Been having fun the past few days emailing Emyr Evans of the Dyfi osprey project In Wales. As some of you may know, Monty now has two nests and two females. It is a behavior I have observed here five times. (It occurred one other time prior to my involvement in the project). So Emyr contacted me to get my thoughts. It's so great to talk to other osprey researchers and share our observations. Sometimes I hate this internet / Facebook thing because in some ways it separates us, but in other situations it allows us to connect and learn from people on the other side of the planet. That, I love. Anyway, it will be interesting to see how things turn out over there with Monty. Out of the five times I have documented polygamous behavior, four times involved a male going between two nests. Sometimes those nests were at least a mile or two apart, and sometimes they were within a few hundred yards (within sight of each other). Only once were chicks produced at both nests. And that male managed to produce three chicks at two nests and all chicks fledged! It surprised me! In fact I predicted that one of the nests would fail, which is what usually occurs. The Ospreys proved me wrong, and it's not the first time! The success was largely due to significant help from those females as well, who did help provide fish for the chicks as they became old enough to for her to leave them for short periods.
One case of polygyny ( polygyny is the term for one male with two females, polyandry is the term for one female with two males, and polygamy is the larger category that includes both of those...for those interested in correct terminology) I observed two females sharing a single nest with one male. They shared fish and shared Incubation duties, but when a single chick hatched one of the females lost interest and departed. The next year she had her own male and her own nest. Did she know the chick was not hers, or was it just too many birds in a nest? ( in 1986, prior to my involvement in the project, two females laid six eggs in a nest with one male, and none of the eggs hatched).
Well, one of our males has done this three times now, including this year. Now we have documented him at both nests. Quite often one nest will get more attention than the other, and it can be sad to watch a male ignoring one of the females as she begs for food while incubating. I often have to remind people that Ospreys are not "bad" for engaging in polygamy. We should not project our anthropomorphic moralistic ideas upon these birds. Ospreys are largely motivated by two instincts....to survive and to reproduce. So when an opportunity arises to reproduce twice in one breeding season, some males will take advantage of it. It is often a result of nests being too close together. It's natural for a male to defend his territory against other males, and yet to allow another female into the territory. Some females would chase away another female, but if the male is allowing it, it sends a signal. I think there are all kinds of subtle signals being sent that we humans may not understand.
When the male does not care for the secondary nest, it can be hard to watch, and our human hearts get upset...but that male is making decisions about his own survival, and how much energy he has to provide for two families. The behaviors of the Ospreys change as our population increases and there may be more opportunities for these situations to occur. We are learning as we go...and now also learning as we communicate with other scientists around the world! Stay tuned!
One case of polygyny ( polygyny is the term for one male with two females, polyandry is the term for one female with two males, and polygamy is the larger category that includes both of those...for those interested in correct terminology) I observed two females sharing a single nest with one male. They shared fish and shared Incubation duties, but when a single chick hatched one of the females lost interest and departed. The next year she had her own male and her own nest. Did she know the chick was not hers, or was it just too many birds in a nest? ( in 1986, prior to my involvement in the project, two females laid six eggs in a nest with one male, and none of the eggs hatched).
Well, one of our males has done this three times now, including this year. Now we have documented him at both nests. Quite often one nest will get more attention than the other, and it can be sad to watch a male ignoring one of the females as she begs for food while incubating. I often have to remind people that Ospreys are not "bad" for engaging in polygamy. We should not project our anthropomorphic moralistic ideas upon these birds. Ospreys are largely motivated by two instincts....to survive and to reproduce. So when an opportunity arises to reproduce twice in one breeding season, some males will take advantage of it. It is often a result of nests being too close together. It's natural for a male to defend his territory against other males, and yet to allow another female into the territory. Some females would chase away another female, but if the male is allowing it, it sends a signal. I think there are all kinds of subtle signals being sent that we humans may not understand.
When the male does not care for the secondary nest, it can be hard to watch, and our human hearts get upset...but that male is making decisions about his own survival, and how much energy he has to provide for two families. The behaviors of the Ospreys change as our population increases and there may be more opportunities for these situations to occur. We are learning as we go...and now also learning as we communicate with other scientists around the world! Stay tuned!
Great article! Now I understand that it's normal for a male to go to two females. Just a shame the one I follow left his mate and went to another but still mates with the first one.
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