Patterns of Population Change in Birds

Summaries of Bird Population Change

The BBS has data from over 421 species of birds, covers most of North America, and has been going on for over 31 years. Summaries of the data are bound to be controversial, because they collapse information over species, space, or time. For example, it appears that rangewide, over the 31 years, about half (51.5 %) of the species have increased, about what you would expect by chance. But, this apparent overall stability hides many increases and declines. Sorting out these patterns is difficult, and here we provide some tools for analyzing the patterns of population change.

Lists of species with significant population increases or declines by region
Overall summaries of the proportion of species with increasing population, for 13 species groupings.
Maps of species richness and mean population trends for the 13 groupings

Species group analyses: Often, it is useful to group species that share some common feature. We group birds based on attributes such as breeding habitat, nest type, migration status, and nest location. If species in the group show consistent trends, and differ from species not in the groups, it suggests that the common feature could be influencing population change for the group. For more discussion on this, click here. For a listing of the species in each guild, click here

Percentage of Increasing Species by Group

These "big picture" summaries are useful in identifying major patterns of population change, such as the long-term decline in grassland-breeding birds. Here, we calculate the percentages using the empirical Bayes method described in Link and Sauer (1996).

Click here for a histogram of the percentages by species group, along with 95% confidence intervals. Note that grassland-breeding birds are the only group showing consistent declines.

Detailed Regional Analysis of Population Change

Here, an interactive program provides summary information and ranked lists of trends for all species found in a selected region, time period, and species group.

Click here for the list.

Maps of Population Change and Species Richness by Species Groups

Here are the maps that show you both where the species groups occur and the relative magnitude of population changes. The survey-wide percentage of species with positive trends are presented in parentheses, and ** indicates that the result is significantly different from 50 %.

Breeding Habitat Species Groups

Grassland Birds
(23.3 %**; N=28)
Trend Map
Species Richness Map

Wetland/Open Water Birds
(66.5 %**; N=86)
Trend Map
Species Richness Map

Scrub/Successional Birds
(39.6 %; N=86)
Trend Map
Species Richness Map

Woodland Birds
(57.4 %**; N=133)
Trend Map
Species Richness Map

Urban Birds
(28.3 %; N=14)
Trend Map
Species Richness Map

Nest Type Species Groups

Cavity Nesting
(61.0 %; N=62)
Trend Map
Species Richness Map

Open-cup
(Passerines and Cuckoos
(43.0 %; N=184)
Trend Map
Species Richness Map

Migration Status
(Landbirds and Hawks)

Permanent Resident
(55.3 %**; N=92)
Trend Map
Species Richness Map

Short-distance Migrant
(46.1 %**; N=107)
Trend Map
Species Richness Map

Neotropical Migrant
(46.3 %; N=136)
Trend Map
Species Richness Map

Nest Location Species Groups
(Passerines and Cuckoos)

Ground or Low Nesting
(36.1 %; N=117)
Trend Map
Species Richness Map

Mid-story or Canopy Nesting
(55.7 %; N=121)
Trend Map
Species Richness Map

All Species

(51.5 %; N=421)
Trend Map
Species Richness Map

Prepared by:

John R. Sauer
Patuxent Wildlife Research Center
11500 American Holly Drive
Laurel, Maryland 20708-4017 USA
E-mail: JRSauer@usgs.gov

Last updated 29 July 1997