Inbreeding

[Thomas Maddox]

Do purple martins inbreed? I assume they don't, but couldn't find any literature on it. Thanks

[C.C.Martins]

Thomas,
GASP!!!!!! NO SIR!!!!! NOT OUR BIRDS!
hahahaha, imagine it happens but nature has a way of making sure the gene pool gets cleaned every once in a while. Those young ones we fledge may not come back to the same colony, they don't have that site fidelity.
Interesting though, imagine it does happen.

[Phil01]

Tom…. Hahaha Definitely not our birds!

Thomas, I remember reading that only about 10% of fledglings return to their natal colony for that very reason. The rest disperse to other colonies.. Not to say that it doesn’t rarely happen.
Phil

[randyM]

I band young-of-the-year martins (prior to fledging) at my colony each year and have a return rate the following spring of about 19%. I have plenty of available nest cavities at my site, so any returning birds that want to nest have ample cavities from which to choose. Interestingly, 63% of the SY band returns are males and 37% are females. During the 2022 nesting season I had banded nestmates from 2021 pair up, lay 4 eggs, and successfully fledge a brood of 4. Their young appeared to be normal and fledged on schedule. I have a fair number of records documenting paired birds that were both previously banded at my site, but from different nests. Never once at my colony has a banded pair that returned the following year paired up again in a subsequent year, so that helps keeps genetics diverse in a population. About 60% of the time at my site returning banded birds will nest in the cavity in which they nested the previous year, and about 80% will nest in the same 28-unit house they nested in the previous year. About 20% of the returning banded birds will nest in a different housing unit at my colony than the previous year even if they had a successful nest the previous year. 90% of the birds at my site prefer wooden housing over gourds even though about 1/3 of the cavities I offer are plastic gourds (Super gourd, Bo11 and Big Bo). I've only had 2 individual banded birds nest in plastic gourds at my site in consecutive years...the other banded birds that nested in gourds as SY birds that returned the next year chose a cavity in a wooden house in subsequent years. I've never documented a bird nesting in a wooden house one year then choose a plastic gourd in any subsequent year.

Randy

[Phil01]

Thanks Randy! Wow! That is some VERY interesting information and numbers! Answers a lot of questions I have always wondered about. Thanks for sharing!
Phil

[Thomas Maddox]

CC and Phil, my birds are Louisianian, so you never know! Lol
Randy, that is awesome and thanks for sharing!
I wonder if the SYs returning that don't go back to where they were born come back to the same area(nearest colony) or go miles away?
Thanks for the replies!

[Thomas Maddox]

Randy, why do you suppose the PMs prefer the wood over the plastic ? Cooler? Better grip?

[randyM]

My colony is in a very rural area, with the nearest city and martin colonies being at least 25 miles away. I have observed a few birds banded at my site at colonies 25 and 40 miles away. I've also seen numerous banded birds from my site at a small (n=~2000) pre-migratory roost about 30 miles north of my colony in ND. A few banded birds from my site have been observed at a roost in MN about 225 miles to the east of my site. I've also had banded birds from my colony show up at my site for the first time as ASY birds 2-3 years after banding. I assume those birds tried to nest and were unsuccessful elsewhere and then came back to their natal colony to nest the following year.

Most of my gourds do not have tunnels on them and only half have porches. Perhaps if I would add tunnels and porches to my gourds, I'd have a higher nesting occupancy in them? Last year I put up one new Troyer gourd with a tunnel under a modified plastic heath house that seldom was used. The gourd was occupied by an ASY male and SY female last year that successfully nested. This year I plan to put up 2 vertical Troyers, 2 more Troyers wit tunnels and add a few tunnels to some of the existing super gourds and Big Bo's to see if gourd nesting occupancy rates increase at my site in those new options.

From my observations, martin housing in this part of their range is about 1/3 aluminum housing, 1/3 plastic gourds and 1/3 wooden housing, so not sure why birds prefer the wooden cavities at my site. It might very well be due to the cooler temps we experience during the early part of the nesting season at this latitude, and wooden houses perhaps provide better insulation than plastic gourds. It also could be due to the design of the wooden houses I have. 60% of the cavities in my wooden houses are 6"x12"x6" with a 90 degree turn for the entrance (i.e., side entrance into cavity rather than front entrance). This type of cavity is usually occupied first at my site. The remaining 40% of cavities on my wooden houses are 6"x9"x6" and are occupied a bit later, mostly by SY birds, but are still preferred over plastic gourds having larger cavities.

Randy

[deancamp]

That is some very good information. Thanks for sharing Randy!!

[Spiderman]

Randy, why do you suppose the PMs prefer the wood over the plastic ? Cooler? Better grip?

Randy has posted some in-depth information that is really valuable to this Forum. I admire you for the time you have devoted to create this knowledge,

Why would they prefer the wood over plastic?

You must remember this is South Dakota so insulation of the eggs and young are the important criteria here. Much different than where I live in Texas where venting the plastic gourds to allow maximum cooling capability is the most important for the nesting Martins.

[Phil01]

Yes, that is some VERY interesting and in depth information! Thank you for sharing that Randy! ALOT of time and effort went into it!

Here in Fl they seem to prefer gourds as well. This is only my observation at my small colony and what I have heard from others.. I assume because of the heat. Many do have houses and they do work though. So I guess unless you have multiple housing and band them as Randi does, and track numbers, it’s hard to know for sure..

I would also add the returning bird percentage to a colony is based on having plenty of available cavities for them to return to should they choose. (Which is EXTREMELY interesting) Colonies at or near capacity would probably have a lower returning percentage rate (unless they add more housing) because there are no or few available cavities by the time SY’s arrive, thus dispersing them to other colonies. But either way, excellent information for those building a colony and for all Landlords in general. VERY COOL!
Phil