“When a bird’s pastures are the tree tops, it is possible for it to live a quite secluded life here in Washington” – Red Crossbill
“To tell the truth, no one hereabouts appears to know much about the …” White-winged Crossbill
Both quotes from The Birds of Washington. 1909. W.L. Dawson and J.H. Bowles.
Some things don’t change much. A century later, basic questions remain about the lives of cone-dependent species, typified by crossbills, particularly at times when their preferred conifers fail to produce cones. In a typical year in the conifer-rich Northwest, most species of conifers produce some cones, and it appears that crossbills of the Northwest make minor movements within the region to areas with greater cone concentrations or they switch from their preferred cone type to those from other trees. As a result, it seems that there are always some crossbills around somewhere in the region, and we don’t get a great deal of insight into what happens when neither of those options are available. It is a very rare year when there are no cones to be found anywhere in the region, so 2017, which was notable for an almost region-wide dearth of cones, provides an opportunity to learn more about their movements in response to a lack of food. In 2017, almost all of the native conifers failed to produce cones in any abundance; no matter whether they were growing in the lowlands or in the mountains, in dry zones or wet zones1. As a consequence, crossbill numbers have been at very low levels across the region, as would be expected for cone dependent species. Large numbers appear to have left the region, as other parts of the continent are experiencing notable incursions of Red Crossbills.
There is one important exception in the Northwest to the nearly universal lack of cones, the Sitka Spruce. They are a primarily coastal tree, abundant along the outer coast and found in small patches further inland. Maybe because of their coastal range, with relatively moderate climate and only mild variations in temperature and precipitation, in the Northwest they produce cone crops every year and 2017 was no exception (Figure 1). A quick comparison of the distribution map of Red Crossbill in Sep-Dec 2017 with the same Sep-Dec map for the last ten years shows a dramatic difference in all areas, except the coastal strip where Sitka Spruce predominate. The ten-year map shows a broad distribution of Red Crossbills throughout, except in the shrub-steppe regions of the interior, with the highest density (the darkest purple shades) in the Cascades and other mountain ranges. The 2017 map displays a low level of abundance in the Salish Sea lowlands, scattered numbers elsewhere with higher densities in the southern Oregon Cascades, and most notably a nearly contiguous, narrow band of higher density along the coast2. This narrow band is the only area that looks similar to the distribution in the all-years map, and shows the importance of Sitka Spruce.
Another, even more dramatic way, to look at the influence of Sitka Spruce this year is to compare White-winged Crossbill maps. The Sep-Dec map for 2017 shows the same, narrow distribution along the outer coast and a light scattering of records elsewhere. The Sep-Dec map for all years, excluding 2017, shows almost no coastal distribution; instead the higher populations densities are in the montane regions of northern Washington with a scattering of records to the south. Clearly, something drew White-winged Crossbills to the coast this year; this picture by Bill Shelmerdine of a White-winged Crossbill in a cone laden Sitka Spruce at Ocean Shores, Washington on 26 December provides clear evidence of the attraction (Figure 2).
What are we learning about crossbills and cones this winter?
Birders know that crossbills are nomadic, and based on band reports, can irrupt over long distances in their search for food. This winter, in addition to witnessing an exodus from the Northwest, we are also learning about the importance of Sitka Spruce as a ‘refuge’ for crossbills that have not simply emigrated when all other food sources fail. It is well known that coastal areas function as traps for migrant or irruptive birds: with the ocean acting as a barrier to further movement, the coastal strip concentrates migrants. Add a consistent food source, such as abundant Sitka Spruce cones, and now two dynamics are working together to concentrate birds: food and reluctance to venture beyond the shoreline. The result is the first substantial occurrence of White-winged Crossbills into coastal lowlands in our experience, which is noteworthy enough, and also a very unusual distribution of Red Crossbills.
How unusual is the Red Crossbill distribution? Since Red Crossbills are permanent residents of the Sitka Spruce zone (mostly Type 10, but other westside types such as 3 and 4 occur regularly) and since crossbill call types are difficult to differentiate for most observers, there is not the same amount of data as we have on White-winged Crossbills, but there are some intriguing reports. Type 2 (the large-billed Ponderosa Pine type) are extremely rare west of the Cascade Crest; this fall there are seven documented records from Neah Bay which had no previous records, and three documented records from coastal Tillamook and Lincoln counties on the central Oregon, also with no previous outer coastal records. Two documented records of Type 1 (Appalachian type) from the outer coast this winter are the first ever for coastal NW, there are three previous southern Salish Sea records from 2012, another year with continent wide Red Crossbill movements. One of the two southern BC records of this type was from the west coast of Vancouver Island earlier in 2017. Clearly, small numbers of Red Crossbills from considerable distance are also finding refuge this winter in the coastal strip.
And, what to make of the unprecedented White-winged Crossbill numbers in the coastal areas (Figure 3)? It can be considered a food-related irruption, although it is different in many ways from previous irruptions into the Northwest, which consisted of movement of large numbers of crossbills into high elevation areas of the Northwest. In this event, the number of individuals is comparatively small; the sum of the peak counts of White-winged Crossbills along the outer coast is 465 birds. Good numbers, but considering the habitat strip is narrow and observer coverage is relatively high, probably not the tens of thousands or more that must be present in previous irruptions when the birds were reported as common throughout large mountainous areas. In a sense, these coastal birds represent the ‘traces’ of an irruption, birds that for some reason departed from the main direction of the movement and have collected like waifs after a storm, in a narrow strip of hospitable habitat bordered by the ocean. The main direction of the movement can be seen in the eBird map for the continent from Sep-Dec 2017, showing some low-density movement into the northern Rockies, somewhat higher densities in the upper Midwest, and the highest densities into New England and the Maritime Provinces.
How can eBirders contribute to our understanding of this event?
This event appears unprecedented for White-winged Crossbills; based on the historical literature dating back to the early 1900s, crossbills have never before occurred in numerous flocks in the coastal strip of the Northwest. Every eBird report contributes to documenting this new phenomenon, with inland reports continuing to document their absence and coastal reports documenting their presence. Going beyond that, eBirders can search coastal areas where White-winged Crossbills have not been reported yet to help determine the magnitude and extent of this event. How late will they stay? How far inland do they occur in the Sitka Spruce zone? Checking isolated islands of Sitka Spruce in inland areas might prove interesting also.
Getting field recordings of all Red Crossbills will prove helpful as well. The recent eBird Northwest note on crossbills includes a section on Documenting and Recording crossbill calls for identification to call type. It is even possible to use the voice recorder function on cell phones to record crossbill call types; providing an invaluable record.
1Andy Bower, Area Geneticist, US Forest Service Pacific Northwest Region and Jeff deGrann, Restoration Specialist, Washington Department of Natural Resources.
2The empty area on the Olympic Peninsula is likely an artifact of low coverage in that area.
Article by: Bill Tweit, Washington Department of Fish and Wildlife