Birding Follow-up: Cerulean Warbler

Seeing birds in the field often prompts me to do a little follow-up when I get home. I might read up on natural history details for a particular species or group of species I encountered, maybe track down the natural history information behind certain behaviors I observed, or the biology behind plumage or structural details I noticed that day. Sometimes that information turns out to be worth sharing, so I’m going start posting some of that info here in the form of “Birding Follow-up” posts.

Cerulean Warbler by Alex Champagne, on Flickr

Cerulean Warbler at Glen Echo Park, Columbus, OH. 4.19.2013. Photo by Alex Champagne.
eBird Checklist: http://ebird.org/ebird/view/checklist?subID=S13805495

Today I came across my second Cerulean Warbler of the year, which was a bit of a surprise given how little I’ve been out birding this spring!  The first individual was last weekend at Glen Echo Park in Columbus, and it put on quite a show (at eye-level!) for my wife and I.

Today, I found bird #2 on the Ohio State University campus, near Mirror Lake (an area I bird frequently during migration).  So why was I surprised?  Because Cerulean Warblers are on the decline, and while not rare, they’re by no means a common bird in Ohio during spring migration!

To illustrate that decline, here’s the BBS data trend for Cerulean Warbler from 1966-2011:

Cerulean Warbler population trend based on BBS data from 1966-2011 (survey wide).

Cerulean Warbler population trend based on BBS data from 1966-2011 (survey wide). These numbers were pulled from the BBS website using the trend analysis tool. The plot was made with the R code at the end of this post.

Not good! Why the declines? As with many species, there are multiple factors involved, most having to do with habitat loss and degradation resulting from human activity, both in North America as well as on their wintering grounds in South America.

For more details, see:


Code for the BBS data figure:

# Graphics package.
library(ggplot2)

# Load BBS Heirarchical Model Results from
# http://www.mbr-pwrc.usgs.gov/cgi-bin/tf11.pl
CEWA = read.table(header=TRUE, text="Year Index CI.025 CI.975
1966 0.91 0.65 1.40
1967 0.81 0.60 1.14
1968 0.86 0.63 1.24
1969 0.83 0.62 1.15
1970 0.83 0.61 1.27
1971 0.77 0.58 1.10
1972 0.76 0.57 1.06
1973 0.72 0.55 0.98
1974 0.66 0.50 0.90
1975 0.62 0.48 0.84
1976 0.69 0.53 0.94
1977 0.59 0.46 0.79
1978 0.53 0.40 0.70
1979 0.56 0.43 0.74
1980 0.50 0.39 0.67
1981 0.51 0.39 0.69
1982 0.45 0.35 0.60
1983 0.50 0.38 0.71
1984 0.46 0.35 0.62
1985 0.47 0.36 0.64
1986 0.44 0.34 0.59
1987 0.42 0.33 0.56
1988 0.43 0.34 0.57
1989 0.40 0.31 0.55
1990 0.41 0.32 0.56
1991 0.38 0.30 0.52
1992 0.38 0.30 0.50
1993 0.36 0.28 0.47
1994 0.34 0.27 0.45
1995 0.37 0.29 0.48
1996 0.38 0.30 0.52
1997 0.35 0.27 0.45
1998 0.30 0.24 0.40
1999 0.27 0.21 0.36
2000 0.27 0.21 0.35
2001 0.26 0.21 0.35
2002 0.26 0.20 0.36
2003 0.29 0.22 0.40
2004 0.27 0.21 0.35
2005 0.25 0.19 0.33
2006 0.25 0.20 0.33
2007 0.25 0.19 0.33
2008 0.22 0.17 0.29
2009 0.23 0.18 0.31
2010 0.22 0.17 0.30
2011 0.21 0.16 0.29")

# Plot
ggplot(CEWA, aes(Year, Index)) + geom_point() + geom_line() +
ggtitle("BBS Heirarchical Model: Cerulean Warbler (1966-2011)") +
geom_ribbon(aes(ymin=CI.025, ymax=CI.975), fill="blue", alpha=0.1)
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