Unmated SY Males Can Be A Problem
From: Steve Kroenke, Tallahassee, Florida
Date: 5/29/00
Time: 4:58:01 PM
Comments
After reading Diane's recent posting about the problem behavior of a particular SY male in her colony, I thought I would re-post an article I had submitted sometime ago. This article shares some of my observations and insights into the behavior of some SY males. I have documented this behavior for a number of years.
They maybe up to no good. Just hanging around, getting into trouble. They have no territory of their own, but want it. And they will sometimes do unspeakable things to try to get it. What are these vagabonds, trouble makers, and just plain nuisances? They are unmated sub adult (SY) male purple martins with no territory that just wander through a martin colony, harassing established pairs and their young.
Here's an example of what one did in one of my colonies...
The unmated SY male sat on one of the crossbars of the gourds, watching a gourd which had an adult (ASY) martin pair nesting there. Their young had just hatched. He was unsuccessful in securing territory in the 32-gourd cluster, as all were occupied and many of the ASY pairs had young. He watched the ASY female leave the nest, and unfortunately, she had not waited for her mate to take over. This was his chance. He flew to the gourd entrance and quickly slipped in. I had no idea what he was up to at this point. To my horror, I saw a small, pinkish object appear in the gourd entrance hole. The SY male was carrying the baby martin out! I rushed toward the gourd cluster and he flew out, still holding the tiny baby martin in his beak. He flew out over a thicket and dropped the baby; I was unable to retrieve the young martin. I had witnessed my first example of "martin infanticide" by an unmated SY male. The SY male was repeatedly attacked and driven away by both ASY parent martins, but he continued to try to usurp their nest. In the end, he successfully eliminated 3 of their 5 babies before the ASY male finally drove the SY male away.
I witnessed several more incidents of unmated, roving SY male martins that removed or tried to remove recently hatched baby martins from their nests. In at least 2 cases, the SY male eliminated all the young, though he was unsuccessful in taking over the nest; the original pair bond of the ASY martins remained intact and they retained control of their nests.
I also witnessed many more incidents of unmated SY males that constantly pecked and harassed large young in their nests or young that had recently fledged. Sometimes their attacks forced the baby martins to prematurely fledge from the houses/gourds. The unmated SY males are one of the primary attackers on recently fledged baby martins and sometimes force the young into thickets or to the ground. I also observed unmated SY males attempt copulation with recently fledged young martins as they perched on exposed tree limbs.
Why would these unmated SY males try to evict baby martins from their nests or attack recently fledged young? It all goes back to competition, territory, mating, and procreation. When they eliminate or try to eliminate baby martins in their nests, I believe they do it in order to break up the original pair bond of the parent martins. This action may "free up" the territory, thereby providing the SY male with an opportunity to breed. The female maybe available for possible mating if her original mate abandons the site. Plus, the only way the SY male would have a chance at claiming the gourd/house compartment would be to eliminate the present young. Also, baby martins are, perhaps, potential competitors for territory/mates in the future. Could this aggressive behavior of unmated SY males toward young martins be an attempt to eliminate or reduce future intra-specific competition for territory/mates? The unmated SY males behavior appears to be an instinctive drive to establish territory, obtain a mate, and procreate. This behavior is not unique to SY male martins and can be seen in other animals.
The "infanticide" behavior of a few SY males is somewhat analogous to that of sub adult male lions in Africa. Male lions are expelled from their prides when they began to show signs of a mane. From a biological perspective, this prevents inbreeding and ensures the males will "cast their genes out" and continue the species. These males live a nomadic existence until they are able to forcibly take over a pride and drive away the current males. Guess what the first order of business is of the males that have taken over the pride? They immediately kill all the young cubs. They do this so the females will go into heat and then the new males can father their own young. They have no biological interest in the cubs of other males. This same behavior can be seen in domestic cats, as males will sometimes kill newborn kittens in order to "force" the female into heat so he can mate with her.
In some cases where recently hatched martins have mysteriously disappeared, house sparrows, starlings or predators may not be the culprits. It may be one of the unmated SY males that is roving through the colony, seeking territory of his own. He may have slipped into an unguarded nest and removed the young. Fortunately, this "infanticide" behavior does not appear to be common, at least it has not been so in my colonies. But unmated SY males without territory can be a potential threat to recently hatched baby martins.
The harassment behavior of unmated SY males on large young, both in the nest and outside, is common. This is particularly noticeable in large colonies which "soak up" the excess SY males like "biological sponges". The established parent martins aggressively attack these unmated SY males when they harass their young or try to enter their nests.
Steve
