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Thursday, 16 March 2017

BeeWalk – taking a walk and counting bumblebees

I was asked to write a blog post about the BeeWalk survey that I do at RSPB Rainham Marshes. This is a slightly modified version of that blog, originally published on their website

This is the start of my second full season recording bumblebees at Rainham Marshes.

Bumblebees in the UK

We have 25 species of bumblebee in Britain.
All but six of these are social bees – they live in a nesting colony dominated by a queen. She lays all the eggs, and her daughters, called workers, collect nectar and pollen to provide food for the growing larvae. During most of the life of the colony, these eggs produce only more workers, but towards the end of the nesting cycle (some species have just one cycle each summer, others have 2) the queen lays eggs that develop into new queens and males. These new queens and males leave the nest to find mates. The rest of the colony (including the original queen) all die, and so do the males after they have mated, leaving just the new queens to start another cycle. Queens late in the year will hibernate over winter and found new colonies in the spring.


A queen Early Bumblebee, Bombus pratorum, one of the Social bumblebees




A queen Garden Bumblebee, Bombus hortorum, another social species (picture taken in April 2016)

The other 6 species are called “cuckoo” bees. These species have queen-like females and males – no workers. The “queen” of a cuckoo species takes over the nest of a social bumblebee, kills or subdues the resident queen and forces the nest’s workers to care for her own eggs and larvae - which all develop into new queens and males.

Bumblebees at Rainham Marshes


Ten species have been recorded at Rainham Marshes, but of special interest and conservation importance are the Brown-banded Carder Bee, Bombus humilis, which is scarce, and the Shrill Carder Bee, Bombus sylvarum, which is rare in the UK.

  
Shrill Carder Bee, Bombus sylvarum. This is a male; females look similar. They get their common name from their buzz. It is higher pitched than other bumblebees and can be quite distinctive (picture taken in September 2016)


In 2015, the then Warden, Nicole, asked me if I would like to join my volunteering colleague Alan to learn about bumblebees and carry out a monthly survey.
Alan and I attended several Bumblebee Conservation Trust (BBCT) workshops with classroom work and then practice in the field, where we learnt about bumblebees and how to identify them. There may be only 25 species, but with 2 or 3 castes (queen, worker or male) of each species, variability in size or patterning, and ageing causing worn or faded colouring, ID can be tricky. We’re learning, but we’re still beginners!

The survey that we do feeds data into the BBCT’s BeeWalk project.


BeeWalk

You can read more about BeeWalk on the BeeWalk website.
In short, you walk along your chosen route at least once each month from March to September, recording the number of each species and caste that you see within a 4m x 4m square in front of you. You record bumblebees and Honey Bees.
Your survey data, once you’ve submitted it via the website, contributes to important long-term monitoring of bumblebee population changes.


Already heavily loaded with pollen,
a Honey Bee, Apis mellifera, worker approaches a Sallow flower to collect more

You can choose a route that’s already been defined, or you can define one of your own. Each route is from 1 to 2 kilometres long, and is split into sections based on the habitat in that part of the route. You keep a separate count for each section.
In our case, one of the RSPB’s own bee-expert ecologists from The Lodge helped us to decide where to walk. 
Our route starts in the Wildlife Garden, then goes onto the reserve through the gate beside the Visitor Centre and on through the Adventure Playground to the Woodland. We go through the Cordite Store, past the Woodland Discovery Zone and up to the Ken Barrett hide. For the last section, we leave the public trail and head back along the service road to the large metal gates by the reserve entrance.

Starting this year’s surveying season

Monday this week was a lovely warm bright spring day, and with the next couple of weeks forecast to not be as good, it was time to get the 2017 surveying season under way. Jamie and Tim joined me for this one.
One of the things about having different habitats along the route is that the bees and the behaviour that you see are different as the year progresses.
This early in the season, most of the bumblebees you see are Buff-tailed Bumblebee queens. They will have very recently roused from hibernation and are finding their first food, searching for a nest site or if they’ve already started their colony, collecting nectar and pollen to feed their first workers. 
Sallow, also known as Goat Willow, is the most plentiful source of nectar and pollen for bees right now, so most of the Buff-tails are seen on the male Sallow flowers.
A queen who is looking for a place to nest flies slowly close to the ground, often landing and crawling through the vegetation to investigate a smell – it may be an unused rodent nest that she can take over.

A queen Buff-tailed Bumblebee, Bombus terrestris (picture taken in April 2015)

This is what we found: mostly Buff-tailed Bumblebees (and Honey Bees) and mostly on the Sallow or flying low to the ground.

One bee on Sallow caught my eye as possibly something different. The abdomen was longer and I thought that the tail colour looked more yellow-and-white than buff. I had an idea what it might be, but wasn’t sure.
  
Is it a cuckoo bee?

The experts on the Facebook group UK Bees, Wasps and Ants are enormously helpful to beginners, so I posted this image and it didn’t take long to confirm that this was what I had hoped – a Vestal Cuckoo Bee, Bombus vestalis.

By the end of our walk, we had seen a total of 39 Honey Bees and 23 bumblebees from 5 species.  We saw 19 Buff-tailed Bumblebees, and one each of Vestal Bumblebee, Common Carder Bee, Early Bumblebee and Red-tailed Bumblebee. A good start to the season!