Mud dam opinions

[C.C.Martins]

All,
What does the group think drives martins to build mud dams? Why do they feel the need to go through the effort?
Is it some birds just go that route? Do they just feel the need to build one? Or is it defensive?
When attracting them i carefully built some mud dams behind the entrances. But they carefully removed them and dumped it in the grass.
My suspicion is defensive but honestly have no clue.
Tom

[SSMartin]

I have only observed martins using mud dams when the compartment is very small. Sizes of 6”x6” for example tend to have them. These are also the same size compartments crows love to reach in and pull out the contents. The dam likely causes this to be more difficult for predators such as crows and hawks.

I haven’t had a mud dam after expanding houses to double compartments and using large gourds.

[paule]

Most of my martins built mud dams before I added crescent entrances. That all stopped until new martins came in last year and they built mud dams in the back compartments on the Trios.. Last year I visited a fellow landlord who had some natural gourds with round holes. The martins built mud dams in the entrances that looked very much like crescent entrances. I tried to convince my friend he needed bigger compartments and starling resistant entrance holes (SREH). After seeing the crescent mud dams he agreed. So, it is my opinion it has something to do with making them feel safer.
Paul

[Phil01]

I’ve never had a mud dam in any of the gourds but in the plastic house I replaced they would build them. It had expanded compartments with round holes. The martins always picked the 3 compartments with the 90 degree turn from the entrance to the nesting compartment, never the ones that went straight back. The mud dams were right against the door which made a mess when I opened it… lol There was no access from the outside to the nest cause that hole was blocked off.. Maybe they did it to help stop water from running off the porch and under the door into the nest? Not really sure but a very interesting topic!
Phil

[C.C.Martins]

Thanks all, seems to be defensive in cases of 6x6 compartments or if feeling vulnerable. I havnt seen them, would like to look at it though, the barn swallows are master builders, wonder how their larger cousins stack up.
Appriciate the feedback and experiences.

[Spiderman]

When I had 6x6 compartments the Martins did build mud dams.

Once I went to gourds that were much larger that stopped even though the gourds had round holes.

[C.C.Martins]

When I had 6x6 compartments the Martins did build mud dams.

Once I went to gourds that were much larger that stopped even though the gourds had round holes.

Interesting! Was the construction messy or worthy of first class engineering in your opinion....I get it, its mud....hahaha.

[G Saner]

Hello Tom,

My guess has always been that the dams help hide the eggs from another bird (sparrow/starling) that is peeking thru the entrance hole. The number of dams in my gourds varies from year to year. It may be tied to a rainy year or a dry year.

When I had Trios, the dam would definitely hide the eggs. Sometimes, the dam was so big that they took up a significant amount of space in those 6X6 rooms.

[C.C.Martins]

Hi Gary! Wow interesting! Gotta be, and yeah all based on water availability, if there's a feeling they need them.
Iv a trio mini castle, be neat to see if they ever do it. Ill have to get pictures for sure.

[Unk Bond]

Hello All
New to me Never had a mud dam
But I find it interesting [ Later

[Martintown33]

Hi Tom. I agree with the consensus. My experience is the same. Before I converted to 6x12 compartments, they would build mud dams in the front of the nest, in the 6x6 compartments. I definitely think it’s a defensive protective measure. Also to hide eggs, and possibly to even try to reduce the amount of wind driven rain , gettin to the nest. Sometimes my martins will still make mud damns even in the 6x12 compartments. There is plenty of wet mud around here. Wetlands, and golf course ponds. The damn construction is amazing and strong . They use wet mud with sticks mixed in to reinforce it, like rebar in cement. When the mud dries it is amazingly hard and strong. Sometimes , during nest building, I see the females coming in with mud filled sticks , or clumps of wet mud in their beaks. It’s very interesting to watch.
Rob

[C.C.Martins]

Thanks Rob!!!! So master builders indeed. Now gotta wonder where they picked up that trait. Eons would teach them that. Its fascinating.

[Martintown33]

Yep Tom, definitely an evolutionary trait I would think. I bet they were using the sticks as reinforcement in the mud, before humans were using rebar in cement! At end of season clean out time, I’m always amazed at how solid and strong the dams are. It takes quite a bit of force to break them up. Sometimes I have to use a screwdriver , and hit it, to get it to start to break apart. And they stick really well to the compartment floors and sides . So I would say, master builders indeed.. Also , agree with the others, I haven’t ever seen a dam in a gourd, only in the house compartments. I’ll post pics of the dams this year, after they complete nest building, so you can have a look..
Rob

[C.C.Martins]

Oh that would be great! Thanks Rob. Appriciate that.

[jhcox]

sometimes i think they build them to assist in keeping young from falling out of the cavities.

[C.C.Martins]

Makes perfect sense, they sound robust and strong enough to do the job doesn't it?

[TBaugh]

I have 36 gourds an have had a variety of houses over the years. All gourds have starling resistant openings. Some martins build dams others don't in my setting. Water and mud is typically available nearby but some dont build. I generally control the sparrow/starling population pretty well. I wonder if maybe the dams might also serve as elevated platforms for the young birds to exercise their wings whe the time arrives.

[C.C.Martins]

Well thats a new twist, building in gourds with SREH...so at your site its not defensive. Its another purpose! You may be onto something there. Iv probably never seen them because our big fresh water source has steep banks and is mostly clay. We have a salt water bay close by though, maybe its the salt water they won't get mud from.
Now I'm getting fascinated. This is interesting.
Thank you sir!
Tom

[Rick H]

The discussion drove me to look back at my notes for the past few years. I also haven't found mud dams in any gourds (there are 28), but have seen them in my wooden 6x11" nest boxes. The number of nests with dams changes yearly in the wooden houses. In 2023 there were 4/31 nests with dams, 3/33 or 9.1% in 2022, but only 1/51 (2%) in 2021. Some dams were so extensive they almost closed off the entry to the rear 6x6 area containing the young. So this makes me feel they use the dam to feel more secure. I dunno, maybe they they just like the privacy.
Rick H

[dsonyay]

Every year it seems, I have a couple of gourds or other type compartments that have mud in them.

It’s funny how that happens- not every compartment has a mud dam in it. And mudded up compartments is definitely The minority. I guess it’s just some of these martins like mud and some don’t.. I don’t know ..and I can’t make rhyme or reason why they do In some, and not in the other. In my case, it’s not limited to gourds. I’ve had them in my chirpy nest box , gourds, and my SK houses.