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About 2000 Red Knots (rufa) feasting on bivalves at fall stopover site on Lower Texas (1 Viewer)

Mark B Bartosik

Well-known member
About 2000 Red Knots (rufa) feasting on bivalves at fall stopover site on Lower Texas Coast beaches

When visiting beaches on Mustang and North Padre during the second part of October I estimated that there were about 2000 Red Knots foraging on bivalves in tidal zone along the shoreline on the Gulf side. This number could be much higher - I documented 120 banded birds (BTW including one with geolocator) and I think ratio of banded birds to none-banded seemed to be higher. All bands were identified (but see a final note). Main reason I did not try to get more accurate count was that I was there to study Piping Plovers and not knots. In fact I was little angry with myself that I lost a lot of my available (and limited) time with knots but couldn’t help myself when seeing so large number birds of this iconic species.

I wonder if there is any new data about were all of these knots are wintering. In the past it was suggested that most of these birds are on the way to wintering grounds in South America. Lately, based on data from 9 geolocators, it was suggested that most (all?) rufa knots coming in fall to South Texas shore are wintering in Laguna Madre and other places along north west part of the Gulf of Mexico and do not migrate to South America.

There are a few interesting facts. After a few fall weeks they almost disappearing from Texas beaches and only a few are recorded in few spots, and not in large numbers during the winter. I can see that they might quite clean tidal zone from the bivalves fast. If my estimation is correct than there was about 1 (or even more) Red Knot per about 50 meters of the beach. Working on the bivalves like I shown here on a video clips (link below) knots might reduce bivalves number drastically during this few weeks period of a very intensive fall foraging in the beach tidal zone making this habitat much less productive to obtain the food needed than tidal flats between the mainland and barrier islands. Also as they spend about 80% (about nine and half months) of the year on the wintering grounds even Texas size beaches might not be enough to provide food (bivalves) to this high number of knots (1 knot per 50 m). But on the other hand can they disappear from the radar (hordes of birders in so popular birding spots in south Texas) almost completely and hide unnoticed for so long time every year? The records in eBird database (sure, not always reliable) are sparse and showing low knot numbers during the winter in Texas. Granted, many places are not easy accessible (even with 4X4 vehicles) and some only accessible by boat. Many birder’s reports are from ‘stationary’ observations so those only cover very limited area, often in very short time. But tidal flats are often flooded drastically reducing foraging area. Other birds, like pipers, are moving back to the beach and forage there. Why would knots almost completely ignore beaches during the winter even in times when other places become, temporarily, not available?

I am not trying to say that it is not possible that most/all knots coming to south Texas during the fall are not wintering here. The available data, even if limited (from only 9 geolocators), is supporting hypothesis that they might. It is just these few questions listed above to which I would like to know the answers. Anybody would like to share more information (if available) or speculate on this subject?

For these who are interested here is a video showing knots foraging on bivalves on Texas shore:

https://youtu.be/4hUOm9NQ0CE - they were in flocks from few up to 100 birds

And here photo of knot with attached geolocator:

http://www.pbase.com/mbb/image/166727430

Final note: I have no idea why banding organization choose flags to use on knots which have engrave painted numbers and letters that are becoming very hard or even impossible to read on some flags in the environment knots are living. I will post more on this subject in a separate thread as I do not want to cloud this one with out of subject matters. I will post a link here for those who are interested.

here it is: http://www.birdforum.net/showthread.php?p=3655711#post3655711
 
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