Chickadee Trends

.

Over the course of a year, I try maintaining enough bird surveys to provide a continuum of meaningful data across seasons. With enough sampling diversity and repitition, patterns may emerge that are not apparent from individual or annual censuses. Long-term data sets are requisite, but individual efforts face real-world time constraints. On the other hand, collective programs remain relatively uncommon or somewhat difficult to access. Moreover, for some sources, quality control can be a huge problem. By analyzing my own material, I can not only discern trends of potential interest but also discover deficiencies that can prompt (and encourage) me to continue or alter future surveys.

.

While examining my Black-capped Chickadee data from the Muskegon Lake Nature Preserve banding station, I was curious whether the strong numerical oscillations were showing a wider pattern. I compared those results from the Muskegon Wastewater CBC and the Gwinn CBC (which I conduct in the Upper Peninsula). I also looked at sex-adjusted totals from my Upper Peninsula Breeding Bird Survey routes. Finally, I added data from the Muskegon Migration Count (conducted every spring) into the mix.

The graph shows general agreement between the two CBC counts (Gwinn was not run this winter). A smaller, but fairly similar pattern exists in the breeding data. Since the breeding surveys do not include juveniles, whereas CBC numbers do, the disparity in numbers makes sense. The reflecting pattern highlights a relationship between breeding adults and total winter population. Although numbers are low, the spring Migration Count trends also match reasonably well, but only if the data is adjusted by one year (to conform to the previous CBC); they show a very poor correlation to totals from the subsequent breeding season.

.

At the banding station, 92% of my chickadee total comprises young birds, most dispersing from breeding areas outside the preserve. Thus, the oscillations offer a fairly direct assessment of breeding productivity - albeit at an unknown geographic extent. The graph shows a weak relationship between breeding and fall numbers and another weak relationship between fall and winter numbers. The relationship would have been fairly strong, but 2009 proved to be anomalous. Consequently, cumulative banding results may be too heavily influenced by local trends or aberrations, and the lack of a strong correlation means that predicting large-scale population values from the annual totals currently remains somewhat limited.

.

Brian Johnson

.