FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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BIRD MONITORS By Lee Franks Sequoia Audubon trained volunteers have been collecting data on bird populations and nesting sites for the past several years, as participants in the Bird Conservation Program at Edgewood Park and Preserve . We recently evaluated this data and came up with the following. Population Density Trends
The spike in the oak woodland bird numbers in 2004 is the result of changes in the behavior of Chestnut-backed Chickadees and Dark-eyed Juncos in the months of November and December. Because food sources decline in the winter months, these two species start looking elsewhere for their food. After the winter rains start, they like to form flocks made up of resident and non-resident birds, and in so doing they become “vagrants” for a few months. These flocks tend to establish foraging circuits that go beyond Park boundaries, causing their presence in the Park to fluctuate randomly. The number of chickadees and juncos encountered by volunteer observers in November and December of 2004 was greater than the number of those encountered in 2002 and 2003, probably because the foraging circuit included more visits to the Park in 2004. Overall, we are pleased that the population density trends in the three habitat types that exist in the Park are moving in the right direction, indicating that the Park birds are finding adequate food and shelter to survive and reproduce. Species of Special Interest There are 3 species that are monitored more closely than the remainder. They are the Western Bluebird, Western Meadowlark, and the California Quail. They are of special interest because two are ground nesters (meadowlark and quail), while the bluebird is a cavity nesting species that is recovering from endangered status. The Western Bluebird recovery is being addressed in the Park and around the country by providing artificial housing in the form of nest boxes. Our interest here is to monitor the survivability of the young produced by the parents using the boxes. The breeding grounds for both the meadowlarks and quail have been located and mapped. Measures are taken each year during the breeding season to protect these breeding grounds from disturbances resulting from Park maintenance activities and various land restoration projects
As Table 2 shows, the trend for the Western Bluebird is very positive, but the quail and meadowlark numbers drop off in 2004. Quail reproduction is closely related to winter rainfall amounts. The rain seems to regulate breeding by influencing the chemistry of the plants that they eat, especially those plants in the pea family. The higher the rainfall amounts, the larger the quail broods. We expect the quail numbers to bounce back in 2005 as a result of record high rainfall amounts this past winter and spring. Western Meadowlark behavior presents a challenge to field observers. While these birds are present in the Park year-round, their numbers vary widely, depending on the time of year. This is because following completion of their breeding cycle in September, they join with non-residents to form foraging flocks, and like the chickadee and junco, they travel on a foraging circuit that includes the Park as well as other surrounding areas like the campus at Canada College. Because they vary the number of trips to the Park in the non-breeding months each year, we expect to see large swings in the number detected in any given year. The number of breeding pair that use the Park to reproduce each year is a better indicator of how this species is doing. Breeding pair numbers have been fairly constant at 7-8 pair each year. Nest Boxes
Western Bluebirds are the species that historically make greater use of the boxes installed in the Park. Table 3 shows bluebird box information collected by volunteers for the past 5 years. The first year boxes were installed, only 3 nests were built. The last two years, 9 nests were built, indicating that the bluebirds not only found the boxes, but that they prefer to use them over natural cavities usually found in trees and old wooden fence posts. Healthy females will normally lay 4-5 eggs per clutch. The average for this 5-year period was 4.37, indicating that the females are getting adequate food from areas surrounding the boxes. Whether all eggs hatch or not is dependent on the skill of the hen in incubating the eggs, the presence of predators in the nest, and whether the eggs were fertilized. The table numbers show that the hatch rate got off to a poor start in the early years (57%) and then improved dramatically in the last two years (99%). The installation of predator baffles beneath the box openings was one action that contributed to this hatch rate improvement. Regarding the fledge rate (# birds leaving nests as young adults), the numbers show only one year where the number of young that fledged fell significantly below the number of young hatched (14 vs. 9). Five young died from starvation in one nest that year most likely because the parents were taken by a predator or died of natural causes. An overall rosy picture is painted by the breeding success of the Western Bluebird in the Park. The population density of this species is increasing yearly as a result of the boxes and the quality and quantity of the food found in the grasslands where the birds nest. Visitors to the Park now have the opportunity to view a sizable number of these handsome birds, that was not possible prior to 2000. Acknowledgments I am grateful to volunteer observers Sue Hecox, Whitney Mortimer, Theresa O’Brien, Sue Rowinski, Marilyn Travis, and Matt Weinand for generously giving of their weekend time to take field censuses each month; to County Park Rangers Ricardo Trejo and Katie Beltrano for their assistance with nest box installations, with purchase of predator guards, and for providing plans and schedules of annual land restoration projects; to Bill Korbholz of Friends of Edgewood for GPS mapping of nest sites; to Sue Cossins and Peter Grace of Sequoia Audubon for acquiring EXCEL software for use in managing the huge amounts of field data collected each year. Volunteers Needed If you would like to be trained to participate in the Bird Conservation Program at Edgewood, contact me. Not only will you be rewarded knowing your efforts are helping the birds, but you will find that participation is a great way to improve your bird ID skills, especially song/call recognition. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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