Local Disturbances

ABSTRACT

A study was conducted to identify the specific factors affecting the fluctuating numbers of American wigeon (Anas Americana) and other waterfowl numbers over time at the Arcata Marsh in Arcata, California as a result from multiple disturbance factors in the surrounding marsh environment. The results found allows for more studies to be conducted and elaborated on for greater detail about how local disturbance factors affect migration and nesting sites. The information gathered from this study and other like this will help in population and predator control in order to protect marsh waterfowl and migrating birds in general.

KEY WORDS abundance, American wigeon, Anas Americana, Arcata marsh, Arcata, California, disturbances.

On an everyday basis, large amounts of various bird species are observed in local coastal marshes, one of which is the American wigeon (Anas Americana). The American wigeon winter in a wide variety of habitats, such as ponds, lakes, saline and brackish marshes that have plenty of aquatic vegetation (Berl and Black 2011). The American wigeon, along with many other waterfowl species, flock to the Arcata Marsh on the California coast in order to use the wide range of resources provided, like food and shelter (Hitchcock et al. 1993). The American wigeon are observed at a local coastal marsh over time and appear to fluctuate in number due multiple factors. These possible factors include limited foraging opportunities, human disturbances, and predation. There are many proposed explanations that hypothesize the cause of the over time fluctuations of American wigeon numbers at local Arcata Marsh. The aim of our study is to explore the possible connection between the variations in American wigeon numbers over time at the Arcata Marsh. The hypotheses that we propose as explanations to this phenomenon are: (1) The range in numbers of American wigeon on a daily basis at the Arcata Marsh are a result of the wigeon foraging at different locations outside the marsh (Berl and Black 2011) and the availability of food resources with regards to the daily tidal cycles of the adjacent bay (Moore and Black 2006). (2) The variation in the number of the American wigeon observed from day to day at the Arcata Marsh is due to disturbances from human recreational activities (Pease et al. 2005) and disturbances from hunting (Burger 1981). The confounding factors that may influence the variation in American wigeon numbers at the Arcata Marsh is due to presence of predators, such as River otter (Lontra canadensis) (Penland and Black 2009) and Peregrine falcon (Falco peregrinus) (Fritz et al. 2000). Another confounding factor may be the variation in climate conditions in the local weather surrounding local wetland habitats, which in turn be causing the number of waterfowl species to decrease from day to day (Jorde et al. 1984). Previous studies have shown to agree that waterfowl population, such as dabbling duck, numbers within wetland areas fluctuate from day to day (Guillemain et al. 2002). We propose that the over time fluctuations in American wigeon numbers at the Arcata Marsh are being altered by the limit in foraging areas and food resources with tidal affects, the daily disturbances by human activities and the opening of the hunting season. If our proposed hypotheses are valid, we can predict that wigeon numbers will increase with the increase in food resources; that wigeon numbers will increase at Arcata Marsh when the tide level in the adjacent bay is too high; that the wigeon numbers will decrease as hunting season starts. Our proposed hypotheses were tested using observational data collection only within our study area and the confounding factors were considered when analyzing the data collected to consider possible skewness in the data.

STUDY AREA

The study was conducted at the Arcata Marsh and Wildlife Sanctuary which is located adjacent to Humboldt Bay in Arcata, California. The map coordinates for the Arcata Marsh and Wildlife Sanctuary is N 40.8665o Latitude, W 124.0828o Longitude (topoquest.com). The Arcata Marsh and the surrounding sanctuary make up 300 acres and are made up of a variety of habitats that range from meadows to brackish marshes (Suutari and Marten 2007). The marshes and ponds of the Arcata Marsh are made of different levels of water quality and different types of vegetation, such as duckweed (Lemna minor). Within the adjacent bay has eel grass, when available by the tides (Moore and Black 2006). The data will be collected at two of the large ponds, Gearheart marsh and Allen marsh, which make up a part of the Arcata Marsh water treatment plant (Higley 1988).

METHODS

We counted the number of American wigeon and Eurasian wigeon (Anas penelope) present, along with coots, grebes, other ducks and geese in two ponds, Gearheart and Allen, at the Arcata Marsh, starting on Oct. 8 and ending on Oct. 31. The data was collected by a group of three people, with two as counters and one as a recorder and within three time intervals of day, morning, afternoon and evening. The tools used to collect the data accurately included: binoculars with an optional spotting scope, a watch, a writing utensil, a clipboard and the data sheet. On arrival to the study area, the recorder wrote the start time and looked out for human disturbance events, such as people in cars, walking a dog(s), riding a bicycle, or jogging/walking and begun to count the number of gun shots heard, as well as the current weather conditions at the start time, such as wind presence, wind direction and speed, sunny or cloudy and fog or rain presence. One of the counters looked for otters and hawk/falcon