Conservation and Management

Effects Of Human Activity

Shooting And Trapping

Isolated incidents of Snowy Plovers being shot on California coast (GWP) probably have not had any significant impact on this population.

Pesticides And Other Contaminants/Toxics

At agricultural waste-water ponds in the San Joaquin Valley, CA, where selenium causes embryonic deformities in Black-necked Stilts and Killdeers, deformities were not unusually high in Snowy Plovers, suggesting selenium is not as toxic to this species as to some other shorebirds (J. Skorupa pers. comm.).

At Point Reyes Beach, Marin County, CA an unusually high proportion of clutches that failed to hatch contained high levels of mercury (Schwarzbach et al. 2005). A sample of eggs from the southern California coast in San Diego County were analyzed for a wide variety of organic and inorganic contaminants in the early 1990s and none were found in sufficient concentrations to be a cause for concern (Hothem and Powell 2000).

On the Pacific coast, Snowy Plovers are often oiled during spills. Many appear to pick up the oil on their feet and transfer it to their plumage (GWP). In one well documented spill, M/V New Carrissa, at least 45 plovers on the Oregon coast were oiled (Magnam et al. 2001).

Collisions With Stationary/Moving Structure Or Objects

Although Snowy Plovers have been killed in San Francisco and Monterey bays by collisions with wire fencing erected to protect nests from predators, numbers have been too small to significantly impact populations (M. Parker pers. comm., GWP). Plovers have also been injured and killed by colliding and sometimes entangling in the net tops of exclosures erected to protect their nests (D. George in litt.). These sources of mortality should be considered in plans promoting fencing or exclosures to protect plover nests.

Fishing Nets And Line

Snowy Plovers have been snared by discarded monofilament fishing line on the California coast (JSW and JCW). This may cause loss of toes or feet or even death of the adult. Effect of this source of mortality on populations is unknown.

Degradation Of Habitat: Breeding And Wintering

On U.S. coasts, habitat degradation, caused primarily by expanding beach-front development and recreation, has likely been responsible for a significant decline in the size of breeding populations. Use of the exotic beach grass (Ammophila arenaria) to stabilize dunes along Pacific Coast has also reduced the extent of open nesting habitat (Page and Stenzel 1981, Wilson-Jacobs and Meslow 1984). Frequent mechanical raking of beaches for removal of garbage, kelp, and other debris on the s. California coast makes beaches unsuitable for nesting and probably harms food resources for wintering plovers (Page et al. 1986). Dugan et al. (2003) report that over 160 km of southern California sandy beaches are groomed regularly and that grooming decreases the species richness, abundance, and biomass of wrack-associated invertebrates that are likely important plover prey resources.

On the U.S. Pacific coast, small numbers of plovers with foot injuries have been found with fine synthetic fibers, or human hair, wrapped around a foot causing swelling and sometimes loss of toes (D. George in litt.).

In the Great Basin, at Farmington Bay, Great Salt Lake, UT, between 2003 and 2008, stands of the exotic common reed (Phragmites australis) expanded from 25 to 130 ha eliminating extensive open areas previously used by nesting by Snowy Plovers (J. Cavitt in litt.).

On Great Plains, breeding habitat has contracted at Great Salt Plains, OK, where half the salt flat has been flooded for water impoundments and exotic salt cedar (Tamarix gallica) has invaded a significant amount of remaining stream-side habitat (Hill 1993). At Salt Plains NWR, OK invasive salt cedar decreased the extent of alkaline flat by >240 ha from 1941-1989 and with water impoundments has likely resulted in a Snowy Plover population decline (Koenen et al. 1996a). The salt cedar also provides cover for predators, such as coyotes, which prey on plover eggs and chicks (Winton et al. 2000). Elsewhere in Kansas and Oklahoma, breeding habitat along rivers is degraded by damming, water withdrawals, and vegetation encroachment (L. Hill pers. comm.). In the Playa Lakes region of Texas, a decrease in the volume of springs from pumping of the Ogallala aquifer and sedimentation from agriculture has a potentially negative impact on plover nesting (Conway et al. 2005).

Disturbance At Nest, Roosts And Feeding Sites

Incubating birds often run from their nests at approach of people or pets; such disturbances may result in increased clutch losses to blowing sand on windy days (Warriner et al. 1986). Humans and dogs also disturb roosting birds on heavily used recreational beaches. At Coal Oil Point, Santa Barbara County, CA, disturbance to wintering plovers was 16 times greater at a public than a protected beach. On average, each plover was disturbed once every 27 min on weekends and every 43 min on weekdays on the public beach. Feeding rates decreased with human activity. Plovers were more likely to fly from dogs, horses or crows than from humans. They reacted to disturbance at 40 m but relatively few people and dogs beyond 30 m disturbed them. At all distances, dogs had a higher probability of disturbing plovers than humans; plovers reacted at about twice the distance to dogs as to people (Lafferty 2001).

Human/Research Impacts

On the central California coast, nests are destroyed by people stepping on them, deliberately taking eggs, trampling eggs while riding horses, crushing eggs (and occasionally incubating adults) with vehicles, and causing abandonment by camping next to nests overnight (D. George pers. comm., JSW and JCW). Also, on the northern California coast, humans have stepped on nests, driven over nests, vandalized exclosures erected to protect nests, and kept adults from brooding chicks (Colwell et al 2005). People were responsible for destruction of at least 14% of 189 nests over 6 yr at 1 coastal California site (Warriner et al. 1986) and 10% of 83 nests in nw. Florida in 1989 (Chase and Gore 1989). At Point Reyes, Marin County, CA, Snowy Plover chick loss was 72% greater than expected on weekends in 1999 and 69% greater in 2000, suggesting increased recreation on weekends negatively affected chick survival (Ruhlen et al. 2003). At Coal Oil Point, CA, one chick was killed by an unleashed dog (Lafferty et al. 2006). At Oceano Dunes State Vehicular Recreation Area, CA, 6 adult Snowy Plovers found dead between 2002 and 2008 were probably killed by being struck by vehicles (R. Glick in litt.). In se. Colorado, cattle trample nests (Mabee and Estelle 2000).

Banding of nesting birds can result in nest desertion and was believed to be responsible for the abandonment of 4 of 187 nests on the California coast (Warriner et al. 1986). Leg injury can be caused by bands that are too small (USFWS size 1B); a special band size (1P) with an internal diameter of 2.85 mm is recommended to minimize chance of leg injury to Snowy Plovers. For Kentish Plovers, injuries caused by mud accumulating between the tibio-tarsus and metal band caused swelling of the leg below the band and resulted in eventual loss of the foot; rate of injury was 1.94% of 412 banded birds. Injuries were eliminated by placing the metal band on the upper leg (Amat 1999). Similar injuries have been observed in Snowy Plovers in California (GWP).

Introduced and expanding native predator populations, deleterious to Snowy Plover reproductive success, arise directly and indirectly from human activity. Since the late 1800s non-native Red Foxes have been introduced into California by escaping from fur farms and fox hunters, and intentional releases by pet and fur farm owners. Their populations have expanded into the San Francisco Bay, Monterey Bay, and southern coastal regions of California (Lewis et al. 1999). By the mid 1980’s they were identified as a major cause of plover nest loss at Monterey Bay (Neuman et al. 2004) where efforts are currently underway to control them (GWP). Invasive red foxes are also predators of nesting Snowy Plovers on the Oregon coast (D. George in litt.).

Common Ravens have recently expanded their range into coastal regions of Monterey, San Luis Obispo and Santa Barbara, counties, CA. They were first reported depredating Snowy Plover nests at Monterey Bay, Oceano Dunes State Vehicular Recreation Area, and Vandenberg Air Force Base between 2001 and 2003 (GWP, D. George pers. comm., N. Francine in litt.). Their arrival is well documented at Monterey Bay where during extensive monitoring from 1983-2008 ravens were not recorded depredating any plover nests until 12 were taken in 2002. Although ravens were responsible for few depredated nests from 2003-2006 they took at least 36 in 2007 and 21 in 2008 (GWP).

Gull-billed Terns, a known predator of Kentish Plover chicks (Fraga and Amat 1996), only began breeding in southern San Diego County, CA in 1986. Their numbers expanded to 24-40 pairs during the 2000s (Molina 2008) and the terns are now a documented predator of Snowy Plover chicks in San Diego Bay (R. Patton in litt.).

At Great Salt Lake UT, success rates of nesting by plovers in some locations are approaching zero because of exploding numbers of raccoons and Red Foxes (J. Cavitt in litt.).

Management

Conservation Status

The population breeding along Pacific Coast of U.S. and Baja California is listed by U.S. Fish and Wildlife Service as Threatened. The species also receives some protection through the following state designations: Washington: Endangered; Oregon: Threatened; California: Species of Special Concern; Mississippi: Endangered; Florida: Threatened; Puerto Rico: Threatened; Kansas: Threatened.

Measures Proposed And Taken

The Pacific Coast population was designated Threatened by the U.S. Fish and Wildlife Service in March 1993; subsequently, critical habitat has been identified and a recovery plan published (USFWS 2007). The plan suggests a recovery target of 3,000 breeding adults for the U.S. Pacific coast and regional targets for six contiguous coastal sub-units between the Canadian and Mexican borders. A population viability analysis indicates 1 fledgling per male per year is necessary for population stability based on adult and juvenile survival rates that might be optimistic (GWP). The recovery plan suggests closing upper beach areas to the public during the nesting season, predator management, and habitat restoration as primary conservation actions. It also calls for and contains protocols for annual range-wide surveys of breeding adults between late May and early June and for wintering plovers in January.

By 2008, many upper beach areas were signed closed and roped off from the public during the nesting season in coastal Washington, Oregon, and in California; habitat restoration, chiefly removal of exotic Ammophila arenaria to open up nesting habitat, was being pursued; and fencing of selected individual nests as a protection against predators, and/or removal of nest predators was employed at some locations (Colwell et al. 2008, Lauten et al. 2008, Page et al 2008, Pearson et al. 2008). The range-wide survey of breeding adults had been conducted annually since 2002 and the winter survey since January 2004.

In response to protection of individual nests with fencing, and later removal of feral red foxes and skunks by the U.S. Fish and Wildlife Service to improve adult and chick survival rates in s. Monterey Bay, CA, clutch hatching success increased from 43% ± 12 SD (n= 7) during pre-management years to 68% ±12 SD (n= 9) during the management period; however, chick fledging rates declined simultaneously from 42% ± 6 SD to 30% ± 12 SD, respectively. The result was a similar number of chicks fledged per male between the two periods (0.86 ± 28 SD and 0.81 ± 0.29 SD, respectively). During the management phase the number of desertions accompanied by the apparent death of an adult increased, suggesting exclosures may increase adult mortality rates (Neuman et al. 2004). At Monterey Bay, CA, small skunks are able to squeeze between the 5 cm by 10 cm wire mesh used for nest exclosures (GWP) but their depredation of nests has not been great enough to negate the overall value of exclosures for increasing nesting success. Also, at this location there have been a few instances of Great Horned Owls entering and becoming trapped inside nest exclosures with netting tops (D. George and C. Eyster pers. comm.).

Hatching success of exclosed nests was significantly greater than unexclosed nests on Humboldt County, CA beaches; however, exclosed nests also experienced a significantly higher desertion rate with adult mortality being the suspected cause of some abandonment (Hardy and Colwell 2008). In se. Colorado there was no significant difference in nest survivorship between nests inside and outside nests exclosures because the fencing did not prevent small rodents and snakes from preying on eggs (Mabee and Estelle 2000).

As a result of these studies, it is recommend that nest exclosures be used only sparingly and temporarily (Neuman et al. 2004). Nest exclosures can be a valuable management tool but because they increase the frequency of nest abandonment and the potential for adult depredation, they should be monitored closely (Hardy and Colwell 2008).

In extreme circumstances captive breeding is also a potential tool for increasing populations; young, reared from eggs in captivity and released 41–72 (median 57) days after hatching, have successfully nested in coastal California (Page et al. 1989). At Coal Oil Point, Santa Barbara County, CA, researchers responded to high rates of nest loss from skunks by replacing plover eggs with wooden facsimiles, placing real eggs in incubators until they were ready to hatch, and then returning them to their original nest where they were hatched by the parent birds (C. Sandoval in litt.). Small numbers of chicks or eggs that were separated from their parents are regularly reared at Monterey Bay Aquarium, CA; they are released after they are able to fly and many subsequently nest on the California coast.

It has been suggested that clearing invasive vegetation in different places in different years to create temporary nesting areas may mimic the cyclical nature of plover habitat and release populations from high predation pressure along the Pacific coast (Powell and Collier 2000).

At Coal Oil Point Santa Barbara County, CA fencing a wintering area resulted in a 50% decline in disturbance of birds, a return to nesting after an absence of decades, and increased protection against trampling of eggs by humans; however, docents are necessary during most daylight hours to enforce compliance of the closed area (Lafferty et al. 2006). Modeling suggests that a 400 m stretch of beach with a 30 m buffer and a prohibition against dogs provides the most protection for wintering Snowy Plovers and the least impact to beach recreation (Lafferty 2001).

In Florida, some larger Snowy Plovers nesting areas are currently protected through signing and roping prior to egg laying around the beginning of March (J. Himes in litt.). At other sites nests are signed and roped-off as they are found. Still, there are many miles of beach where nesting occurs, nests are not posted, and human disturbance is an issue (R. Pruner in litt.).

Inland, at Salt Plains NWR in Oklahoma, ridges constructed on playa to prevent nests from flooding and electrical fences erected around nesting areas to reduce mammal predation did not reduce losses to flooding or significantly reduce annual egg depredation (Koenen et al 1996b).

Effectiveness Of Measures: The Species’ Response

Along the U.S. Pacific coast an increase in adult numbers on range-wide surveys from 2002-2004 (see Population: trends) may have been the response to protective actions at many coastal sites. However, since then numbers on the range-wide surveys have declined, possibly due to low overwinter survival (GWP). Since initial coast-wide surveys in California from 1977-80, plovers have disappeared as breeders from Del Norte Co. (M. Colwell, pers comm.), and are absent to nearly absent on San Miguel I. where 84 adults were found in July 1979 (Page and Stenzel 1981). In contrast, intensive protective actions have resulted in the recolonization of Coal Oil Point, Santa Barbara County, CA by nesting Snowy Plovers (Lafferty et al. 2006). The size of the breeding population has increased in Oregon (D. Lauten pers. comm.) but the populations in Washington State and in Humboldt County, CA, have recently found to be sinks that rely on immigrants from California and Oregon for sustaining their viability (Colwell et al. 2008, Pearson et al. 2008).

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