The curious incident of the empty nest

Flanders Moss NNR

Whilst cutting gorse the other day, we came across a small treasure tucked away amidst the spines: a mossy green nest with a small entrance hole. Birds don’t nest on Flanders Moss at this time of year, so we were confidently able to remove the nest from the gorse and have a proper look. There’s always something new to learn… (Note: it is illegal to disturb birds on their nests and to damage or destroy nests during the breeding season).

Whose nest was it?

The globe-like shape of the nest narrowed down possibilities as to its architect – in the UK, most nest-building birds build cup-like constructions. Wrens and long-tailed tits are amongst the few to add a roof dome, which helps retain warmth. Whilst we’ve seen both of these species nearby on the reserve, the nest materials suggested it was a wren’s nest – being early breeders, long-tailed tits often weave lichen into their nests to help camouflage them. This green mossy nest was lichen-free, relying upon the gorse foliage to conceal and protect it.

Gently opening up the nest, we discovered that it was also moss-lined – again, pointing to wren and not long-tailed tit, who line their nests with feathers.

The mossy nest looked wonderfully cosy. Indeed, in a break from writing about death and daffodils, the poet William Wordsworth wrote that “Among the dwellings framed by birds/In field or forest with nice care/Is none that with the little wren’s/In snugness may compare.”

Yet there were no signs of use in this perfect construction – no shell, feathers or droppings.

Why was the nest empty?

Wrens are one of our most familiar birds – tiny, dumpy and brown, frequently seen with an upright tail, and with a tendency to shout irritably at you from the undergrowth. Some of this crankiness might be explained in male wrens by the fact that, in order to win approval from their mates, they must construct not one nest but several cock nests (like chickens, wrens are ‘cock’ and ‘hen’). The hen then peruses the nests and makes her choice. The remaining nests, perfect to our eyes, are usually left empty – though on occasion a cock wren may successfully woo a second mate.

What was the nest made of?

Back at base, we dismantled the nest, drawing on Steve’s botanical expertise to understand what plants the wren had – and hadn’t – used in nest-building, how far it would have had to travel, and what species were growing within its foraging area. Armed with reference books, eye glasses and large cups of tea, we set to work.

We discovered that the wren had used 11 species in its nest building. 7 were mosses: Kindbergia praelonga, Common Feather-moss; Pseudoscleropodium purum, Neat Feather-moss; Hylocomium splendens, Glittering Wood-moss; Rhytidiadelphus squarrosus, Springy Turf-moss; Hypnum cupressiforme Cypress-leaved Plait-moss; Eurhyncium striatum, Common Striated Feather-moss, and Sphagnum papillosum, Papillose peatmoss.

All of these species were present within 20m of the nest site – almost all were present within about 4 metres. The wren, then, would not have had to travel far.

Also present were Agrostis stolonifera, Creeping bent; Cerastium fontanum, Common mouse-ear; Anthoxanthum odoratum, Sweet vernal grass; Festuca ovina, Sheep’s fescue, Male fern sp., and Juncus sp.

But how many trips did he have to make?

The wren’s nest weighed 122g. It was damp when weighed – but as the wren was collecting mostly damp mosses it is probably a good reflection of the how much weight the wren carried. Quite a feat for a bird weighing only about 9 grams.

In 20g of the nest – a sixth of it – there were 850 pieces of moss and other plants. Multiplied by six, this gives the staggering figure of 5100 pieces in a nest. Of course, we have to allow for the fact that some of these pieces may have come apart over time within the nest. Nonetheless, if a wren carried, say, 5 pieces in its beak in a journey, that would mean 1000 trips per nest.

Multiply that by three, four, five – and perhaps we can understand why the cock wren calls so crossly. But then, few birds have a sweeter song.

What have we learnt?

This is, of course, not a rigorous scientific study – here, one part observation is met with at least one part speculation! However, it gave us a chance to learn, to understand and to marvel at yet another aspect of Flanders Moss – and to admire the industry of the tiny wren.

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9 Responses to The curious incident of the empty nest

  1. Anne says:

    This is wonderful! I frequently inspect nests that get blown out of trees or found abandoned during the winter and am always astounded at the materials used by different birds. This close inspection of your nest takes it to a different level. Thank you for sharing.

    Liked by 3 people

  2. Beautiful and fascinating! Here in the eastern US, we have two breeding wren species. Their nests couldn’t be more different. One is a secondary cavity nester that constructs its nests entirely from sticks. The other uses a mix of grasses, leaves and varied materials, creating side-entrance nests in shrubs, vegetation, door wreaths, coat pockets, etc. What they have in common are “cock” and “dummy” nests to claim territory. And they are plenty chatty too.

    Liked by 1 person

  3. Jo says:

    This is fabulous – a fascinating and insightful account. We always have a quick look at the nesting materials when clearing out our nest boxes but have never taken it to this level!
    The 2 bogs blog is always a great read and this post is one of my all time favourites, thanks!

    Liked by 2 people

  4. Hushwing Ranger says:

    Hi, absolutely great investigation work. Well done.and a story well told. We have also seen wrens using these sort of nests in the winter (I guess as warm roosts) in the Trossachs in Scotland. One for the last four years has added the moss ‘nest’ on top of our seasonal swallow nest.

    Liked by 2 people

  5. mosslady1 says:

    This is a wonderful article! Would it be OK if I forwarded the link to a friend who is writing an online Bryology textbook?

    Liked by 2 people

  6. Sarah eno says:

    Really glad to read this fascinating piece aas it means the wrens nest in a comfrey plant was probably naturally abandoned and not because I had watched him building.

    Liked by 1 person

  7. Mark Hope-Urwin says:

    Really great piece of research and an extremely well written article. Congrats to all concerned. Thank uou

    Liked by 2 people

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