Infanticide: An Unfortunate Fact of Life Among Purple Martins
by Jace G. Stansbury
This will be my ninth year as a Purple Martin landlord and I can say that so far it has been an absolute wonderful experience. Being able to observe a species of bird from compartment selection, to nest building, egg laying and finally the rearing of their young is a blessed gift in itself.
Rather than just read about what occurs at an active colony site, I want to experience it. So I spend as much time as possible just sitting and observing. You can learn a great deal by doing this and become a better landlord as well. On Friday May 9, 2003 this paid off in a big way because I observed something that I will never forget.
After performing a nest check I sat in my backyard with binoculars to age all of the martins that were nesting at my colony as they would come and go from their respective gourds. I normally wait until I have active nests before I do this. During the last few days I had been noticing three SY (subadult or bachelor) males hanging around the colony site. While watching I saw what I thought was one of these enter a gourd that had an active nest belonging to an ASY male and female. What was he up to? Through my binoculars I watched the gourd entrance to be sure that I did indeed see a SY male enter it when the unthinkable happened. Not only did I confirm that it was in fact a SY male, but I also saw something that caused my jaw to drop. Firmly held in the beak of this male was a tiny pink 2-day old writhing nestling. I was witnessing infanticide in the making.
Infanticide by definition is basically the killing of young by adults. This behavior occurs in other bird species as well such as House Wrens, Tree Swallows, Barn Swallows, Cliff Swallows, English Sparrows and European Starlings. It is believed that unmated SY 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 the young or destroying eggs it causes the mated pair to “divorce” so to speak due to reproductive failure. This gives the SY male the chance to take advantage of the situation and possibly mate with the now “free” female.
I shuddered as I watched the usurping male fly from the gourd out over the lot where my two racks reside and drop the nestling to the ground. I immediately ran to the area and began a hurried search in hopes that I would find the confiscated nestling. After a few minutes of frantic searching I saw a small pink spot in the deep green San Augustine grass and picked it up to find to my surprise that it was unharmed. I lowered the rack and placed it back into the nest alongside its four siblings. Not two minutes after I raised the gourd rack the same SY male returned possibly to remove the others. About the same time the ASY female that had laid the clutch arrived and knocked him from the gourd driving him to the ground where a fight ensued. He then flew back up and perched on the gourd rack. The ASY female then entered the gourd where the five nestlings were waiting. Again he landed at the entrance of the gourd and peered in. The ASY female burst from the gourd and once again fought him to the ground. This went on several more times as he tried to gain entrance to the gourd. Each and every time the ASY female defended before finally it appeared that the SY male had given up for the time being. This event lasted only ten minutes at best. Where was the ASY male during all of this? Out feeding I assume. He returned not long after the altercation ended. When I look back on this I realize that had I glanced away for one second I would have missed this event entirely. The next nest check would have shown a missing nestling and I more than likely would have attributed that to the workings of a starling or sparrow. By way of nest checks I have also come across missing eggs from several other nests. It makes we wonder if this SY male or one of the others is responsible for this also.
With House Sparrows and European Starlings we can install SREH’s, trap, and shoot. With predators we can install predator guards and baffles. With ectoparasites we can do nest change outs. With weather extremes we can perform housing modifications. With infanticidal SY males we can literally do nothing but watch. Unless you happen to be in the right place at the right time observing like I was that day and are able to intervene. But we can’t be there at all times. The sole responsibility lies with the parents to protect the eggs and nestlings from this unfortunate type of invasion.
Chek, Andrew A., Robertson, Raleigh J. 1991. "Infanticide in Female Tree Swallows: A Role For Sexual Selection". The Condor 93:454-457.
Hill, James R. 2001. "The PMCA Videotapes an Entire Nesting Season Inside a Natural
Gourd". Purple Martin Update 10(3):8-13.
Hill, James R. 1997. "Sex/AgeDifferences in the Breeding Success and Mate Choice of Purple Martins". Purple Martin Update 7(3):28-29.
Loftin, Robert W., Roberson, Don. 1995. "Infanticide by a Purple Martin". Purple Martin Update 6(3):7.
Lombardo, Michael P., Power, Harry, Romagnano, Linda, Stouffer, Philip, C. 1986.
"Suspected Infanticide in the Starling". The Condor 88:530-531.
Jace Stansbury is a 46 year old product tester at a local oil refinery. He is entering his ninth year as a martin landlord.