Wrens are delightful little birds that can bring joy to any garden. With their loud and complex songs, active behaviour, and willingness to use nest boxes, they are a pleasure to have around. When putting up a nest box for wrens, one of the key considerations is the size of the entrance hole. This helps determine both which species can enter and how accessible the box is to predators. So what is the ideal hole size for a wren house?
Quick Summary
The recommended hole size for a wren nest box is 1-1.5 inches in diameter. This allows wrens access while excluding larger birds like starlings. The hole should be located 4-6 inches from the box floor, and ideally on the side rather than the front. Holes should not be too big, as this makes eggs and chicks more vulnerable to predators.
What are the Different Wren Species in the UK?
There are three species of wren found in the UK:
- Eurasian Wren – The most common and widespread species.
- St Kilda Wren – A distinct island subspecies restricted to the St Kilda archipelago.
- Fair Isle Wren – Another localized subspecies only found on Fair Isle.
Of these, it is the Eurasian Wren that uses nest boxes. St Kilda and Fair Isle Wrens are limited to their island homes. So when putting up wren boxes, it is the Eurasian Wren’s requirements you need to meet.
What Size Hole Should be Used for Eurasian Wrens?
The Eurasian Wren is a very small bird, measuring just 9-10.5 cm long and weighing 7-13 grams. This means the entrance hole to its nest box can be very small:
- The recommended hole diameter is 1-1.5 inches (25-38 mm).
- Oval holes of 1 x 1.5 inches work well too.
- Much larger holes may allow other birds like starlings to occupy the box.
A 1-1.5 inch hole is large enough for wrens to pass through easily. However, it is too small for larger species to enter. Songbirds like blue tits and great tits require a hole width closer to 1.5 inches.
Where Should the Hole be Positioned?
The exact positioning of the entrance hole matters too:
- It should be located 4-6 inches above the box floor.
- Holes on the side rather than the front may be preferable as they offer added protection from the wind and rain.
- Orienting the box so the hole does not face the prevailing wind and weather is also advised.
Avoid placing the hole too close to the floor, as chicks could prematurely fledge by climbing out. Equally, it should not be positioned too high up, as wrens prefer a middle nest box height.
Why is the Hole Size Important?
Getting the hole size right serves several important purposes:
- Allows wrens access while deterring larger species – The 1-1.5 inch width restricts access to wrens and possibly treecreepers, but excludes larger birds like starlings, sparrows and tits.
- Prevents predation – Smaller holes help keep out predators like stoats and squirrels. They also prevent chicks from leaving too early.
- Lets wrens assess the box – Wrens prefer to be able to enter their nest to assess it before completing it.
- Provides insulation – A snug hole helps retain heat and provides a sheltered entrance.
Getting the size wrong could mean other birds, predators or severe weather can impact wrens’ nesting success. It is better to slightly undersize the hole if you are unsure.
How Can You Adjust the Hole Size?
There are a few options for altering hole size if needed:
- Use a craft knife, rasp or sandpaper to enlarge or neaten a pre-cut hole.
- Cut a new custom hole of the desired dimensions.
- Pad out a hole with extra wood if it turns out slightly too large.
- Attach a wooden restrictor plate around an existing hole to reduce the size.
Take care when adjusting hole size and consider trying it out on scrap wood first. Remember that wrens are tiny birds, so the hole only needs to be an inch across for them to fit through.
Where Should You Position the Wren House?
To boost the chance of wrens using and successfully raising young in the nest box, follow some key positioning guidelines:
- Place boxes 5-10 ft high on tree trunks, walls or fences.
- Choose a sheltered spot away from prevailing wind and rain.
- Face the entrance away from the elements.
- Ensure cats, stoats and squirrels cannot access the box.
- Avoid areas frequented by larger birds like magpies that may predate chicks.
Wrens are active, acrobatic birds, so they will use nest boxes in a wide range of positions. But providing some shelter and protection from predators is advised. Ensure access for monitoring and cleaning the box annually too.
When to Put Up Wren Nest Boxes?
You can put nest boxes up at any time of year, but most wrens will begin prospecting for nest sites in late winter. Follow these tips on timing:
- Late winter is ideal, installing boxes from January to February.
- Avoid disturbance during nest building from March to July.
- Clean out old nesting material each autumn.
- Wrens may use nest boxes as winter roosts too.
Leaving boxes up permanently is fine as wrens will reuse favoured sites. But carrying out maintenance when birds are not nesting avoids disturbance.
How to Attract Wrens to Nest Boxes
To encourage wrens to use your nest boxes:
- Ensure the hole size is suitable for wrens to enter but not larger species.
- Place boxes in sheltered, discreet locations wrens favor.
- Have some shrubs, branches or trailing plants around the box.
- Provide supplementary food like mealworms nearby.
- Avoid disturbing or moving the boxes once wrens start nesting.
Wrens are inquisitive and sociable birds that readily use nest boxes. With the right positioning and hole size, they should inspect and move into available sites.
How Many Broods do Wrens Have?
Wrens are extremely productive birds, with each pair typically raising 2-3 broods per breeding season. Here are some key facts about their breeding productivity:
- The main breeding season is April to July.
- Each brood consists of 5-8 eggs, which hatch after 13-15 days.
- Chicks fledge just 14-19 days after hatching.
- New nests are built for each brood.
- Pairs can produce up to 20 chicks in a season from multiple broods.
This rapid rate of breeding from such a tiny bird is impressive. It explains why wrens can be so abundant and widespread despite their small size.
How Many Eggs do Wrens Lay?
Wren clutch sizes are quite large for such a small bird. Each clutch contains:
- Usually 6-7 eggs.
- Ranges from as few as 3 to as many as 10.
- Larger clutches late in the season.
- New nest and eggs for each brood.
The female alone incubates the eggs. She needs to be well fed by the male to sustain such frequent egg laying. Large clutches maximize the number of chicks that can fledge from each brood.
What do Wren Chicks Eat?
Young wrens are totally dependent on their parents to provide food. The chicks hatch naked and blind but develop quickly. Their diet consists of:
- Small caterpillars and insects.
- Spiders.
- Worms.
- Adult wrens must find huge numbers of small insects and spiders to sustain their chicks.
- They make hundreds of feeding visits per day.
Supplementing wren pairs with mealworms may help them feed more demanding broods. But natural insect food supplies are vital for breeding success.
How Long do Wrens Live?
Wrens have relatively short lives compared to other garden birds. Some key facts about wren longevity include:
- Average lifespan is just 1-2 years.
- Oldest recorded wren in the wild reached age of 5 years and 10 months.
- High nest predation means many chicks die before fledging.
- Adults also suffer heavy predation from cats and sparrowhawks.
Wrens compensate for their low survival by having multiple broods and large clutches each season. Their high productivity allows them to maintain population levels.
How to Clean out Wren Nest Boxes
Wren nest boxes require annual maintenance to keep them clean and useable. Follow these tips:
- Timing – Clean boxes out after breeding ends in late summer.
- Remove old nest material, droppings and parasites.
- Wear gloves and a mask to prevent disease risks.
- Use boiling water and disinfectant to kill any parasites.
- Avoid disturbance in spring and early summer.
Discarded wren nests make lovely decorative items. Just be sure to clean and sterilize them thoroughly first to remove any potential parasites.
Conclusion
A hole diameter of 1-1.5 inches is ideal for wren nest boxes. This provides an entrance they can easily use while deterring larger species. Position the hole 4-6 inches above the box floor for maximum protection. Careful hole size and placement, along with appropriate siting, can encourage wrens to successfully raise multiple broods.
