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To date, there have been no large-scale investigations of mule deer (Odocoileus hemionus) from a single site using stable isotopes, but CA-ALA-554 provides the perfect opportunity for such research. CA-ALA-554 is an ancestral Ohlone site in modern-day Pleasanton that yielded abundant deer remains across 83 burials. AMS radiocarbon dates indicate that people lived here and deposited the deer bones between 400 and 2,000 calibrated years before present. Our goal is to document shifts in deer ecology, especially diet and migratory behaviors, across this swath of time using isotopic signals. Analysis of carbon and nitrogen isotopes reveal overall similarity in diet across the sampled population, with slight variation between individuals. Notably, an increase in variation for both δ13C and δ15N is observed between 800 and 1,000 cal BP, indicating that deer were either diversifying their diet locally or coming to CA-ALA-554 from a greater variety of places during this time than they were either before or after. We argue that the increased variation reflects the ecological stress faced by both mule deer and people during the Medieval Climatic Anomaly (650-1,220 cal BP), which forced one or both to alter their respective foraging and hunting practices. 

Stable isotope analysis has been widely used to investigate dietary and geographical information of organisms, but few studies have applied it to archaeological avian remains. Through carbon and nitrogen stable isotope analyses of bone collagen, this study examines the diet sources of several wild bird species in an attempt to discover their foraging patterns and associated human hunting behavior. These avian remains are from CA- ALA-554 in the East San Francisco Bay Area and represent a time span of 900 years, partly overlapping with the Medieval Climatic Anomaly (MCA). We compare the isotopic signatures of samples from different windows of time represented at the site to investigate the influence of droughts during the MCA and the responses of birds and humans. Our findings show that during the MCA, geese had a larger variance in δ13C and δ15N and avian fauna included a greater range of species. This suggests that birds might have migrated farther and widened their diets and ancient humans might have expanded their hunting range and diversified their prey, possibly in response to more challenging environmental conditions.