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Least Terns with novel banding scheme - flag on lower leg: asking for problems? (1 Viewer)

Mark B Bartosik

Well-known member
I hope that all members here not only have great knowledge about banding but also are concerned about any band design/placement that might have a negative impact on a specific species. So, I want to bring for a public discussion revaluation of observations I will present below.


Last year I found one Least Tern with an alphanumeric flag put on its tarsometatarsus (“lower leg”). I could not find any information published on the web about by whom and where these flags were used. I was very busy at that time and as we all know time can fly very fast and I did not see any more birds banded with those flags I was very slow to put the video for upload. Now as I found a second one and, unfortunately, we are living in a very difficult time dealing with the virus pandemic but have more time in home to catch up with delayed tasks I want to try to solve the problem. I have two flagged LETEs; K6 and L0. I will appreciate any help to locate the bander so I can exchange the data.

Let me clear one thing. I am not against banding birds – quite appositive, as I not only promote many reasons to do that but also am benefiting a lot from working on marked birds. My lifetime interest is in animal behavior (for the last two decades mostly birds) and for the last several years molt in selected birds. One of them is the Least Tern. Studying marked individuals makes my work not only easier but also eliminates the guesswork in many cases. On the other hand, I do believe that animal welfare should be always put first; we should monitor bands’ impact on bird health, behavior, etc all the time and take corrective actions immediately when needed. We should only band a minimum number of birds from large populations necessary to conduct the study and limit/justify a number of individuals from endangered species.

Recently (see above – I start writing this note year ago) I encountered Least Tern marked with a single alphanumeric flag (no other markers or metal USGS band) placed on its right “lower leg”. When first noted I thought that this was an injured bird limping when walking but when I started to take photos I saw something attached to its leg. Again for a few moments, I thought it was a piece of garbage attached but then I realized that this tern has a large flag attached to its leg.

Walking/running/resting of the Least Tern with large ANF, even during the short time of observation, indicated serious problems that this bird is facing including the constant problem of possibly injuring skin facing inside of the flag band. As you will see in the photo, the flag was often in a position that made flag end hit the ground before the foot was placed on the ground. That made the part of the flag band apply pressure to the leg skin and if sand or other particles are stuck inside the band (see next paragraph for more information) those might irritate or even make injury, perhaps serious if the process is repeated constantly for a prolonged period of time. When stepping the feet down with flag reaching ground first this flag is forced to turn – this will make an additional impact of sand stuck inside band grinding skin when the band is rotating.

Least Terns spend a large part of the day on the beach or on the edge of the water where (see photo) it can easily collect sand and other small particles between the band’s inside surface and skin on the leg. As mentioned above these particles can later irritate/injure the skin.

I can only speculate about a few more possible problems. I had only a short-lasting opportunity to observe this bird before it got spooked and I was not able to relocate it later. I made a huge mistake to not video this incident, but I was trying to make sure that I have photo documentation first.

Updated: Week later I was able to refund this tern and I took some video footage during the short encounter to make visual documentation for better presentation.

I would not be surprised if LETE male banded with that large ANF on lower legs have some problem to mount the female. Not sure how a female would react to be poked with the flag when a male is landing on her back; and have a possible problem with the balance in some cases as well. I can expect some problems with landing, especially on hard surfaces, etc.
Least Terns are great fliers capable of performing incredible maneuvers, especially during foraging, when diving to catch the fish. I see them using legs to help with maneuvers; slowing down (when spreading webbed feet) etc. Perhaps the impact of the flag won’t be critical, and birds can make the adjustments, but we must remember that these seabirds are often exposed to very harsh conditions and maintaining excellent body condition is vital for them to survive.

Interior Least Tern population is listed as endangered. Some authors question the validity of this subspecies. In the past, I had similar doubts about it and mostly looked at protection benefits. But with data, I collected over many years I am pretty convinced for a quite long time that there are strong arguments for the interior population to have valid, subspecies status. I will not go deeper into this subject as I do not want/need to open another can of worms, and, I am still working on putting all arguments together.

In the end, I would like to ask for discussion to validate, or dispute, the potential risk associated with flag placement on LETE’s lower legs.

Best regards,

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