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Previous BSSC lists
Remsen 1978 (pdf)
BSSC 1992 (pdf)

How species are considered for the list
The Criteria and Ranking Scheme (pdf)
Definition of a BSSC

This page was updated March 2008

Previous Lists

Remsen’s (1978) and CDFG’s (1992) prior BSSC lists; information on these lists and state threatened and endangered species can be found at CDFG’s website http://www.dfg.ca.gov/endangered/birds.html.

BSSC Criteria and Ranking Scheme – this explains the definition of a BSSC, how nominees for the list were selected, the objective criteria by which all nominees were scored, and the ranking process by which taxa were selected for the draft list and placed within three levels of conservation priority.

Definition of a BSSC
"Bird Species of Special Concern" (BSSC) in California are those species, subspecies, or identified populations that currently satisfy one or more of the following criteria:
(1) may meet the state definition of threatened or endangered but have not formally been listed.
(2) are extirpated from the state totally or in their primary seasonal or breeding role and were never listed as state threatened or endangered.
(3) are listed as federally, but not state, threatened or endangered.
(4) are experiencing, or formerly experienced, serious population declines or range retractions that if continued, or resumed, could qualify them for state
threatened or endangered status.
(5) have naturally small populations exhibiting high susceptibility to risk from any factor(s) that if realized could lead to declines that would qualify them
for state threatened or endangered status.

Hence, SSC generally share one or more of the following characteristics: (1) show marked population declines or range retractions (population estimates are unavailable for the vast majority of taxa),
(2) occur in small, isolated populations or in fragmented habitat and are threatened by further isolation and population reduction,
(3) depend on habitat(s) that historically or recently has declined substantially in size (infers population viability of a taxon is influenced by trends in suitable
habitats),
(4) occur only in or adjacent to areas where habitat is being converted to land uses incompatible with the species’ survival, and
(5) occur largely on public lands for which current management practices are inconsistent with the species’ persistence.

BSSC Scoring Criteria
We scored all nominated taxa for each of the following seven criteria. As noted above, we weighted (doubled) the scores for population trend, range trend, and
threats to reflect their emphasis in the definition of a BSSC. For each taxon, we scored just the population in the season for which the taxon is of concern in California. For example, scores for the Northern Harrier apply only to state’s breeding population, since it is much more numerous and of much less concern in the
state in winter. Scores generally are approximations given the lack, in most cases, of precise data. Both the linear and categorical schemes use the criteria scores in different ways, described below, to identify taxa of concern.

Population Trend (PT)
This criterion estimates the change in a taxon’s population size from the time of the publication of Grinnell and Miller (1944) to the present. Scores are based on quantitative or anecdotal data on the magnitude of population change or, if lacking, data on changes in the availability or condition of a taxon’s habitat.

Population size:

seriously (>80%) reduced 20
greatly (>40-80%) reduced 15
moderately (>20-40%) reduced 10
slightly (>10-20%) reduced or suspected
of having been reduced but trend unknown 5
stable (<10% reduced) or increasing 0

Range Trend (RT)
The range trend criterion estimates the change in the size of a taxon’s breeding or wintering range in California from the time of publication of Grinnell and Miller
(1944) to the present. Scores are based on gross changes to a taxon’s range polygon (i.e., the outlying boundary of the range), which may be inferred by loss of habitat. The trend does not estimate the extent of local extirpations within the overall range.

Range size:

seriously (>80%) reduced 20
greatly (>40-80%) reduced 15
moderately (>20-40%) reduced 10
slightly (>10-20%) reduced or suspected of having been reduced but trend unknown 5
size stable (<10% reduced) or increasing 0

Population Size (PS)
This criterion estimates the number of individuals of a taxon in California during the season of concern (breeding, wintering or otherwise).

Population size:
<1000 individuals 10
>1000 but <10,000 individuals 7.5
>10,000 but <100,000 individuals 5
>100,000 but <1,000,000 individuals 2.5
>1,000,000 individuals 0

Range Size (RS)
The range size criterion estimates the percentage of California occupied by a taxon, measured by the range polygon’s outlying boundary. Seabirds or other
waterbirds restricted solely to coastal estuarine, inshore, or pelagic waters are evaluated based on the marine environment from the California coastline west 200
miles (American Birding Association Checklist Area). All other species are evaluated based on terrestrial California, i.e., the political boundary of the state exclusive
of ocean waters.

Range size (% of California occupied):

<10% 10
>10%-50% 5
>50% 0

Percentage of Entire Range within California (EN)
This criterion measures what proportion of a taxon’s North American range or population occurs within California. Taxa with a high proportion of their range or
population within California are considered of greater concern than taxa with only a small proportion of their range or population in the state.

Proportion of North American range and/or population within California:

100% (endemic) 10
>80% but <100% (near-endemic) 7.5
>50%-80% 5
>20%-50% 2.5
<20% 0

Population Concentration (PC)
This criterion estimates how concentrated a taxon is within its California range. Highly concentrated taxa generally are considered more vulnerable to predation,
disease, or other catastrophic events than are widely dispersed taxa.

Majority (>50%) of population concentrated at:

1-3 sites. 10
4-30 sites. 5
>30 sites. 0

Vulnerability to Threats (THR)
This criterion estimates the approximate impact of realized known threats and (secondarily) potential irregularly occurring catastrophic events (e.g., oil spills, disease events) known to periodically affect some taxa. Scores are based on projected long-term realized impacts of single or multiple threat factors and not on speculative
threats for which there is no historical basis.

In the next 20 years, habitat loss, habitat degradation, or other human-induced threats are projected to:

seriously reduce (>20%) a taxon’s population in California 20
greatly reduce (>15-20%) a taxon’s population in California 15
moderately reduce (>10-15%) a taxon’s population in California 10
slightly reduce (>5-10%) a taxon’s population in California 5
have no substantial net impact, i.e., a taxon’s population should
remain stable (<5% reduced) or increase in the next 20 years 0

Linear Ranking Scheme
The BSSC version is actually a weighted linear ranking scheme in that the PT, RT, and THR scores are doubled relative to other criteria to emphasize the importance
of declines and vulnerability. Regardless, the scores for all criteria for each taxon are summed and arranged from highest to lowest. After inspection of the initial list
of scored taxa, we drew an arbitrary line thereby including on the linear BSSC list all taxa with scores >37.5. We further divided the linear BSSC list into three levels
of priority:

First Priority: Scores > 60 and < 90
Second Priority: Scores > 47.5 and < 60
Third Priority: Scores > 37.5 and < 47.5

Categorical Ranking Scheme
Like the linear scheme, the categorical scheme outlined here emphasizes PT, RT, and THR scores. Instead of adding all scores for all criteria, however, the
categorical approach uses one or several scores to simultaneously develop the list and discriminate between three levels of priority. The criteria scores needed for
inclusion in each of three priority levels, their verbal equivalents, and the list of the 60 taxa that qualify are as follows:

First Priority: PT or RT = 20 OR THR = 20 and PT or RT = 15. Population or range size seriously reduced OR population or range size greatly reduced and threats projected to seriously reduce the taxon’s population in California in the next 20 years.

Second Priority: PT or RT = 15 OR THR = 15 and PT or RT = 10. Population or range size greatly reduced OR population or range size moderately reduced and threats projected to greatly reduce the taxon’s population in California in the next 20 years.

Third Priority: PT or RT = 10 and PS, RS, or PC > 7.5 OR THR = 15 and PS, RS, or PC > 7.5. Population or range size moderately reduced and population is at high risk because of at least one vulnerability factor OR threats projected to greatly reduce a taxon’s population in California in the next 20 years and the taxon’s population is at high risk because of at least one vulnerability factor.