Monday 28 August 2023

Tales From The Riverbank

I don't want to repeat myself, but it has been another quiet week since I last posted, some eight days ago. We have been out, walking the quay and the riverbank on several occasions, and we even ran our light trap for moths in the garden a couple of times. And this past week I finished with a sea watch from the coastal farm fields, but more of that later. 
As I said above, we ran our moth trap twice this last week, and the catches were poor in terms of species, but quite large for us in terms of numbers, thanks to a number of Large Yellow Underwings. We added eight new species for the garden, in the form of Rhomboid tortrix, Acleris hastiana, Copper Underwing, Bird-cherry Ermine, Rosy Rustic, Vine's Rustic, Dark Fruit-tree Tortrix and Garden Rose Tortrix, and incidentally, we just caught one of each of these eight species. Over both days the combined totals of the other moths we caught were, 96 Large Yellow Underwings, four Agriphila geniculeas, a Bright-line Brown-eye, two Lesser Yellow Underwings, a Common Rustic, a Garden Carpet, five Lesser Broad-bordered Yellow Underwings, a Flame Shoulder, and a Setaceous Hebrew Character.
A few of the Large Yellow Underwings
I noticed some larvae were munching my Willows, and after a bit of research I identified them as Lesser Willow Sawfly Nematus pavidus. They aren't rare, in fact they are very common, but it is one of the joys of looking at invertebrates in that virtually everything is new. Well, it is to me anyway! 
Lesser Willow Sawfly
During the week, Gail and I had a wander along the quay, and along the bank of the River Wyre to Fleetwood. All our visits were mid - late morning, and all our visits were fairly quiet, with the exception of visit number three. 
Our first visit was very quiet, even though the southerly wind seemed to give the impression that there might be a migrant or two about, but there wasn't. Looking back at my notebook as I write, it was meagre pickings, and all I will mention is the eighteen Redshanks and fourteen Oystercatchers out on the mud. 
For visit number two, the wind had swung round to the northwest, and for some reason, even though it felt a little cooler, a few common butterflies were on the wing. We had seven Small Whites, five Common Blues, two Red Admirals and a Small Tortoiseshell
Red Admiral (above & below)


Ten Swallows were in the air at one point, alarm calling away, but we couldn't see/find what had upset them. By the way they were behaving, we suspected something mammalian, rather than avian. 
Our third visit, which was in fact yesterday, coincided with a falling tide, and we did have a few birds. It was overcast with a chilly north-westerly wind. There were a number of waders feeding in the quay itself, and along the river's edge in the main channel as the tide fell, exposing foraging areas. There were also birds flying downstream. Some stopped off for a few seconds before heading off again, but others just motored past. I've lumped my totals together for all three scenarios, and we had 112 Oystercatchers, 287 Redshanks, a Whimbrel and three Curlews
As we neared the mouth of the river, we could see onto one of the muscle beds, or scars as they are known, and there were at least 800 Oystercatchers, along with four Little Egrets. This is obviously where all the birds flying downstream were heading. 
In addition to the waders heading downstream, we also had 33 Sandwich Terns doing the same. We watched all this activity as we sat on the side of the quay wall overlooking the river. As we were sat watching the natural world go by, a flock of thirty Starlings dropped in just a few metres from us, and they were busy feeding on invertebrates amongst the sparse vegetation along the sea wall. All of a sudden, they were in the air, and a juvenile Kestrel made a very clumsy attempt at catching one, and then perched up on the quay just a few metres from us. 
The juvenile Kestrel (above & below). You will need to look carefully!

It looked quite comical as it had a bit of a walk about amongst the same vegetation that the Starlings were feeding in. I suspect that if it could have found a large enough invertebrate morsel it would have taken it, but it would have been a poor substitute for a Starling! Whilst we were sat watching the Kestrel, a few Swallows were flying back and forth hawking for insects, and the young Kestrel made a few half-hearted, or poorly executed, attempt of catching a Swallow. The Swallows weren't in any danger!

A male Peregrine was on his usual high tide perch, and now that the tide was dropping, he headed off towards the mouth of the estuary in search of a wader to feed on. On the seaweed encrusted slopes of the sea-wall, Gail spotted a white rump 'bouncing' away, that belonged to a migrant Wheatear. The only other migrant passerine that we had was a juvenile Whitethroat that we encountered on our return leg. 
It was a solo outing this morning for me, to the coastal farm fields to have a look over the sea on the in-coming tide. I had 6 oktas cloud cover, with a force 3 - 4 north - westerly wind. Whilst it remained cloudy the visibility was fairly good, but when the clouds cleared a little, there was a heat haze making the visibility not so good.

I'm not sure what I was expecting, but I didn't really expect it to be 'rocking', so when my first bird was a close-in dark morph Arctic Skua heading north, I thought that maybe it might rock a little bit, but it didn't really. There was a supporting cast of 61 Sandwich Terns, 47 Common Scoters, 48 Gannets and a Shelduck, and that was it. 

The most unusual birds I had at sea, were a group of five white herons, quite a long way out, heading north. I couldn't make out what they were at all, but I assume that they were Little Egrets. It wasn't a particularly strong north-westerly wind, but they were making slow progress, and I picked them up again a few minutes later and two climbed, and peeled off from the other three, but I couldn't see where they headed. 

As the tide ran in, there were a number of Turnstones roosting on the rock armour just off-shore, and I counted 134 in total. The only other waders I had were twelve Oystercatchers and a couple of Sanderlings.
I had a walk round the farm fields and hedgerows after I had finished my sea-watch, and the only migrant I had was a single Whitethroat. A group of fifteen Common Gulls roosting on the front fields with some Black-headed and Herring Gulls is worth mentioning. 

I'm not sure why, but I called in at the cemetery on my way home, as I knew there wouldn't be any migrants, but I suppose it's the fact that it is autumn after all, that made me call. And there weren't any migrants!
The weather is looking quite unsettled for the coming week, and I don't know how many blog posts of late that I have ended with that statement! It will be what it will be, and Gail and I will endeavour to make the most of it.

Sunday 20 August 2023


It has been a quiet week, and Gail and I have struggled to populate the notebook with sightings, but we have been trying. The week started off with a couple of nesting bird checks for work, and these were completed in sometimes trying conditions with plenty of heavy rain. 
The forecast for Wednesday morning was good enough to tempt us to have a ringing session at the Nature Park, and at first light we had almost clear skies with a light northerly wind. When putting a couple of nets up, it felt like a bit of a 'clear-out' morning, and our ringing totals backed this up. We ringed eleven birds as follows:
Reed Warbler - 1
Great Tit - 3
Sedge Warbler - 1
Cetti's Warbler - 1
Whitethroat - 2
Wren - 2
Blackbird - 1
Look at the bill on this gorgeous Reed Warbler
Sedge Warbler

As usual, as we were putting the nets up the Starlings exited their reedbed roost with the usual whoosh, and when you are close to them the noise of their wings as they swirl around, sounds like waves rolling onto the shore. 
A few Swallows seemed to be heading north into the wind, as they often do, and a hovering Kestrel is the only other thing of note worth mentioning. However, we do count everything we see and hear, so we can enter a complete count on the British Trust for Ornithology's (BTO) BirdTrack. 
Over that following evening we ran our light trap in the garden, for one of our not so regular moth trapping sessions. We trapped 35 moths of 16 species; 2 Lesser Broad-bordered Yellow Underwing, 2 Willow Beauty, 15 Large Yellow Underwing, 2 Common Carpet, 1 Common Plume, 1 Marbled Beauty, 1 Setaceous Hebrew Character, 2 Brown House Moth, 1 Yellow Shell, 1 Dotted Clay, 1 Flame Carpet, 1 Agriphila latistra, 2 Agriphila geniculea, 1 Garden Carpet, and 1 Acleris notana/ferrugana. We also had a 'moth trap intruder' in the form of the caddis fly, Mottled Sedge.
Common Carpet
Setaceous Hebrew Character

Willow Beauty

On Friday morning I had a solo outing around the coastal farm fields. I was there for first light under 6 oktas cloud cover with a 3 - 4 easterly wind. The tide was a long way out, so I dispensed with any thoughts of sea-watching, and had a walk around the fields and hedges instead. It was quiet, very quiet, and even though I counted absolutely everything, I haven't much to report here.

As I walked along the sea wall there were several House Martins and Swallows continually flying up and down the length of the wall hawking insects, as a number of flies were on the wing. Over 200 Herring Gulls were out on the shore, and a Little Egret fed in one of the tidal pools. I looked for a few plants, but didn't record anything unusual, or should I say, anything that I could identify that was unusual for me! Some Sea Holly was flowering, and these are one of my favourite coastal plants, in fact one of my favourite plants full stop. I think it is a combination of their beauty, and adaptability of their harsh environment that makes them one of my favourites. 
Sea Holly (above & below)

I had a saunter through Larkholme Grasslands, and it was another quiet hour here also. Swallows were hawking insects along this stretch of coast as well, and again about 200 Herring Gulls were on the shore. I had two Little Egrets feeding in a tidal pool, so when I saw those five Little Egrets exiting their roost last week, they were very probably heading to some of the tidal pools along this stretch of coast. 

I found some more Strawberry Clover, but they are probably in the same tetrad as the coastal farm fields, and that was it. I told you it was quiet!

The forecast is a bit of a mixed bag over the next week, which is typical when I don't have any work next week and could get out lots. I think it is called Sod's law!

Sunday 13 August 2023

Warblers and Strawberries

I'm not the most committed moth trapper, and can run my light trap a couple of times in a week, or a couple of months between sessions! I ran my light trap about a week ago, and not since (I know shame on me), and caught just fourteen moths of seven species, but Nutmeg, Hypsopygia glaucinalis and Mouse Moth were new species for the garden, so I was pleased about that.

During the past week, Gail and I made two visits to the Quay on the Wyre, to see if we could catch up with a few butterflies and plants. I think the real reason was so that Gail could pick some Blackberries, so I'm looking forward to an apple (from our garden) and blackberry crumble, or such like. 

Our first visit was fairly early in the morning, so just a handful of butterflies were on the wing; six Small Whites, two Common Blues and two Red Admirals, and a day flying Silver Y moth. The tides were very high earlier in the week, around the 10 metre mark, which means that they go out along way, and areas of mud that aren't regularly exposed are exposed. This attracted 97 Oystercatchers, 19 Redshanks, 160 Herring Gulls, eight Lesser Black-backed Gulls, three Great Black-backed Gulls, two Grey Herons and a Little Egret. And a walk along an estuary in August wouldn't be complete without a calling Whimbrel
Herring Gull
Lesser Black-backed Gull
Silver Y

There's still a few Swifts about, and we had three during our walk, but the best bird was reserved for our return leg, when we flushed a Great Spotted Woodpecker from some scrub on the quayside. Not a scarce bird by any means, but a new bird for us for the site, and it made our morning! This is the beauty of working a patch, and staying local. That 'Great Spot' gave me the same kicks that I used to get four decades ago, when I had a spell of chasing rarities, and driving hundreds of miles across the UK in pursuit of said rarities.
This got me thinking about a brilliant, thought provoking blog post from Steve Gale on his excellent blog North Downs and Beyond. He wrote a blog post entitled What did you do during the climate crisis?, and it is well worth a read. You can read it by clicking HERE
Our second visit to the Quay was just a couple of days ago, and it was on a very hot, but blustery, afternoon. We were hoping for a few more butterflies, but the 15 mph south-easterly wind restricted them to just four Small Whites, two Common Blues and two Red Admirals. 

We'd just set off, when all the wreck nesting Swallows started alarm calling, and there must have been a good thirty of them in the air shouting at the top of their hirundine voices. And the cause of all this commotion, was a male Sparrowhawk that had dared to flap-glide across the Swallows air space. The Sparrowhawk was duly escorted to the other side of the quay, and peace and quiet returned. 

We had our highest count of Little Egrets for some time, with two feeding along the river's edge, and a flock of eight flying downstream towards the mouth of the estuary. At the far end of our walk, at the mouth of the estuary, is the former fishing and ferry port of Fleetwood, and very handily is an ice cream parlour selling Walling's ice cream. In our opinion, you would struggle to find a better ice cream than Walling's, and with a choice of over 40 different flavours it's virtually impossible not to call, particularly on a hot afternoon. I availed myself of two scoops, raspberry swirl and strawberry, and Gail, who isn't as greedy as me, just had one scoop of raspberry sorbet. After this essential pit-stop, we were ready to walk back. Our walk back was quiet, but we did have an adult Mediterranean Gull in the quay. A nice end to a pleasant, if not a hot and sweaty stroll.  

Wednesday morning dawned with conditions conducive to ringing, so Gail and I found ourselves at the Nature Park at 5:30 am, under 1 oktas cloud cover, with a 5 - 10 mph west-north-westerly wind, putting a couple of nets up in the reedbed and scrub. As we were putting the nets up, some early Brown Hawkers were up and about crashing through the reeds. It's amazing how much noise these large dragonflies make as they move through the vegetation.

Brown Hawker

The Starlings were up earlier than usual, so the 700 that we observed exiting the roost, was probably just the last birds leaving. Five Little Egrets went over early, and they were probably exiting a roost as well. They were heading in a north-westerly direction, so were probably heading to feed on the Irish Sea coast. 
A few House Martins and Swallows, a Great Spotted Woodpecker, and a croaking Raven was probably it from a pure birding perspective. We ringed 18 birds as follows (13 being warblers):
Cetti's Warbler - 2
Whitethroat - 5
Blue Tit - 1
Great Tit - 2
Sedge Warbler - 1
Wren - 2
Chiffchaff - 3
Willow Warbler - 1
Reed Warbler - 1

At the end of the week Gail and I were doing our weekly shop (why are you telling us this I hear you ask), and we bumped into Barry and Ellen. Barry is one of those all round brilliant naturalists, and I tend to only bump into him once a year or so. I have known Barry for about 47 years, and when I was a young birder, he was very encouraging to me, and I am forever grateful for that. Anyway, I digress. we were chatting about birds, birders, naturalists, inverts and plants, and Barry asked me if we ever visited Larkholme Grasslands, to which we answered no, even though it is only five minutes from home! He told us that there was a good selection of insects and plants there, so on Friday afternoon we went to have a look.
Larkholme Grasslands is a Biological Heritage Site (BHS), known as a County Wildlife Site (CWS) in other parts of the UK, and it was restored in 2018 when the sea defence work in the area was completed. 

It was a hot afternoon when we visited, but the blustery north-westerly wind meant that any butterflies were keeping low, and we just had five Common Blues, a Small White, a Meadow Brown and two Small Coppers (one of my favourite butterflies). 
Small Copper
A lot of wildflowers have gone over now, but we had species like Lady's Bedstraw, Common Knapweed, Bird's-foot Trefoil, Oxeye Daisy, Chicory, Scentless Mayweed, Purple Loosestrife, Field Scabious, Common Vetch, Creeping Cinquefoil, Red Clover, Sea Campion, Ribwort Plantain and Yarrow to name but a few, but I think you get the picture. 
There are two small ponds on the site, and in the first one there were at least 80 Pond Snails sp. At the second pond we had three Common Darters, and at least three Emperor dragonflies. There was at least one female Emperor ovipositing, but the view of her was always slightly obscured by vegetation, so I couldn't get any pictures. And the two battling males, well, they were just too fast for me. Gail and I spent several minutes stood by this pond marvelling at these large, metallic blue and green dragons. I like the way that Emperors seem to be inquisitive, as they will often come and have a look at you when you stand for some time, and these two boys were no exception. Like the Brown Hawker of Wednesday, these large dragonflies crash through marginal vegetation as well, and you often hear them before you see them.  

Common Darter
Pond 1
Pond 2

We walked back to the car park with calling Whimbrel and Sandwich Tern as a backdrop. The car park is next to the coastal farm fields that I like to bird regularly when I can, and I remembered a visit a number of years ago now, with the late Eric Greenwood, who besides being a lovely man, is probably the best botanist that I have ever known. My signed copy of his Flora of North Lancashire sits proudly on my book shelf. 
Eric's Flora of North Lancashire
During that visit from several years ago he was pointing out to me some Strawberry Clover that can be found just behind the sea wall. It isn't rare by any means, in fact in his book, Eric describes it as 'occasional', occurring in 28 tetrads. Anyway, Gail and I had a look, and sure enough there it was flowering away in the same place that Eric had pointed it out to me all those years before. It's a funny looking flower, and I always think it looks more like a raspberry than a strawberry!  
Strawberry Clover
The distribution of Strawberry Clover in north Lancashire

I've got two nesting bird checks to do tomorrow, and then I have a meeting Tuesday morning, and then the rest of the week is free. So hopefully, we'll be back out several times during the week.

I'm beginning to really like the good people of the University of Sussex as I read about another great piece of research they recently carried out alongside Butterfly Conservation. There is widespread concern about the decline in wild pollinating insects like bees and butterflies, and the researchers at the University of Sussex have discovered that moths are particularly efficient night-time pollinators. 

Throughout July 2021 they studied ten sites in the south-east of England, and found that 83% of insect visits to Bramble flowers were made during the day. While the moths made fewer visits during the short nights, only 15% of the visits, they were able to pollinate the flowers more quickly. 

The researchers concluded that moths are more efficient pollinators than day-flying insects such as bees! While day-flying insects have more time available to transfer pollen, moths are making an important contribution during the short hours of darkness. 

The study also highlighted the importance of Bramble, a shrub widely thought of as unfavourable (not by us) and routinely cleared, when in fact it is critical for nocturnal pollinators. So now that we know that moths are important pollinators, we need to ensure that Bramble, and other flowering scrub plants, are encouraged to grow in our parks, gardens, road verges and hedgerows. So, leave some Bramble in your garden if you can please.

Thursday 10 August 2023

Nest Box Design and Ectoparasite Load

I never thought that I would write a blog post with a title like that, but I read a very interesting paper recently in Bird Study - Volume 70, Part 1 - 2, February-May 2023 entitled Influence of nest box design and nesting material on ectoparasite load for four woodland passerines by Thomas Blunsden and Anne E. Goodenough. If you check nest boxes every year like I have since 1985, you too would find this paper very interesting. I'll have a go at summarising the findings of the paper, so bear with me! 
I suppose the first question, is what is an ectoparasite, and what effect can they have? An ectoparasite is an organism that lives on the skin of a host, and from which they derive sustenance. And nest ectoparasites constitute a threat to the fitness and survival of chicks and parents. These parasites can cause anaemia, a lack of weight gain for chicks and weight loss for adults. The authors go on to say that some ectoparasites can also cause disease, either because they act as vectors, or because puncture wounds or scratches become infected. This can potentially reduce post-fledging survival of young, or post-breeding survival of adults. So, they can have quite a negative impact. 
For passerines nesting in woodland in the UK, the two most important nest ectoparasites are Hen Fleas, and parasitic Blowfly spp. I had never heard of Hen Fleas, and was aware of Blowflies, but didn't really have any understanding of their relationship and impact on nesting passerines. What is important, is that both of these ectoparasites undertakes key stages of their life cycle within nest material alongside their avian host. Hen Fleas synchronise their reproduction with that of birds to enable them to complete two generations during the birds' nesting period. The parasitic Blowflies lay their eggs when the chicks are approximately 30% grown, so that the larvae can take direct meals of blood from the growing chicks, and then pupate within the nest. Because of the potential cost of these parasites on breeding success, Great Tits in Switzerland, in an experiment, actively chose nest sites without Hen Fleas, when they were avialable! When only infested nest sites were availiable, the laying of clutches was delayed, desertion was higher, and hatching success was lower. 
Pied Flycatcher nest and eggs in what looks like an old box
The authors stated that a number of different parameters can influence the presence and abundance of nest ectoparasites. Bird species is important, as understandably some ectoparasites are host specialists e.g., Hen Fleas are particularly abundant in the nests of tits. Nest type plays a key role as well: open nests generally have a low ectoparasite load but a high predation risk, but birds using natural cavities and nest boxes tend to have a high parasitic load, but low predation risk. Within nest boxes, the fact that birds tend to use the same nest site over successive years can be a major determinant of ectoparasite load, especially for ectoparasites that pupate within the nest or use nest sites to overwinter. 
Nest composition and the amount of nest material can also influence ectoparasites. The materials used to construct a nest varies between bird species, with climate conditions, geographic location, and local availability of materials also having an impact. Vegetative material, twigs, bark and dead leaves, is often used to form a structural layer to provide the shape of the nest, while dry grass, feathers, wool and animal hair can provide an insulative lining. I found it interesting that fresh plant material, such as green leaves, are also used by some bird species, possibly because they contain chemical aromatic compounds that fill the air of the nest box, and act as repellents or natural fumigants. A study by Rendell & Verbeek in 1996, found positive correlations between the volume of nest material used by Great Tits and the number of Hen Fleas.   
Nuthatch nest and young
Nest boxes are often used to provide a safe place to nest for certain bird species, and they provide the opportunity to monitor the populations of the bird species utilising them. However, the nest box construction, maintenance or management could affect ectoparasite loads e.g., older nest boxes could have higher ectoparasite loads if parasites overwinter in the box. Also, nest box dimensions can affect nest volume, as larger nests are built in larger boxes, and again this could affect parasite loads, which tend to increase with nest volume. The authors looked at the interrelationships between ectoparasite abundance, bird species, nest box design, amount of nesting material and nest composition. 
They stated that their aim was to advance the understanding of bird and ectoparasite relationships and inform the optimization of nest box design for conservation and management, especially for declining woodland specialists such as the Pied Flycatcher, of which Gail and I are very interested in. The nest boxes studied were 'old' wooden nest boxes, 'new' wooden nest boxes of the same dimensions (like ours for Pied Flycatchers and Tree Sparrows) and 'new' deep wooden nest boxes (thought to be predator proof as the extra depth increases the distance between eggs/chicks and the entrance hole).      
The research took place on a reserve in Gloucestershire, and before the start of the 2019 breeding season, the authors erected 100 new deep nest boxes, and 100 new wooden nest boxes of standard size alongside pre-existing old wooden nest boxes, giving 200 trees with a choice of two nest boxes on them. Territoriality would prevent both nest boxes on a single tree being used. All of the boxes had a 32 mm hole, the same size that we use for both our Pied Flycatchers and Tree Sparrows, and the deeper boxes were 55 mm deeper than the standard size. The rationale for using the deep nest boxes was to mitigate potential increases in predator pressure due to the imminent reintroduction of Pine martens, as well as the existing predation pressure by Grey Squirrels. 
Post-fledging, 78 nests were collected for analysis. The nests were weighed, frozen at minus 18 Celsius to kill parasites and preserve them until the nests could be processed. The collected nests were then subdivided between species and nest box design. All the parasites were identified, as well as mosses used in the nest construction, and all tree material was recorded. In addition to this, any animal hair used in the lining of the nests was identified to species level. 
Great Tit nest and young
I'm going to skip over all the data analysis bit, even though it is hugely important, as it's tricky trying to explain it an understandable way, and that's assuming that I understand all the non-parametric U tests and Poisson distribution, to name but a few. So, I am going to jump straight to the results and discussion. 

Where there was a choice of two nest boxes of standard size, there was no significant difference between the number of new nest boxes selected compared to the number of old nest boxes selected. However, when there was a choice of either a deep nest box (predator proof?), or an old nest box of standard dimensions, there was a significant avoidance of deep nest boxes. Given that both new nest boxes of standard dimensions and deep nest boxes were added immediately before the breeding season, it suggests that the dimensions of the nest boxes, rather than age were driving the bird's choice. Very interesting!   

In their 'discussion' the authors reported that the abundance of Hen Fleas and Blowfly in the nests of the cavity-nesting bird species that they studied, was influenced by bird species, amount of nesting material, and nest composition. Both ectoparasites were found at their highest loads from deep nest boxes, nests from old nest boxes had intermediate loads, and nests from new nest boxes had the lowest loads. Greater amount of nest material increased the abundance of both ectoparasite species. 

It was interesting that the authors noted that nests in deep nest boxes had high ectoparasite loads, and the positive correlation between nest mass and ectoparasite abundance, is likely to be partly connected. They observed that birds nesting in deep nest boxes continued adding nesting material until the top of the enlarged nest was a similar distance to the entrance hole as it would be in a nest box of standard dimensions. A greater amount of nest material increases the habitat available for ectoparasites! 

Also, the difference between old and new wooden nest boxes showed that the former had a significantly higher abundance of ectoparasites compared to the latter. This could mean that the ectoparasite load increases with nest box age. Connected to this, was that the authors results suggested that cleaning the nest box was ineffective, perhaps because pupating hen Fleas, for example, are hard to remove if they are within the feather dust at the bottom of the box, rather than within the nest itself. 
At the end of the paper, a couple of key recommendations are made, and they are ones that I will certainly consider in relation to our nest box scheme, and these are that boxes are regularly replaced to keep ectoparasite loads down, and that deep nest boxes are not used, as they result in larger nests, and are associated with increased loads of two ectoparasites. And the behaviour of birds in building up the nest structure in deep boxes, negates the reason for using them in the first place in terms of reducing predation risk, as the nest contents are within reach of mammalian predators. 
I was particularly interested in the recommendation to regularly replace boxes, as I tend to replace mine based on their condition. What the authors didn't say, unless I missed it, is how old is an old box, and at what stage does the ectoparasite start to increase, whereby it is having a negative impact on the outcome of the breeding attempt. Mmm......