New Oecologia paper: How within-year variation in valley oak acorn crops affects seed predation and dispersal
In our newest paper, which was just published in the journal Oecologia, we investigated how within-year variation of valley oak (Quercus lobata) acorn crops affect the acorn foraging and dispersal behavior of western scrub-jays (Aphelocoma californica) and acorn woodpeckers (Melanerpes formicivorus) at the Hastings Natural History Reserve. We selected 37 trees with different acorn crops and observed them several times from September to December. After estimating the acorn crop by counting all acorns two observers can see within 15 seconds, the tree was observed for an hour. During that hour, each visit by a bird or other animal was recorded, and we noted the fate of all the acorns they handled. Our analysis of almost 200 hours of observation revealed that in trees with large acorn crops, scrub-jays took a larger proportion of acorns (compared to the acorn woodpeckers) than in trees with smaller crops. This is likely due to the different spatial scales over which each species optimize their foraging. Jays don't spend much time defending territories during the non-breeding season, while the acorn woodpeckers defend nesting and acorn-storage trees year-round. Because the jays hide acorns in the ground rather than sticking them in the bark of trees like the woodpeckers do, they provide much higher quality seed dispersal. The trees with large crops thus have higher dispersal-related fitness benefits than trees with smaller crops. Our results also hint at the proximate mechanism by which masting trees benefit from the annual variation in acorn crops.
Pesendorfer, MB & Koenig WD (2016) The effect of within-year variation in acorn crop size on seed harvesting behavior by avian hoarders. Oecologia (doi:10.1007/s00442-016-3557-x) link: http://link.springer.com/article/10.1007/s00442-016-3557-x