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 33 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.

Users can access:

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 using 1966-1996 results, 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, using data from 1966 - 1998.
Click here for the list.

Maps of Population Change and Species Richness by Species Groups 1966 - 1996

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 pct N

Grassland Birds 23.3%** N=28 tend map    species richness map

Wetland/Open Water Birds 66.5%** N=86 tend map    species richness map

Scrub/Successional Birds 39.6% N=86 tend map    species richness map

Woodland Birds 57.4%** N=133 tend map    species richness map

Urban Birds 28.3% N=14 tend map    species richness map

Nest Type Species Groups pct N

Cavity Nesting 61.0% N=62 tend map    species richness map

Open-cup (Passerines and Cuckoos) 43.0% N=184 tend map    species richness map

Migration Status (Landbirds and Hawks) pct N

Permanent Resident 55.3%** N=92 tend map    species richness map

Short-distance Migrant 46.1%** N=107 tend map    species richness map

Neotropical Migrant 46.3% N=136 tend map    species richness map

Nest Location Species Groups (Passerines and Cuckoos) pct N

Ground or Low Nesting 36.1% N=117 tend map    species richness map

Mid-story or Canopy Nesting 55.7% N=121 tend map    species richness map

All Species pct N

all species 51.5 N=421 tend map    species richness map

Breeding Habitat Species Groups	pct	N
Grassland Birds	23.3%**	N=28	tend map	species richness map
Wetland/Open Water Birds	66.5%**	N=86	tend map	species richness map
Scrub/Successional Birds	39.6%	N=86	tend map	species richness map
Woodland Birds	57.4%**	N=133	tend map	species richness map
Urban Birds	28.3%	N=14	tend map	species richness map

Nest Type Species Groups	pct	N
Cavity Nesting	61.0%	N=62	tend map	species richness map
Open-cup (Passerines and Cuckoos)	43.0%	N=184	tend map	species richness map

Migration Status (Landbirds and Hawks)	pct	N
Permanent Resident	55.3%**	N=92	tend map	species richness map
Short-distance Migrant	46.1%**	N=107	tend map	species richness map
Neotropical Migrant	46.3%	N=136	tend map	species richness map

Nest Location Species Groups (Passerines and Cuckoos)	pct	N
Ground or Low Nesting	36.1%	N=117	tend map	species richness map
Mid-story or Canopy Nesting	55.7%	N=121	tend map	species richness map

All Species	pct	N
all species	51.5	N=421	tend 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 3 December 1999
horizontal bar