WETLAND AVIAN SURVEY. Observation and Monitoring of Birds at the Lake Yosemite Leakage Wetland. Katharine W. Cook

Transcription

1 WETLAND AVIAN SURVEY Observation and Monitoring of Birds at the Lake Yosemite Leakage Wetland Katharine W. Cook

2 Abstract A leakage wetland on the northeastern edge of Lake Yosemite, Merced County, California, between the extensive grasslands of the Cyril Smith Trust Lands and the Gallo Brothers Ranch and the deep waters of Lake Yosemite, appears to be an important habitat for water birds. This wetland is about 1 km northwest of UC Merced s Vernal Pools and Grassland Reserve. I surveyed the birds at this wetland to collect information on avian abundance and diversity. A portion of this wetland has been proposed by the US Fish and Wildlife Service and California Audubon for consideration as a nesting habitat restoration project for the threatened Tricolored Blackbird. In anticipation of this future action, we wanted to understand the current bird use of this wetland. I documented the birds and their activities on fifteen weekly surveys between November 2014 and April Fifty one species and 2,100 individuals were documented. The muddy shoreline attracted various species of Calidris sandpipers and other shorebirds. Green-winged Teal and Bufflehead sought the shallow waters for food and places to rest. Northern Harriers, White-tailed Kites and other raptors were seen searching for prey or perching on fence posts. A Peregrine was seen on one day. We found that this small wetland supported a rich diversity and sizeable numbers of birds. Shallow wetlands are not common in eastern Merced County, making this an important habitat for waterbirds. I completed this project to fulfill the requirement for a BIO 199, Independent Study course. Introduction Bird surveys are useful for documenting the occurrence and relative abundance of birds in an area. They can help to determine the habitat needs of species and by cataloging observed behaviors of species, surveys can fill gaps in knowledge. Surveys are especially important for determining the occurrence of species with populations at risk. Conservation and restoration acts tend to have the same goals, no matter what the target species. The overall goal is to sustain species distribution, diversity, and populations, as well as to maintain abundant breeding, migratory, and nonbreeding habitats (Waterbird Conservation for the Americas 2007). Documented observations of ecosystems and interacting species can assist project planning for habitat restoration efforts. By surveying how avian species utilize an area, we can characterize the state of the wetland habitats and determine their use, which can further help in developing a plan for restoration. This tactic has proven useful in waterbird habitat restoration projects in the Central Valley such as the one described by Shuford, (et al. 1998). The interest in restoration of the Lake Yosemite leakage wetland habitat is related to the conservation of the Tricolored Blackbird. Tricolored Blackbird populations have been declining for many years (The Tricolored Blackbird Working Group 2014). This species was given an emergency listing as Endangered by the State of California in 2014 (see Center for Biological Diversity petition, 2014). Tricolored Blackbirds were once abundant in the Central Valley, breeding in large colonies in the tall native grasses that used to spread across the valley. Much of the native grassland is gone and replaced by farmland, forcing the Tricolored Blackbird to shift to nesting in agricultural fields. However, their large concentrated breeding numbers makes them

3 extremely vulnerable if crops are harvested before the young have fledged. Due to these conflicting conditions, the Tricolored Blackbirds have been unable to establish large numbers in new generations. (Swarth 2014) These factors have made this species a concern for conservationists and the Tricolored Blackbird Working Group works to secure habitat and protect land utilized by this species. (The Tricolored Blackbird Working Group 2014). Other groups, organizations, and scientists conduct nesting population surveys. For example, Dr. Robert J. Meese of UC Davis holds statewide Tricolored Blackbird surveys. His work, and that of others (see Conard and Airola, 2015; a special issue of the Central Valley Bird Club devoted entirely to articles on the current status of Tri-colored Blackbird populations), have led to efforts to petition and list the Tricolored Blackbird as endangered. Emergency listing did occur, but this species was removed from the list in June There have been efforts, encouraged and supported by California Department of Fish and Wildlife and California Audubon, where farmers with nesting colonies in their fields are subsidized to delay harvesting until the breeding period is over. Unfortunately, many farmers do not participate in this program. For this and other reasons, scientists are hoping to lure Tricolored Blackbirds away from nesting in croplands by restoring and enhancing nesting habitat in natural areas adjacent to the Valley or in the nearby low-elevation foothills. For this study, the avian activity of species at the leakage wetland at Lake Yosemite has been monitored over the course of six months (November 2014 to April 2015). Using a spotting scope and binoculars, the marshland was scanned from several pre-designated survey points. Surveys were carried out at least once a week and all data were collected and transferred to computerized spreadsheets. Methods The main bird observer was Katharine Cook. Daniel Toews joined me on 13 surveys and Chris Swarth on three surveys. On a few surveys I was accompanied Ian Ojeda-Vasquez and Becca Fenwick. Surveys were made using 8.5X and 10X binoculars, and a 20X Vortex spotting scope. Sightings and behavior were recorded on a data sheet. We had copies of the Audubon field guide and the Sibley field guide to aid in identification. Weather condition, time of observation, and behavior of the birds, as well as the portion of wetland utilized (i.e. swimming or shore feeding) were documented. Surveys lasted 45 to 60 minutes. If birds flew off before we could identify or make an accurate count, we made a best guess as to the species and we made an estimation of abundance. Columns were set up on the data sheet for each variable and rows were designated for the species as they were observed and identified. Data were entered into an Excel spreadsheet to analyze the results.

4 Study Area Lake Yosemite is a man-made freshwater reservoir that receives water from the Merced River (Figure 1). The water is used for crop irrigation and the lake is managed as County Park used primarily for picnicking, boating, jet skis, and water skiing. The reservoir is owned and managed by the Merced Irrigation District, which distributes the water via two south-flowing canals (Fairfield and Le Grand) to eastern Merced County farmers to support Central Valley agriculture. Water flows into the leakage wetland from the Merced canal on the northwest portion of the lake, flowing alongside the northeast border. Figure 1. Aerial photograph of Lake Yosemite. Leakage wetland boundary is highlighted in pink. During times of drought, the lake is utilized primarily for agricultural and recreational use is put on hold. (Merced County. 2014) During normal seasons, water may still be distributed but this does not bring as large of an affect as it does during a drought. Because of this, water levels fluctuate seasonally. The leakage wetland study area, which is within The Nature Conservancy s Cyril Smith Trust Reserve, is about 200 m in length and about 150 m in width (Figure 2). Maximum depth during this study was about 0.5 m. Based on my observations during this study, the leakage wetland was not at full capacity because of the on-going, four-year drought. The primary survey point was located on the east side of the wetland at UTM coordinates 10S Easting , Northing Additional survey points were at 10S E , N ; 10S E , N ; and 10S E , N (see Figure 2). Emergent marsh vegetation rims the west, north and eastern edges of the wetland. This vegetation is most extensive on the northeastern edge. Cattails (Typha sp) and Figure 2. Aerial photograph of Northeast shore of Lake Yosemite showing leakage wetland just north of canal.

5 rushes (Juncus sp.) dominate the marsh. A few copses of wild rose (Rosa sp) and blackberry (Rubus sp.) bushes occur along the wetland edges. As the water receded, in late spring the smectic clay dried and cracked, restricting most plant growth, however patches of grasses and other low vegetation were observed around the water s edge. Results Out of a total count of 2,100 individual birds encountered during this study, 51 different avian species were observed using the Lake Yosemite leakage wetland. The most common waterfowl were Mallards, Gadwall, American Wigeon, Northern Shovelers, and Buffleheads. Mallards were found in high frequencies in December and February, with a maximum count on 3 December of 47 individuals. Mallards were found in the leakage wetland on 13 of 15 survey days. A total of 60 Gadwall were documented on 10 November and were found utilizing the area on 11 survey days. On 10 November, 34 American Wigeon were documented. High numbers of American Wigeon were also observed between 16 January and 5 February, with 30 to 36 birds encountered. American Wigeon were present on 10 of 15 surveys. Waterbirds tended to rest along the southeastern edge of the wetland near the mouth of the outflowing canal. Northern Shovelers were often found swimming or feeding in the water here. The maximum number of shovelers was on 22 January with 35 birds present, and they were found on nine survey days. Green-winged Teal were frequently seen in early December, but were in highest abundance on 5 February. Like other waterfowl, the teal were found swimming and feeding on the water, but were also seen feeding on the western shore. Individuals were found on nine survey days. Bufflehead were also common but were not found in as large numbers as the dabbling ducks. The highest counts were on 26 November and 3 December with eight individuals (one male and seven females.) Usually only one pair or three individuals were present. Bufflehead were found on 10 of the 15 survey days. On 19 February and 5 March, 50 unidentified ducks flew off before they could be accurately identified. American Avocets arrived in early March and on 21 April they were performing territorial displays and squabbling with one another. These shorebirds were found on six survey days. Common small shorebirds in the area were Western Sandpipers, Least Sandpipers, and Dunlin. Western Sandpipers were found in greatest abundance on 16 January, with 29 recorded individuals and they were found on nine surveys. As for Least Sandpiper, on 3 December there were 40 individuals. They were found on seven surveys. 60 Dunlin were recorded on 10 December and this species was found on nine surveys. Dunlin and the other small sandpipers foraged along the water s edge by probing in the mud for invertebrates. On seven of the survey days, it was difficult to identify the Calidris species due to heat waves, poor lighting, distance, or disturbance. Therefore in the Appendix I have a row for the unidentified Calidris sandpipers. The largest count of unidentified sandpipers was 40 individuals on 5 March. From early November to early February, a single female Northern Harrier was spotted foraging over the wetland on 10 of the 15 days. A female was spotted again on 20 March, suggesting that she frequented the area in search of prey such as sandpipers, Western Meadowlarks or American

6 Pipits. Infrequent visitors included Lesser Scaup, Double-crested Cormorant, Great Egret, and Snow Geese. A single Peregrine Falcon was spotted just prior to the survey, an exciting observation of this once-endangered species. On 26 November, a group of seven possible Eurasian Wigeon (all males) were observed. These rare ducks were identified by their buff white forehead stripe and darker chestnut head. The bodies were also pale gray instead of the light brown of the American Wigeon and they lacked the distinctive green eye band. Red-winged Blackbirds began appearing in early February and their numbers started to peak in mid-april. They were seen on six surveys. Males perched on fence posts, cattails, and rushes calling for mates and establishing territories. It is possible that Tricolored Blackbirds were mixed with the Red-wing flocks based on Tricolored-like calls we heard on one survey, but we could not confirm this with a sighting. The only certain sightings we ve made of Tricolored Blackbirds in the area were made at the lone eucalyptus tree at the UC Merced barn on 30 March 2015 (2 birds) and on 2 April 2015 (35 individuals). A number of waterbird species that were common on Lake Yosemite, but were not observed on the wetland. These include White Pelicans, Western/Clark s Grebes and California Gulls. These species generally foraged over deeper waters and the leakage wetland was not suitable. On the other hand, some bird species found frequenting the leakage wetland, such as dabbling ducks, small sandpipers and avocets, were not common on Lake Yosemite, perhaps because they prefer shallower water.

7 Table 1. Lists of bird species based on frequency of observation on 15 survey days. This survey was focused mainly on the water birds utilizing the wetland area. At times we observed songbirds such as sparrows and Horned Larks. The occurrence of these species was not a focus of my study, however, so the few songbird sightings reported here are not an accurate assessment of their actual presence in the study area. Discussion Current Waterbird Use of the Wetland: This study gives a picture of how the leakage wetland was used by waterbirds during one fall, winter and spring season. A wide range of species was found to be using this area for foraging, resting, and swimming. The presence of stopover species such as Snow Geese and other migrating birds, suggests that these species use the leakage wetland, and also most likely Lake Yosemite as well. The Central Valley is part of the Pacific Flyway, a route that many migrating waterbirds follow from Alaska to as far south as Patagonia in southern South America. This explains why some species were observed only during the transition from winter to spring, between December and February. In March, waterfowl use of the area dropped considerably. This is at the time that the water levels began to recede from the leakage area as Lake Yosemite started getting drained for agricultural use. This trend was most noticeable in the duck species, but was also seen with the

8 shorebirds; though not as noticeably. The dynamics of avian species utilizing the area can then be correlated in some way to the amount of water available on the wetland. Which makes sense, as ducks tend to prefer deeper water and shorebirds prefer shallow habitats. As outlined in the Colwell and Taft (2014), it was found that bird density is often correlated with the depth of the wetlands surveyed. Wading and shorebirds as well as dabbling ducks were found in higher densities in shallow wetlands whereas diving birds were found in deep wetlands. They found that shallow wetlands support a greater density of waterbirds, but a range of depths will bring a wider diversity of avian species. Restoration Impacts on the Current Waterbird Community: Based on observations from this survey and the results of other surveys of waterbird communities, the most beneficial route of improving this wetland would be to increase topographical variance instead of simply making the wetland deeper. It would be optimal if the shallow, intermediate, and deeper water areas could remain in order to accommodate species with different foraging preferences. Converting some of the shallow shore to intermediate depths and carving out deeper portions in the middle of the wetland could direct more of the water from the canal further into the leakage wetland area while keeping topographical variance. This could maximize habitat variety, maintain the current diversity of species, and improve the likelihood that Tricolored Blackbirds might colonize this wetland for nesting in the future. Through observations of the trends of bird use of this wetland, I suggest that habitat restoration work take place in the winter. In winter Lake Yosemite had the most water, and at this time no species would be nesting. Populations would then be able to transfer easily over to portions of the much larger lake, or to other parts of the reserve that would still have water at that time rather than during the spring when the water would be low due to irrigation needs and perhaps to a continuing drought. This study provides a picture of how the leakage wetland was used by waterbirds during one fall, winter and spring season. Further surveying and monitoring of this wetland would be beneficial before fully deciding the course of habitat restoration for nesting Tricolored Blackbirds and to minimize waterbird community disturbances. The survey may be improved in the future by 1) recording water depths. 2) setting up a grid of the study area for more accurate information about where the birds are located. Acknowledgments I thank Daniel Toews and Chris Swarth for helping with bird surveys. I thank Chris Swarth for comments on earlier drafts of the report. Adrian Frediani with The Nature Conservancy allowed this survey to take place on the Cyril Smith Trust Reserve. This projects was completed to fulfill the requirement for BIO 199, an independent study course at UC Merced.

9 Citations Center for Biological Diversity Report A Petition to List the Tricolored Blackbird (Agelaius tricolor) as Endangered under the California Endangered Species Act and Request for Emergency Action to Protect the Species. Petition presented to the California Department of Fish and Game Commission. Conard, C., and D. A. Airola Special Issue on the Status, Ecology, and Conservation of the Tricolored Blackbird. Central Valley Bird Club Bulletin 17 (Nos. 2-4): Merced County, CA. CivicPlus. Web May Swarth, Chris Tricolored Blackbird Information. PDF 6 May 2014 The Tricolored Blackbird Working Group. Conservation Plan for the Tricolored Blackbird. PDF 6 Dec 2014 Waterbird Conservation for the Americas. U.S. Geological Survey, Website checked on 4 May, Further Reading Bleneky, L Petition to List the Tricolored Blackbird as Endangered with Emergency Regulations. PDF file. Central Valley Joint Venture Conservation Bird Habitat Central Valley Joint Venture Monitoring & Evaluation Plan: Shorebirds and Waterbirds. PDF file. 10 June Colwell, M.A., and O. A. Taft Waterbird communities in managed wetlands of varying water depth Waterbirds: The International Journal of Waterbird Biology 23.1 (2000): JSTOR. PDF file. Meese, R., Department of Environmental Science & Policy, University of California Davis, CA. Results of the 2014 Tricolored Blackbird Statewide Survey. PDF file. Shuford, W. D., G. Page, and J. Kjelmyr, Patterns and dynamics of shorebird use of California s Central Valley. The Condor : JSTOR. PDF file.

10 Appendix 1. Summary of bird surveys made at Lake Yosemite leakage wetland. Date 10- Nov Nov Nov Dec Dec Jan Jan- 15 Time 9:16-10:20 9:19-9:53 9:52-10:40 12:57-1:36 1:07-1:36 12:15-12:51 1:45-2:13 Observers KC, CS KC, DT KC, DT KC, DT KC, CS, DT, BF KC, DT, IO KC, DT, IO Species Greater White- fronted Goose Canada Goose 50 Snow Goose 1 Wood Duck 2 Mallard Gadwall No. Pintail 3 1 Am. Wigeon Eurasian Wigeon 7 No. Shoveler Green- Winged Teal Canvasback 1 Ring- necked Duck 1 Greater Scaup Lesser Scaup Bufflehead Hooded Merganser 2 Ruddy Duck 1 3 Unidentified Duck Species Double- crested Cormorant 1 Great Blue Heron Great Egret Snowy Egret 1 No. Harrier Osprey 1 1 White- tailed Kite

11 Date 10- Nov Nov Nov Dec Dec Jan Jan- 15 Time 9:16-10:20 9:19-9:53 9:52-10:40 12:57-1:36 1:07-1:36 12:15-12:51 1:45-2:13 Observers KC, CS KC, DT KC, DT KC, DT KC, CS, DT, BF KC, DT, IO KC, DT, IO Species Black- necked Stilt Am. Avocet 1 Greater Yellowlegs Lesser Yellowlegs (1 heard) 2 (1 heard) Willet Long- billed Curlew Western Sandpiper Least Sandpiper Dunlin Long- billed Dowitcher Calidris sp Wilson's Snipe Mew Gull 1 California Gull 1 Black Phoebe 1 Say's Phoebe 1 Loggerhead Shrike Horned Lark Cliff Swallow Am. Pipit 3 1 Savannah Sparrow White- crowned Sparrow Redwinged Blackbird Western Meadowlark 20

12 Date Time Observers 5- Feb Feb Feb Mar Mar Mar Apr- 15 3:06-3:43 10:21-10:44 4:27-4:52 10:53-11:26 10:35-10:59 12:03-12:43 9:24-10:07 KC, DT KC, DT KC, CS KC, DT KC, DT KC, DT KC, DT 21- Apr :03-10:55 KC, CS, DT Species Greater White- fronted Goose Canada Goose Snow Goose Wood Duck Mallard Gadwall No. Pintail Am. Wigeon Eurasian Wigeon No. Shoveler Green- Winged Teal Canvasback Ring- necked Duck Greater Scaup Lesser Scaup Bufflehead Hooded Merganser Ruddy Duck Unidentified Duck Species Double- crested Cormorant 1

13 Date Time Observers 5- Feb Feb Feb Mar Mar Mar Apr- 15 3:06-3:43 10:21-10:44 4:27-4:52 10:53-11:26 10:35-10:59 12:03-12:43 9:24-10:07 KC, DT KC, DT KC, CS KC, DT KC, DT KC, DT KC, DT 21- Apr :03-10:55 KC, CS, DT Species Great Blue Heron 1 Great Egret Snowy Egret No. Harrier Osprey White- tailed Kite 1 2 Am. Coot Semipalmated Plover Killdeer Black- necked Stilt 3 Am. Avocet Greater Yellowlegs Lesser Yellowlegs 1 Willet 1 Long- billed Curlew Western Sandpiper Least Sandpiper Dunlin Long- billed Dowitcher Calidris sp

14 Date Time Observers 5- Feb Feb Feb Mar Mar Mar Apr- 15 3:06-3:43 10:21-10:44 4:27-4:52 10:53-11:26 10:35-10:59 12:03-12:43 9:24-10:07 KC, DT KC, DT KC, CS KC, DT KC, DT KC, DT KC, DT 21- Apr :03-10:55 KC, CS, DT Species Wilson's Snipe Mew Gull California Gull Black Phoebe Say's Phoebe 1 Loggerhead Shrike Horned Lark Cliff Swallow Am. Pipit Savannah Sparrow White- crowned Sparrow Red- winged Blackbird Western Meadowlark