Predicting a Clark's Nutcracker Irruption

I photographed this Clark's Nutcracker in northern Utah on 28 July 2013, but if it can't find enough pine nuts, it might be headed to your neighborhood.

I've seen two unusual events in the last few days that make me think this year might be a big one for vagrant Clark's Nutcrackers in the ABA area.  On Sunday, I was birding in typical Clark's Nutcracker habitat at about 8,100 ft. elevation near my home in northern Utah.  This is a species that is relatively common here, but we were doing a big day, and it's not so common that it is guaranteed to be found in the two or three hours we could afford to spend in its habitat.  In two or three hours of birding, we would expect to probably run in to a few of them.  Our expectations were off: in just a few hours last Sunday, we counted almost a hundred, moving around high overhead in flocks of up to 40.  Although the species is expected here, these kinds of numbers are not typical for this area and time of year in my experience.

This view of Cache Valley is from a point almost high enough to expect Clark's Nutcrackers.  That species is also expected across the valley, in the peaks covered with snow in this picture.  To find one down in the bottom of the valley, where you can see Cutler Reservoir shining, is very unusual, and is unheard of any time other than winter.

On Tuesday, a couple friends and I were birding in the middle of Cache Valley, at about 4,500 ft. elevation.  This is well below typical Clark's Nutcracker habitat, especially in summer.  In the seven years I've lived in this area, I know of just a few credible reports from the valley, almost all from the "benches" very near the mountains and all between October and December.  Yesterday, we saw a flock of 28 Clark's Nutcrackers flying over the middle of the valley, barely in to September.

This is what a Clark's Nutcracker can look like in a good year, with a crop full of pine nuts that it will cache around the area to feed on in the winter.  I photographed this one in 2011 in northeastern Nevada.

The Birds of North America account for the species indicates that Clark's Nutcracker irruptions are most likely to happen when two years of above average pine cone production is followed by a year of very poor production.  In years of good pine nut production, Clark's Nutcrackers are successful in raising young and mortality is low.  Two years of good production can build up population sizes well above normal.  When a bad year follows, there are way more Clark's Nutcrackers than nutcracker food, and the birds have to wander widely to find the nuts they need to survive.

In both 2011 and 2012, pine cone production by whitebark pines, one of the nutcracker's two main food sources, was higher than average.  The very dry winter last year (about 60% of typical snowpack locally, and around that or lower in much of the inland west) has caused poor production by whitebark pines this year, in Wyoming the lowest since about 2002.  Coincidentally, in 2002, Clark's Nutcrackers were reported from as far out of range as Alabama and Missouri.

This figure shows the standardized whitebark pine production from the Greater Yellowstone ecosystem for the last 24 years.  Note that both 2011 and 2012 were above average years, but 2013 is about the lowest since 2002.  This figure is from here and is in the public domain.

Based on my observations over the last few days, and the current status of whitebark pine production compared to previous years, I'm guessing that this will be a good year for vagrants of this species in North America.  Most movements of Clark's Nutcrackers are relatively local, so this is most likely to affect birders who live near Clark's Nutcracker habitat, but are a bit outside their usual range.  However, there is also potential for long-distance wandering, perhaps well outside of the species' expected range.  It might be helpful to study the call, and to be sure you're familiar with this species, so you're prepared if a Clark's Nutcracker should find its way near you this winter.