red Crossbill (Loxia curvirostra)
As its name indicates, the mandibles of a Red Crossbill are crossed, which is an adaptation for prizing apart scales of conifer cones to obtain the seeds upon which the crossbill specializes. Keen birders easily associate kip-kip-kip calls with Red Crossbills and conifers, but in the coming years, determining which species of crossbill one is hearing likely will become more complicated. Red Crossbills exhibit a high degree of morphological variation that has resulted in a confusing array of subspecies. A major step toward clarifying the issue occurred with the discovery that bill size is correlated with the type of cone a crossbill favors, large-billed birds seeking cones with harder scales, and small-billed birds preferring cones with softer scales. Next was the realization that bill size corresponds with the type of flight call produced, and that birds of like bill size and call type mate preferentially with one another, thereby maintaining reproductive isolation among call types. Ten call types have been identified to date, some of which are thought to represent distinct species (Groth 1993, Benkman 1999). Indeed, birds that give call type 9 recently were described as a new species, the South Hills Crossbill (L. sinesciuris), which resides year-round in lodgepole pine forests in two isolated mountain ranges in sc. Idaho (Benkman et al. 2009). In the near future, birds that give other call types also may be elevated to full species. Red Crossbills are permanent residents in conifer forests from Alaska east to Newfoundland and south through the Cascade and Sierra Nevada ranges to n. Baja California, through the Rocky Mts. and mountains of Mexico to Nicaragua, and down the Appalachian Mts. to North Carolina and Tennessee. During irruption years they range as far south as Texas, Louisiana, Mississippi, Alabama, and Georgia. Red Crossbills also occur in the United Kingdom and across Eurasia from Scandinavia to Japan.
Subspecies: L. c. bendirei, L. c. benti, L. c. minor, and L. c. sitkensis (AOU 1957), although taxonomy is confusing. Call types 2 to 5 and 7 are present in Montana (Adkisson 1996, Parchman et al. 2006).
Status and Occurrence: Fairly common to abundant permanent resident statewide where conifers are present, with abundance depending on cone crops. Most populations are nomadic and may undergo local movements during any season in search of conifer seeds; winter numbers fluctuate widely. Flocks usually contain fewer than 12 birds, but up to 50 have been reported. Breeding can occur in just about any month (Adkisson 1996). A nest near Bigfork contained four eggs when visited on 27 Jul 1903 (Silloway 1905b); this is the only published record of a nest in the state. Kristi DuBois watched a pair building a nest near Ashland on 16 Feb 1981. The female was incubating on 4 Mar, and two downy nestlings were present on 21 Mar. Fledglings have been seen at scattered locales in the state from Apr to early Aug (MBD).
Montana’s first specimens were obtained by John Pearsall in the Bitterroot Valley in 1859 or 1860 (ANSP 25691) and by James G. Cooper between Helena and Mullan Pass on 15 Aug 1860 (USNM 22052). Other 19th-century specimens include eight taken by R. S. Williams in the Little Belt Mts. between 8 Jun and 6 Jul 1889 (MCZ 191167-191174) and one each at Great Falls on 28 May 1892 (MCZ 191164) and Columbia Falls on 6 Apr 1894 (MCZ 191163), six by Platte M. Thorne at Lame Deer on 2 and 17 May 1891 (USNM 171960-171965), one by Vernon Bailey at Hot Springs on 19 Jul 1895 (USNM 139123), and seven by Morton J. Elrod at Missoula from 22 Feb to 10 Apr 1897 (UMZM 2742-2747, 2762).
Habitat: Crossbills favor mature coniferous forests and occasionally use deciduous woods, burns, and clearcuts. They are closely associated with ponderosa pine and Douglas fir in Montana but use all conifer forest types (Hutto 1995, Hutto and Young 1999). Occasionally, they occur above tree line in summer (Hendricks and Norment 1986). The nest is a well-concealed cup of conifer twigs lined with grasses, shreds of bark, lichens, and hair. The nest found by Silloway was built 20 m above the ground in a western larch, 3 m out from the trunk. The nest observed by DuBois was about 6 m high in a ponderosa pine. Nests can be easy to find during construction but difficult afterward (C. Benkman, pers. comm.), perhaps in part because crossbills feed their young by regurgitation and thus do not carry food to the nest in their bills.
Crossbills eat conifer seeds primarily but also the seeds of birch, alder, and box elder; they consume a variety of insects in summer. Conifer preference is related to bill size and call type; type 2 birds specialize on ponderosa pine, type 3 on western hemlock, type 4 on Douglas fir, type 5 on lodgepole pine, and type 7 generalize on pines and spruces (Adkisson 1996, Parchman et al. 2006).
Conservation: BBS data from Montana indicate a non-significant decline in numbers of 2.7% per year from 1980-2007; a significant decline of 2.5% per year occurred survey-wide for the same period. The global population estimate is 15 million birds, 38% of which occur in the U.S. and Canada (Rich et al. 2004). Tree harvest and fire are expected to lead to declines in populations of conifer-seed specialists such as Red Crossbills owing to the decreased age and area of conifer forests, which lower overall conifer seed production and increase the frequency of cone-crop failures. Management recommendations include protecting large tracts of mature and old-growth stands of each of the key conifer species used by the various crossbill types and increasing the length of time between harvest rotations (Benkman 1993a,b).
Historical Notes: The first published observation that could pertain to Montana was by Hayden (1862: 165), who found the species “Quite abundant in the mountain ranges [of the Upper Missouri], where it feeds upon the seeds of the different kinds of Pine cones.” J. A. Allen (1873: 55) remarked that Red Crossbills were “Quite frequent from the mouth of the Big Horn to Pompey’s Pillar, and also on the Musselshell, in the vicinity of the pine covered bluffs, and ravines.” These undoubtedly were type 2 birds in ponderosa pines. Coues (1878), who probably spent little time in pine forests, made no mention of the species.
The pair observed by Silloway (1905b) at the Flathead Lake Biological Station was building a nest 30 m up in a larch on 19 Jul 1903. When he climbed to the nest a week later, Silloway found “only a collection of small twigs” (p. 175). Such “dummy” nests apparently have not been reported for the species before or since. The real nest was found close to the dummy nest the next day. Red Crossbills were “Common in the pine hills” surrounding the lower Yellowstone R. soon after the turn of the 20th century (Cameron 1907: 402). Birds “of all ages and plumages” regularly visited Cameron’s water trough from late May through mid-Dec in 1904 and 1905. Cameron was especially impressed with plumage variation, which ranged from vermilion and black in adult males to vermilion and brown, orange and brown, and bright green and yellow in females and young birds.
In the summer of 1954, when the cone crop was excellent, Thomas Kemper (1959) captured and collected a large series of crossbills at the Flathead Lake Biological Station. Arrivals began in late Jun and peaked from late Jul to early Aug, by which time many birds were in breeding condition, even during the early stages of molt. No juveniles were seen, and Kemper concluded that the birds began breeding in response to the high availability of conifer seeds.
Contemporary Work: Based in part on work in Montana, Craig Benkman and colleagues investigated the role that Red Squirrels play in the evolutionary arms race between type 5 Red Crossbills and lodgepole pine (Benkman et al. 2003, Siepielski and Benkman 2005). The researchers examined a suite of reproductive traits of the pines (cone dimension, number of seeds per cone, number of cones per tree, cone age) and the amount of area of pine forest in mountain ranges with and without squirrels. Montana ranges without squirrels included the Sweet Grass Hills, Bears Paw Mts., and Little Rocky Mts., and those with squirrels included the Highwood Mts., Judith Mts., and Little Belt Mts.
Because squirrels preferentially harvested pine cones that were longer and had more and larger seeds, trees that produced cones with low seed mass relative to cone mass, and cones that were wider relative to their length, were favored by natural selection. On average, crossbill density was six times higher in ranges that did not have squirrels. Cone and seed defenses aimed at deterring crossbill predation increased with higher crossbill densities, and cones in larger forests without squirrels diverged more in structure from those in the main Rocky Mts. than did cones in smaller squirrel-free forests.
Benkman and colleagues concluded that smaller ranges (Bears Paw and Little Rockies) represent coevolutionary “warm spots,” where cones have diverged from the main range because of seed predation by crossbills, but local adaptation in crossbills is restricted owing to gene flow among nomadic immigrants. Nevertheless, crossbills in these ranges had deeper bills, and lodgepole cones were longer and had thicker scales and more seeds than cones in the main Rocky Mts. The population of crossbills in the Sweet Grass Hills was very small and contained mostly transients, thus negating the likelihood of local adaptation by crossbills to the pines. Crossbill densities were low wherever squirrels occurred, regardless of forest area, and lodgepole cones were uniformly structured in the main Rocky Mts., where squirrels are always present.
Red Crossbills were reported every winter on Montana CBCs from 1979-80 to 2008-09, albeit with wide fluctuations in numbers. The highest total was 1,527 birds (1.12 per party hour) on 14 counts in the winter of 1995-96, and the lowest was 22 birds (0.01 per party hour) on two counts in the winter of 1986-87 (mean = 445 per year).
Sponsored by Craig, Patricia, and Nina Barfoot, Polson
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