Carolina Wren

Thryothorus ludovicianus

Winter Trend: Increasing

Graph showing Carolina Wren winter population trend in New Hampshire from 1987 to 2025, with model prediction and 95% confidence interval.

Carolina Wren, 1987–2025.

 The dark purple line shows the trend overtime predicted by our statistical model, while the shaded purple area shows where we are 95% confident the true trend lies. Gray points are the numbers of Carolina Wrens actually observed in participants’ backyards, averaged per observer.

What’s the Story?

In the last few decades Carolina Wrens have made a remarkable range expansion into New Hampshire. Prior to the 1990s they were a rarity here, but today they are regularly reported south of the White Mountains. Warmer winters have made this expansion possible, though their populations still remain vulnerable to severe cold snaps. During harsh winters, many Carolina Wrens can die, but their numbers typically rebound in subsequent years. Carolina Wrens are a clear reminder of how even small shifts in snowfall or temperature can dramatically affect bird populations.

Our statistical analysis shows their remarkable and recent increase: a negative binomial regression shows a significant upward trend (β = 0.120 ± 0.006 SE, z = 18.63, p < 0.001). Note that a record number of Carolina Wrens were reported in 2025!

This translates to reports of Carolina Wrens increasing by about 13% per year, even when accounting for changes in the number of Backyard Winter Bird Survey participants over time.

Bird feeders have also been credited with helping facilitate their range expansion, providing Carolina Wrens food during a vulnerable part of the year. It’s no wonder they’ve become favorites at feeders. Who doesn’t enjoy the sight (and sound) of these bold, buzzy little wrens?

Feeding Tips

  • Carolina Wrens enjoy a wide variety of foods including suet, mealworms, peanut hearts, and hulled sunflower seeds.
  • Place suet feeders near dense shrubs or sheltered spots to provide a quick escape from predators lurking nearby.

In Your Backyard

  • Provide dense shrubs or brush piles to give wrens essential shelter on cold nights. Carolina Wrens are also known to tuck themselves into porches, garages, or sheds for warmth.
  • Carolina Wrens have a variety of buzzy songs and calls. They can be feisty, chasing away other birds at feeders.

ID Tips

Carolina Wren with white eyebrows and decurved bill in winter.

Carolina Wren by Caitlin McMonagle on her 2025 BWBS.

The Carolina Wren has a bright white eyebrow. Otherwise, the bird is buffy brown with a slightly decurved bill. Also look for the tail which usually sticks straight up.

Want to Learn More? Visit the State of the Birds!

Thryothorus ludovicianus

Understanding the Graph and Statistics

Observed Data (gray points):

The average number of birds counted per participant each year.

Model-Predicted Trend (dark purple line):

A line from a statistical model that estimates the overall trend in bird numbers over time, smoothing out year-to-year fluctuations.

95% Confidence Interval (shaded purple area):

The range around the predicted trend where we are 95% confident the true trend lies. Gray points inside this band indicate observations that are consistent with the predicted trend.

Other Stats You Might See in the Story:

  • β (slope) and SE (standard error): These numbers tell us how strongly and precisely the bird counts are changing each year.
  • p-value and z-value: These tell us whether the observed trend is statistically significant (i.e., very unlikely to be due to random chance). For example, a p-value less than 0.05 usually means a statistically significant trend in either direction.

The Takeaway: These graphs show how bird populations are changing over time. The model helps us see the overall trend and the confidence interval shows how certain we are about that trend.