Category Archives: Statistics

Bird nerd part 7: blackcap’s back

I’m not a fan of winter, but it does make watching the birds in my garden a little more exciting. This week I was thrilled to see a blackcap for the first time since 2012. Blackcaps are a pretty type of warblers, with soft grey feathers and a striking black (if it’s male) or brown (if it’s female) cap.

Male blackcap
Male blackcap

Blackcaps aren’t the only unusual visitor I’ve seen in the garden recently. I saw a female chaffinch the other day. I’d only seen chaffinches in the garden twice before, both times back in 2013.

While few days go by without a visit from woodpigeons, feral pigeons are much rarer in my garden. But I have seen them twice in the last couple of weeks, having not seen them since 2013.

Obviously the food we put out is attracting more customers, despite the relatively mild and calm winter we’ve had so far. Better make sure I keep the feeders topped up!

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Bird nerd part 6: four years of garden bird data

I now have four years worth of data about the birds that visit my garden, so I thought now would be a good time to look at the latest stats, and how they compare to previous years.

In the year from June 2013 to May 2014 I was able to keep records on 38 days. On average I saw 15 individual birds of 7 species per day, although that varied a lot by month. November was the best month for bird watching, with an average of 29 individuals from 8 species per day,  while July was the quietest month, with only 10 birds of 4 species per day. The highest number of species seen per day was only 10, which is down from 13 last year.

Woodpigeon in the snow
Woodpigeon in the snow

The most regular visitors were house sparrows and woodpigeons, with at least one of each seen on every observation day. The most numerous visitors were house sparrows, with an average of 4.6 seen per day. They were followed by starlings, with an average of 2.8, woodpigeons (2.3) and blackbirds (1.4).

Young starlings
Young starlings

How does this compare to previous years?

Average total number and total types of birds seen per observation day, 2010-2014
Average total number and total types of birds seen per observation day, 2010-2014

Well, the overall average number of birds and number of species is pretty similar. But there have been some winners and losers in the last few years, as the bar graph shows.

Average number of individual birds seen per observation, 2010-2014, by species
Average number of individual birds seen per observation, 2010-2014, by species

Winners

Male house sparrow on seed feeder
Hungry house sparrow
  • male blackbird on lawn
    Male blackbird on lawn

    House sparrows (from an average of 1.7 to 4.6 per day)

  • Dunnocks – the average number seen per day in the last year is roughly double that of 2010-11
  • Woodpigeon numbers have also doubled since 2010-11
  • Blackbirds – increased from 0.9 last year to 1.4
  • Magpies – slight increase

Losers

  • Bluetit gathering nesting material
    Bluetit gathering bits of twine to use as nest material
    Robin in the snow
    Robin in the snow

    Bluetits – these used to be some of the most regular visitors to the garden, but are now seen much less frequently

  • Jackdaws
  • Robins – the average number of robins seen has halved in the last year.

If you’re interested in how these figures compare to national observations, read this post on the Big Garden Birdwatch results.

Bird Nerd part 5: Big Garden Birdwatch 2014 results

Last week the RSPB released the results of the 2014 Great British bird watch. Once again house sparrows topped the list, with an average of 3.8 seen per garden.

The survey was carried out by almost half a million volunteers  across the UK. It involved watching a garden or park for an hour during one weekend in January, and recording the maximum number of birds of each species seen at one time.
So how do the results compare to the average number of birds I saw in my garden this January? The table below shows the mean number of birds observed per site in the UK as a whole, Surrey, and my garden. As you can see, the results are pretty similar.
House sparrows also topped my list. Unlike the rest of Surrey and the UK, I didn’t see any goldfinches. Dunnocks did make it onto my list though.
Top 10 bird species seen: Big Garden Birdwatch 2014 and my garden
Top 10 bird species seen: Big Garden Birdwatch 2014 and my garden
But how does this compare to previous years? Compared to last year there has not been a huge amount of change in the average numbers of birds seen for the top 10 species nationally. For my garden, there has been a drop in the number of starlings, and smaller drops in the numbers of several other birds, but that may be down to the mild winter meaning birds don’t need to visit the feeders in my garden as much as last year.
Top 10 birds seen in my garden in January 2013 vs January 2014
Top 10 birds seen in my garden in January 2013 vs January 2014

Big Garden Birdwatch 2014

It’s the last weekend in January, which means it’s time once again for the RSPB Big Garden Birdwatch. I’m doing my hour of observation as I type, (lunchtime on Sunday) and conditions aren’t promising. It’s tipping down with rain, and blustery with it, so I don’t expect to see many birds. I put out food first thing this morning, but had to refresh supplies before I started counting as most of it had already gone.

Last year more than half a million people took part across the UK. The data generated by this annual event helps us keep track of how garden birds are doing across the UK. Headline findings from last year’s event included the continuing decline of starlings and house sparrows, both of which are ‘red listed’, which means they are of highest conservation concern. We have to hope that this year will see better results for them. On a more positive note, sightings of siskins, fieldfares and jays increased last year compared to 2012.

So, what I have seen in my garden over the last, blustery hour? No big surprises.

  • 5 house sparrows
  • 2 starlings
  • 1 dunnock
  • 2 blackbirds
  • 2 collared doves
  • 2 woodpigeons

I think if the weather had been kinder I would have expected to see a robin and a bluetit or two, based on my ‘bird nerd’ sightings over the last couple of weeks. But who can blame the birds for finding somewhere sheltered to keep out of the rain. Now I’ve finished my hour I think it’s time to light the fire and settle in for the afternoon!

Bird Nerd part 3: feeding habits

As I mentioned in my last bird nerd post, I have quite a lot of data on the birds that visit my garden, and am keen to hear ideas for questions I could look at with it. Someone suggested that it might be worth looking at whether birds with similar feeding habits have similar patterns of visits over the year. So I gave it a go.

First I tried to work out how I could group my avian visitors, and settled on the following categories:

  • those that feed from the seed feeder (house sparrows, great tits, chaffinches)
  • those that feed from the suet pellet feeder (blue tits, coal tits, black caps, long-tailed tits)
  • those that eat seed from the table (wood pigeons, collared doves, feral pigeons)
  • those that eat suet pellets or mealworms from the table (starlings, magpies, jackdaws, crows)
  • those that feed from the ground / other sources (blackbirds, song thrushes, pied wagtails, wren, dunnock, robin)

Of course there is a certain amount of overlap. For example, sparrows and bluetits will feed from both the seed feeder and suet pellet feeder, but do seem to have preferences.

I then created some simple line charts, using the average number of each species seen per observation day for each month of the year, based on data from June 2012 – May 2013. Here are the charts.

seed

suettableseed  tablesuetground

For most of them it looks like the average number seen per observation day is independent of feeding habits. But there may be some relationship for those that feed from the ground or suet pellets or mealworms from the table.

The patterns are unlikely to be driven by changes in the availability of food in my garden, as this is broadly steady throughout the year. However it could be linked to the availability of other food sources beyond my garden. It may be that birds in this category are more influenced by the weather than the other categories, so fluctuations are more in line with each other.

It’s not conclusive evidence, but it’s an interesting hypothesis. When I have time I will use data from the whole 3 years to draw up scatter plots for pairs of birds whose average numbers seem correlated. Can you think of other ways I should test for a relationship? Are there any other questions you think I should look at?

Bird nerd part 2: summary stats

So, having collected all this lovely data, what do I know about the birds that visit my garden? Here are some summary stats from the last three years of data collection.

  • In 2010-11 I saw on average 7 different species per observation day. In 2011-12 this went down to 6, and in 2012-13 it went up to 8.
  • In 2010-11 I saw on average 14 individual birds per observation day. In 2011-12 that went down to 12, and in 2012-13 it went up to 15.
  • These averages hide quite a bit of seasonal variation: September is generally pretty quiet, while the bird table is unsurprisingly busy in December and January.
  • The most regular avian visitors to the garden were: bluetits in 2010-11, being seen on 55 out of 64 observation days, starlings in 2011-12, being seen on 35 out of 43 observation days, and woodpigeons in 2012-13, with only one observation day out of 44 when they didn’t make an appearance.
  • The most numerous visitors to the garden were starlings by far (which won’t surprise anyone who has seen hoardes of them descend on a bird table), although in the last year house sparrows have almost managed to catch them up.

    Bluetit
    Bluetit gathering nesting material

Changes in which species visit over time

As I mentioned in the first ‘Bird nerd’ post, altogether I’ve seen 26 different species of bird in the garden, although never all in the same year. In 2010-11 I saw blackcaps on 15 observation days (in the winter), but only once in 2011-12 and once in August 2012-13 (which is a shame, as they are pretty birds).

There have been no records of jays since 2010-11, but even then they were not frequent visitors. Other birds missing in 2012-13 that I have seen (infrequently) in other years include crows, greenfinches and siskins.

On the bright side, in 2012-13 I saw chaffinches and some kind of warbler for the first time. It’s quite encouraging that 4 years after moving here we’re still spotting new species.

Future analysis to be done

The few stats I’ve presented here are only the tip of the iceberg in terms of what I could examine from my data. One question I would like to look at is how the weather affects bird numbers. I’ve got very basic data on weather for most observation days, but only as far as whether it was sunny, snowy, rainy or overcast. Since we had solar panels installed last June I now have data on sunlight. My theory is we get more bird visits on sunny days than rainy or overcast (controlling for the month of the year), but we’ll see if the data supports that…

Let me know if there are any other questions you would like me to look at – for example, if you’re interested in a particular species or comparison over time…

Amateur ecology

Over the last few years I’ve been doing quite a lot of reading about wildlife, as well as going on courses. One of the biggest surprises I’ve had is there’s so much we don’t know, even about some of our most familiar species. For example, we don’t really know what water voles do all winter, or where basking sharks go. Linked to the realisation of how much we don’t know about our wildlife, is the discovery that normal people, like you and me, can make a meaningful contribution to scientific research about wildlife.

The other day I read, in Hugh Warwick’s book The Beauty in the Beast, about Denis Summers-Smith. It was inspirational. Denis is a mechanical engineer and an amateur birdwatcher, who has written five books and over forty scientific papers on the house sparrow. He has discovered many things about house sparrows, including that they mate for life. And all this has been done in his spare time…

For those of us not quite ready to write a book based on our own discoveries, there are many citizen science projects that rely on the contributions of hundreds (or thousands) of volunteers to gather data from across the country. The commitment and expertise involved varies considerably.

For example, each year in January the RSPB run the Big Garden Birdwatch. Almost 590,000 people took part in it in 2013. This involves spending an hour counting the different types of birds that come into your garden on a specific weekend. From this, they can analyse the data from across the country, and spot any significant changes in the bird population. This is important to inform conservation work.

Many other organisations run similar surveys. This BBC Nature article contains a good list.

At the other end of the spectrum, the National Dormouse Monitoring Programme is rather more indepth, requiring trained and licensed volunteers to carry out box checks each month (except over winter). The data collected from this programme is providing new insights into these lovely creatures. At a dormouse conference I attended a couple of years ago, it was very exciting to hear scientific presentations based on data that I helped (in a very small way) to collect. We now know much more about this species than we did before the programme started.

Like many girls of my generation, I gave up studying science after I finished my GCSEs, despite getting my best grades in science and maths. I didn’t think science was for me. I didn’t realise how exciting science could be, and the range of things it could involve. It has been thrilling to learn, somewhat belatedly, that science is for me, and I can contribute to finding answers to questions about our native wildlife. These answers may help us better protect our beautiful and vulnerable creatures, for this generation and those to come.

House sparrow explosion

House sparrows have been fairly regular visitors to our garden. We see them all year round, with an average number of 3 per observation day. But in the last few weeks the sparrow population in our garden seems to have exploded. Before September this year, the most we’ve seen at one time was 9. Now there are more than I can count (they keep moving!).

They’ve been hanging around our garden quite a bit, and getting through the bird seed faster than I’ve ever seen before. I’ve no idea why we have had the sudden increase. In previous years there hasn’t been a large increase in numbers around this time of year.  Perhaps they’ve had a particularly good breeding year?

They’re not the most spectacular of birds, but it’s great to see so many of them, as their numbers have plummeted in recent years. In the 1970s there were around 12 million pairs in the UK. Now there are between 6-7 million pairs. The good news is, data from the British Trust for Ornithology suggests that the decline has stabilised. Now we just need to work out how to help them recover.

Earlier this year we installed a sparrow terrace (to try and tempt them away from our gutters as a nest site). The boxes weren’t used this year, but hopefully some of our new visitors will decide they’re a good nest spot for next year. I’ll let you know!

Have you noticed anything similar in your garden?

Bird nerd part one: a confession

I have a confession to make. I am the garden bird equivalent of a trainspotter. For the last three years I have not only been watching birds in my garden, but recording details of the numbers of individuals of each species I see.

Each day that I work from home I keep an eye (and ear) out for birds in the garden, and record the maximum number of individuals seen at the same time from each species. Over the last 3 years I have clocked up 153 days worth of observations, and lots of completed forms.

Bird observation forms
Some of the completed forms…

While I appreciate that this makes me seem slightly obsessive and sad, it also means I have lots of lovely data to play with. This allows me to monitor trends over time, and see how changes in the garden, weather and seasons affect my feathered visitors.

This behaviour came as a surprise to me. I’ve always considered myself more of a mammal person than a bird fan. I saw birds as nice, but a bit dull (unless they were spectacular kingfishers or powerful birds of prey).

Then we moved house and got a garden. I don’t know when I changed my mind, but soon after moving we installed the bird feeding station, and waited for our first feathered visitors. And waited. And waited.

We had to wait almost a month before we saw the first bird in our garden. Our first visitors were a pair of collared doves. Then more and more types of birds started visiting. Something clicked, and I realised that the garden birds were wild creatures I could watch from the comfort of my own home. And they had their own characteristics. And I could watch real life mini dramas being played out in front of me.

I’m still not sure where the urge to obsessively keep records comes from. I think it must be from working with statisticians for too long. And the transformation is not complete – real twitchers wouldn’t consider me as one of their own. I don’t travel the country in the hope of seeing a rare small brown bird. I’d still choose a glimpse of otter or badger over the rarest of feathered migrants any day.

But I do enjoy watching the birds in the garden. Observing a species we’ve never seen in the garden before makes my day.

Having got that confession out of the way, I’ll try and share some of my observations with you in future posts…