One of the easiest places in the Silicon Valley area to see acorn woodpeckers up close is Guadalupe Oak Grove Park in the Almaden area of San Jose. The park, nearly 50 acres, is noted in the City of San Jose’s 1987 Masterplan Report as one of the last notable areas of deciduous oak savanna and oak woodland remaining on the Santa Clara Valley floor.
Guadalupe Oak Grove Park’s small trail system provides birdwatchers with excellent access to observe acorn woodpeckers and other California native bird species such as the California scrub jay, California thrasher, oak titmouse, tree swallow, and violet-green swallow.
The flat trails in the lower part of the park wind through oak habitats, while the more challenging upper area trails wind through a small hill adorned with Blue Oak, California Buckeye, and Sagebrush Scrub. These trails also offer opportunities to encounter rock outcroppings and an abandoned sandstone quarry.
Visiting Guadalupe Oak Grove Park
The park is located in the middle of a single-family residential neighborhood near the junction of Guadalupe River and Los Alamitos Creek. There is a small parking lot off Thorntree Drive with space for about five cars, which typically fills up quickly soon after the park opens at 8 a.m. However, ample street parking is available throughout the neighborhood.
Plant communities at Guadalupe Oak Grove Park
Guadalupe Oak Grove Park is home to three primary plant communities. Oak savanna dominates the western, eastern, and southern-facing slopes of the hills, while an oak forest thrives on the flat areas characterized by Pleasanton gravelly loam. Along the north-facing slope near Porto Alegre Drive, a Buckeye-oak community can be found. Additionally, a transitional slope bridges the oak woodland and the hillside savanna.
Hillside Oak Savanna: This community consists of grasses, forbs, and scattered oaks, predominantly blue oaks and hybrids of blue and valley oaks. Live oaks are also found along ridge tops and western slopes.
Oak Forest: Situated on flat alluvial soil, this closed-canopy forest is dominated by blue oaks, valley oaks, and live oaks.
Buckeye-Oak Community: Found on north-facing slopes near Porto Alegre Drive, this shady forest is primarily composed of buckeyes, with occasional blue oaks.
Transition Slope Area: Located between the oak forest and the oak savanna, this area features blue oaks on a moderately sloped terrain.
Snags at Guadalupe Oak Grove Park
In addition to live oaks, the park also maintains the presence of snags that play an equally critical role in supporting acorn woodpeckers. Dead or decaying trees, known as snags, are essential for nesting and granary building. Woodpeckers prefer the softer wood of snags for drilling holes, and the branches of dead trees provide an ideal surface for resting.
Snags at Guadalupe Oak Grove Park are often turned into granary trees, with hundreds of carefully drilled holes packed with acorns. These granaries become focal points of the woodpeckers’ territories and support multiple generations of birds.
Identifying acorn woodpeckers
Guadeloupe Oak Grove Park’s diverse oak species, including Valley Oak, Blue Oak, and Coast Live Oak, make it an ideal habitat for many bird species, especially the acorn woodpecker (Melanerpes formicivorus). Almost all areas of this small natural park in an urban area are used by these woodpeckers.
Acorn woodpeckers are easy to spot thanks to their distinctive black-and-white plumage, bright red caps, and pale, expressive eyes. Their calls—a mix of laughing chatter and sharp, repetitive notes—are often the first clue that they’re nearby. Listen for the distinctive “waka waka waka” calls.
Acorn woodpecker social structure
Acorn woodpeckers are unique among birds for their highly organized, cooperative social structure. They live in territorial family groups, which can include up to a dozen or more members. These groups work together to gather acorns, maintain their communal granary tree, and defend their territory from competitors like squirrels, jays, and even other woodpeckers outside of their family group.
Granaries
As their name implies, acorns are an essential food source for these woodpeckers, particularly during the winter months when insects, their other primary food source, are less abundant. Acorns are high in fat and carbohydrates, providing a reliable energy reserve. To maintain a steady supply of acorns, families of woodpeckers maintain what are known as granaries.
What are Granaries?
A granary, also known as a granary tree, is essentially a massive acorn pantry. Acorn woodpeckers drill thousands of holes into the bark of live trees or the wood of dead trees (as well as wooden buildings or poles), each sized just right to hold an acorn. Depending on the size, these granaries can hold hundreds or thousands of acorns, often built up over generations of birds working together.
Building and maintaining the granary tree
The granary tree is a central feature of an acorn woodpecker’s territory. This tree, which might already contain thousands of acorn-filled holes from previous years, becomes a hive of activity during the fall. Group members drill new holes to accommodate the mast year’s crop and carefully insert each acorn into a snug-fitting cavity.
Acorn woodpeckers frequently revisit their granary to inspect the stored acorns. Loose acorns are pushed back into place or moved into smaller holes. Rotten or unsuitable acorns are removed.
Seasonal behaviors and viewing tips
Acorn woodpeckers’ behavior changes with the seasons so repeat visits to this park are worthwhile. During the fall, their activity peaks as they collect and store acorns in preparation for winter. Winter months are ideal for observing their social interactions around granary trees, while spring and summer bring heightened nesting activity, with fledglings often seen around family groups.
For the best birdwatching, arrive early in the morning or late in the afternoon, when the woodpeckers are most active.
A great spot to watch acorn woodpeckers
Guadalupe Oak Grove Park is a great spot to watch the seasonal activity of acorn woodpeckers and learn more about their connection to the oak woodlands. From storing acorns in the fall to raising young in the spring, their behavior changes throughout the year. The park’s trails make it easy to see these birds up close and enjoy a quiet walk through one of the few remaining oak savannas in the area.
References
MacRoberts, M. H., & MacRoberts, B. R. (1976). Social organization and behavior of the acorn woodpecker in central coastal California. Ornithological Monographs, (21), iii-115.
Stacey, P. B., & Koenig, W. D. (1984). Cooperative Breeding in the Acorn Woodpecker. Scientific American, 251(2), 114–121.
