In September 2006, I set up a experimental two-hole mansion trail with 5 boxes made and donated by Linda Violett of California (see photo, courtesy of Linda Violett). The boxes are hanging from trees on a small town green surrounded by farms and residences. There were 7 existing HOSP-infested, pole-mounted boxes there (see photos) that I stumbled across and obtained permission to manage. Bluebirds have been seen in the area.
The Experiment: The existing pole mounted boxes (no baffles) were plugged in 2007. No HOSP trapping will be conducted, in order to evaluate whether EABLs are able to secure and successfully defend the two-hole mansions despite HOSP competition. I am removing any HOSP nests and eggs.
I'm doing this experiment for two reasons: 1) I believe that about half of serious bluebirders prefer passive alternatives to HOSP control or are unwilling to take any steps to keep HOSp out of boxes, and 2) I want to gather data about two-hole box usage by EABLs. I can't wait to see what happens, although I admit it will be hard to potentially allow some losses to HOSP. I also want to limit the variables so I can assess the two-holers. (I do use ground and inbox traps as needed on my other trails). Squirrels may be an issue with the hanging boxes, as red, grey and flying squirrels are common in this area.
Conclusions SO FAR (as of 04/08):
Here are my opinions, based on 1 full season (2007) and one partial season (2008). However, be aware that I only have four hanging two holed boxes, and one new hanging TX Bluebird Society box (no occupants yet this year). I also have 70+ pole mounted boxes.
PROS:
Increased species diversity (which is something I WANT). In 2008, the only TUTI nesting I have so far is in one of the two-holed mansions, along with one of only two WBNU nestings. In 2007, I had only three TUTI's attempts on my trail, of which two were in the hanging boxes (unfortunately both failed due to HOSP and HOWR competition.)
One EABL pair able to successfully fledge two young in HOSP-infested territory in 2007.
Safer from predation compared to a tree or telephone-pole mounted box. The large overhanging roof, hook and deep box probably offer some protection against raccoons and definitely against almost all cats. (No snakes in my area.) The two-hole mansion is deeper which offers additional protection (although I find users build bigger, higher nests.)
Safer from vandalism or stealing, especially if camoflaged (if hung high enough in a tree that is not readily climbed.
The two hole mansion may enable adults to escape more readily from a HOSP inbox attack.
CONS:
Harder to monitor than a pole-mounted box, and takes longer (must have lifter or ladder on hand, takes about 2-3 times longer to monitor, tricky to get the technique down, concern about dropping box and disturbing contents and incubating female.) The two-hole mansion is very heavy.
Harder to vandalize (as long as they are hung high enough in a tree that is difficult to climb) BUT the only box I have had stolen ever was one of the beautiful hanging ones Linda made, and it was apparently too close to a school, too low in a climbable apple tree.)
May appeal to Flying Squirrels, which may predate nestbox contents. (Personally, I think it is cool to have Flying Squirrels nesting in a box though.) I have never had Flyers in my pole mounted boxes, but in year one had them in 2 out of 4 hanging boxes (however, Linda's boxes are larger than a typical single-holed box.)
Predator problems: Snake access? (no direct experience). Roof rats (not in my area.) Honeybees? (I have only had bumblebees in mouse nests in pole-mounted boxes.)
Low utilization by bluebirds SO FAR. No bluebird attempt until trees had leafed out and HOSP pressure declined.
Some people don't have good "hanging" trees in suitable habitat.The two-hole mansion has a large interior, and users tend to build larger, bulkier nests which takes more time and energy.
UNANSWERED QUESTIONS:
Do bluebirds, HOSP, HOWR or TRES PREFER hanging or pole-mounted boxes if given a choice? So far it seems like TUTI's prefer the hanging boxes, and possibly nuthatches.
Do hanging boxes get fewer paper wasps? (A BIG problem on my trails.)
Will I be able to duplicate Linda Violett's success raising bluebirds in HOSP infested areas with few losses?
NOTE: THE 2006 LOG BELOW and drawing SHOW USE OF THE TRAIL BEFORE TWO-HOLE HANGING MANSIONS WERE INSTALLED
ID
Type
Attempt #, Species & Fate 8/10/06
Roosting
Evidence
1/07/07
1
NABS
HOSP - blue feathers
None.
2
SLOT
HOSP - saw male perching
Pine needles - EABL?
3
NABS
HOSP
Chewed hole. Cracked.
4
NABS
HOSP? TRES?
grass and lots of white poop - HOSP? Top is split.
5
NABS
HOSP
Mouse nest? Grass and leaves without cup.
6
NABS
HOSP - active, 4 eggs on 8/10
EABL (pine needles, saw them attempting to enter after plugging)
KEY
BCCH = Black-capped Chickadee
EABL = Eastern Bluebird
HOSP = House Sparrow
NABS = NABs style nestbox
PETE = Peterson style nestbox
PW=paper wasp
SLOT = Slot style entrance on nestbox
TRES = Tree Swallow
8/10/06: cleaned out contents of all boxes. Some split roofs. Looks like boxes had not been emptied in years. See photos. No sign of paper wasps.
9/06: Installed 5 new two-holed mansions in trees. Saw at least one male EABL. See 2007 log of activity.
Daddy dear, tell me please, is the world really round? Tell me where is the bluebird of happiness found?
- Little Child (Mon Enfant), Wes Montgomery, Ralph Towner, Spike Jones
