Nestbox Styles: Pros and Cons

THIS PAGE IS EVOLVING. INPUT DESIRED!
Need plan links for some. Need floor dimensions and hole-to-floor depth! More pictures/drawings would be good – but I don’t have them for all styles, and it might make page load too slowly. ACCURACY IS VERY IMPORTANT and is being verified.

Ask a dozen people what their favorite nestbox style is, and you will probably get a dozen different answers. Probably the most commonly used are NABS, Peterson, Slot, and Gilbertson. If I bought ONE box for Eastern bluebirds, it would probably be a Gilwood (which they seem to prefer in my experience) or maybe a Troyer (a box used successfully by Bluebirds Across Nebraska – see info). If I had House Sparrow problems, I would go with a Gilbertson PVC nestbox. If I bought four boxes, I would probably get a Gilwood, Gilbertson, Peterson and NABS. But that’s just me. Some box styles are shown below (move your cursor over each to see the name, and click to go to a description). See links to various plans. Also see REALLY useful website on Nestwatch.org with plans and recommended habitat, height and spacing.

Generally Accepted Good Nestbox Design Specifications: Use a box designed specifically for bluebirds. The North American Bluebird Society (NABS) has specifications for nestbox designs. See Basics for more info. If I were looking for the ideal box, I would want:

• a roof that will shed rain and provide shade. (A 2-5″ overhang may deter predators. A shallow saw kerf (groove or drip edge) will help keep rain from soaking into box.)
• no perch (gives House Sparrows an advantage)
• a suitable size entrance hole that will keep out bigger birds, without rough edges (round 1.5″ diameter hole for Eastern Bluebird [EABL], or 1.375″ x 2.250″ oval hole, or 1 3/16″ high slot opening. Mountain and Western Bluebirds need a 1 9/16″ hole, and EABL like that size too.) Larger holes or slots allow starlings to enter. Hole guards to make a 1 9/16″ hole are hard to come by, but some suppliers do have them – e.g., www.mcmaster.com. (Use a Forstner bit instead of a spade/paddle bit or hole saw for a nice clean, perfect hole.)
• ventilation to prevent overheating but not so much that it will get too cold or wet inside. (Note: some boxes in Wisconsin use no side ventilation due to black fly problems.) When drilling holes in the sides, aim the drill at an upward angle to prevent water from running inside the nestbox.)
• drainage holes in the floor (wet nest preferred by blow fly?), recessed to prevent moisture entering via capillary action
• designed to prevent water from getting inside the box (e.g., roof design, recessed floor placed inside of nestbox walls). Can also cover exterior with clear silicone caulk, with extra silicone on inside and outside seams
• deep enough so predators can’t reach in and get to eggs/nestlings, but not so deep that fledglings will have trouble exiting
• a door that opens for cleaning and monitoring, but closes securely so predators can’t enter
• ability to mount (e.g., on a pole) or hang
• usually made of wood (untreated, unpainted 3/4″-1″ thickness is commonly used, or painted a LIGHT color on the exterior only), PVC, or hardiboard type material.
• If rough wood is not used, add saw grooves or kerfs to the inside under the entrance hole to enable fledglings to climb out if Tree Swallows (TRES) nest in your area.

Other key criteria (predator protection, mounting, location, etc.) are discussed on the basics page.

Personal preference may be associated with:

• material:
  • the most common are wood, PVC and occasionally poly (which is not the same as PVC), which vary in weight (and thus usefulness for tree hanging), durability, ease of cutting, heat retention, warping, the look, etc.
  • Some choose not to use aromatic (red) cedar because of concerns about oils that could potentially irritate a nestling’s skin.  For this reason, it might be best not to put cedar shavings (esp. freshly milled) inside a box.
  • White pine and white spruce hold up pretty well.
  • Screws are preferred over nails (or glue) because they are easier to tighten, remove and replace. Use galvanized stainless screws which won’t rust.
• ease of construction (for DIYers – see links to suppliers for the not-so-handy)
• ease of mounting or hanging
• ease of monitoring (need ability to see even tall nests without door obstructing view)
• durability (ability to withstand weather, predators, vandals, horses/cows, etc.)
• access: where and how it opens (see pros & cons)
  (note: you can make a box that opens in multiple places – you can make an inexpensive hinge for the roof with a tire innertube strip and staples)
  • front – easier to clean and remove blow flies or see inside and to install inbox trap. May be a problem with wren guard or monofilament installed. With hinge on top, can be hard to see paper wasps building on roof or to treat roof – bottom hinge is better for this. Also during monitoring, bird only has one exit choice (front that is being opened), so be careful not to squish an escaping bird.
  • side – easier to clean and remove blow flies or see inside; easier to see paper wasps building on roof and to treat roof (e.g., with vaseline or soap); easier to install wren guard and monofilament to deter HOSP; allows startled incubating female to exit the front entrance when monitor opens side; may be harder to install inbox trap.
  • top may be good for fotos, nestcam mounting, paper wasp control or monitoring (easy to count) on horseback or HOSP trapping and preventing premature fledging, and for banding. Hard to adjust nest height or remove blow flies from under nest, may be a problem with sparrow spooker installed, if large wasp nest is attached, may be hard for short people to monitor.
  • I do NOT recommend boxes that open from the bottom – nests could fall apart, eggs roll out, premature fledging likely
  • some have multiple choices.
• closure (e.g., must unscrew door – good for vandals but slows monitoring. Doubleheaded nail [or one on each side, angled down] keeps it from getting lost in a hole. Hinge from top or bottom affects visibility, cleaning and risk of eggs/nestlings falling out. In areas with raccoons, need a mechanism they can’t open) (Note: A small block of wood as a “door stop” will help you close it just right.)
• floor size (Western Bluebirds [WEBL] may require a larger box. Eastern [EABL] may prefer smaller boxes – Raymond Marr reported almost twice as many 4×4″ boxes were used as 5×5″ boxes in RI [Sialia, Spring 1993]). A larger floor size offers birds opportunity to place the nest cup in the back which helps deter some predators. I TRY to note finished (post-construction) interior floor size in the table below, but sometimes plans or suppliers provide the total floor dimension.
• floor drainage (to keep inside and nesting material dry), recessed or not
• toeholds for adults (kerfs on the OUTSIDE of the box below the entrance hole.) Note perches are NOT recommended as they offer an advantage to House Sparrows.
• utility for trapping or banding
• total interior volume (A Year 2000 TBN study indicated floor size had no effect on bluebird clutch size),
• size and weight of box (especially for large trails or hanging boxs)
• depth (overall, and depth from the bottom of the entrance hole to the floor)
• cost (to build or purchase)
• whether or not it is preferred by House Sparrows. Note that despite any claims you may read, HOSP can and may use or enter any box suitable for bluebirds. IMO, the only box with any (limited) HOSP deterrent effect is the Gilberston.
• ease of inbox trapping – is it easy to install a Van Ert or Huber style inbox trap (difficult on narrow, side-opening boxes, Troyers. Slot boxes can leave room for escape.)
• roof size (overhang for shade/shedding rain), style, single/double roof (for insulation)
• slant of roof (flat, forward tilt [which may drench birds at entrance], backward tilt, rounded, slanted to side) and rain grooves
• entrance hole size and shape
• ventilation (and ability to cover/plug holes for roosting/cold weather – the Texas Bluebird Society box performs very well in heat)
• insulation (heat and cold)
• ease of cleaning
• predator deterrence
• location of box (weather and predator factors. E.g., rat snakes are not a concern in CT but may be a primary predator in FL)
• old vs. new (it’s not clear whether bluebirds prefer “used” boxes)
• finish (sealed, exterior painted, exterior stained or treated with linseed oil, coated with one coat of Thompson’s Water Seal or clear silicone etc.) Tom Comfort likes Shingle Saver (dries clear in less than an hour, clean up with plain water) to protect roofs from weathering – DAP clear silicone also works.
• number of boxes needed (e.g., cost or ease of construction is a big factor for a trail with hundreds of boxes)
• species of birds (e.g., a box that appeals to a Prothonotary warbler [PROW] may be different than one that appeals to an Eastern Bluebird)
• demonstrated performance (and whether it has been adequately tested)
• cavity nester preference (probably more dependent on the location of the box than the box style), and
• cavity nester productivity (number of eggs, clutches and fledglings).

Many bluebirders (who tend to be creative, committed people) modify boxes based on experience or for experimental purposes.

This webpage doesn’t address other variables like orientation, height,mounting method, hole guards, predator guards, toe holds, lumber thickness, variations for roost boxes, etc., which in themselves often trigger spirited debates.

Here are some pros and cons associated with boxes designed for bluebirds, which may also be used by secondary cavity nesters such as chickadees, Tree Swallows, House Wrens (HOWR), House Sparrows (HOSP), tufted titmice, etc. Many are my personal opinion, and none are intended as endorsements. See references for more information on formal nestbox comparison studies, etc. There is probably no “best box” that works best in all areas, under all conditions, for all species.

Links to plans or makers are listed where I could find them. Also see list of nestbox suppliers. Commonly available boxes are shown with a yellow background. If I wanted bluebirds, and got one box it would be a Gilwood. If I had House Sparrow problems, I would use a Gilberston PVC box. On my trail, I offer a variety of styles to the birds.

The bottom line? Offering a variety of boxes in good locations, coupled with responsible monitoring and maintenance will probably produce the best results. In reality, cavity nesters may not be as fussy as we are. They have even been known to use a box that flipped upsidedown. They just need to be able to get inside the box to build a nest, lay eggs and feed young, and end up with strong, healthy nestlings that fledge successfully.

Other boxes I’m trying to get info on are V. Olson, Zabel Z-50 and Z-50 PG and Sommer (mentioned on BRAW website).

• Loren Hughes Sparrow Resistant? Box

Acknowledgments: Thanks to:

• *Designers are listed because they are usually the ones who did the fiddling, found out what works best and what the problems are, have access to plans, and have real world experience with that style, or “popularized” the style. Some of the designers did not name the boxes after themselves, but the naming has become a convention as a reference. Perhaps a naming system that is more informative (e.g. indicating basic style, floor size and depth to hole) would be more useful. A unique name does help people identify and discuss a box.
• Linda Violett for floor sizes and information
• Many comments from Bluebird_Listserv participants and archives
• The Bluebird Monitors Guide, 2001
• The Bluebird Box for posting plans online and Jim McLoughlin for his input (many pages on Sialis.org were retrieved from his website with permission)
• Wendell Long for Gilbertson photo with blue

More Information and References:

On this website (Sialis.org)

• Bluebirding Basics including minimum requirements for a nestbox
• Monitoring
• House Sparrow Management, including discussion of nestbox style preference
• Nestbox Plans (links)
• Neglected Nestboxes
• The Wrong Nestbox
• Nestbox Material
• Nestbox Mounting Styles – Pros & Cons
• Nestbox Opening Styles – Pros & Cons
• Compare nestboxes (game for children)
• Heat control experiment
• Pressure-treated lumber

Other wonderful resources:

• Nestbox Builder – Fred Stille’s site with plans for many wood and PVC boxes that appeal to bluebirds
• Nestbox Comparison Studies from New York http://audubon-omaha.org/bbbox/bbrp/nestbox_comparison_studies.htm
• Nestbox Preferences
• BRAW nestbox plans and comparison data – 2002, 2003, 2004
• That Remarkable Peterson Entrance by Wayne H. Davis
• Those Oval Holes http://audubon-omaha.org/bbbox/bbrp/those_oval_holes.htm
• The great entrance-hole debate by Myrna Pearman
• Starlings and oval-holed nest boxes by Kevin Berner
• Bluebird Nestbox Drawings http://audubon-omaha.org/bbbox/nestbox/nestbox.htm
• Nestbox Mounting Methods
• Nestbox, Sparrow Trap, Coon Guard Drawings http://audubon-omaha.org/bbbox/nestbox/nestbox.htm#Guards
• Roost Boxes http://audubon-omaha.org/bbbox/nestbox/nestbox.htm#Roost
• Other Nestboxes http://audubon-omaha.org/bbbox/nestbox/nestbox.htm#Other
• Descriptive Nesting Histories Of Possible Bluebird Box Occupants http://audubon-omaha.org/bbbox/bbtabl1.htm
• ROOFS –   Everything  MORE THAN You Wanted to Know by Steve Eno http://audubon-omaha.org/bbbox/ban/roofs.htm
• Winterizing Your Bluebird Boxes Permanently by Svante Humbla http://audubon-omaha.org/bbbox/bbrp/shutters.htm
• Results of Additional Research Regarding the Bauldry/Open Topped Box Design by Diane Barbin http://audubon-omaha.org/bbbox/openroof.htm
• Pairing houses: How do you do the math? by Linda Janilla
• Log nestboxes – Bluebirds over Georgia, Frances Sawyer 5858 Silver Ridge Dr. Stone Mountain, GA 30087 Tel: 770-469-6672 E-mail: fgsawyer”at”bellsouth.net
• Is it safe to use a nestbox made of PVC?