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IMPORTANT! When
viewing the graphs, please pay close attention to the scale of the
vertical axis.
Two graphs below look
identical at first glance, but the numbers (indices) on the y-axis tell us
otherwise.
The 1st graph shows the trend of a species
increasing at a rate of 3% a year.
The 2nd graph shows
the trend of a species
increasing at a rate of 34% a year.
The indices on the y-axis (vertical) represent an
increase relative to the first year (NOT the average number of birds
recorded). Think of the indices like percentages. A change
from 1 to 1.25 over seven years is like a 25% increase over seven
years.
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Avg. Yearly Rate of Change: Estimated annual
decrease or increase in the population.
 This number
shows how much a species is increasing or decreasing each year. The
percentage changes presented here, especially for the 1997-2004 data
may be exaggerated (higher than the actual yearly change of the
species). Also, species with small sample sizes and/or poorly
known trends are more likely to have exaggerated numbers and graphs. |
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Conservation Concern:
The current conservation status of a species.
Lists endangered species (highest concern),
threatened species
(next highest concern), and then the three watchlist categories.
The watchlist categories include:
"WL-R "/ "WL-Y" (Audubon
Watchlist - Red / Yellow), "FW" (USFWS
Birds of Conservation Concern), & "PIF" (Partners
in Flight Watchlist). |
Population Trend:
The overall population trend of the
species.*
Substantial Decrease
- a certain or almost certain yearly decrease (at least moderate
credibility)
Decreasing
- an uncertain but likely yearly decrease
Stable - almost certainly
very little yearly increase or decrease
Increasing - an uncertain
but likely yearly increase
Substantial Increase
- a certain or almost certain yearly increase
(at least moderate credibility)
Poorly Known - a conclusion cannot be made due to
insufficient data, excessive error, or a stable but uncertain trend.
*Loosely based on "A
procedure to classify trend estimates"
(Van Strien et al. [in press]), (Pannekoek & van Strien 1996)*
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Credibility: A generalized
rating of the accuracy of the trend for a given species.
The rating takes into account the Sample Size
(num. of records of a species), the possible Range of the Trend when
the level of error is taken into account, and the Consistency of
the model ("high, if trend estimates are predominately 'one-sided', i.e.
either mostly all positive or mostly all negative"). Ratings are
occasionally decreased one "level" for species that are not
adequately monitored by the BCN Census (eg. Urban and Agricultural birds)
and increased one "level" for species with extremely high consistence.
This rating is meant to be used to compare the data quality of the various
species within this database only. A rating of "Very Good" only
implies that the trend for that species is very good in relation to other
trends presented in this analysis.
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SAMPLE SIZE |
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RANGE |
CONSISTENCE |
<10 |
10-30 |
30-50 |
50-200 |
>200 |
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Low |
High |
Mod. Poor |
Moderate |
Mod. Good |
Good |
Very Good |
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Low |
Low |
Poor |
Mod. Poor |
Moderate |
Mod. Good |
Good |
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High |
High |
Poor |
Mod. Poor |
Moderate |
Mod. Good |
Good |
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High |
Low |
Very Poor |
Poor |
Mod. Poor |
Moderate |
Mod. Good |
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 Trend
Level: A general representation of how
much a species is increasing or decreasing annually.
A trend level of "0" represents a
less than 2% annual increase or decrease. A trend level of "1"
represents an increase of between 2% and 3%. A trend level of
"2" represents an increase of between 3% and 10%. A trend level
of "3" represents an annual increase of more than 10% (negative levels
follow the same scale, but inversed). |
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