Linking Life Zones, Life History Traits, Ecology, and Spatial Cognition in Four Allopatric Southwestern Seed Caching Corvids

This report will review the similarities and differences of four species of pine seed caching members of the avian family Corvidae that live on the slopes and base of the San Francisco Peaks in north-central Arizona. The four species include the Clark’s nutcracker (Nucifraga columbiana), pinyon jay (Gymnorhinus cyanocephalus), western scrub-jay (Aphelocoma californica), and Mexican jay (A. ultramarina). These corvids demonstrate a specialization gradient for the harvesting, transporting, caching and recovering of buried pine seeds. This gradient is reflected in their dependence on cached pine seeds for winter and early spring survival and reproduction. Species most dependent on these cached seeds have the greatest number of adaptations for utilizing these seeds which is especially evident in their spatial memory abilities to locate their caches. The two most dependent species, nutcrackers and pinyon jays have spatial memory abilities more accurate than in the species less dependent on cached seeds, western scrub-jays and Mexican jays. Using converging operations to test these memory abilities, comparative tests were conducted in an open field cache/recovery experiment, an analogue radial maze test and operant tests of spatial and non-spatial memory. Also discussed are the techniques used by nutcrackers to recognize and relocate caching sites. These birds have the ability to learn and generalize geometric rules about the placement of landmarks. This geometry, especially using multiple landmarks, aids this species greatly. The use of the sun compass by pinyon jays, scrub jays and nutcrackers reveal that in experimental conditions where birds are clock-shifted they respond to this shift, thus digging for caches in locations predicted by the shift. It appears that pinyon jays are converging on a distant relative the nutcracker in many characteristics, thus diverging from their close relatives the western scrub-jay and Mexican jay. Each species has a suite of adaptive traits that reflects its natural history and life history. Chapter Outline and Navigation The Ecology and Life History of Seed Caching Corvids http://www.pigeon.psy.tufts.edu/asc/Balda/Default.htm 1 of 32 11/16/2009 1:38 PM Figure 1. C. H. Merriam (white shirt)