Foraging patterns of acorn woodpeckers (Melanerpes formicivorus) on valley oak (Quercus lobata Née) in two California oak savanna-woodlands

Abstract

Landscape characteristics and social behavior can affect the foraging patterns of seed-dependent animals. We examine the movement of acorns from valley oak (Quercus lobata) trees to granaries maintained by acorn woodpeckers (Melanerpes formicivorus) in two California oak savanna-woodlands differing in the distribution of Q. lobata within each site. In 2004, we sampled Q. lobata acorns from 16 granaries at Sedgwick Reserve in Santa Barbara County and 18 granaries at Hastings Reserve in Monterey County. Sedgwick has lower site-wide density of Q. lobata than Hastings as well as different frequencies of other Quercus species common to both sites. We found acorn woodpeckers foraged from fewer Q. lobata seed source trees (Kg = 4.1 ± 0.5) at Sedgwick than at Hastings (Kg = 7.6 ± 0.6) and from fewer effective seed sources (Nem* = 2.00 and 5.78, respectively). The differences between sites are due to a greater number of incidental seed sources used per granary at Hastings than at Sedgwick. We also found very low levels of seed source sharing between adjacent granaries, indicating that territoriality is strong at both sites and that each social group forages on its own subset of trees. We discovered an interesting spatial pattern in the location of granaries. At Sedgwick, acorn woodpeckers situated their granaries within areas of higher-than-average tree density, while at Hastings, they placed them within areas of lower-than-average tree density, with the outcome that granaries at the two sites were located in areas of similar valley oak density. Our results illustrate that landscape characteristics might influence the number of trees visited by acorn woodpeckers and the locations of territories, while woodpecker social behavior, such as territoriality, shapes which trees are visited and whether they are shared with other social groups.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-010-1828-5) contains supplementary material, which is available to authorized users.

Gene flow and natural selection shape spatial patterns of genes in tree populations: implications for evolutionary processes and applications

“…Although woodpeckers are more likely to acts as seed consumers than dispersers, they transport acorns to 'granaries', which are storage sites often in the barks of trees, and can be considered to be seed pools (Grivet et al 2005). Woodpeckers can fly kilometers on any given day, but our analyses showed that the effective number of maternal trees found in any single granary (each containing the combined collection from a single woodpecker family's efforts) is 2-3 local trees (Scofield et al 2010;Scofield et al 2011), as would be predicted by optimal foraging theory (Thompson et al 2014).…”

Impacts of Mating Behavior on Plant–Animal Seed Dispersal Mutualisms

“…Direct observational studies of dispersal are likely to miss rare but important longer-distance dispersal events, and can pose significant challenges for tracking movement of individual seeds (Koenig et al, 1996;Nathan, 2006;Scofield et al, 2011). Currently, molecular and observational estimates of seed dispersal are rarely combined in a single study system, despite the fact that both approaches have potentially significant limitations when employed in isolation.…”

“…Unlike umbrellabirds, acorn woodpeckers live in highly territorial social groups and tend to forage in the trees proximal to their storage sites, with each territorial group gathering acorns from non-overlapping territories and hence from different trees (Grivet et al, 2005;Scofield et al, 2010Scofield et al, , 2011). However, because lek-breeding among frugivorous bird species is essentially absent from the temperate zone, we must limit our comparisons to species that exhibit other mating systems.…”

Is the distribution of the Acorn Woodpecker (Melanerpes formicivorus flavigula) associated with oaks and granaries? A local study in an urban area in northern South America

“…Extensive studies about its diet (Stacey 1981, Rosas et al 2008), parental care (Koenig & Walters 2011), population ecology (Koenig & Mumme 1987) and use of habitat (Stacey 1979, Ligon & Stacey 1996) have been done in North and Central America. A well known aspect is their strong relationship with different oak species of the genus Quercus and Notholithocarpus; from which they rely on as a food source (Scofield et al 2011) and as nest cavity sites (Koenig & Walters 2014), allowing them to survive during the winter season (Koenig & Haydock 1999). A behavior associated with the use of oaks is the accumulation of acorns or seeds in small holes in the bark of these trees (MacRoberts & MacRoberts 1976).…”