Monday, June 25, 2007

Purple Martin Report, June 24

Purple Martin groups like PMCA and PMS,NA recommend checking the nests of your martin colony every 5 days, counting eggs and young, looking for problems like signs of parasites or predation, and just monitoring their status in general. Many people don't check their colonies, for fear of scaring the birds away, but research shows that monitored colonies produce more offspring than those that are left alone.

I am used to monitoring bluebird boxes, and raising bluebirds has always been easy. It is rare that I have any problems. Once I had a house wren pierce the eggs and toss them out of the box, building a nest of little sticks on top of the bluebird nest. One year, a house sparrow destroyed 5 bluebird eggs from a second clutch, causing the bluebirds to abandon me for the rest of that season. (This was when I began trapping HOSP.) Aside from those two instances, I never have any trouble. Rarely, an egg doesn't hatch or a nestling vanishes, but I have a pretty high success rate, if you leave out the wren and sparrow attacks.

I do my Purple Martin nest checks on Thursdays and Sundays, because I am off those days and can do my checks in mid-day, when I am least likely to disturb the birds. While they do circle overhead squawking at me and occasionally dive-bombing me, they don't seem too bothered by what I am doing. I am finding a number of things I'm not used to in my bluebird monitoring. I'm learning that Purple Martins are high-maintenance birds!

Six eggs from an adult pair of Purple Martins

On June 14, I had a total of 50 eggs in 11 nests. After my nest check on Sunday, it is obvious I am not going to have 50 babies fledge. I found some problems. Most of my colony, all but one pair, are SY (Second Year, or Subadult) birds. These are the "teenagers," having babies for the first time, and smaller clutches with more losses are the norm for them.

One clutch of four eggs should have hatched on June 17. Now, it looks like that pair is building a new nest over the unhatched eggs.

I found several other unhatched eggs, including this one in a clutch
of three day old nestlings:

The saddest thing I found was in this nest of 6 young that looked fine on June 21. On Sunday, there were 5 strong six days old nestlings and one dead one. Don't know why, especially because this is my one ASY (After Second Year, or Adult) pair. In theory, they should be more experienced and have larger clutches with fewer losses. Maybe the drought we have been experiencing is decreasing the numbers of flying insects?

Can you see the ear holes on these chicks?

I pulled out the dead baby and an unhatched egg that has been there for a week. I left the two unhatched eggs in nests with 3 day old young. If they are still there on Thursday, I will remove them, too. I probably should have pulled the 4 eggs that are a week overdue. I guess that is another job for Thursday.

Martins are a lot of work!


LauraHinNJ said...

I'm surprised to see the fresh green leaves in the nests. Is that common to martins?

Susan Gets Native said...

Hey....any martins your gourds produce is fantastic. Who knows why things like that happen.
I'm just jealous. Grr.

KatDoc said...

Yes, Laura, green leaves are typical of Purple Martin nests. You can tell your martins are nearly ready to lay eggs when you see them start bringing green leaves in. Mine have utilized maple, white birch, and willow leaves.

They keep bringing leaves in as they lay, and eggs are often hidden under a layer of leaves.

There are several theories as to why they do this; one theory is that the leaves have some sort of anti-parasitic effect, another is that the leaves contribute extra moisture to the nest, maintaining a proper humidity level. I don't think anyone knows for sure why they do it, though.


Julie Zickefoose said...

Maybe because they think they're pretty? All of the above?

Hats off to you, KatDoc, for ridding those nests of the dead and unhatched. What seems to be too much trouble for many people pays back in so many ways--learning, and sharing with us. Thanks for the fabulous look inside martin nests. It eases the pure envy many of us are feeling! Says Zick, who has had gourds up for 14 years...with nuttin' but starlings and once, a tree swallow using them. Oh, and bluebirds roosting in them all winter! Worth it!