Blue Jay

Cyanocitta cristata

Winter Trend: Decreasing

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

Blue Jays, 1987–2025.

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

What’s the Story?

Blue Jays are instantly recognizable for both their loud calls and their striking blue plumage. While many remain in New Hampshire year-round, some migrate south in winter. This movement is closely tied to food supply. When acorns and other food sources are abundant, Blue Jays stay. When food is scarce, more Blue Jays head south in search of resources.

Our analysis of Backyard Winter Bird Survey data reveals a significant downward trend in winter reports of Blue Jays. A negative binomial regression shows a decline (β = -0.018 ± 0.004 SE, z = -4.539, p < 0.001).

This translates to reports of Blue Jays deceasing by about 2% per year, even when accounting for changes in the number of Backyard Winter Bird Survey participants over time.

There is, however, no need for alarm. Status and Trends data from eBird show that Blue Jay populations are actually increasing during the breeding season across much of the northeastern U.S. (check out the map here).

This contrast highlights the importance of monitoring birds throughout their entire annual cycle. A decline in winter numbers may not always signal an overall population decline. It could reflect changes in migration patterns or shifting food availability.

Feeding Tips

  • Blue Jays enjoy whole peanuts, cracked corn, and sunflower seeds.
  • At the feeder, Blue Jays can sometimes be aggressive toward smaller birds. To reduce conflicts, consider setting up a separate feeding station with peanuts to keep Blue Jays busy. They prefer feeding on elevated platforms.

In Your Backyard

  • You’ll often hear a Blue Jay before you see it! They are common across many different habitats.
  • Planting oak trees provides a long-term food source for Blue Jays and many other wildlife species. If you already have mature oaks, leave fallen acorns on the ground. They’re an important food source for wildlife.

ID Tips

Blue Jay perched on a wire.

Blue Jay by Caitlin McMonagle, 2025 Backyard Winter Bird Survey.

Blue Jays are large and blue overall. Look for the prominent crest on head and listen for their noisy “jay” calls.

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

Cyanocitta cristata

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.