Field Notes

2018 Bluebird Wrap-Up

And it came to pass that it was time for the annual, post-Christmas cavity nesters report. And what a wet and soggy year it was. From record warmth in February into the cold and damp of March and April, followed by the sudden leap into summer in early May that included copious rainfall through the rest of the year, 2018 was a year for the record book.

How did that affect our summer cavity nesting birds? Let’s dig in a little deeper. Once again about 20 birdhouses were monitored weekly with most being located on the Green Bank Observatory grounds.

Observations such as “number of eggs found, number of young hatched, number of young fledged, species involved” were recorded, and latter submitted to Nestwatch, a data base maintained out of Cornell University. In 2017, several dozen citizen scientists contributed nearly 25,000 nesting observations. Multiple research papers came out of that data, and we were happy to participate for the 12th year and there is always something to be learned.

The primary occupants are usually Bluebirds, Tree Swallows and a few House Wrens but it might be interesting to look at some totals just for fun. For instance, summer 2018 had a total of 34 nesting attempts. That is, a nest was built and at least one egg was laid in it. So, many of the birdboxes supported two and sometimes three nesting attempts.

Of those 34 attempts, 27 were successful at hatching and fledging at least one young bird for a success rate of nearly 80%. Open nests in nature are much less successful with barely 25% producing young. Predators reign in the wild and that may explain why many bird species have evolved into cavity nesters.

To continue, a total of 153 eggs were laid in these boxes, 125 young hatched out, and eventually 104 young fledged and flew away.

If we break it down by species, we find that Bluebirds had a banner year with 15 out of 19 successful nests that produced a total of 61 young. A week of record heat in early July may have set back the second nesting, but overall it was still a great summer. Previous best were in 2015 and 2017 when 50 young fledged each year. In 2012 only 13 birds survived due to heavy predation and disease.

If we look at the Tree Swallow numbers, we find 10 out of 12 nests were successful, producing 33 young. The swallows appear to be showing a steady decline from the peak year of 2011 when 58 young fledged and 2014 produced 49 birds. Attempts are down and eggs produced are down but the reasons are unknown.

But that is why we do this. Surely observations by interested folks will show us trends and allow us to identify problems within the bird world. As many as half of the bird species on earth are in decline with many on the edge of extinction. We can blame this on many things; global warming, pollution, habitat loss, evolving predators and diseases, etc.

Hopefully we can identify the problems and take corrective measures before our own species is affected and eliminated.

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