Avian Pox hits Great Tits - Planet Earth

Avian pox affects a number of bird species, but it was discovered in UK's population of great tits in 2006.  As avian pox is spreading, scientists are monitoring birds using trapping and ringing in order to study the disease.  Sue Nelson visited the Wytham field station in Oxfordshire where she met the Field Manager Ross Crates and Oxford University's Dr. Shelly Lachish...

Shelly -   It's actually a very distinctive disease.  The birds develop large tumour-like lesions and they develop them on the head, particularly around the beak and the eye area, but also on their legs and on their wings.  Basically, when we catch the birds and we have them in the hand, if they have a lesion, it's very hard for us to miss it.

Sue -   Walking down the extremely muddy path...

Ross -   We've actually got the mist net set behind the feeder.  As we're walking down through it from here, we can't see it, but we can certainly see that we've caught a few birds in it.  It looks like there's about 7 or 8 at the moment.

Shelly -   It looks like we've got a nuthatch as well, just behind the cage there.

Sue -   Right.  So, you've got several great tits.

Shelly -   Lots of blue tits.

Sue -   Lots of blue tits, I recognise them.

Shelly -   Most of these we've been looking at here are blue tits then there's a nuthatch there, and a coal tit.

Sue -   Aren't they gorgeous?

Shelly -   This is a good example of a re-trap here, so you can see its metal ring on one leg, and its passive integrated transponder on the other leg, just a little plastic ring here.

Sue -   Oh yes, it's got little tiny rings on each leg.

Shelly -   So what we do is we have antenna on our feeders and on the nest boxes, and when the birds come to feed or come to their nest boxes, we can record them without having to be there at all.

Sue -   We've got two little white bags now with the birds in and you're putting all the birds in little bags...

Shelly -   Yes.  So here's another one that's already - we've already caught this one previously, so he has a little black pit tag on his right leg and a metal silver band on his other leg.  So, we can look up the number on that ring and we can find out all the history about this bird - where he was caught last time, how much he's grown and whether he's breeding the last time he or she was caught, and we'd tally that information up and that feeds into our records.  And he's still pecking me... 

An avian pox is actually - we have noticed it in all of these species except for the nuthatches, but it's by far, more prevalent in great tits than any of the other birds.  We're not actually sure why that is and that's one of the things that we would like to find out.

Sue -   Well, I will let you continue extracting the birds and bagging them before we head back to the table.

Shelly -   So now, we have our birds in their little bags, hanging here, waiting their turn to be processed.  And so, one by one, we'll go through, we extract them from the bags like I have done with this little blue tit and I have it in my hands now.  And now, begins the process of ringing and pit tagging, and measuring.  And so, the first thing you'll always do is put on a ring because that's the identifier for the bird.

Sue -   You just affixed that one very deftly.

Shelly -   I have.

Sue -   So, will you check in the future now to see whether when you catch a bird that has been previously tagged and ringed, whether it has the virus or not?  All those birds that we trap looked quite healthy to me here.

Shelly -   At this time of year, we do expect avian pox prevalence to be very low because it is a vector disease.  It's mosquito vectored and winter is not a very good time for mosquitoes to be around.

Sue -   Do they all die or do some survive?

Shelly -   We've had 105 cases of avian pox in great tits, at least in this wood, and some extras in some blue tits and other species.  And we've seen 14 of those had been recaptured again, and they've been asymptomatic so they haven't had lesion whereas they did previously.  And so, we do know that recovery is possible, but our analyses are also telling us that this disease definitely kills the birds.  It reduces the survival rate of individuals.

Sue -   What have you discovered so far in terms of how far this viruses is spreading while you measure its wing - the blue tits wing there?

Shelly -   The disease arrived in England in the southeast of England around the east Sussex area and that was in 2006.  Since that time, we've seen it spread westwards right into Wales and as far north now as around the Mersey River around Manchester region.  So, it has really spread quite a fair distance in just a number of years.

Sue -   Is there anything that can be done at the moment other than monitoring it and studying it?

Shelly -   That's our key focus at the moment, to track its spread, to know exactly what we're dealing with in the sense that whether we are dealing with something that will eventually be population wide amongst the great tits.  But we are also continuing to look at genetic studies to try and isolate, further understand where the disease originated from and how it's mutated and suddenly appeared in this great tit population.