Ed,
Would a smaller number of gourds allow you to conduct the recomended nest replacements or was this an experiment?
Are you asking could I have found the time to clean out the gourds? Um, yes.
What percentage of the eggs laid in your 49 gourds have fledged?
I'm not looking at the data right now but no, there have been no discernible changes in clutch losses or nestling survival. Certainly, over the past thirteen years of records, this has been one of our better years.
Two of 49 clutches failed to hatch, a normal failure rate here it seems.
Overall success this year, including these failed clutches, has been an average of 4.2 nestlings successfully fledged per nesting attempt. A "nesting attempt" being defined as beginning when one or more eggs actually appears in a gourd.
"Four point something" fledges per nesting attempt is about as high as our colony gets.
This is the first year of any I can recall with NO mite problems, and also only the second time all the martins came back to old nests.
What drives purple martin success in this part of the world is rainfall, pure and simple. The critical window appears to be the last two weeks when the martin nestlings are large and their food requirements greatest.
I have watched them many times through an entire foraging flight. Around here in this urban environment, leaving the colony they climb steeply into the prevailing breeze until they are high up and hard to see, they then actively forage, darting around and drifting downwind, before returning to the colony in a series of steep dives.
If they cannot do this about every two or three minutes during peak foraging times, returning with large insects each time, they will lose nestlings.
Hence our colony success depends on the number of large insects passing high overhead in a window of sky over the colony perhaps as much as a mile across.
This is a good year so nestling losses have been minimal.
In contrast the drought year of 2011 was our worst year when almost NO nestlings survived among 47 nests.
Secondly, what circumstances led you to abandon nest changes as a management tool?
We are a high school and I am a science teacher so so EVERYTHING is an experiment.
Probably the last four or five years I have left some old nests in, the reason being simple curiosity and a sound knowledge of ecology (actually, both my degrees are in entomology - insects, my MS is from Texas A&M and my BS is from the College of Environmental Science and Forestry, Syracuse NY). Only an idiot brags on their college education, I post those just to indicate I'm grounded in the principles.
Why some gourds develop mite problems and others to not, even when all started identically clean, seems a mystery.
I do keep shredded cypress bark mulch on hand and would have switched out a nest in a heartbeat had mites been a problem.
Next year I'll formalize this and do half and half, equally interspersed through our four gourd pole locations.
Anyhow, this is what our colony looks like from the outside, here's a couple of photos I snapped just yesterday at dusk. Probably half the broods are already gone by this point...
Our Gemini...
..and our old Carrol pole, which just bent this year in a windstorm and so will need replacing. Fortunately it still lowers enough that with a step ladder we can still access the gourds.
This is our S&K pole in the fenced-in school garden out back, I'll admit some of the arms are a tad droopy, a tendency of the design...
Our fourth pole is an SS with 17 gourds attached.
Mike
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