What do you think,"Returning to same cavityor not??????

[Guest]

I don't have a problem with the PM's returning to the same geographic site year to year but to the actual same cavity is kind of far out,many Landlords do report this and I guess feel it is commonplace.

I think I recall reading somewhere where banded birds were recorded as having done this,this too may have been coincidence.I don't doubt this happens on occasion but think it is the exception rather than the rule.

Has anyone /organization done a study on this to establish a trend of the PM's habits?

Whacha think???

dick

[Louise Chambers]

Dick,

Banding studies show that some martins return to the same cavity or gourd from one year to next, but most do not - returning to the same site, but not the same cavity. Ditto with mate choice.

There are also data showing that some birds change to a new site, even though they successfully raised young at their old site prior to the change. And some stay at their site despite nesting failure. I guess there will always be some exceptions to the norm, and that there is a wide range of normal too.

Louise

[Guest]

My sentiments exactly,thanks for confirmation ......

dick

[Guest]

Hmmm. Let me see if I understand your cogitation here. You have no problem thinking that a bird can migrate back and forth to the same colony. But you do have a problem thinking that once he gets there, once he returns to this colony, there is little chance he's going to go back to the place he stayed last year, the place he flew in and out of a couple zillion times, perched on, defended. Is that what you're saying?

Just so I understand,

[Guest]

Yep ,Thats what I'm saying as a general rule,,,,,,I do think that they will chose a cavity by its location within the colony and that may lead people to think they chose it for old times sake and also by the amount of security it may present etc but not the same cavity because thats where they nested last year.

dick

[Emil Pampell-Tx]

I think some males leave their old colony to go nest with a female at a different colony as they are choosing partners. Sometimes the opposite happens, they bring a female to their home colony. Just my opinion, I think that there may be a lot of switching, after all, they are wild birds!

[Daniel Airola]

Here is a reply I prepared to a similar request several year ago.

I am colleagues have been studying a color-banded martin population nesting in bridges in Sacramento, CA. We have looked at fidelity of martins to their previous nesting cavity and previous nesting colony. This is a report from a previous post in response to this same question in 2007.

Over the last 6 years, I have recorded the nest holes used in >1 year by 27 individual birds (recognized by codes on color bands). In only 4 (15%) of these instances did the birds re-use the same nest cavity.

If you ask the question from the standpoint of "What are the chances that the birds nesting in hole X will be there next year?", then you also have to factor in survival (since the 27 birds above were all survivors until the next year). Of 136 SY and ASY birds we banded at nest sites over 5 years, an average of 60% survived to the following year.

So multiplying the survival rate by the cavity re-use rate (for birds that return) = 0.15 x 0.6 = 0.09, or a 9% chance that a bird nesting in one cavity will return to the same cavity the next year.

Again, my data are for western martins nesting in bridges, not eastern housing, and I don't know how that affects the outcome reported here.

[Guest]

Thanks Dan your studies it seems do support the general opinion thus far,thanks for the insite.I probably read this answer before but memory fades as so do the years.

dick

[Guest]

Well, I'm not a statistician or anything, but I'm guessing that the "survived" numbered is gathered by human beings spotting the "survivors" and writing the band number or color on a piece of paper. Then they would submit this piece of paper to someone to process, or process it themselves by entering data into a computer which is then processed in a central database where totals are tabulated and "results" are published based on queries to the database. Not to mention that these were probably Western martins in a non-managed colony on a bridge.

What I'm guessing is not tabulated are those that are not "spotted", and about a hundred variables as to time, energy, amount of data asked for, who writes the queries, how accurate the data entry person is, and whether or not anyone realizes that 84.9 percent of statistics are made up on the spot. (<--------humor) (<----for those with no sense of humor about statistics who thought . . . oh never mind)

So anyway, somewhere between 9 and 15 percent if we use your data. That is not "far out" or "on occasion" but a pretty significant number. I think somewhere around less than 1% would fit better in the "far out" category. Not that I'm nitpicking. Okay, maybe I am. Not that there is anything wrong with picking an occasional nit.

I'd say the number at my place is probably 10% but that's just a guess cuz I doesn't have me no banding purmitt.

[Daniel Airola]

Just to clarify my basis for our survival estimate a bit. We have a small number of banded martins (30-45 per year) that we follow in a relatively small population (70-175 pairs over the last 6 years). We record the total number of "band checks" (check of a bird for bands that we make) and we make thousands each year. We also make multiple observations of many of the banded birds over the course of the season.

The most telling indication of the completeness of the data are the number of birds missed in one year that turn up the next. If we found many that were not observed the previous year, that would indicate that we are not doing a good job of detecting all the birds in our population, and thus exaggerating mortality (by characterizing missing birds as mortalities). When we started banding and reading bands, the number missed in one year and seen in the next was relatively high (about 15%, but I'm going from memory here). Over the years, we have intensified the band reading effort, and now have only 0-1 birds from the total pool of 30-45 banded birds that escape our detection in one year and show up in the next. This strongly indicates that our mortality estimates, at least for the banded birds we track, is with 5% of the true value.

Eue to our relatively small sample sizes, we have not been able to use some of the more complicated statistical programs that more accurately calculate survival rates for the entire population, based on results of monitoring of a smaller sample of banded birds. But similar survival rates were calculated by recently studies from PMCA banding efforts of many thousands of birds, that were subjected to the most rigorous peer review in high level scientific journals.

[John Barrow]

Hi Friends,

While I have never published any data concerning reuse of cavities by purple martins, I did note a trend over a 3 year period at my personal colonies in Port O'Connor and Corpus Christi, Texas, of extensive reuse of cavities, priimarily by banded ASY males, that in my case would lend credence to Dwight's proposition that martin's would naturally return and reuse a cavity used repetitively in a prior year.

My colonies are highly managed, but only a small part of my adult martins are banded as I have never made an attempt to trap and band adult birds (in 2009 a significant number of adults were banded in connection with the geolocator project done in Corpus Christi). Each year most of the same gourds are rehung in the same position as in prior years. Over a three year period (2006-2008) between 65% and 75% of my banded ASY males reused the same compartment. In cases where the same cavity was unavailable upon their arrival, they consistently used a cavity immediately adjacent to the original one. Whether similar percentages of unbanded males reused cavities is unknown, but there is no reason to suspect their behavior would be significantly different.

I have also observed some cavity re-use by banded females, which, because they spend so much time within the cavity, are more difficult to identify and track. One of my first year class of banded females used the same cavity in my Lone Star Goliad for three consecutive years, and one unbanded female that we fed eggs to over a two year period utilized the same compartment each year. I believed her to be the same bird because of her tendancy to beg food for her nestlings, and to fly over to within a couple of feet of us to accept a pitch-out of egg to feed nestlings. During the first year of our feeding the bird (we named her "Eggmom"), she had lost her mate, and with the help of supplemental feeding successfully fledged her entire brood.

In July, 2008, I sold my house in Port O'Connor, donating much of my housing to several area landlords. I have made no effort to quantify reuse of cavities by banded birds from 2009 data in Corpus Christi. Off hand, I would say that there was a general absence of the males calculated in the 2006-2008 observation, but there was significant reuse of cavities by several other banded ASY males from 2008 to 2009.

I have no explanation for this trend, but suspect it is more likely a result of general location within the colony and not connectivity to a particular house. However, the banded Port O'Connor female using the goliad repeatedly chose a metal house, which never achieved complete occupancy, over natural gourds that nearly always filled up before arrival of sub adults. This, to me, would indicate some specific attraction to the type of housing.

While I feel the trend of reuse of the same cavity by a majority of ASY males is significant and consistent, I do not draw any other conclusions from the data.