Purple Power

Julia and I took over land lording duties at Hornsby Bend’s active Purple Martin colony this year. We are happy to report a very successful year, with over 115 fledglings! We can also report that our maintenance efforts were partially responsible for at least 22 of these fledglings. We have detailed records and some distilled statistics.

So what did we do? Approximately once a week between March and July, we checked each of the 37 Purple Martin nesting housing cavities, which were in a combination of gourd racks, and metal houses, and gourds on light poles. Our checks were centered on 3 maintenance tasks:

• Removal of non-native bird nests. Purple Martins have 2 aggressive competitors for nest sites, both non-native introduced birds from Europe: House Sparrows and European Starlings. Both species will destroy martin eggs, and Starlings will even attack and kill adult martins. As non-native birds, their nests can be legally removed, and we removed 27 House Sparrow nests, and 3 European Starling nests. The starlings quit nesting after we replaced all the round-holed gourds with crescent- or bat-shaped excluder holes.
• Removal of hazards. This category included removing a dead adult (allowing a successful nest, probably by another couple), removing addled and sparrow- or starling-pecked eggs, and replacing nest material that had become infested with mites.
• Gathering of data. This task was the least useful to this batch of martins, but useful to us, and hopefully of long-term use to the species. We counted eggs and young, and kept tally sheets. We’ll report these numbers to the Purple Martin Conservation Association, who does long-term martin research. We’ll also try to use the numbers to determine which types of housing work best for martins in Central Texas.

Then there were some interesting stories we could gather from the data:

• Disaster House. One family of 4 youngsters had an unexplained disappearance of 1 sibling, and later we found all the remaining young dead. We cleaned the cavity and it was filled with a second nest. This produced 1 young, who we also found dead. Perhaps this cavity was the home of an inexperienced couple who just couldn’t feed their young, or perhaps it was just haunted by ghosts.
• Egg Mysteries. About 1/5 of the eggs just disappear. Whether they’re bad, or whether they’re pecked or tossed out by sparrows or starlings, we don’t know. 
• Nest fight. In one gourd, we found a dead adult female hanging out of a gourd in which sparrows had built a partial nest over what looked like a successful martin nest. We can only conjecture that she died in some kind of struggle, perhaps defending her young from the sparrows’ incursions.
• Happy Stories. Although they don’t make exciting stories, there were many nests that followed the idyllic “eggs laid, babies hatch, babies grow, youngsters fledge” story line. Several gourds had failed nests, only to have a new nest built and young successfully fledge from it. And those are the stories that make all the work worthwhile.

We learned a few lessons:

• Tanglefoot is a great tool to keep fire ants off the houses. We found we needed to re-apply it after a month, as the ants eventually got past it and overran 2 of the housing units (luckily after fledging had occurred).
• Housing that can’t be lowered with a pulley or winch is too much of a pain to check regularly. We had some single hanging gourds on poles, which we needed a ladder to access. We ended up checking them only every 2 weeks or so, which was too big a gap to learn anything much about the outcome of the nests.
• Although it is a small data set, we found that the gourds were much more conducive to egg survival than metal houses. Egg mortality was 4 times greater in the aluminum houses. Whether that was due to more sparrow and starling attacks or just the heat addling the eggs, we cannot tell. After hatching, survival was about the same in both housing types, though all 15 deaths of young occurred in crescent, as opposed to excluder-shaped holes. In addition, the few round holes were simply an open starling invitation and a disaster.

And we are left with fascinating questions:

• When a nest fails, is it the same couple or a different one that re-nests in the cavity?
• Do adults remove bad eggs or dead young on their own sometimes?
• What do they think about us benign intruders who seem to scare them, yet from whom they won’t nest more than 100 ft away?
• What goes through a martin fledgling’s mind when less than two months out of the nest, she has to leave and fly south to Brazil?

The martins are all fledged now, and are preparing for their long journey by learning to hunt and fattening up.

We are happy to answer questions about Purple Martins, or to have visitors as we check the houses in the spring. Just contact us at . We have photos available.

© 1998-2005, Andrew Balinsky. All Rights Reserved.