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The Red-naped Sapsucker (Sphyrapicus nuchalis) is a keystone species in montane/subalpine ecosystems of the Rocky Mountains of Colorado. By excavating nest cavities in aspen trees and sap wells in willow shrubs, sapsuckers indirectly provide nest holes and food, respectively, to many other species. The objective of my project was to determine which characteristics of willow shrubs were most important to sapsuckers in their choice of stems to drill for sap. The most important factors revealed in my study were the frequency of past sap well excavation. The probability of a stem being excavated for sap wells decreased as the frequency of past foraging increased, as measured by the proportion of stems that were dead (sap well excavation kills the willow stem) and/or had old sap well scars. Presumably willow shrubs with a higher frequency of past sap well excavation were less healthy and thus less optimal for new sap drilling, possibly due to decreased sap flow potential. The negative relationship between the frequency of past sap feeding and new sap well excavation may have ecological and evolutionary implications; these include the possibility that sap-foraging occurs in a way that allows willow shrubs to recover, thus maximizing their long-term sap-producing potential, and the possibility that sapsucker feeding patterns reflect coevolution of defenses against sap-feeding by the willows and counter-adaptations by the sapsuckers.
Knowledge graph centered on Patterns of sap-foraging on willows (<i>Salix spp. with 18 nodes and 61 connections. Top connected: Rocky Mountain Biological Laboratory, Gothic, Colorado East River Valley, Salix lucida subsp. lasiandra, Populus tremuloides.
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