Pine Siskin

Availability of thistle seed in specially designed bird feeders (and bird feeding in general) has increased in recent years in the count circle. Such feeding stations have proven highly attractive to siskins, which may concentrate at such spots in much greater numbers than elsewhere in the circle. Thus, siskins may seem sparse overall, but very locally numerous at thistle seed feeders. If they are greatly concentrated at feeding stations in some years, then the count results from recent years may be biased downwards, as few stations offering thistle seed are censused on count day.

Figure 16. Pine Siskin on the Santa Cruz County CBC, 1957-2000.

Raw counts ranged from 25-4,128 birds. Irruptions (counts >150% of the standardized average, 3.45 per party hour) were recorded in six years (14%): 1963, 1972, 1974, 1975, 1984, and 1987. Numbers in 1984 far exceeded those of any other year. Counts >100% of average occurred in 17 years (39%), and counts <25% of average occurred in 10 years (23%). Major irruption years recorded on the count have been variably followed by years of lower, similar or higher abundance (Figure 16).

Numbers on the five neighboring counts were moderately well correlated during the 16 years examined, especially during years of very high or very low abundance (Figures 17 and 18). Año Nuevo (avg 4.6 per party hour) and Santa Cruz County (avg 3.7) had the most siskins, probably due to the greater extent of potential habitat, especially forest with Douglas fir and well-developed alder riparian. Siskins were notably less numerous at Moss Landing (avg. 0.07), Monterey Peninsula (avg 0.07) and Palo Alto (avg. 0.07). However, if the very high counts at Año Nuevo in 1984-1985 and 1987-1988 and at Santa Cruz County in 1984-1985 (Figure 17) are excluded, then the average numbers are only marginally greater than in the other circles.

Figure 17. Pine Siskin on the five neighboring counts, 1983-84 to 1999-2000.
 
 

									Year
Count Circle	83	84	85	86	87	88	89	90	91	92	93	94	95	96	97	98	99
Año Nuevo						n.d.
Palo Alto
Santa Cruz
Moss Landing
Monterey Peninsula
Legend		0-50%			51-100%				101-150%				>150%

Figure 18. Comparison of Pine Siskin annual abundance among the neighboring counts as measured by % of each count’s average. (Note: for year, “83” = “83-84”, “84” = “84-85, etc.; n.d. = no data.)

American Goldfinch

American Goldfinch was recorded on 43 of 44 counts (98%), missed only on the second year (Figure 19). This species breeds locally in the count circle in coastal willow riparian habitat. It is unknown if breeding birds are resident. Many more are often present during the non-breeding season. Wintering American Goldfinches occur throughout the count circle in a variety of habitats, but especially favor riparian woodland, ponderosa pine forest, weedy fields, rural residential, orchards, and suburban settings. During irruption years they are generally widespread and may be locally common in riparian and suburban areas. As with the siskin, thistle seed feeders may concentrate large numbers of goldfinches at feeding stations. For example, the tally from one Santa Cruz feeding station on the 2000 count provided 19% of the American Goldfinches observed in the entire circle! As few feeders are censused, count results may have been biased downwards in recent years.

Figure 19. American Goldfinch on the Santa Cruz County CBC, 1957-2000. Raw counts ranged from 0-1,565 birds. Irruptions (counts >150% of the standardized average, 2.19 per party hour) were recorded in 10 years (23%): 1964, 1967, 1974, 1979, 1984, 1985, 1989, 1991, 1993 and 1997. Counts >100% of average occurred in 16 years (36%), and counts <25% of average occurred in 11 years (25%). Major irruptions years recorded on the count were followed by years of notably lower abundance on all but one occasion (Figure 19).

Evening Grosbeak

Evening Grosbeak was recorded on 22 of 44 counts (50%), the fewest years of all the species considered here (Figure 20). Its more frequent detection from the late 1970s onwards likely reflects improved coverage of its preferred habitats and locations. Evening Grosbeaks are present in the circle from fall through mid-spring, but often only from late fall through late winter. It is apparently absent or present in only tiny numbers in the majority of years. Wintering birds are often highly localized in riparian forest containing numerous box elders, especially along the San Lorenzo River and its tributary Zayante Creek. In some years they occur in ponderosa pine forest, and more rarely in other forest types, orchards, rural residential areas and at conifers in suburban areas and parks. They almost never visit feeders in Santa Cruz County. During irruption years they may be more widespread but are often simply more numerous in their preferred haunts.

Figure 20. Evening Grosbeak on the Santa Cruz County CBC, 1957-2000.

Raw counts ranged from 0-139. Irruptions (counts >150% of the standardized average, 0.10 per party hour) were recorded in seven years (16%): 1961, 1977, 1979, 1984, 1986, 1990 and 1992. Counts >100% of average occurred in 9 years (20%), and counts <25% of average occurred in 30 years (68%). Major irruptions years recorded on the count were all followed by years of apparent absence or notably lower abundance (Figure 20).

Trends among Groups of Irruptive Species

Moderate to substantial invasions for most or all of the 10 species coincided in 1968, 1977, 1984, 1987, 1990 and 1996. 1987 was clearly the peak year in the count’s history when all species are considered together. Notably low numbers for most or all of the species coincided in 1962, 1971, 1978 and 1982. While there seems to be little ecological meaning to considering all the species together, two subsets of species can be formed based on diet: fruit-eaters (Hermit Thrush, American Robin, Varied Thrush and Cedar Waxwing) and seed-eaters (Red-breasted Nuthatch, Red Crossbill, Pine Siskin, American Goldfinch and Evening Grosbeak).

The fruit-eating guild showed a more or less stable long-term trend (Figure 21). Substantial annual peaks occurred in 1968, 1977, 1981 and 1987. From 1975 to 1997 annual counts swung up and down on alternate year cycles, except for longer intervals in 1978-1981 and 1984-1987 (Figure 21). Peaks in the 1990s were lower than in the 1970s and 1980s, but were more frequent.

Figure 21. Annual variation and trends in numbers of irruptive fruit-eating species on the Santa Cruz County CBC, 1957-2000. Species include Hermit Thrush, American Robin, Varied Thrush and Cedar Waxwing.  *Y-axis values are the sum of scores of the four species’ annual abundance measured as a percent of each species’ average abundance.

The seed-eating guild showed a stable long-term trend through the 1970s, then a substantial increase in the early 1980s, followed by a steady decrease from the mid-1980s to the present (Figure 22). Substantial annual peaks occurred in 1969, 1979, 1984, 1987 and 1990. The 1996 peak would likely have been considerably higher if that count were not hampered by rain all day that year. From 1977 to the present, peaks were often separated by two to three years, with some longer intervals up to five years.

Figure 22. Annual variation and trends in numbers of irruptive seed-eating species on the Santa Cruz County CBC, 1957-2000. Species include Red-breasted Nuthatch, Red Crossbill, Pine Siskin, American Goldfinch, and Evening Grosbeak.* Y-axis values are the sum of scores of the four species’ annual abundance measured as a percent of each species’ average abundance.
 

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