Wednesday, June 19, 2013

Co-evolution of the red-naped and red-breasted sapsuckers

The red-breasted Sphyrapicus ruber and red-naped Sphyrapicus nuchalis sapsuckers are two woodpecker species that overlap in their range near the crest of the Cascades.  These two species are sympatric, meaning that during the evolution process, they became two new species while inhabiting the same geographic region. Generally speaking in Washington, the red-breasted live on the west side, the red-naped on the east side.   At the North Cascades Basecamp in Mazama, we’ve had the opportunity to observe both species in a cedar and birch grove that is unique to the upper Methow watershed.

This year, a male red-breasted sapsucker was observed late in the winter along the Basecamp trail.  He drummed his broken drum on local snags, showed off his beautiful red head, called his quiet “mewing” call, and even excavated a perfectly round cavity in a birch snag.  A female red-naped sapsucker was often seen in the same area, licking (not drinking) up sap with her barbed tongue, making frequent visits to his territory, and exploring the newly constructed cavity with intrepidation (poking her head up to the entrance but not entering).  Finally in mid-June, after many hours of observation, we saw the red-breasted male and the red-naped female both enter and exist the nesting cavity with food in beak for the hungry nestlings, and he was being a good dad and dropping fecal sacs to the ground as his housecleaning duties ensued.   

These two species of sapsuckers are known to hybridize in south-central Oregon, northeastern California, along the California-Nevada border, and in southern Nevada.  Genetic studies by Johnson et al (1983, 1985) showed that red-naped and red-breasted sapsuckers have the highest avian genetic relatedness ever reported, similar to that found between avian subspecies.  They also found the hybrid F1 generation to produce viable offspring, although it seems that certain F2 backcrossings may have partial sterility issues.  These studies and others confirm that although these two species are nearly genetically identical, there is a low degree of hybridization while encountering each other regularly, and therefore they are still considered as separate biological species. 

It will be interesting to see what our new fledgling hybrid sapsuckers look like, and who they choose as mates into the future.

Ned K. Johnson and Robert M. Zink. 1983. Speciation in Sapsuckers (Sphyrapicus): I. Genetic Differentiation.  The Auk: 871-884.

Ned K. Johnson and Carla Bowman Johnson.  1985.  Speciation in Sapsuckers (Sphyrapicus): II. Sympatry, Hybridization, and Mate Preference in S. ruber daggetti and S. nuchalis.  The Auk: 1-15.

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