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Summer arrives Thursday, bringing with it a reader favourite: Postmedia’s occasional series on the Science of Summer. Today Tom Spears looks at loons that wait for years for a chance to nest and raise chicks.
Walter Piper has been studying loons on Wisconsin lakes for a quarter of a century, learning a lot about the vicious fighting for territory among birds that seem calm and placid to the casual onlooker.
It was about four years ago that he started to notice the odd behaviour of one female loon.
The background: Male loons fight other males for territory. Females likewise try to drive away rival (nesting) females.
On a part of Piper’s study area called Blue Lake, a particular female was having no luck. But she was persistent.
The young female is called White-Green (for the coloured bands placed on her leg as a chick.) In 2014 she tried to invade the territory of a much older female on Blue Lake but was driven away. But she has come back over and over, despite being driven away each time.
Piper, from Chapman University in California, tells the story in his wonderful blog, the Loon Project: “Since then, we have so often seen White-Green on Blue Lake — and never on adjacent lakes that we also monitor — that she must live there, hiding out in the swath of unoccupied space between the two breeding pairs. And waiting,” he writes.
Two weeks ago she attacked again and lost again. Piper: “It would seem that the writing is on the wall: White-Green is not strong enough to subdue the breeding female at either end of the lake and seize their breeding position. Shouldn’t she move on? Isn’t she wasting valuable time in the prime of her life?”
But he took another line of reasoning. Maybe it pays White-Green to wait.
Male loons have relatively short lives. Many die young, and the survivors decline rapidly after about age 15. Females live longer, making a surplus of females. They can reach age 30.
“We’ve known that females are playing the long game for a long time,” he said in an interview. They have to, with a constant shortage of males to pair up with.
“They hang around, even if not on (nesting) territory, for a long time, and sometimes spend years waiting for a vacancy to open up,” he said.
For one thing, loons are drawn to lakes similar to the lakes where they are born: Same acidity, same size of lake.
“We presume it’s maybe because they have familiarity with the lakes. So Blue Lake in the case of this particular female does match quite closely the lake in another county 35 miles (60 km) away that is her natal lake.”
There’s also a strategic advantage to focusing on a narrow range of lakes where White-Green might make a hostile takeover, Piper suggests.
“By getting to know the behaviour of a few breeders (i.e. nesting birds) well, young nonbreeders might be able to pick up subtle changes in breeder behaviour that signal weakness and allow them to time their eviction attempts effectively,” he writes.
As a result, “females live long enough that what at first appears to be an unhealthy obsession with one territory or two might ultimately be rewarded.”
We’ll end this with a note on the first day of summer. Thursday is the longest day of the year — a fraction of a second longer than Wednesday, and a full three seconds longer than Friday. At the Science of Summer, we treasure this.
tspears@postmedia.com
twitter.com/TomSpears1
查看原文...
Walter Piper has been studying loons on Wisconsin lakes for a quarter of a century, learning a lot about the vicious fighting for territory among birds that seem calm and placid to the casual onlooker.
It was about four years ago that he started to notice the odd behaviour of one female loon.
The background: Male loons fight other males for territory. Females likewise try to drive away rival (nesting) females.
On a part of Piper’s study area called Blue Lake, a particular female was having no luck. But she was persistent.
The young female is called White-Green (for the coloured bands placed on her leg as a chick.) In 2014 she tried to invade the territory of a much older female on Blue Lake but was driven away. But she has come back over and over, despite being driven away each time.
Piper, from Chapman University in California, tells the story in his wonderful blog, the Loon Project: “Since then, we have so often seen White-Green on Blue Lake — and never on adjacent lakes that we also monitor — that she must live there, hiding out in the swath of unoccupied space between the two breeding pairs. And waiting,” he writes.
Two weeks ago she attacked again and lost again. Piper: “It would seem that the writing is on the wall: White-Green is not strong enough to subdue the breeding female at either end of the lake and seize their breeding position. Shouldn’t she move on? Isn’t she wasting valuable time in the prime of her life?”
But he took another line of reasoning. Maybe it pays White-Green to wait.
Male loons have relatively short lives. Many die young, and the survivors decline rapidly after about age 15. Females live longer, making a surplus of females. They can reach age 30.
“We’ve known that females are playing the long game for a long time,” he said in an interview. They have to, with a constant shortage of males to pair up with.
“They hang around, even if not on (nesting) territory, for a long time, and sometimes spend years waiting for a vacancy to open up,” he said.
For one thing, loons are drawn to lakes similar to the lakes where they are born: Same acidity, same size of lake.
“We presume it’s maybe because they have familiarity with the lakes. So Blue Lake in the case of this particular female does match quite closely the lake in another county 35 miles (60 km) away that is her natal lake.”
There’s also a strategic advantage to focusing on a narrow range of lakes where White-Green might make a hostile takeover, Piper suggests.
“By getting to know the behaviour of a few breeders (i.e. nesting birds) well, young nonbreeders might be able to pick up subtle changes in breeder behaviour that signal weakness and allow them to time their eviction attempts effectively,” he writes.
As a result, “females live long enough that what at first appears to be an unhealthy obsession with one territory or two might ultimately be rewarded.”
We’ll end this with a note on the first day of summer. Thursday is the longest day of the year — a fraction of a second longer than Wednesday, and a full three seconds longer than Friday. At the Science of Summer, we treasure this.
tspears@postmedia.com
twitter.com/TomSpears1
查看原文...
