Category Archives: Statistics

Dormouse activity in my site in 2016

I have been in partial hibernation this last couple of months, hence the lack of blog posts. But I have managed to do somethings, one of which is sift through my dormouse data from last year. I’ve made a little animation showing how dormice and other animals have used the boxes at my monitoring site over the last couple of years.

 

It’s great to see dormice making use of the boxes we put up in 2015. Hopefully it means this year they’ll start making use of the boxes we put up at the start of 2016.

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Bird Nerd part 15: 2015-2016 data – catastrophe

If you have followed this blog for a while, you’ll know that I keep records of the birds I see in my garden. I have finally got round to entering and analysing the data from June 2015 to May 2016. The results make gloomy reading.

I have data from 36 observation days, spread across the year. On average, I saw eight individual birds from 4.5 species per day. This is the lowest average number of birds and species in the six years I have been collecting data, by quite some way. It’s a fall by more than half on the previous year’s average number of birds.

Average number of individual birds and species, 2010-2016
Average number of individual birds and species, 2010-2016

This averages hide a range from no birds at all (one day in February) to 19 birds from 9 species in June. In total, I saw birds from 16 different species.

As the graph shows, I started off with high numbers, which declined steeply in the first couple of months (as is fairly usual for the time of year). But the numbers never really picked up again, and December, which is usually the busiest month, saw very few birds visiting the garden.

Total number of individual birds and species, 2016
Total number of individual birds and species, 2016

How did different species get on?

The most regular visitor to the garden was woodpigeon, being recorded on 81% of observation days, followed by the reliable robin, on 78% of observation days. House sparrows were on seen on 36% of observation days, but turned up in numbers, giving a mean average of 1.8 individuals per observation day.

As the next chart shows, it was a bad year for most of the common species. The house sparrow population seems to have dropped dramatically from last year. I saw fewer starlings, collared doves and blackbirds than any previous year. Numbers of woodpigeons, magpies, dunnocks and jackdaws also seemed to be down on the previous year. Two species had their best ever year in our garden: robins and feral pigeons.

Average number of birds from common species, 2010-2016
Average number of birds from common species, 2010-2016

How does this fit with the national picture?

According to the British Trust for Ornithology’s Garden Birdwatch survey (which my data feeds into), There were low average numbers during the second half 2015. But they report that many of the seed-eating and insectivorous species were seen in very high numbers toward the end of the year,  something my data doesn’t reflect. There were low winter migrant numbers, which could have been driven by relatively mild winter.

Looking at the individual species, the latter half of 2015 does seem to have been bad for house sparrows, collared doves, blackbirds and starlings nationally.

What caused this decline?

I don’t really know what caused the decline. I haven’t changed the food, water or shelter features in the garden for birds. A couple of possible factors spring to mind.

  1. Last winter was very mild, so maybe birds didn’t need to visit the garden so much for food
  2. Cats and kittens: our garden is now used by next door’s cat – he probably arrived during this period. And our backdoor neighbours have got a couple of naughty kittens. So perhaps these are scaring the birds away.

And of course there’s the bigger picture that’s affecting birds nationally: Jazz, Roja and Kiki are not responsible for low numbers of birds nationally. Climate change, habitat loss and farming intensification are part of the longer-term story.

What to do?

I can’t change the weather, so I guess if I want to see more birds, I may need to discourage the neighbourhood cats. I am not sure how best to achieve this, without making the garden unappealing to Fat Cat as well, which would be a shame (she’s not a hunter – she once got scared out of the garden by a baby bluetit). Maybe we could use some kind of cat repelling sound device that we could turn off when Fat Cat is taking her constitutional stroll.

What do you think?

  • Have you noticed any decline in the number of birds visiting your garden?
  • Do you have any alternative hypotheses for why the birds have disappeared?
  • Do you have any suggestions on how I can discourage the neighbours’ cats while not spoiling Fat Cat’s chance for fresh air and grass?

What I found at my dormouse site in 2015

I have been meaning for ages to look at how dormice, woodmice and birds used different parts of my site over the course of last year. The burst of energy that spring gives me, and being relatively on top of the gardening, meant I had time on Sunday to play with presenting my data visually. I’ve made a short video to show which boxes were used by what, when.

As you can see, birds dominated the site for the first few months. But quite a few bird nests were subsequently taken over by dormice, once the birds had finished with them. By the end of the year there were an encouraging number of boxes with dormouse nests in.
What do you think of this way of showing the data? What strikes you from it?

It’ll be interesting to look at this year and last year side by side.

Bird nerd part 13: Big Garden Birdwatch 2016: where were they all?

Last weekend was the RSPB’s annual Big Garden Birdwatch, where hundreds of thousands of people around the country spend an hour recording the birds that visit their garden or park. Bird nerd that I am, of course I took part. But my sightings this year were far from impressive.

I didn’t get off to a good start. Sunday was a damp, blustery day. The sort of day when I see far fewer birds than normal. And Jazz, our neighbour’s cat, spent the first 20 minutes sitting under the buddleia, getting into the birdwatching spirit. Not helpful. Dr C offered to chase him off, but I demured – the count is not a competition, it’s trying to get reasonably representative snapshot. As Jazz spends quite a bit of time lurking in our garden, I figured his presence was fairly typical.

Still, I was relieved when he disappeared under the fence. No birds were foolish enough to visit the garden with him around (the pigeon feathers on our lawn hint at what happens to foolish birds). And it would just be embarrassing not to see any birds.

The timer sped on, and my concern increased. Finally, I heard a robin. Heard him, but couldn’t see him. Then eventually he showed himself. I could put something down on my list. Sadly he remained the sole avian visitor to our garden that hour – a big contrast with my results in 2014.

image

We have been seeing far fewer birds than usual for this time of year. I think that might be because of the mild weather we’ve had so far. Those that do visit the garden seem uninterested in the seeds, suet pellets and mealworms we put out, preferring the ivy berries. In recent weeks I’ve been recording around 5 species a day – about half what I usually expect in January.

Hopefully this means that the birds are finding plentiful food elsewhere, rather than a dramatic decline in the bird population. Data from the BTO’s Garden Birdwatch survey (collected every week, rather than once a year) will give us a better idea of the impact of our weird winter weather beyond the boundaries of my garden.

How was 2014 for dormice in Surrey?

This article is adapted from one that I wrote for the spring/summer issue of the Surrey Dormouse Group (SDG) newsletter, and is reproduced here with their kind permission. It's based on data collected by dozens of volunteers across the county. If you would like to find out more about the work of SDG, visit their website

Last year SDG members checked a total of 7076 boxes from 18 sites. Data from each SDG box check gets reported to the National Dormouse Monitoring Programme, to feed into their national analyses – you can read about how 2014 was for dormice nationally in the Dormouse Monitor.  Here’s a summary of the data from Surrey.

How many dormice?

We saw a total of 487 dormice over 2014. That works out at a mean average of 3 dormice per 50 boxes checked, but there was quite a range of numbers seen at box checks: from 0 per 50 boxes to 27 per 50 boxes. At a third of box checks no dormice were found. The median number of dormice found per 50 boxes checked was 1, which is probably a representative average, given that a few large numbers are skewing the mean. Some sites that had quiet starts to the season saw large numbers later on. On average, we also found 2 empty dormouse nests per 50 boxes (ranging from 0 to 18).

Number of dormouse found per 50 boxes checked, Surrey, 2014
Number of dormouse found per 50 boxes checked, Surrey, 2014

When did we see them?

The earliest dormouse was a 20g torpid male, found on the 6th March, and the latest ones were 3 found at the beginning of December (that’s not to say others weren’t around earlier or later – just we weren’t checking so didn’t find them). As you can see from the graph above, average numbers were highest in August to October, and lowest in March and April.

How much did they weigh?

Females weighed slightly more on average than males (19g vs 18.7g), but this changed considerably over the course of the year, as you can see from the graph, with weights at their highest just before hibernation. The heaviest dormouse recorded was a 33g female found in October.

Average weight of dormouse found in Surrey, 2014
Average weight of dormouse found in Surrey, 2014

Other interesting features

Dormice with white tail tips were reported 36 times over the year, including a family of juveniles, all with white tail tips. There were 9 dormice with stubby tails.

Youngsters

The earliest pinkies were found on 20th July. (Pinky is a technical term describing baby dormice before they grow fur). On that same box check the earliest greys (babies that have their first coat of fur, which is much greyer than an adult) were also found. The latest pinkies were found on 25th September, and the latest greys were found on 20th October. Dormice born later in the year have more of a struggle to fatten up in time for hibernation, but those born too early in the year may struggle with their mother not being able to find enough food for herself.

The largest number of dormice found in one box was 8 (mother with young): boxes with 8 dormice were found at two sites.

Other box occupants

Apart from birds (which seem to take over a large number of boxes in spring at some sites) and invertebrates, the most common other occupant were wood mice (162 were seen, 21 of which were found in dormice nests) and yellow necked mice (29 were seen, only one of which was in a dormouse nest). There were also 12 unidentified apodemus mice (wood mice or yellow-necked mice). The rarest other box occupant was the pigmy shrew, with only 7 reported over the whole year (2 of which were in one box).

Bird Nerd Part 11: headlines from the last year

Another year has passed, so I have another stack of data about my garden birds to wade through. I started recording data about the number of birds I see back in June 2010, so I’ve now got 5 years of data. In this post I’ll just share some of the headlines for the last year (June 2014 – May 2015).

Methods

This post outlines how I collect the data. In brief, I record the maximum number of individuals of a bird species I see at the same time in my garden, while sitting in my study working from home for the day.  This year I have 23 days of observations, which is the lowest so far – I think I must have had more meetings at work. Darn this paid employment thing getting in the way of birdwatching! (I love my job really.)

Averages, minimums and maximums

On average, I saw 18 individual birds of 7 different species per observation day. This did vary quite a bit over the year – the lowest was 2 birds of 2 species (in September) and the highest was 39 individual birds (in October) and 12 species (in December). The total number of species I saw over the year was 17.

The species league table

Average numbers of birds seen per observation day, and proportion of observation days seen on
Average numbers of birds seen per observation day, and proportion of observation days seen on

Notable visitors…

We had one visit from each of the following birds (having had none the year before):

Chaffinch
Chaffinch
Male blackcap
Male blackcap
  • Chaffinch
  • Blackcap
  • Pied wagtail
  • Song thrush

…and noticeable absences

goldfinch
Goldfinch

This year we had no visits from wrens, goldfinches or siskins on observation days. This is the first year with no wrens or goldfinches recorded.

Coming soon

I’ve got another post or two planned looking at changes over the last five years, and also seasonal patterns in my garden visitors. (I even have hopes of presenting some of data in a more visual way than usual).

Bird nerd part 10: feral pigeons

Feral pigeons are regarded as pests in many towns. Lots of effort and expense goes into discouraging them from perching on ledges by placing spikes, and scaring them away with birds of prey. But in my garden feral pigeons have been rare. In 2013-14 I recorded none at all, and the year before that I only recorded them on 3 occasions. Now I’m seeing them all the time.

So far this year I’ve recorded data from 13 observation days. I’ve seen feral pigeons on 9 of those 13 days. And it’s not just one or two. In the four preceding years, the most I’ve seen on any single day was two. This year I’ve had up to six on a single day. I’ve seen feral pigeons on as many observation days in 2015 (and we’re still only in May) as in the previous 4.5 years put together.

I’m not sure why there’s been this change. I’m still getting regular visits from their country cousins, the woodpigeons. The type of food I’m putting out is the same. And there hasn’t been any significant changes in land use nearby.

Feral pigeon
Feral pigeon

While not everyone’s a fan of feral pigeons, I quite admire the beautiful colouring on their necks. And they look a bit brighter than woodpigeons (who always strike me as dopey). As far as I can see they’re not causing any problems in the garden, so they’re welcome visitors (as are the crows, jackdaws and magpies that other garden birdwatchers are often less keen on).

 

Bird nerd part 9: finding a home for my data

I’ve been keeping records of the birds that come into my garden since 2010. By now, that’s quite a lot of data. Once a year I get round to entering it into a spreadsheet, and trying to analyse it a bit. But apart from a few posts on my blog, and my own personal interest, the data are not really achieving much. Now I’ve finally found a use for the data, as part of the British Trust for Ornithology’s Garden BirdWatch survey.

I found out about Garden BirdWatch (which is different from the RSPB’s Big Garden Birdwatch that takes place in January each year) at an event organised by the local BTO representative. Members of the BTO, and people like me, who have taken part in previous surveys (Nestbox Challenge, in my case) were invited to hear about the different surveys the BTO run, and a fascinating talk by Ed Drewitt on Urban Peregrines. I’m not a proper ornithologist (mammals are more my thing), so I felt a bit like an imposter at the event, but the Garden BirdWatch does sound like it’s designed to take the sort of data I collect each week.

Garden BirdWatch summary data
Garden BirdWatch summary data

So, I signed up, and have now entered my data back to July last year. I haven’t worked out how to enter my earlier data yet, but I hope this can also be uploaded somehow. Once the data is on the website you can look at summaries of it, although I’m not sure if they go into the level of detail I try to when I analyse my data. But at least it’s now helping researchers to monitor the health of our bird populations.

 

Bird nerd part 8: Big Garden Birdwatch 2015

The last weekend in January was the annual Big Garden Birdwatch, when hundreds of thousands of people from across the UK record the numbers of birds they see in one hour. This year I was down in Cornwall that weekend, staying with my parents, so there were four pairs of eyes to keep watch.

The list of what we saw is a little different from what I’d expect if we were at home (see my report on last year’s birdwatch). Here’s what we saw down in Cornwall:

Great British Birdwatch results from my parents' garden
Great British Birdwatch results from my parents’ garden
  • 4 Blackbirds (we usually get a couple)
  • 2 Bluetits
  • 4 Chaffinches (we rarely get chaffinches)
  • 2 Dunnock
  • 2 Great tits
  • 3 House sparrows (we’d beat them on sparrows)
  • 2 Magpies
  • 3 Robins (we usually only get 1)
  • 30 Starlings (We rarely see more than 10 at home)
  • 1 Woodpigeon (we’d beath them on woodies as well – we usually get 2 or 3)
  • 1 Wren
  • 1 Greater spotted woodpecker (We’ve never seen a woodpecker in our garden)
  • 25 Rooks (there’s a rookery in the trees by their house)

No collared doves though – we usually get 2 or 3.

Chaffinch
Chaffinch
Blue tit
Blue tit
Great tit
Great tit
This chaffinch is too fast for me!
This chaffinch is too fast for me!

Later this year they’ll release the full results, which will give a useful snapshot of how the nation’s birds are doing.