Purple Martin Occupancy Levels By Cavity Type

[Steve Kroenke]

Purple Martin Occupancy Levels By Cavity Type

I have been managing purple martin colonies for over 45 years and have used a variety of cavity types. This has included homemade wooden and aluminum houses, commercial aluminum houses, natural gourds, and commercial plastic gourds. My martin colonies have been located in several small communities in north Florida around the Tallahassee area and now in northwest Louisiana.

What I have observed over these years is that some cavity types tend to have higher purple martin occupancy levels in many situations though the abundance of the local martin population may be the determining factor irregardless of the cavity used. That is, martins may prefer a cavity style but when there are huge numbers of martins in an area then all cavity types tend to be well occupied. Also other factors such as housing design, age of colony and number of cavities no doubt impact occupancy levels. And a certain behavioral characteristic of purple martins called nest domination can impact occupancy levels. So it can be difficult to truly isolate the key determinant when you factor in multiple variables that could impact occupancy levels.

I have pulled together a chronology of martin occupancy levels of cavity types in my current martin colony in northwest Louisiana. I started this colony in 2005. Here are the stats of martin occupancy levels by year and cavity type:

Year 2005 Occupancy Levels

75 natural gourds, 57 pairs, occupancy level 76%
29 Super Gourds, 13 pairs, occupancy level 45%
26 Lone Star Alamo (1 house) and Goliad (1 house) aluminum house compartments, 11 pairs, occupancy level 42%

Totals: 130 cavities, 81 pairs, occupancy level 62%

Year 2006 Occupancy Levels

102 natural gourds, 96 pairs, occupancy level 94%
21 Super Gourds, 18 pairs, occupancy level 86%
34 Troyer Horizontal gourds with cling plates, 26 pairs, occupancy level 76%
50 Lone Star Alamo (1 house), Goliad (2 houses), and San Jacinto (1 house) compartments, 27 pairs, occupancy level 54%
12 Trio M-12 (2 houses on multi-purpose pole) compartments, eight pairs, occupancy level 67%

Totals: 219 cavities, 175 pairs, occupancy level 80%

Year 2007 Occupancy Levels

107 natural gourds, 100 pairs, occupancy level 93%
33 Super Gourds, 29 pairs, occupancy level 88%
70 Troyer Horizontal gourds with cling plates, 60 pairs, occupancy level 86%
24 Trendsetter (2 houses) 24 compartments, 19 pairs, occupancy level 79%
28 Lone Star Goliad (2 houses) compartments, 24 pairs, occupancy level 86%
12 Trio M-12 (2 houses on multi-purpose pole) compartments, 10 pairs, occupancy level 83%
12 Trio Castle double nesting compartments, 12 pairs, occupancy level 100%

Totals: 286 cavities, 254 pairs of martins, occupancy level of 89%

Year 2008 Occupancy Levels

74 natural gourds, 73 pairs, occupancy level 99%
45 Super Gourds, 41 pairs, occupancy level 91%
70 Troyer Horizontals with cling plates, 62 pairs, occupancy level 89%
69 Troyer Horizontals with tunnels/porches, 60 pairs, occupancy level 87%
12 Trio Castle double nesting compartments, 10 pairs, occupancy level 83%
24 Trendsetter (2 houses) 24 compartments, 20 pairs, occupancy level 83%
28 Lone Star Goliad (2 houses) compartments, 22 pairs, occupancy level 79%
12 Trio M-12 (2 houses on multi-purpose pole) compartments, 12 pairs, occupancy level 100%
24 Sunset Inn (4 houses on multi-purpose poles) compartments, nine pairs, occupancy level 38%

Totals: 358 cavities, 309 pairs of martins, occupancy level of 86%

Year 2009 occupancy levels

36 Excluder Gourds, 32 pairs, occupancy level 89%
66 Super Gourds, 57 pairs, occupancy level 86%
71 Troyer Horizontals with cling plates,65 pairs, occupancy level 92%
95 Troyer Horizontals with tunnels/porches,76 pairs, occupancy level 80%
32 Natural Gourds,31 pairs, occupancy level 97%
24 Trendsetter compartments,19 pairs, occupancy level 79%
12 Trio M-12 (2 houses on multi-purpose pole) compartments, 11 pairs, occupancy level 92%
12 Trio Castle double nesting compartments, 11 pairs, occupancy level 92%
24 Sunset Inn (4 houses on multi-purpose poles) compartments, 13 pairs, occupancy level 54%

Totals: 372 cavities, 315 pairs, occupancy level of 85%

Year 2010 Occupancy levels

12 Troyer Vertical Gourds, 12 pairs, occupancy level 100%
36 Excluder Gourds, 36 pairs, occupancy level 100%
81 Super Gourds, 75 pairs, occupancy level 93%
75 Troyer Horizontals with cling plates, 69 pairs, occupancy level 92%
103 Troyer Horizontals with tunnels/porches, 90 pairs, occupancy level 87%
24 Trendsetter compartments, 22 pairs, occupancy level 92%
12 Trio M-12 (2 houses on multi-purpose pole) compartments, 12 pairs, occupancy level 100%
12 Trio Castle double nesting compartments, 11 pairs, occupancy level 92%
24 Sunset Inn (4 houses on multi-purpose poles) compartments, 10 pairs, occupancy level 42%

Totals: 379 cavities, 337 pairs, occupancy level of 89%

Generally speaking natural gourds have tended to be better occupied than other cavity types in my colony initially though this occupancy level is not that significant as my colony aged and grew. In fact, I eliminated all my natural gourds in 2010 and substituted plastic ones. The martins readily accepted the change.

Also gourds, either natural or plastic, have one major advantage over many multi-compartment houses, particularly those with entrances side by side and common porches. Gourds provide martins with territorial privacy and give that space that martins may prefer between each other. Though martins are communal, they still have some territorial drives and males in particular may try to dominate multiple cavities. Male may dominate multiple cavities to reduce competition for females, provide females with a variety of nest sites since the female does the selecting, and such behavior may reflect territorial drives common to many birds. Since gourds are separate nest cavities and are not attached to another cavity like found in houses, gourds provide more territorial space. Just having a gourd a mere 12 inches away from another one on a rack may give martins that “breathing space” and keep pairs “out of each others’ feathers”! Gourd racks with gourds facing different directions or suspended so male martins can’t easily see the entrances of adjacent or nearby gourds can be fully occupied each season.

Additionally gourds provide a larger cavity for martins compared to many commercial martin houses and homemade ones. The roomier interiors of gourds may be more attractive to martins, particularly to the females which actually select the male and his territory. Female martins may look for cavities which provide seclusion and depth that will help protect their eggs/young from predators.

Over here in northwest Louisiana, most folks offer multi-compartment houses, particularly aluminum ones. I have seen many Trios, Coates and Heath houses and martins readily colonize these houses. Many of these houses have the smaller 6” x 6” square or similar pie-shaped cavities and are rarely modified with double nesting chambers or enlarged compartments. You don’t see many gourds and the only naturals I have seen have been at my colony and at Bob’s site.

In our personal and satellite martin colonies we use many multi-compartment houses and the martins readily nest in them. We do offer houses with standard enlarged cavities such as those in Trendsetters and Lone Stars and modified compartments in the Trios. The Trendsetters offer separate porches and staggered entrance hole placement. All of our houses with compartments side by side have porch dividers to help minimize nest domination issues. The occupancy levels of our houses are about comparable to those of gourds. The enlarged house compartments and house designs with separate porches or staggered entrances and porch dividers can help to minimize nest domination issues and be about as attractive as gourds.

However, martins readily nest in both plastic and natural gourds though they are not commonly offered in our area. Even though martins have been primarily “raised” in houses in our area of northwest Louisiana for many years, martins don’t appear to be imprinted on them and the high occupancy levels we have achieved with gourds in our personal and satellite colonies tends to validate that. Gourds with their territorial privacy feature and larger cavity dimensions are highly attractive to martins.

Of course having an abundant purple martin population base helps, too! Northwest Louisiana has a large number of martins so almost any suitable cavity in an open location can often attract occupants. This factor no doubt insures an almost guaranteed chance of attracting martins. The use of gourds and well-designed houses tends to increase that occupancy level. You can have a well occupied colony of martins with either gourds, houses or a combination of the two in northwest Louisiana.

Steve


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[Tim Stover]

Thanks Steve for the info i am gonna have a mixed bag this year naturals and plastic on six racks turned every direction all going up this weekend

[Steven Spencer]

Good writeup Steve. I've noticed at my colony the gourds tend to have a slightly higher occupancy rate that houses. I'm not sure if its just preference or due to nest domination with the houses. When you first started you colony in Louisiana, what was the first compartment chosen by the very first pair of martins? With me here I started with a Trio house so they didn't get a choice of housing types.

Steven

[Billy Stephens]

not bad for a "Led Head"! I am one too.

[Owens]

Thanks for the great data. We have had a house in which we enlarged the compartments resulting in 6 nesting compartments. We had two gourds hanging below. We had much interest in the gourds and lots of lookers but not one resident in the house. Our loyal male always dominated both gourds (apparently from your info..we had the openings way too close) This year we have gone to all BO9 Plus Gourds and are very hopefu to get more martins. Thanks for confirming our suspicions...

[Keith]

Steve,
Thanks for posting this data. It was my intention to go with only natural and some plastic gourds along with modified trio houses this year as this is what the Martins preferred last year at my place. Your numbers seem to help me in this endeaver. I had been wanting to ask about the possibility of Purple Martins just preferring a cavity that had no corners, hence the interest in gourds. After all, this is likely all they had in ancient times.
Keith

[Steve Kroenke]

Hey Tim,

I hope you have a great martin season with all those gourds and racks! By offering a variety of cavities and suspending the gourds so they face different directions, this arrangement can minimize nest domination issues and possibly increase occupancy level. You may see some nest domination early in the season, but this behavior tends to weaken later on.

Steve

Hey Steven,

My first martins chose natural gourds in 2005. Then later that season, the martins tended to spread out among the other naturals, Super Gourds and Lone Star houses.

Bob also used natural gourds for several years when I first moved out here. He had high occupancy levels in them. He also use a bunch of Super Gourds with similar results.

Eventually he took down all the naturals and most of his gourds racks and substituted Trio Castles. Apparently the martins moved right into the Castles and they were about full the first time used.

Steve

Hey Billy,

May the mighty Zeppelin always fly over!

Steve

Hey Owens,

A gourd rack with gourds hanging in different directions is one of the best systems around to maximize martin occupancy levels. This gives the martins more territorial privacy. You will probably see a lot more martin activity around your colony this year. Good luck.

Steve

Hey Keith,

I do prefer using gourds over houses, but I still like to offer some diversity in my colony to give martins a choice.

The American Indians in the Deep South provided gourds for martins and so there is "history" there! Also martins nested probably for thousands of years in woodpecker and similar natural cavities and these sites tend to be solitary or they may occur together in small scattered numbers.

I think you are taking a good approach with gourds and houses. Good luck with your colony.

Steve

[Sparky]

Great write up Steve. Glad you are keeping the data and posting it to the community! I'm in my 11th year and the funny thing is that the returning early birds will choose the T-14 first, then the gourds start to fill up. Of course over time, early in the season, some will choose the gourds before the T-14. But the T-14 fills up much faster.

[Guest]

Steve

Thanks for the info. Your insight is very important to all of us Martin
Landlords trying to improve our sites each season

Mike

[Steve Kroenke]

Hey Sparky,

Thanks for sharing that information about your martin preferences in your colony. Perhaps those martins like the dark wooden insides of the T-14. Has a natural feel to it just like the inside of a natural gourd or woodpecker cavity.

I try to keep sharing as much information about my martin colony as I can! The martins seem to teach me something new each season.

Steve

Hey Mike,

I am pleased my observations and insights have been helpful to you and others. I, too have learn much from other landlords on the Forum. We all have much to offer each other and we are all trying to help the purple martin survive for future generations to enjoy. Hope you have a great martin season.

Steve