Purple Martin Survival

[Guest]

If there were 1000 pair of ASY in a colony and they averaged 3 fledgling per nest that would be a grand total of 5000 birds to head south. Lets say that 40% of this total does not survive for the return trip to there last years nest site. It would still leave 3000 birds to start the probagation of the species all over again.

An increase of 50 % seems like it would not take to many years to have a flood of PM's in the annual return migration.

There has to be something wrong with the numbers

any answers????


dick

[Mary Dawnsong]

1. I believe the breeding success rate is much lower than your estimate across the population as a whole. Remember, most colonies are unmanaged and unmanaged colonies have lower breeding success. Also, some martins don't find mates and don't even nest.

2. The mortality rate is much higher, owing to very high mortality of fledglings in their first year.

3. Only a tiny percentage of martins return to their natal colony to breed.

4. The populations of most species of songbirds can fluctuate a lot from year to year, in a given area. Vast numbers of martins can die in just one week of bad weather.

For more info, see the information gleaned from martin banding studies:

http://purplemartin.org/update/BandingPM11(3).pdf (page 5-6 is a good summary)

http://purplemartin.org/update/NatalDispersal12(2).pdf

And papers about weather-related martin die-off:

http://purplemartin.org/update/Suppleme ... g11(3).pdf

http://purplemartin.org/forumarchives/a ... inHogs.htm (see the last paragraph about Hurricane Agnes)

Paper on breeding success rate:

http://www.purplemartin.org/update/RElBreed.html (and these are success rates in managed colonies, unmanaged would surely be lower)

[Guest]

Thanks Mary ,you are a wealth of info

Wonder how that double post happened?

dick