophus californianus), har- Elkhorn Slough area (Roberson 1991; appendix 11.1). Mos t bor porpoise (Phocoena phocoena), and juvenile gray whale ar e seasonal visitors, but approximately 40 are yea r - r ound res i - (Eschrichtius robustus) are sighted infrequently in the lower dents. Aquatic birds — s h o re b i r ds, seabirds, herons, and water- reaches of the slough (Richman 1997). fo wl—account for much of the slough’s avian diver s i t y . Roberson (1991) lists 137 aquatic species, including 57 that In this chapter, we describe bird and mammal species and com- ar e common at some time each yea r . Many of these species munities in Elkhorn Slo u g h ’s primary aquatic and terres t r i a l ar e migrants. In fact, as one of the largest estuaries in habitats.* Although each habitat supports a characteristic assem- California, Elkhorn Slough is a major stopover for birds blage of species, birds and mammals are highly mobile and migrating along the Pacific flyway. Mor e than 20,000 sand- often move to different habitats in response to seasonal changes pipers, plovers, and their rel a t i v es may be present at the peak in environmental conditions, prey avai l a b i l i t y , and habitat of migration (Senner and Howe 1984; Ramer, Page, and needs. We also discuss the effects of pollutants, nonnative red Yoklavich 1991; Page et al. 1992). A number of these aquatic fo xes, and other human activities on these faunas. Fin a l l y , we species nest in the Elkhorn Slough watershed: Great Egre t s , pr esent recommendations for future study and management of Great Blue Her ons, and Dou b l e - c r ested Cormorants nest in a these highly visible members of the Elkhorn Slough bi o t a .

* This chapter covers the coastline and nearshore waters,including the harbor, from Jetty Road to Sandholdt Road,and slough and upland habitats within the borders of Highway 1,Salinas Road,Elkhorn Road, and Dolan Road. 188 A PROFILE OF ELKHORN SL O U G H

A typical scene at Elkhorn Slough depicting some of the many birds and mammals that inhabit the slough’s channels and mudflats. Among the species that forage, breed, and rest in and around the slough are harbor seals and sea otters, and more than 265 bird species,

History of Study aquatic birds as part of his natural resource survey for the California Department of Fish and Game. A formal checklist Naturalists have observed birds and mammals in Elk h o r n of the birds in Elkhorn Slough and adjacent habitats fol- Slough for over a century, but there have been few long-term lowed (Ramer, Ramer, and Warriner 1978) and was updated studies or systematic surveys of these populations. The first bird by Don Roberson (1991). This checklist, based primarily on su r veys, conducted by George Mac G initie from 1926 to 1935, sightings by local birdwatching groups, is currently being documented species composition and described the natural revised. A thorough survey of birds nesting in the Elkhorn history of the slough’s more common aquatic species Slough watershed was conducted in the early 1990s (MacGinitie 1935). Half a century later, Bruce M. Browning (Roberson and Tenney 1993). (1972) produced a more comprehensive list of the slough’s CHAPTER ELEVEN u BIRDS & MAMMALS 189

including pelicans, terns, cormorants, ducks, and shorebirds. Illustration credit: Carleton Eyster.

Detailed studies, focused primarily on aquatic species, have whether shoreb i r d abundance and distribution in Elk h o r n become much more common in recent decades. In the late Slough have changed during the past twenty years (unpubl. data, 1970s, Ramer (1985) documented seasonal abundance, habitat fig. 11.1). Res e a r chers at Moss Landing Marine Laboratories use, and diet of migratory shoreb i r ds in Elkhorn Slo u g h . (MLML) have studied habitat use, diet, and other aspects of the Bet w een 1988 and 1993, shoreb i r ds wer e censused one to four biology of harbor seals, sea otters, and nesting seabirds (Caspian times each year as part of a larger effort by the Point Rey es Bir d Tern, For s t e r ’s Tern, and Western Gull). Since 1984, the slough’s Obs e r vat o r y to detail critical habitats and population changes population of threatened Sno wy Plo vers has rec e i v ed consider- th r oughout central California (Page et al. 1992). From early able attention in order to direct conservation strategies, specifical- 1998 through the spring of 2000, graduate student Sar a h ly by monitoring nesting success and predation on the beaches of Connors replicated Ramer’s original surveys to determine Mon t e r ey Bay and in the salt ponds. 190 A PROFILE OF ELKHORN SL O U G H

waters and beaches. The more seagoing species typically rem a i n near the mouth of the slough but sometimes follow the chan- nel well inland. Others, including many of the ducks and geese, prefer calmer pond waters and only occasionally visit the main channel. About half of these species are seasonally com- mon; the rest are seen infreq u e n t l y , preferring either offshore waters or other latitudes. In fact, Moss Landing Harbor is wel l kn o wn as a spot to see species that are unusual in the reg i o n . Yel l o w-billed Loon, Red-necked Grebe, Harlequin Duc k , Long-tailed Duck, and Black Skimmer are among the rare bi r ds seen at the mouth of Elkhorn Slo u g h .

Diving seabirds—heavy-bodied, underwater foragers such as cormorants, loons, grebes, and sea ducks—are common in the lo wer slough. Many probably visit the slough to rest or avoi d stormy wea t h e r , but others take advantage of the rich prey res o u r ces. Most are seasonal visitors from breeding colonies on fr eshwater lakes farther north or inland. They are most numer- ous fall through spring, but some nonbreeding individuals may linger through summer. Species composition varies from year to Figure 11.1. Abundance of Western Sandpipers at Elkhorn Slough from the mouth to Kirby Park in the late 1970s (Ramer 1985) and late 1990s (Connors,unpubl.data).The histogram shows median (bars), minimum,and maximum numbers per month.Note difference in y-axis values. Differences in abundance between studies may be due to changes in habitat availability in the slough and surrounding areas.

Ter r estrial ver tebrates in Elkhorn Slough have rec e i v ed much less attention than their aquatic counterparts. Land bird studies ha v e included the breeding bird survey (Roberson and Ten n e y 1993) and an ongoing nest box project for cavity nesters, initi- ated on the ESNERR in 1992 (Thompson, unpubl. rpt.). Species composition, distribution, and habitat use of local ter- restrial mammals are virtually unknown .

Large flocks of shorebirds often can be seen during fall and win- Aquatic Habitats ter, when they overwinter at the slough, and during migration in March and April. Photo credit: Monterey Bay Aquarium. Channel, Harbor, and Coastal Waters The deeper waters of the harbor and main slough channel yea r , but there are some trends. Common Loons usually are attract seabirds and marine mammals from Mon t e r ey Bay . mo r e common than Pacific and Red - t h r oated Loons. The larger Most are visitors seeking food or shelter from rough ocean Western and Clark’s Grebes outnumber the smaller Horned and waters and predators. A few marine species enter Elk h o r n Ea r ed Grebes. Sur f and White-winged Scoters, the most com- Slough to bear young. mon sea ducks, form sizable rafts (flocks of resting birds) near the slough mouth. Other diving ducks seen in the main channel About 50 species of seabirds and 35 species of waterfo wl have include the Red - b r easted Mer g a n s e r , Common Gol d e n e ye , been observed in the slough and harbor or on adjacent bay Greater and Lesser Scaup, Bufflehead, and Ruddy Duc k . CHAPTER ELEVEN u BIRDS & MAMMALS 191

Plunging terns are a familiar sight in the main channel in all seasons except winter. Of the nine species rec o r ded in Elk h o r n Slough, three are seasonally common: the Caspian Tern and For s t e r ’s Tern, which nest in the slough area, and the Ele g a n t Tern, which, like pelicans, visits from southerly bree d i n g colonies during summer and fall. The larger Caspian Terns cap- tu r e primarily shiner surfp e r ch, smelt, Pacific butterfish, north - ern anchovy , Pacific herring, and staghorn sculpin in the main channel, whereas For s t e r ’s Terns usually catch threespine stickle- back, northern anchovy , jacksmelt, and shiner surfp e r ch and fr equently feed in the smaller tidal sloughs (T. Har vey 1982; Par kin 1998). Although both terns feed on shiner surfp e rc h and northern anchovy , the Caspian Tern primarily captures adult fish whereas the smaller For s t e r ’s Tern favors juven i l e s , illustrating res o u r ce partitioning between two species with simi- lar foraging methods (Baltz, Mor ejohn, and Antrim 1979).

Gulls are common inhabitants of the slough, making their Numerous duck species can be found in Elkhorn Slough’s small- living by capturing near-surface prey, scavenging, or stealing er channels and surrounding wetlands. Photo credit: Monterey from their neighbors. Fifteen species of gulls have been Bay Aquarium. recorded (see appendix 11.1). Nine of these are fairly com- mon during winter as visitors from inland and high-latitude colonies. Glaucous-winged, Thayer’s, Herring, and Mew Gulls are usually restricted to coastal waters and beaches. In contrast to the aforementioned species, three cormorant California, Ring-billed, and Bonaparte’s Gulls are more likely species are yea r - r ound residents of Elkhorn Slough and to venture up the slough. Heermann’s Gulls are unique, nest- Mon t e r ey Bay . Pelagic and Bra n d t ’s Cormorants, species that ing farther south and visiting the region in summer and fall, pr efer open coast habitats, usually forage near the mouth of the the same time as the pelicans they kleptoparasitize. The slough and roost on rocks and pilings. Dou b l e - c re s t e d Western Gull, the only resident species, is common all year Cormorants feed and roost throughout the slough. Flocks res t and often accompanies feeding otters, optimistically awaiting and dry their wings on steep banks and mudflats. Act i v ely feed- scraps of shellfish. ing birds sometimes form lines along the channel edge to trap schools of fish. Only two species of marine mammals are consistently pres- ent in the channel waters of the slough: the harbor seal and Some seabirds, including the familiar Brown Pelicans and the sea otter. graceful terns, feed in the slough by aerial plunging; that is, they use gravity to plummet headfirst into the water to capture Harbor seals are year-round inhabitants of Elkhorn Slough. small fish below the surface. Brown Pelicans from nesting Hundreds of seals often haul out and rest on banks and mud colonies farther south are common during summer and fall. flats in the lower reaches, especially around Seal Bend. Soaring on large wings, adult (white heads with gray bodies) Harbor seals occur solitarily or in small groups throughout and immature (brown with white bellies) pelicans cruise up the main channel. Although the harbor seal’s diet is com- and down the slough in search of prey . Mor e than 1,000 peli- posed of many fishes commonly found in the slough, includ- cans also roost along the steep banks of the lower slough. Muc h ing Pacific staghorn sculpin, shiner surfperch, and topsmelt mo r e rare are American White Pelicans that occasionally visit (Oxman 1995), many of the fishes consumed are larger than the slough from inland colonies. Unlike their seagoing rel a t i ve s , those which inhabit the slough; this evidence indicates that white pelicans do not plunge, but instead capture fish by harbor seals feed primarily along the nearshore oceanic shelf scooping while swimming. 192 A PROFILE OF ELKHORN SL O U G H

Figure 11.2. Mean abundance of common shorebird species in the Elkhorn Slough watershed from Spring 1999 to Spring 2000; note differences in y-axis values (Connors,unpubl.data).

outside the slough (Harvey, Helm, and Morejohn 1995). evening before departing for Monterey Bay to forage during Thus, the primary importance of the slough for harbor seals the night (Oxman 1995; Eguchi 1998); seals begin to return may be as a place to rest, molt, and pup in safety. to the slough in the morning, with numbers peaking in the afternoon (S. Oates, pers. comm.). Harbor seal abundance in Exact numbers of seals in the slough vary seasonally the slough appears to be greatest from May through August, (Richman 1997) and with time of day (Oxman 1995). On a when pupping and molting take place. Since regular censuses daily basis, harbor seals are most abundant in the daytime began in 1994, the highest single count was 339 seals in July when individuals enter the slough to rest and remain until 1997 (Richman 1997). CHAPTER ELEVEN u BIRDS & MAMMALS 193

bilitated sea otters released in the slough by the Mon t e r ey Bay Aquarium wer e females (M. Sta e d l e r , pers. comm.); if these individuals remain in the region, the sex ratio may even t u a l l y become more balanced.

Sea otters returned to their historic range in Elkhorn Slough in the early 1980s, but their numbers remained low until the mid-1990s. The first systematic counts of the entire slough in July 1994 averaged only 5 otters per survey , but by July 1997 the average had increased dramatically to 43 individuals (Richman 1997). Reasons for the increase are unclear, but the rel a t i v ely protected slough may provide a safe haven from Harbor seals. Photo credit: Jim Harvey. rough weather and white sharks as well as plentiful prey , such as clams and crabs. Sea otters are currently counted weekly dur- ing wildlife tours guided by Yohn Gideon and by personnel Harbor seals began to breed and give birth in Elkhorn Slo u g h fr om the Mon t e r ey Bay Aquarium. We hope that this effort in 1989 (Osborne 1992), soon after the California Dep a rt m e n t will continue so that we have a continuous rec o r d of the num- of Fish and Game closed human access to the harbor seal haul- ber of sea otters using Elkhorn Slough. out sites near Seal Bend. Harbor seal pups are quite prec o c i a l , able to swim within hours of birth, so the actual number of In Elkhorn Slough, sea otters eat mostly clams, mussels, and pups born in the slough is not easily determined. The number other bival v es (Kvitek et al. 1988; Jolly 1997). Considering that of pups seen in the slough has increased steadily in the last ten each otter consumes prey at the rate of approximately 25% of years; at least 30 pups wer e present in 1999 (Har vey , unpubl. its body weight per day (K. Maye r , pers. comm.), there has data). The reduction of human disturbance (e.g., fewer people been concern that otters might be affecting bival v e and other walking along the dikes) has probably been the most importa n t in ve r tebrate populations in the slough. Ini t i a l l y , the arrival of factor in the increased number of harbor seal births and preg - otters in the mid-1980s had no obvious effects (Kvitek et al. nant females; females with young pups have recently estab- 1988), but by 1995, after ten years of otter occupancy and ris- lished new haul-out sites in other parts of Elkhorn Slough (D. ing numbers, bival v e abundance, distribution, and average size Greig, S. Oates, pers. comm.). had declined significantly (Jolly 1997).

Sea otters are found throughout the slough but are observed most regularly foraging in the lower sections (Kvitek et al. Beaches 1988; Jolly 1997) or resting in rafts in the vicinity of Sea l Although exposed to high winds, wave action, and human Bend. Otters form rafts of as many as 50 individuals, floating disturbance, the outer beaches provide seasonal feeding habi- and resting close to each other, perhaps gaining an advantage in tat for shorebirds and roosting sites for gulls and terns. Gulls detecting potential predators. Individuals occasionally come roost on beaches throughout the year; during the nonbreed- as h o r e along the banks of the slough, a common practice in Alaska but unusual in California. Some individuals apparen t l y le a v e the slough during midday, enter the harbor or ocean, and return later in the afternoon (Richman 1997; T. Darc e y , pers. comm.). Most of the otters in the slough appear to be you n g males. In 1995, males accounted for 91% of the slough’s otters, and 89% of these appeared to be juveniles (Feinholz 1998). This skewed sex ratio may explain why, since 1994, only two otter pups have been observed in the main channel (T. Ki e c k h e f e r , pers. comm.). Howeve r , since 1997, 8 of 12 reh a - Sea otter. Photo credit: Jim Harvey. 194 A PROFILE OF ELKHORN SL O U G H ing season (late summer through winter) mixed-species predation by native and nonnative animals including red fox, roosting aggregations may total thousands of birds. Species feral cats, skunks, American Kestrels, Common Ravens, composition varies seasonally. During fall, Heermann’s Gulls, Northern Harriers, and Loggerhead Shrikes. Introduced red Elegant and other terns, and sometimes Brown Pelicans pre- foxes (Vulpes fulva), which were initially brought to dominate. These species usually head south by December California for hunts and fur farms, are now resident and are replaced by California, Glaucous-winged, and other throughout coastal central California. In recent decades, more northern-nesting gull species. their populations have grown and reduced or eliminated many populations of ground-nesting birds. The most noticeable shorebirds on coastal beaches are the Sanderlings. During the winter season, large flocks of these Bet w een 1985 and 1990, increased Sno wy Plo ver nest loss on small, energetic birds scurry along the water’s edge, staying Mon t e r ey Bay was attributed to red fox pred a t i o n . just out of reach of incoming waves, actively probing in the Co n s e q u e n t l y , in 1991, biologists began constructing wire fenc- wet sand for small crustaceans, primarily sandcrabs (Emerita ing around nests in an effort to reduce predation. By 1993, analoga) and isopods (Excirolana spp.; Estelle 1991). Also most nests on beaches wer e protected by these excl o s u r es. In common are Willets, Marbled Godwits, and Whimbrels, 1994, the U.S. Fish and Wildlife Ser vice initiated red fox probers with sensory cells at the tip of their bills for detect- rem o val in select regions of the Mon t e r ey Bay . Fewer excl o s u re s ing movement of prey, and Black-bellied and Snowy Plovers, ar e needed in areas where fox control has been effective and large-eyed visual hunters that detect and capture invertebrate human disturbance is minimal. Although successful in keeping prey on the sand surface. out mammalian predators, excl o s u r es may be used as perch e s by avian predators such as shrikes, kestrels, and ravens, which The upper beach (above the high tide line) provides impor- pr ey on the precocial chicks as they leave the security of the tant nesting habitat for the Snowy Plover, a tiny sand-colored exc l o s u r e within hours of hatching. The future of this delicate shorebird whose West Coast population was federally listed bi r d at Elkhorn Slough and throughout its Pacific coast range as threatened in 1993. Snowy Plovers have historically nested remains tenuous. on undisturbed beaches, habitat that is becoming scarce along the Pacific coast. The nest, a modest scrape in the sand Mudflats often adorned with small shell fragments and situated near a Mudflats are areas of little or no vegetation, exposed during low tuft of vegetation or piece of driftwood, is virtually invisible tides and typically borde r ed by salt marsh vegetation on one to the untrained eye. The Point Reyes Bird Observatory has side and channel waters on the other. At Elkhorn Slough, they closely monitored the breeding population on Monterey Bay pr ovide safe haul-out and roost sites for harbor seals and since 1984. Exposed ground nests are highly vulnerable to se a b i r ds and are especially important as feeding areas for waders trampling and disturbance by humans and dogs as well as to and shoreb i r ds (Ramer 1985).

Elkhorn Slough, recently identified as a critically importa n t sh o re b i r d site (one of forty-six officially rec o g n i z ed sites in se v en countries) by the Western Hem i s p h e r e Sho re b i r d Res e r ve Net w o r k (WHSRN), is an essential link among several migra- tion stopovers along the Pacific flyway. Th i r ty-eight species of sh o re b i r ds—sandpipers, plovers, and their rel a t i ve s — h a v e been rec o r ded in Elkhorn Slough (Senner and Howe 1984; Ramer, Page, and Yoklavich 1991; Page et al. 1992; see appendix 11.1). From 1977 to 1980, the most abundant shoreb i r d species along the main channel (in descending order of abundance) wer e the Western San d p i p e r , Dunlin, Least San d p i p e r , Sho rt - billed and Long-billed Dowitchers, Marbled Godwit, American Avocet, Willet, Black-bellied Plo ver , Long-billed Cur l e w, and Snowy Plover. Photo credit: Thomas Rountree. CHAPTER ELEVEN u BIRDS & MAMMALS 195

Marbled Godwit with a just-cap- tured clam in its bill. Photo credit: Thomas Rountree.

Sanderling (Ramer 1985). During that period, the most abun- Due to their active lifestyles and high metabolic rates, shore- dant species, the Western San d p i p e r , accounted for more than bi r ds req u i r e reliable, abundant food res o u r ces, particularly dur- 75% of the shoreb i r ds in the slough in all months except May ing migration (Schneider and Harrington 1981; Senner and and June. Rec e n t l y , Western and Least Sandpipers generally Howe 1984). The Elkhorn Slough mudflats provide the most made up 60–80% of all shoreb i r ds in the slough watershed, im p o r tant feeding areas for shoreb i r ds in this region (Ramer with number of Least Sandpipers often exceeding that of 1985). Mudflats harbor vast assemblages of inver tebrates and Western Sandpipers (Connors, unpubl. data). often attract and sustain large shoreb i r d populations. Th e ar r i v al and departu r e of migrating shoreb i r ds can be highly syn- Species diversity and abundance var y seasonally. Most of the ch ro n i z ed with the annual breeding cycle of the inver tebrates in sh o re b i r d species are visitors from distant breeding colonies at that region (Harrington 1983; Myers et al. 1990), but this rel a - higher latitudes or inland and thus are present only seasonally. tionship has not been examined at Elkhorn Slo u g h . Seasonal movement patterns and peaks in abundance var y con- siderably among species. Some species, such as Long-billed and In Elkhorn Slough, shorebirds feed primarily on a wide vari- Sho r t-billed Dowitchers and Dunlin, are most numerous dur- ety of benthic invertebrates, including various copepods, ing migration as they stop to feed and rest on their way south clams, polychaetes, and crabs (Ramer 1991). The distribu- to wintering areas or north to breeding areas. Others, including tion of the many different prey species is partly a function of Willets, Marbled Godwits, Black-bellied Plo vers, and Wes t e r n mudflat substrate. Mudflats are mostly sand near the slough Sandpipers, are winter residents in the slough, arriving in fall entrance but become increasingly “muddier” (composed of and staying until early spring when conditions on bree d i n g finer-grained silt) farther up the main channel (Nybakken gr ounds become suitable for nesting. Only four (Sno wy Plo ver , and Jong 1977). Therefore, different types of shorebirds can Ki l l d e e r , Black-necked Stilt, and American Avocet) are consid- be seen as you venture up the slough. Ramer (1985) found er ed permanent residents. Total shoreb i r d abundance is grea t e s t that smaller shorebirds (e.g., Western Sandpiper, Least during spring and fall, sometimes exceeding 20,000 birds at the Sandpiper, and Dunlin) occurred in greater densities along peak of migration, and lowest in late spring and early summer the upper reaches of the slough, where they ate the smaller (fig. 11.2; Senner and Howe 1984; Ramer, Page, and Yok l a v i c h invertebrates associated with muddier habitats. Larger shore- 1991; Page et al. 1992). birds (e.g., Marbled Godwit and Long-billed Curlew), which eat larger sand-dwelling prey, were more abundant near the mouth of the slough. 196 A PROFILE OF ELKHORN SL O U G H

Inter- and intraspecific competition for prey may be significant for shoreb i r ds. Species or age classes can minimize competition by migrating at different times or along different routes, or by feeding in different places within a region. During spring migration, the peak of Least Sandpiper migration occurs before the peak of a morphologically similar species, the Wes t e r n San d p i p e r , thus reducing competition for food during this crit- ical time (fig 11.2; Connors, unpubl. data). Competition among shoreb i r d species that co-occur and feed together is reduced by differences in bill design and leg length, allowi n g di f f e r ent species to utilize different microhabitats (Gree n 1968); species with longer bills and longer legs, such as the Long-billed Cur l e w and the Marbled Godwit, can probe deep- er in the substrate and feed in deeper water than smaller, short- er-billed species like the Least San d p i p e r .

Sho re b i r d distribution in Elkhorn Slough varies throu g h o u t the day in response to changes in tide level. In mudflats and other tidal habitats, food availability is intermittent. As tide le v el recedes and more mudflats are exposed, more prey become accessible. Sho re b i r ds coordinate their daily move- ments in order to maximize foraging opportunities when res o u r ces are available at low tides. Available foraging space is In spring and summer, Great Blue Herons and Great Egrets be l i e v ed to be the most significant factor in determining the nest in a Monterey pine and eucalyptus grove at the Elkhorn si z e of migratory shoreb i r d populations (Recher 1966). Tid a l l y Slough Natural Estuarine Research Reserve. Photo credit: Paul restricted mudflats adjacent to the main channel of the slough Zaretsky. offer excellent opportunities for habitat enhancement. Wit h pr oper water level management, these regions can provi d e alternate foraging and roosting areas for shoreb i r ds during high tides when most other mudflat regions are flooded. Th e s e regions, such as the salt ponds and the marshes along Elk h o r n Road, are important during migration when birds must maxi- mi z e food intake (Connors, unpubl. data).

Her ons, egrets, and other large wading birds also forage along the edges of Elkhorn Slo u g h ’s mudflats. They do not feed by pr obing but instead use long legs and beaks to wade and catch small fish in the shallow waters along the slough channel (B yrnes 1997). Of the 9 such species rec o r ded in the slough, only the Great Blue Her on, Geat Egr et, and Sno wy Egr et are common throughout the yea r . These aquatic birds also feed in ponds, marshes, and fields and roost and nest in trees. In 1987, for unknown reasons, Great Egr ets and Great Blu e Her ons established a nesting colony in the ESNERR. Pairs of Figure 11.3. Peak numbers of Great Blue Heron and Great Egret nests at both species built their large stick nests in a stand of Mon t e re y the ESNERR rookery in 1998 and 1999 (note differences in y-axis values). CHAPTER ELEVEN u BIRDS & MAMMALS 197 pine and eucalyptus trees near the main channel of the slough. In 1993, 27 pairs of Great Blue Her ons and 61 pairs of Grea t Egr ets nested in the res e r ve from Mar ch through June (Wee d 1993a,b). In recent years, the efforts of dedicated docents have pr ovided the res e r ve with valuable information on nesting activities in the roo k e r y (fig. 11.3). In 1998, the greatest num- ber of Great Blue Her on nests was rec o r ded early in the season, with 16 nests counted in mid-Mar ch. Great Egr et nesting activity appeared to peak in early May , with a total of 38 nests found. In 1999, heron nesting peaked in June with a high count of 13 nests, and egret nesting peaked in May with a count of 40 nests, with a large number of nests still active until the end of Jul y . Dou b l e - c r ested Cormorants have also main- tained a presence at the roo k e r y since they wer e first observed An egret stabs the water in pursuit of prey. Photo credit: Thomas nesting there in 1997 (A. Baldridge, pers. comm.). The num- Rountree. ber of cormorants appears to be increasing in the roo k e r y, which may lead to competition for nest sites among the egret s , species at Elkhorn Slough. One such species, the elusive he r ons, and cormorants (ESNERR, unpubl. data). The entire California Clapper Rail, previously sustained a breeding popu- colony may be short- l i v ed, as guano from nesting birds appears lation in the slough’s salt marshes. These shy waders relied on to be killing the trees (M. Silberstein, pers. comm.). pa s s a g e ways through dense vegetation to come and go betwee n nests built above tide level in the higher zones and feeding sites Tidal [Salt and Brackish] Marshes in the soft mud of the lower marsh. Clapper Rails wer e last Salt marshes are tidal areas where saline-tolerant picklewee d seen in the slough in 1980 (Roberson 1993a). The exact cause (Salicornia virginica) predominates. Lower zones are flooded of extirpation is unknown, but loss of salt marsh veg e t a t i o n , by tidal waters, although less often than mudflats. Upper zon e s contaminants, and predation by nonnative red foxes are likely usually stay dry except during the highest tides. Thus, salt factors (Thelander and Cra b t r ee 1994). marshes support wading birds but also provide breeding habitat for less aquatic birds and mammals. Tod a y , after years of tidal inflow and saltwater intrusion perco - lating through the substrate, the majority of the slough’s marsh- Salt marshes are important to wading birds, particularly during es are salty (see chapter 4, “Hydro g r a p h y ”). In the nineteenth higher tides when mudflats are unavailable. Larger shoreb i rd s ce n t u r y, when the mouth of the Salinas River was located north and waders, such as egrets, Great Blue Her ons, Wil l e t s , of Moss Landing, the marshes in Elkhorn Slough wer e primari- Marbled Godwits, and Long-billed Cur l e ws, roost and forage ly fresh or brackish water. Although there are few historical for polychaete worms, crabs, and fish. During exce p t i o n a l l y rec o r ds, these marshes undoubtedly supported quite differen t high tides when the uppermost sections of salt marsh are sub- flora and fauna. In recent years, managers have begun to res t o r e merged these birds move to salt ponds, river mouths, and ce r tain marshes to their natural seasonally variable condition in coastal beaches. hope of reviving these lost ecosystems. For example, in 1995 tide gates at the head of the slough wer e rep a i r ed in order to Since the Moss Landing Harbor was constructed in 1946, cre- pre v ent saltwater from the main channel from flowing into ating a direct channel between Elkhorn Slough and Mon t e re y Por ter Marsh, a pickleweed marsh that had once been a season- Bay , salt marsh vegetation has deteriorated (especially in the al freshwater/brackish wetland and pasture. Now, this marsh is upper slough) and been replaced by mudflat (Crampton 1994; regaining its seasonal character. During winter storms, the Lo we 1999). Conversion to mudflat has created additional for- marsh floods with rainwater and flow from Carneros and aging habitat for shoreb i r ds, but the value may be outwei g h e d Watsonville Creeks; this freshwater completely covers the by the loss of roosting areas for shoreb i r ds and nesting habitat underlying salt marsh vegetation, and the area fills immediately for marsh-dependent species. Little is known about these with visiting ducks and geese that remain until the rainwater 198 A PROFILE OF ELKHORN SL O U G H drains out into the slough. When spring arrives, a Nort h e r n malian predators and offer a safe roosting site for the endan- Harrier pair builds a nest in the salt marsh and hunts the ge r ed California Brown Pelican. Brown pelicans disperse to marsh and surrounding grasslands for rodents and small birds feed during the day but return each evening and congregate in to feed their young. The harriers have fledged three young each large communal roosts in places that are safe from pred a t i o n year from 1997 to 1999. Pairs of White-tailed Kites, Red - and disturbance (Jaques and Anderson 1988). On a summer or sh o u l d e r ed Hawks, and Green Her ons have begun to nest in fall night, as many as 5,000 pelicans may roost on the salt adjacent stands of trees. Spring also brings Common pond levees or the dikes along the main slough channel (Bri g g s Yel l ow t h r oats, Ora n g e - c r owned Warblers, Bla c k - h e a d e d et al. 1983). Grosbeaks, and other bird species to the lush riparian veg e t a - tion that borders the marsh to build their nests. In the fall, the The salt ponds are especially important as a nesting site for the dr y pickleweed turns a brilliant reddish purple, and provi d e s Sno wy Plo ver . Management efforts such as limiting human forage and cover for returning migrants. access and controlling predators have contributed to increa s e d pro d u c t i v i t y . Furt h e r m o r e, since 1995, Point Rey es Bir d Salt Ponds Obs e r vat o r y biologist Doug George has carefully manipulated Just north of the slough entrance is a series of ponds formed by the amount of tidal water entering the salt ponds during the le v ees and characterized by rel a t i v ely low tidal flow. From 1916 br eeding season to create a mosaic of nesting and foraging until 1973 these wer e used as evaporation ponds for salt min- habitat for the plovers. This successful management strategy has ing (Gor don 1996). Tod a y , the area is managed for wildlife by led to greater numbers of nests and higher rep ro d u c t i v e success. the California Dep a r tment of Fish and Game, and public For instance, during spring and summer 1997, 67 pairs of access is limited. Sno wy Plo ver nested in the salt ponds, rep r esenting about one- th i r d of all Sno wy Plo ver nests in the Mon t e r ey reg i o n . Especially high hatching rates (88%), greater than in any other region in Mon t e r ey Bay , produced 168 chicks and 82 fledglings (P age et al. 1997).

Salt pond management efforts have also benefited other nesting waders such as Black-necked Stilts, American Avocets, and Ki l l d e e r . Howeve r , the breeding biology of these species has not been closely studied in this area .

Ov er the years, the salt ponds have also supported three species of nesting seabirds—Caspian Tern, For s t e r ’s Tern, and Wes t e r n Gull. Caspian Terns wer e first rec o r ded nesting in the salt ponds in 1970 (Baldridge, Chandik, and DeS ante 1970) and br ed intermittently until 1978, by which time the colony had Brown Pelican. Photo credit: Jim Harvey. gr own to 85 nesting pairs. Sometime after 1980, for unknown reasons, most of these birds relocated to dredged islands on the The salt ponds provide valuable habitat for birds. Even during ESNERR (Par kin 1998). One of the earliest rec o r ds of For s t e r ’s the period of salt mining, the ponds supported numerous avian Terns breeding along the Pacific coast is from Elkhorn Slo u g h . visitors. Slightly higher in elevation than the slough’s mudflats, Some unknown number of pairs nested on small, marshy the salt ponds serve as an important refuge when high tides islands in 1932 (Ray, unpubl. data, in Har vey 1982). inundate the rest of Elkhorn Slough (Str ong 1990). Cur re n t l y , Sometime later, these terns established a breeding colony on the ponds offer important feeding, roosting, and nesting habi- the remnant dikes bordering the salt ponds; from 1978 to tat for a wide variety of shoreb i r ds and seabirds . 1980, 90 to 300 breeding adults wer e present (Har vey 1982). In the mid 1990s, approximately 15-20 For s t e r ’s Tern nests When flooded, the salt ponds become inaccessible to mam- wer e identified in the salt ponds. Howeve r , all the nests wer e CHAPTER ELEVEN u BIRDS & MAMMALS 199

which the terns picked up through the food chain. Although the use of DDT in the U.S. was banned in 1972, residues of this persistent pesticide continue to contaminate soil in the watershed (see chapter 13, “Land Use and Contaminants”).

Pollutants have not been the only threat to the Caspian Ter n co l o n y . In 1996 Caspian Terns started to nest, but an unidenti- fied mammalian predator swam to the island and destroyed all the eggs. The terns abandoned the colony and attempted to renest at the Salinas River mouth; howeve r , the few chicks that hatched at the new site wer e eaten by an avian pred a t o r , prob a - Caspian Tern parent and chick. Photo credit: Thomas Rountree. bly an owl (J. Par kin, pers. comm.). Fol l o wing unsuccessful nesting efforts at the Salinas River mouth in 1997 and 1998, abandoned before hatching, although eggs wer e still intact (D. Caspian Terns returned to nest on the islands in Elkhorn George, pers. comm). Since then, there has been no documen- Slough in 1999 and 2000, but again abandoned the site each tation of breeding For s t e r ’s Terns in the salt ponds. year after a predator disturbed the colony. The terns bred successfully in 2001 due in large measure to researchers’ Western Gulls nest along the salt pond levees and on var i o u s efforts to deter predators. The future of the Elkhorn Slough ar tificial struc t u r es, but the Elkhorn Slough colony has rec e i ve d Caspian Tern colony remains uncertain until predator access little systematic study. The number of nesting pairs declined can be controlled. significantly between 1979 and 1989, from 61 to 5 (Rob e r s o n and Tenney 1993), after levee breaks in 1982 increased tidal action and flooding in some ponds. Terrestrial Habitats Bir ds and mammals inhabiting the terrestrial habitats of the Dredged Islands Elkhorn Slough watershed have rec e i v ed ver y little attention In 1983, several small islands wer e constructed on the fr om the res e a r ch community. The only extensive studies—the ESNERR using dredged bottom sediments in an effort to cre- br eeding bird survey conducted from 1988 to 1992 by ate habitat for birds. Safe from disturbance and predation, these Roberson and Tenney (1993) and an ongoing nest box proj e c t islands quickly became a popular roosting site for Brown for cavity nesters—are summarized below. We also present gen- Pelicans and Dou b l e - c r ested Cormorants, and a nest site for a eral descriptions of the fauna in each habitat, based primarily colony of Caspian Terns. on the opportunistic observations of local naturalists and bird- ing organizations. In the late 1980s, Caspian Terns, presumably from the salt pond colony, began to nest on the dredge islands. In 1992 Breeding Bird Survey and Nest Box Project th e r e wer e 90 nesting pairs (Bailey 1993a). The colony Bet w een 1988 and 1992, a team of observers conducted inten- in c r eased to 110 pairs and approximately 134 chicks in 1993; si v e bird surveys throughout all of Mon t e r ey County to deter- 200 pairs produced 189 chicks (150 of these fledged) in 1994. mine the breeding distribution of birds (Roberson and Ten n e y Une x p e c t e d l y , in 1995 colony production plummeted: approxi - 1993). This rep o r t provides ESNERR with solid baseline infor- mately 160 tern pairs nested and laid eggs, but only 14 chicks mation of birds that breed on the res e r ve. hatched and only half of these fledged (Par kin 1998). Subsequent analysis of tern eggshells and unhatched chicks In 1992, a project was initiated on the res e r ve by Andrew rev ealed high levels of the pesticide residue DDE (a metabolite Thompson, a professor from Santa Clara Uni ve r s i t y , to provi d e of DDT; Par kin 1998) and indicated that the colony failure ar tificial nest sites (nest boxes) for cavity-nesting birds in oak had been caused by exposure to pollutants. Runoff from agri- woodlands. The project remains active today, managed by vol - cultural fields following heavy rainfall during the winter of unteers who faithfully maintain the nest boxes, determine 1995 had probably contaminated slough waters with DDE, species use and occupancy, band chicks, and rec o r d fledging 200 A PROFILE OF ELKHORN SL O U G H success. Th e r e are 151 nest boxes located in nine differen t The more open savannahs and grasslands provide seasonally woodlots on the res e r ve. Since 1998, the nest boxes have been abundant food for grazers, browsers, and seed eaters, but little closely monitored by project coordinator Shirley Murphy and co ver . For this reason, many species feed in grasslands but use other dedicated volunteers. The Chestnut-backed Chickadee other habitats for resting and breeding. Common mammals in has been the most common occupant of the boxes during this this habitat include California ground squirrel (Spermophilus time, followed by the Oak Titmouse. During the 1988–2000 beecheyi), California meadow mice (Peromyscus sp p. ) , seasons, the peak egg-laying period occurred during the first California vole (Microtus californicus), valley pocket gopher two weeks of April for both of these species. Other species (Thomomys bottae), mule deer (Odocoileus hemionus), and the in f r equently using the nest boxes include the Tree Swa l l o w and om n i vo r ous coyote (Canis latrans). Western Mea d ow l a r ks and Bewi c k ’s Wren. Continued monitoring of nest box use provi d e s Sav annah Spa r r ows typically nest in dense grasses, but cattle the res e r ve with baseline information that may prove useful in grazing has substantially reduced suitable nesting habitat for assessing the health of this habitat over time. these species (Roberson and Tenney 1993). Predators such as owls, Golden Eagles, White-tailed Kites, Red-tailed Haw k s , Oak Woodland–Savannah–Grassland and American Kes t r els often hunt in open fields but return to The predominant native terrestrial habitat in the Elk h o r n oaks for roosting or nesting. In winter, large mixed flocks of Slough region is a mix of oak woodland (dense stands of tree s sp a r r ows (usually including Gol d e n - c r owned Spa r r ow, Wh i t e - separated by small grassy areas), savannah (grasslands with scat- cr owned Spa r r ow, Sav annah Spa r r ow, and Song Spa r r ow) , finches, and blackbirds forage in open habitat.

Seasonal shifts in habitat use appear to be common, especially for small mammals. For example, California voles primarily inhabit grasslands during winter and spring when grasses are gr een and lush; howeve r , during summer voles leave the dry grassland and move into the gree n e r , more succulent salt marsh vegetation (E. Har ding, pers. comm.). In this season, the salt marsh may provide more food and protection from avian pred - ators. In years when California vole density is especially high, the western harvest mouse may be forced out of salt marshes and into other habitats, probably due to insufficient res o u rc e s for both species (Har ding 2000).

Young White-Tailed Kites roosting above Porter Marsh, with Chaparral American Crows in the background. Chaparral or coastal scrub habitat consists of dense stands of Photo credit: Carleton Eyster. co yote brush (Baccharis pilularis), manzanita (Arctostaphylos te r ed trees), and grassland (trees absent). The oak canopy serves sp p .), black sage (Salvia mellifera), ceanothus (Ceanothus sp p. ) , as a valuable foraging habitat for insectivor ous foliage gleaners, and other shrubs. Both seedeaters and insectivor es such as including resident Oak Titmice, Chestnut-backed Chickadees, California Quail, goldfinches, Song Spa r r ow, towhees, Bewi c k ’s Hut t o n ’s Vir eos, and Bushtits; summer visitors such as Ora n g e - Wren, Wrentit, and Bushtit flourish in this dense, shrub b y cr owned Warblers; and winter visitors such as Ruby - c r own e d habitat. The brush rabbit (Sylvilagus bachmani) is abundant in Kinglets and Town s e n d ’s and Yel l ow - r umped Warblers. Fal l ’s chaparral, where it finds sufficient cover and an abundant release of acorns provides a generous seasonal supply of food so u r ce of food in herbaceous and woody vegetation (Chapman, for the Western Scrub - Ja y , Acorn Woo d p e c k e r , and California Hockman, and Edw a r ds 1982). Chaparral stands sometimes Quail, as well as mammalian denizens such as the western gray merge with oak woodlands. Mule deer commonly inhabit this sq u i r r el. Beneath the trees, California Towhees, Spo t t e d oak woodland/chaparral ecotone, the oaks providing cover and Towhees, and Dark - e y ed Juncos persistently search or scratch food and chaparral providing abundant browse material in the leaf litter for seeds and invert e b r a t e s . (M ackie, Hamlin, and Pac 1982). CHAPTER ELEVEN u BIRDS & MAMMALS 201

Riparian Woodland often spend the winter on freshwater ponds, feeding on the Riparian woodlands lining the streams and rivers of the gr een surface film of duckweed and other aquatic plants and Elkhorn Slough area are composed of willows (Salix sp p. ) , animals. Most depart in spring, but a few Mal l a r ds and other alders, maples (Acer sp p .), and various water-loving understory ducks stay to raise broods. Th e r e appears to be suitable shore- species. These narrow corridors of lush streamside veg e t a t i o n line nesting habitat for American Coots, Pied-billed Greb e s , attract many bird and mammal species, especially during the and American Bitterns, but few nests have been found dr y summer and fall months. Bir ds that nest in this habitat (R oberson and Tenney 1993). include the White-tailed Kite, American Robin, Pac i f i c - s l o p e Flyc a t c h e r , Wil s o n ’s War b l e r , Common Yel l ow t h r oat, Bla c k - Eucalyptus Forest headed Grosbeak, Purple Finch, and Swa i n s o n ’s Th ru s h . Some areas of the Elkhorn Slough watershed feature nearly Mammalian denizens include the raccoon (Procyon lotor), pu r e stands of nonnative eucalyptus trees (Eucalyptus sp p. ) . opossum (Didelphis virginiana), and dusky-footed woodrat The species’ allelopathic prop e r ties prev ent most other tree s (Neotoma fuscipes), all nocturnal species that req u i r e abundant and understory plant species from becoming established. water and cover (Bur t and Grossenheider 1976; Gar dner 1982; Eucalyptus forests are thought to support fewer bird and mam- Kaufmann 1982). mal species than other wooded habitats in the watershed. During winter, large flocks of Yel l ow - r umped Warblers feed Some residents of riparian woodlands rely on bordering habi- within the towering canopy. In the spring, Red-tailed Haw k s tat to meet their energy requirements. For example, White- often build their nests in the upper branches, which provide a tailed Kites often nest in large trees within a riparian corridor commanding view of surrounding foraging area s . but hunt for rodents in nearby grasslands (Roberson 1993b). Long-tailed weasels inhabit the riparian woodland but may Dunes move to neighboring grasslands to feed on small rodents, The coastal dunes system is a harsh environment, deficient in shrews (Sorex spp.), and brush rabbits (Svendsen 1982). The fr eshwater and continuously exposed to winds and salt spray. gray fox (Urocyon cinereoargenteus) is commonly found in Still, the sparse assemblages of dune-binding vegetation support grassland/riparian woodland ecotones that provide open a few species of birds and mammals. In fact, some terres t r i a l hunting grounds as well as sufficient cover (Samuel and mammals are well adapted to these conditions: the brush rabbit Nelson 1982). finds sufficient cover and food in herbaceous and woody veg e - tation; the western harvest mouse (Reithrodontomys megalotis) Freshwater Marshes and Ponds can drink saltwater to obtain fluids; the California grou n d Freshwater marshes and ponds are scarce in the Elkhorn Slo u g h sq u i r r el and California mole (Scapanus latimanus) find a sandy watershed and provide a rich environment for many species, substrate conducive to extensive burrowing. Sev eral bird species some which are unique to this habitat alone in the slough. ar e resident in dune habitat. Wh i t e - c r owned Spa r r ows com- Typically surrounded by emergent cattails (Typha latifolia), bu l r ush (Scirpus californicus), and rush (Juncus sp p .), fres h w a - ter ponds provide protected nesting habitat for terrestrial birds such as Marsh Wrens, Common Yel l ow t h r oats, and Red - winged Bla c k b i r ds. In summer, Barn, Cliff, Tree, and Vio l e t - gr een Swa l l o ws hunt flying insects above the water surface; bats (h o a r y bat, Lasiurus cinereus; pallid bat, Antrozous pallidus; western pipistrel, Pipistrellus hesperus; California myotis, Myotis californicus; and big brown bat, Eptesicus fuscus, are the most likely species) replace the swallows after sundown. Hero n s , eg r ets, and shy Soras and Virginia Rails forage along shorel i n e s for fish, amphibians, and inver tebrates. Wat e rf o wl, primarily dabbling ducks such as Mal l a r ds, Nor thern Pintails, Gad w a l l s , Cinnamon and Green-winged Teals, and Nor thern Sho vel e r s , Bobcat. Photo credit: ESNERR. 202 A PROFILE OF ELKHORN SL O U G H monly perch on bush lupines. Predators such as the duction and survi v al of harbor seals; sea otter abundance in the Loggerhead Shrike and Say ’s Phoebe, though not numerou s , slough and effects of foraging on prey populations; rel a t i v e ar e highly visible as they perch on posts or tall shrubs, search - abundance of shoreb i r ds, herons, and egrets in regions throu g h - ing for prey . In winter, Water Pipits search for grou n d - d we l l i n g out the watershed in relation to habitat changes; and bree d i n g insects on the upper beach. ch r onology and food habits of Caspian Terns and effects of pol- lutants on rep ro d u c t i v e success. Agricultural and Residential Lands Grazing pastures and row crops cover a large part of the A great deal of basic res e a r ch topics still remain largely unex- Elkhorn Slough watershed. In spite of intense human activities, pl o r ed, including studies of the breeding biology of res i d e n t these lands support large populations of some species of birds marine and terrestrial birds, effects of changing habitats on sur- and mammals. Enormous flocks of Red-winged, Tri c o l o re d , vi v al, and rel a t i v e importance of prey species to birds and and Brewer ’s Bla c k b i r ds feed on grain near livestock and on mammals in Elkhorn Slo u g h . in ve r tebrates in newly tilled fields. Non n a t i v e Euro p e a n Starlings and parasitic Brown-headed Cowb i r ds often join these Conservation and Management flocks. Mix ed flocks of sparrows and finches are also pres e n t . Conservation-based research and informed management Swa l l o ws diligently search for insects over fields in summer. strategies are critical for future protection of the slough’s birds and mammals. The most pressing concerns relate to anthropogenic factors, specifically habitat degradation, pollu- Management Issues tants, and nonnative species. We recommend that the follow- and Research Recommendations ing subjects be studied in detail.

Bir ds and mammals are ecologically important and highly visi- Impacts of Habitat Changes The aquatic habitats in ble members of the Elkhorn Slough watershed. In recent yea r s , Elkhorn Slough have undergone dramatic changes in the last harbor seals, sea otters, Sno wy Plo vers, and several other species century. Tidal scour, erosion, and sedimentation continue to ha v e been the focus of directed res e a r ch and management affect mudflats and marshes throughout the slough (ABA ef f o r ts. But overall, the bird and mammal communities in 1989; Crampton 1994; Malzone and Kvitek 1994; see also Elkhorn Slough remain poorly studied. A thorough under- chapter 4). Some of the key questions are: How have these standing of the status and biology of these species is essential if changes in habitat affected shorebirds and waterfowl? Is one fu t u r e restoration and conservation efforts are to be successful. habitat more beneficial than another or is a balance of several Basic information about habitat req u i r ements, population size, habitats the best way to maximize diversity? Is it necessary or and community struc t u r e is missing for many species, especial- even possible to manage or restore freshwater marshes or ly terrestrial mammals. Without this baseline information, it is other declining habitats? Will future management practices nearly impossible to detect changes and assess the effects of affect harbor seals or other species that appear to be thriving human activities in the slough. From both a scientific and under current conditions? management perspective, the opportunities and need for both basic and applied res e a r ch on the bird and mammal species at We recommend that the amount and causes of scour be con- Elkhorn Slough are enormous. tinually monitored, and that the effects of scour on marine bi r ds (specifically shoreb i r ds) and mammals be assessed via Basic Research monitoring of habitat use. Monitoring of the Por ter Mar s h Basic biological res e a r ch, studying the ecology of individuals, should continue to assess the value of restoring freshwater and species, and communities, is essential to understand the brackish marshes to the Elkhorn Slough area . sl o u g h ’s complex ecosystems. Res e a r chers have taken a close look at the biology of a few slough inhabitants. Continued Ter r estrial habitats have also undergone dramatic changes. res e a r ch documenting changes in the patterns of these species is Th r oughout the Elkhorn Slough watershed, agricultural lands essential for an awareness of overall changes in the slough sys- and housing developments have replaced native habitats. tem, including: movement patterns, foraging ecology, rep r o- Ter r estrial bird and mammal communities have undoubtedly CHAPTER ELEVEN u BIRDS & MAMMALS 203

Although sea otter numbers have increased in Elkhorn Slough in recent years, the population is declining statewide. Do sea otters that regularly feed in the slough live as long and reproduce at the same rate as sea otters in the open ocean? Contaminant testing on sea otters that frequent the slough may shed some light on these questions. Long-term monitoring of contaminant levels in slough inhabitants would help us track the overall health of the ecosystem.

Control of Nonnative Species and Native Predators Th e ne g a t i v e impacts of introduced plant and animal species on an ecosystem can be sever e, and often are irrev ersible. The effects of these introductions have rec e i v ed little attention in Elk h o r n Long-tailed weasel. Photo credit: John Sorenson. Slough, but could be widespread. Non n a t i v e species may out- compete native species, resulting in a precarious, unbalanced been altered, but these changes have not been documented. At system. As species at risk struggle to regain viable population this point, thorough assessment of populations in native and si z es, additional pres s u r es from nonnatives could potentially disturbed habitats is necessary to identify species at risk and pr eclude rec o ver y. Continued monitoring and selective rem o val plan appropriate management actions. of introduced species, such as the red fox, are necessary for the persistence of native species. Eff o r ts to continue and expand monitoring of all bird and mammal communities to assess the effects of increasing devel - As human use along the Mon t e r ey Bay coast continues to opment in the Elkhorn Slough area should be implemented. As in c r ease, direct and indirect effects pervade our natural habitats. mo r e lands are conver ted from agricultural or open space into Par ticular native species, usually habitat “ge n e r a l i s t s ” such as housing, wildlands and migratory corridors decrease in size and raccoons, crows, and ravens, tend to thrive amidst human habi- number; the effects of such changes must be studied. tation and become a threat to species at risk. Add i t i o n a l l y , the ne g a t i v e impact of domestic species (e.g., dogs, cats, and rats) Effects of Pollutants Pollutants from agricultural activities on native populations can be significant; the magnitude is gen- and residential and commercial development pose a serious erally linked to proximity of human communities to natural threat to birds and mammals in Elkhorn Slough. Still, very ar eas. With increased awareness of the sensitivity of our natural little is known about the effects of many pollutants on most habitats and their inhabitants to our presence, we can positivel y birds and mammals and their prey in the slough. Toxins influence the fate of Elkhorn Slo u g h ’s unique environ m e n t . entering the food chain can adversely affect the health of individuals and lower reproductive rates (Parkin 1998). 204 A PROFILE OF ELKHORN SL O U G H

Appendix 11.1. Birds of Elkhorn Slough

Seasons: Winter, November–February; Spring,(February) March–May; Summer, June–July; Fall,(July) August–October Abundance: c: common, almost certain to be seen in suitable habitat; u: uncommon,present but not certain to be seen; o: occasional,seen only a few times during a season; r: rare,not present every year; x: extraordinary, 1 or 2 records

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Loons — Family Gaviidae Red-throated Loon Gavia stellata c u o u Pacific Loon Gavia pacifica o o – o Common Loon Gavia immer c c o c Yellow-billed Loon Gavia adamsii x – – –

Grebes — Family Podicipedidae Horned Grebe Podiceps auritus u o o u Eared Grebe Podiceps nigricollis c u x u Pied-billed Grebe Podilymbus podiceps c u u u Red-necked Grebe Podiceps grisegena o o – o Clark’s Grebe Aechmophorus clarkii u u u u Western Grebe Aechmophorus occidentalis c c u c

Pelicans — Family Pelecanidae American White Pelican Pelecanus erythrorhynchos r r r r Brown Pelican Pelecanus occidentalis u u c c

Cormorants — Family Phalacrocoracidae Double-crested Cormorant Phalacrocorax auritus c c o c Brandt’s Cormorant Phalacrocorax penicillatus c c u c Pelagic Cormorant Phalacrocorax pelagicus u u u u

Herons, Bitterns — Family Ardeidae American Bittern Botaurus lentiginosus r r o r Black-crowned Night-Heron Nycticorax nycticorax r o – r Green Heron Butorides virescens u o r u Reddish Egret Egretta rufescens – – – x Cattle Egret Bubulcus ibis o r – r Snowy Egret Egretta thula c c u c Great Egret Ardea alba c c c c Great Blue Heron Ardea herodias c c c c

Ibises — Family Threskiornithidae White-faced Ibis Plegadis chihi r – r r

Scientific and common names follow the Check-list of North American Birds (7th ed.,1998) of the American Ornithologists’ Union.Original species account compiled by B.Ramer, D. Ramer, and J. Warriner (1978); updated by D.Roberson (1991). CHAPTER ELEVEN u BIRDS & MAMMALS 205

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Ducks, Geese, Swans — Family Anatidae Tundra Swan Cygnus columbianus r – – – Greater White-fronted Goose Anser albifrons o – – r Snow Goose Chen caerulescens r – – r Ross’s Goose Chen rossii r – – r Emperor Goose Chen canagica x – – – Canada Goose Branta canadensis o r – r Brant Branta bernicla o u r u Wood Duck Aix sponsa o – – o Mallard Anas platyrhynchos c c c c Gadwall Anas strepera c c c c Green-winged Teal Anas crecca c u – c American Wigeon Anas americana c u – u Eurasian Wigeon Anas penelope x x – – Northern Pintail Anas acuta c c u c Northern Shoveler Anas clypeata c c u c Blue-winged Teal Anas discors r u x u Cinnamon Teal Anas cyanoptera r c u u Canvasback Aythya valisineria c u – u Redhead Aythya americana r r – r Ring-necked Duck Aythya collaris u r – r Tufted Duck Aythya fuligula x – – – Greater Scaup Aythya marila c u o u Lesser Scaup Aythya affinis c u o u King Eider Somateria spectabilis x x x – Black Scoter Melanitta nigra o r – r White-winged Scoter Melanitta fusca c u o u Surf Scoter Melanitta perspicillata c c c c Harlequin Duck Histrionicus histrionicus o x – – Long-tailed Duck Clangula hyemalis o r x – Barrow’s Goldeneye Bucephala islandica x – – – Common Goldeneye Bucephala clangula c u – c Bufflehead Bucephala albeola c u – c Common Merganser Mergus merganser x x x x Red-breasted Merganser Mergus serrator c u o u Hooded Merganser Lophodytes cucullatus r – – – Ruddy Duck Oxyura jamaicensis c c c c

New World Vultures — Family Cathartidae Turkey Vulture Cathartes aura r c u u

Hawks, Kites, Eagles — Family Accipitridae Osprey Pandion haliaetus o o x o White-tailed Kite Elanus leucurus u u u u Northern Harrier Circus cyaneus u u o u Golden Eagle Aquila chrysaetos u u u u Bald Eagle Haliaeetus leucocephalus x – – – Sharp-shinned Hawk Accipiter striatus u u – u Cooper’s Hawk Accipiter cooperii u u o u Red-shouldered Hawk Buteo lineatus u u u u Red-tailed Hawk Buteo jamaicensis c c c c Rough-legged Hawk Buteo lagopus r – – – Ferruginous Hawk Buteo regalis r – – – American Kestrel Falco sparverius c c u c Merlin Falco columbarius o r – r Prairie Falcon Falco mexicanus r r x r Peregrine Falcon Falco peregrinus o r r r 206 A PROFILE OF ELKHORN SL O U G H

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

New World Quail — Family Odontophoridae California Quail Callipepla californica c c c c

Rails, Coots — Family Rallidae Clapper Rail (not seen since 1980) Rallus longirostris ? ? ? ? Virginia Rail Rallus limicola u o – o Sora Porzana carolina u o – o Common Moorhen Gallinula chloropus r r – r American Coot Fulica americana c c c c

Plovers — Family Charadriidae Black-bellied Plover Pluvialis squatarola c c u c American Golden-Plover Pluvialis dominica x – – o Snowy Plover Charadrius alexandrinus u u u u Semipalmated Plover Charadrius semipalmatus u c x c Mongolian Plover Charadrius mongolus – – – x Killdeer Charadrius vociferus c c c c

Stilts, Avocets — Family Recurvirostridae American Avocet Recurvirostra americana c c c c Black-necked Stilt Himantopus mexicanus c c c c

Sandpipers, Phalaropes — Family Scolopacidae Willet Catoptrophorus semipalmatus c c u c Greater Yellowlegs Tringa melanoleuca c c r c Lesser Yellowlegs Tringa flavipes o o – u Wandering Tattler Heteroscelus incanus x x – x Spotted Sandpiper Actitis macularia u u o u Whimbrel Numenius phaeopus u c r c Long-billed Curlew Numenius americanus c c o c Marbled Godwit Limosa fedoa c c u c Ruddy Turnstone Arenaria interpres c c r c Black Turnstone Arenaria melanocephala – r x r Surfbird Aphriza virgata – x – x Red Knot Calidris canutus o u x u Sanderling Calidris alba c c u c Dunlin Calidris alpina c c x c Semipalmated Sandpiper Calidris pusilla – – – o Western Sandpiper Calidris mauri c c x c Least Sandpiper Calidris minutilla c c r c Baird’s Sandpiper Calidris bairdii – – – u Little Stint Calidris minuta – – – x Pectoral Sandpiper Calidris melanotos – – – u Sharp-tailed Sandpiper Calidris acuminata – – – r Buff-breasted Sandpiper Tryngites subruficollis – – – x Ruff Philomachus pugnax x – – x Short-billed Dowitcher Limnodromus griseus c c x c Long-billed Dowitcher Limnodromus scolopaceus c c – c Stilt Sandpiper Calidris himantopus – – – r Common Snipe Gallinago gallinago u u – u Wilson’s Phalarope Phalaropus tricolor x u o u Red-necked Phalarope Phalaropus lobatus x u r c Red Phalarope Phalaropus fulicaria r r x o

Jaegers, Gulls, Terns — Family Laridae Parasitic Jaeger Stercorarius parasiticus – – – o CHAPTER ELEVEN u BIRDS & MAMMALS 207

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Heermann’s Gull Larus heermanni u o c c Franklin’s Gull Larus pipixcan x x x r Laughing Gull Larus atricilla x – – – Bonaparte’s Gull Larus philadelphia c c o c Ring-billed Gull Larus delawarensis c c u c Mew Gull Larus canus u o – o California Gull Larus californicus c c u c Herring Gull Larus argentatus c o – o Glaucous Gull Larus hyperboreus r x – – Thayer’s Gull Larus thayeri c o – o Western Gull Larus occidentalis c c c c Glaucous-winged Gull Larus glaucescens c c o c Black-legged Kittiwake Rissa tridactyla x x – x Sabine’s Gull Xema sabini – – – x Swallow-tailed Gull Creagrus furcatus – – x – Elegant Tern Sterna elegans x r c c Royal Tern Sterna maxima – – – x Caspian Tern Sterna caspia x c c c Forster’s Tern Sterna forsteri u c c c Common Tern Sterna hirundo – u r u Arctic Tern Sterna paradisaea – o – o Least Tern Sterna antillarum – o r o Black Tern Chlidonias niger – o – o Black Skimmer Rynchops niger – x – x

Auks, Murres — Family Alcidae Common Murre Uria aalge r r r r Thick-billed Murre Uria lomvia x – – – Pigeon Guillemot Cepphus columba – – – r Craveri’s Murrelet Synthliboramphus craveri – – – x Ancient Murrelet Synthliboramphus antiquus x – – – Cassin’s Auklet Ptychoramphus aleuticus r – – – Rhinoceros Auklet Cerorhinca monocerata o – – r

Pigeons, Doves — Family Columbidae Band-tailed Pigeon Columba fasciata u c u u Rock Dove Columba livia c c c c Mourning Dove Zenaida macroura c c c c White-winged Dove Zenaida asiatica – – – x

Roadrunners — Family Cuculidae Greater Roadrunner Geococcyx californianus – x – x

Owls — Families Tytonidae and Strigidae Barn Owl Tyto alba u u u u Short-eared Owl Asio flammeus r r r r Long-eared Owl Asio otus x – – – Great Horned Owl Bubo virginianus c c c c Burrowing Owl Athene cunicularia u u u u

Swifts — Family Apodidae Vaux’s Swift Chaetura vauxi – o – o White-throated Swift Aeronautes saxatalis – x – –

Hummingbirds — Family Trochilidae Anna’s Hummingbird Calypte anna c c c c Rufous Hummingbird Selasphorus rufus – o – o Allen’s Hummingbird Selasphorus sasin – c c – 208 A PROFILE OF ELKHORN SL O U G H

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Kingfishers — Family Alcedinidae

Belted Kingfisher Ceryle alcyon u u u u

Woodpeckers — Family Picidae Acorn Woodpecker Melanerpes formicivorus u u u u Northern Flicker Colaptes auratus c c u c Red-breasted Sapsucker Sphyrapicus ruber o o – o Nuttall’s Woodpecker Picoides nuttallii c c c c Downy Woodpecker Picoides pubescens u u u u Hairy Woodpecker Picoides villosus u u u u

Tyrant Flycatchers — Family Tyrannidae Olive-sided Flycatcher Contopus cooperi – u u – Western Wood-Pewee Contopus sordidulus – – – u Pacific-slope Flycatcher Empidonax difficilis x c c u Black Phoebe Sayornis nigricans c c c c Say’s Phoebe Sayornis saya u r – u Ash-throated Flycatcher Myiarchus cinerascens x u u r Western Kingbird Tyrannus verticalis – r x r Tropical Kingbird Tyrannus melancholicus x – – r Scissor-tailed Flycatcher Tyrannus forficatus – x – –

Shrikes — Family Laniidae Loggerhead Shrike Lanius ludovicianus u u u u

Vireos — Family Vireonidae Hutton’s Vireo Vireo huttoni c c c c Red-eyed Vireo Vireo olivaceus – – – x Warbling Vireo Vireo gilvus – c u c

Crows, Jays — Family Corvidae Steller’s Jay Cyanocitta stelleri r r – – Western Scrub-Jay Aphelocoma californica c c c c American Crow Corvus brachyrhynchos c c c c Common Raven Corvus corax r r r r

Larks — Family Alaudidae Horned Lark Eremophila alpestris u r – u

Swallows — Family Hirundinidae

Tree Swallow Tachycineta bicolor u c c c Violet-green Swallow Tachycineta thalassina r c c c Bank Swallow Riparia riparia x r r r Cliff Swallow Petrochelidon pyrrhonota – c c c Northern Rough-winged Swallow Stelgidopteryx serripennis x o r r Barn Swallow Hirundo rustica x c c c

Babblers — Family Timaliidae Wrentit Chamaea fasciata c c c c

Chickadees, Titmice — Family Paridae Oak Titmouse Baeolophus inornatus c c c c Chestnut-backed Chickadee Poecile rufescens c c c c CHAPTER ELEVEN u BIRDS & MAMMALS 209

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Bushtits — Family Aegithalidae Bushtit Psaltriparus minimus c c c c

Creepers — Family Certhiidae Brown Creeper Certhia americana u u u u

Nuthatches — Family Sittidae Red-breasted Nuthatch Sitta canadensis o – – o Pygmy Nuthatch Sitta pygmaea u u u u

Wrens — Family Troglodytidae House Wren Troglodytes aedon x u – u Winter Wren Troglodytes troglodytes u r – r Bewick’s Wren Thyromanes bewickii c c c c Marsh Wren Cistothorus palustris c c c c

Kinglets — Family Regulidae Ruby-crowned Kinglet Regulus calendula c c – c

Thrushes — Family Turdidae Western Bluebird Sialia mexicana u r – – Townsend’s Solitaire Myadestes townsendi x – – – Swainson’s Thrush Catharus ustulatus – c u r Hermit Thrush Catharus guttatus u u – u Varied Thrush Ixoreus naevius u r – r American Robin Turdus migratorius c c u c

Mockingbirds, Thrashers — Family Mimidae Northern Mockingbird Mimus polyglottos u u u u California Thrasher Toxostoma redivivum o o o o

Starlings — Family Sturnidae European Starling Sturnus vulgaris c c c c

Wagtails, Pipits — Family Motacillidae White Wagtail Motacilla alba x – – – American Pipit Anthus rubescens c u – c Red-throated Pipit Anthus cervinus – – – x

Waxwings — Family Bombycillidae Cedar Waxwing Bombycilla cedrorum c c – c

Wood-Warblers — Family Parulidae Orange-crowned Warbler Vermivora celata u c c c Nashville Warbler Vermivora ruficapilla x r – r Yellow-rumped Warbler Dendroica coronata c c – c Black-throated Gray Warbler Dendroica nigrescens – o – o Townsend’s Warbler Dendroica townsendi c u – u Yellow Warbler Dendroica petechia – u o u MacGillivray’s Warbler Oporornis tolmiei – o – o Wilson’s Warbler Wilsonia pusilla – c c c Northern Waterthrush Seiurus noveboracensis x – – – Common Yellowthroat Geothlypis trichas u u u u American Redstart Setophaga ruticilla x – – – 210 A PROFILE OF ELKHORN SL O U G H

COMMON NAME SCIENTIFIC NAME Winter Spring Summer Fall

Tanagers — Family Thraupidae Western Tanager Piranga ludoviciana – u – u

Emberizids (Towhees, Sparrows) — Family Emberizidae

California Towhee Pipilo crissalis c c c c Spotted Towhee Pipilo maculatus c c c c Brewer’s Sparrow Spizella breweri – x – – Grasshopper Sparrow Ammodramus savannarum r – – r Saltmarsh Sharp-tailed Sparrow Ammodramus caudacutus – – – x Fox Sparrow Passerella iliaca u u – u Lark Bunting Calamospiza melanocorys – – – x Savannah Sparrow Passerculus sandwichensis c c c c Lincoln’s Sparrow Melospiza lincolnii u u – u Song Sparrow Melospiza melodia c c c c Swamp Sparrow Melospiza georgiana o – – o White-throated Sparrow Zonotrichia albicollis x – – – White-crowned Sparrow Zonotrichia leucophrys c c c c Golden-crowned Sparrow Zonotrichia atricapilla c c – c Dark-eyed Junco Junco hyemalis c c u c Smith’s Longspur Calcarius pictus – – – x

Cardinals (Grosbeaks) — Family Cardinalidae Black-headed Grosbeak Pheucticus melanocephalus – u u u

Blackbirds — Family Icteridae Bobolink Dolichonyx oryzivorus – – – r Western Meadowlark Sturnella neglecta c c c c Yellow-headed Blackbird Xanthocephalus xanthocephalus x o – o Red-winged Blackbird Agelaius phoeniceus c c c c Tricolored Blackbird Agelaius tricolor c u o c Rusty Blackbird Euphagus carolinus x – – – Brewer’s Blackbird Euphagus cyanocephalus c c c c Brown-headed Cowbird Molothrus ater u u u u Bullock’s Oriole Icterus bullockii r u – u

Finches — Family Fringillidae Purple Finch Carpodacus purpureus c c c c House Finch Carpodacus mexicanus c c c c Red Crossbill Loxia curvirostra r – – – Pine Siskin Carduelis pinus c c u c American Goldfinch Carduelis tristis c c c c Lesser Goldfinch Carduelis psaltria c c c c Lawrence’s Goldfinch Carduelis lawrencei – r – –

Old World Sparrows — Family Passeridae House Sparrow Passer domesticus c c c c CHAPTER ELEVEN u BIRDS & MAMMALS 211

Appendix 11.2.Mammals of the Elkhorn Slough Area

Marsupials — Order Marsupialia Rodents — Order Rodentia Virginia opossum Didelphis virginiana California ground squirrel Spermophilus beecheyi western gray squirrel Sciurus griseus Shrews and Moles — Order Insectivora eastern gray squirrel Sciurus carolinensis Trowbridge’s shrew Sorex trowbridgii fox squirrel Sciurus niger vagrant shrew Sorex vagrans Botta’s pocket gopher Thomomys bottae ornate shrew Sorex ornatus California pocket mouse Chaetodipus californicus shrew-mole Neurotrichus gibbsii Heermann’s kangaroo rat Dipodomys heermanni broad-footed mole Scapanus latimanus narrow-faced kangaroo rat Dipodomys venustus beaver Castor canadensis Bats — Order Chiroptera western harvest mouse Reithrodontomys megalotis little brown bat Myotis lucifugus parasitic mouse Peromyscus californicus Yuma bat Myotis yumanensis deer mouse Peromyscus maniculatus long-eared bat Myotis evotis piñon mouse Peromyscus truei fringed bat Myotis thysanodes dusky-footed woodrat Neotoma fuscipes long-legged bat Myotis volans California meadow vole Microtus californicus California bat Myotis californicus muskrat Ondatra zibethica western small-footed bat Myotis ciliolabrum house mouse Mus musculus western pipistrel Pipistrellus hesperus Norway rat Rattus norvegicus big brown bat Eptesicus fuscus black rat Rattus rattus western red bat Lasiurus blossevillii hoary bat Lasiurus cinereus Rabbits — Order Lagomorpha pallid bat Antrozous pallidus black-tailed jackrabbit Lepus californicus guano bat Tadarida brasiliensis Audubon’s cottontail Sylvilagus audubonii brush rabbit Sylvilagus bachmani Carnivores — Order Carnivora raccoon Procyon lotor Ungulates — Order Artiodactyla ringtail Bassariscus astutus black-tailed deer Odocoileus hemionus long-tailed weasel Mustela frenata sea otter Enhydra lutris badger Taxidea taxus Whales — Order Cetacea spotted skunk Spilogale putorius gray whale Eschrichtius robustus striped skunk Mephitis mephitis harbor porpoise Phocoena phocoena coyote Canis latrans red fox Vulpes vulpes gray fox Urocyon cinereoargenteus mountain lion Felis concolor bobcat Lynx rufus

Sea Lions and Seals — Order Pinnipedia California sea lion Zalophus californianus harbor seal Phoca vitulina

List compiled by E.Schafer (1986) for the Elkhorn Slough National Estuarine Research Reserve.Little information is available regarding occurrence and abundance of mam- mal species in this region and therefore is not presented in this appendix.Known information is included in the text.This list represents both known and potential pres- ence at the slough. 212 A PROFILE OF ELKHORN SL O U G H

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