Thursday, June 05, 2008

2008 Purple Martin Colony Update Part 2

The season is going along quite well except for a few lost nestlings. So far my records indicate that I have 8 nestlings that are missing. This could be the result of several different factors.

Infanticide- It is believed that unmated SY (second year) male martins perform this act because of limited nesting sites, mates, and food which then is intensified by the urge to mate. By removing and/or killing purple martin young or destroying eggs it causes the mated martin pair to "divorce" so to speak due to supposed reproductive failure. This gives the SY male a chance to take advantage of the situation and possibly mate with the now "free" female.

Fallouts- caused by overcrowding leading to a nestling being pushed from the housing by one of its siblings during the rush to the entrance to be fed. The SuperGourds I use are really roomy so I don't think this was the cause, but then again it could still happen.

Ectoparasites- massive infestations of nest mites could cause nestlings to jump from the housing. Don't think this was the cause either due to the fact that I watch for this when I perform nest checks. If I find a large amount of mites I remove the nestlings, wash out and dry the gourd and then add fresh nest material in the form of pine straw and leaves.

Predators- crows, hawks, owls, snakes, etc. To my knowledge I've never had a problem with predators, but that doesn't mean it didn't happen.

Nest site competitors- such as the larger European starling or English sparrow could be responsible for their removal.

Since I didn't find any bodies on the ground below the colony it's difficult to say exactly what happened. This is just one of those things martin landlords go through each season.

Note in the photo below the “formation” that the 2-day old nestlings are in. When temperatures are cool outside nestlings will huddle up together to share each others body heat, but when it is hot out they will get into this type of spread out formation in order to stay cool. The two eggs that are remaining are past the hatching date and assumed infertile.

These three older nestlings below are due to fledge any day now. I’m betting that when I check again in 5 days they’ll be gone. Fledged nestlings usually remain with the parents for several weeks after fledging. I’ve seen fledglings being fed by adults while on the wing and when perched in treetops. In the evenings the fledglings return to the gourd they were born in to roost for the night and will continue to do this until they’re independent which usually happens before they migrate with the adults back to South America.
As you can see here this gourd is being used by a persistent pair of English sparrows. The more I tear out the more they build- as if by some act of defiance they continue their quest to procreate, to advance their species no matter how long it takes. That my friends is the way of the English sparrow. As much as I despise them I must give credit for their unbridled determination. I've been too busy to insert a trapping device. When one is installed you must under no circumstances leave it unattended. A martin or other bird could enter, become trapped and possibly die.

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