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Do satellite tags hinder our woodcock?

One of our kind sponsors recently asked whether the satellite tags we use to track our woodcock ever hinder them in terms of flight, feeding or courtship.

Here was our response:

With regards to the potential impacts of the tags upon the birds: these are clearly questions we are constantly asking ourselves.

Obviously the welfare of the bird is paramount and the continued use of the tags depends entirely upon their safe use.

Additionally, it is important to us that the tags are comfortable and have no impact upon the bird as we are seeking to record normal behaviour that is unaffected by the presence of the device.

Tags are under 3% of the birds body weight. The 3% figure is a benchmark used by most ornithologist when considering the added weight of a tracking device. It is widely agreed that at this level, the tag's impact will be minimal.

Nevertheless we need to be certain that the tag (both its weight and means of attachment) poses no detrimental effect upon the bird. This is understandably hard to measure.

However, we have been able to re-capture three of our tagged birds in subsequent winters - these bird's tags had stopped transmitting, probably as the result of 'battery issues' and so were removed and re-used.

Having a bird in the hand, that had carried the tag for a year or more, allowed us to check for physical signs of wear or damage resulting from the tag. In all cases, there was no evidence of this.

Additionally, the birds were all still healthy weights, similar to those when first caught, indicating that the tag was not impacting upon fitness or the ability to feed.

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How do we interpret the data we receive?

The satellite tags we use to track our woodcock provide us with data every three days, with the information presented in tables like the one below:

The columns highlighted in red show the information required to build a ‘flight map’ on Google Maps, such as the one on the Woodcock Watch website.

'Program' is the unique program number that our project has been allocated and ‘PTT' is the identification number for each bird’s satellite tag.

'Location class' provides an indication of the accuracy of the data. A number denotes a position which is accurate to within 1km and a letter indicates a margin of error too large to display on the map.

All the data we receive from these files is automatically processed by a computer program every 24 hours. As new files are received the program scans them for the appropriate location data so the map you see on the Woodcock Watch website is updated accordingly.

Simple!

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Latest woodcock locations

Our birds appear to have mostly settled at their breeding grounds now with no major movements recorded recently. New data received from Garth on the 10th June however indicates she is still making her way toward the Russian border with Kazakhstan.

Latest location data

 

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How do we catch and tag woodcock?

Before fitting woodcock with satellite tracking tags we first need to catch them. This is done by dazzling them with a spot-lamp on fields at night and using mist-nets across woodland rides to catch them leaving or returning to woodland at dusk or dawn.

Unfortunately for us, dark, windy nights are best for catching woodcock, usually around the time of the new moon.

Once we have captured each bird we measure them and attach a small numbered metal leg ring provided by the BTO. Catching and ringing requires training and practice and therefore our work is performed under license.

After ringing each bird we then fit a satellite tag and geolocator to the lower back with an elasticated leg-loop harness. Hypo-allergenic tubing is then applied in order to prevent abrasion or discomfort. The tagging process takes between 3 and 4 minutes and the birds are then released from their capture location.

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5 things we’ve learnt from our woodcock satellite research

With satellite technology improving all the time we've been able to conduct our woodcock research over the last three years by attaching small satellite tags to each of our birds.

The information provided by the tags has provided some fascinating insights including the following:

1. Departure times are typically mid-March to early April from winter sites and late September to late October from breeding sites.

2. There is a mixing of migrants at wintering sites – birds tagged at the same winter site often flew to different breeding locations.

3. Some birds fly extraordinary distances – three birds have travelled distances of 6,180-7,100km (3,860-4,440 miles) to breeding sites in Siberia. One male, tagged as an adult in 2012, is estimated to have flown at least 38,000km (23,750 miles) during his lifetime!

4. Journey times to reach breeding sites can vary from three weeks (northern Norway) to eight weeks (central Russia).

5. Evidence from a few of our woodcock followed for more than one year indicate they use exactly the same winter and breeding sites each year.

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The tags we use are solar powered - and look where Nellie is!

As you probably know, the satellite tags attached to each of our woodcock are solar powered which is why we sometimes go weeks without hearing from certain birds, depending upon their location.

It is therefore quite amusing to note that Nellie is currently in the Norwegian town of Rjukan, located in a valley where three giant mountainside mirrors are used to reflect natural sunlight on to residents in the winter months. Read more about the mirrors here.

Please help us continue our woodcock research