The Red-naped Sapsucker (Sphyrapicus nuchalis) feeds on sap by drilling shallow holes (sapwell) into the bark of trees. Over time, the tree bark grows back over the sapwell, producing noticeable scarring, and sapsuckers drill new holes the next year. Little research has been done regarding sapwells and how the sapsuckers choose their placement on trees. I predicted that sapwells are more likely to be found >2m off the ground and on vertical branches and trunks. Sapwells at this height and orientation may be to mitigate terrestrial predation and for better perching. In the City of Rocks Natural Reserve, Idaho, we researched commonalities among sapwell placements on quaking aspen (Populus tremuloides). We measured the height of trees, height of the sapwells, diameter at breast height (DBH) of sapwell trees, and angle of branch or trunk from vertical at location of sapwell. Sapwells were separated into active (drilled that season) and inactive (drilled last season or earlier) based on level of scarring. The app “Bubble Level,” by Gamma Play, was used to measure branch trunk angle. Tree and sapwell height were calculated by combining sight angle and distance from observer to tree. DBH was derived from circumference as measured by a standard measuring tape.
Active sapwells were most commonly found on branches and trunks that were <5° from vertical, while the older, inactive sapwells were found on branches and trunks of slightly wider angle (5-15°). Active and inactive sapwells occurred most frequently 2-4m off the ground, and there is a loose, positive correlation (R2=0.3786) between overall height of the tree, and how high up the sapwell is located. Sapsuckers may choose more vertical branches and trunks to make their wells for ease of perching while feeding, given their zygodactyl toe configuration. There were few sapwells below 2m, which may help with predator avoidance. This helps sapsucker conservation by providing preliminary insight into sapsucker preferences for sapwell locations. By learning how Red-naped sapsuckers select their feeding trees, we can better inform management decisions to promote sapsucker habitat.