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Should I stay or should I go?

posted Jun 8, 2011, 7:31 AM by Clemens Kuepper
Early June, we passed the half time mark of the breeding season and things at Bahía de Ceuta are super busy. The Snowy Plover number have turned out more promising than we expected after the slow start. The field team has found 50 nests until now and there are still plenty of Snowy Plover males scraping, so there will be soon more. 20 of these nests had hatched until yesterday and 20 are still incubated. However, more importantly chick survival is still very good, there is still some water left. Over the last two days we re-sighted 16 families with 32 chicks alive. Incredibly, apparently the field crew has not missed a single nest so far. All families in the salt works come from known nests. This is a fantastic job by Medardo, Rene and Wendy! The first chick 'fledged' - well, 'fledged' may be a bit exaggerated since it isn't exactly able to fly yet, but after 23 days looking after it day and night its father decided that it is now big enough to look after him/herself. The dad is now looking for a new mate to try to squeeze in one more nest and if he is lucky he can bring up a few more chicks.

There has been an interesting switch in behaviour lately: females are staying now more often with the broods than before. However, desertion has not completely stopped yet. Some females are still deserting and looking for a new male but others remain with the brood. Why do some stay whilst the others desert?  This is actually one of our research question. It can be best described as a trade-off between a) remating again and producing more young b) staying and providing care to make sure that your current offspring survives best. In the beginning of the season this decision is easy, one parent is enough to look after the chicks and nearly all females desert. But when things get harder both parents are needed and the females tend to stay with the brood. This of course means they forego further reproduction because once they finished with these chicks the breeding will have ended. During this time it is fascinating to watch the individual plovers when this happens and I haven't found a way yet to be able to foretell whether they stay or desert
. I often wonder how exactly the females decide whether they will stay or desert. It doesn't appear to be so trivial like: 'if the chicks hatch after 1 June I will stay if they hatch before I will desert'. Do they count the prey items that available and divide them by the number of existing families? Then they would be mathematical geniuses. Do they check out the condition of the chicks from other families? If they good and growing they desert if they look poor they rather stay. Do they count the number of available males to pair with or do they check their quality? If there are a lot of males or very sexy males available they desert if there are few, they rather stay. Is there some interaction going on with their mate?

Birds are not known to be able to count. Plovers are probably not different, they don't recognize (or don't care) whether there are 1 or 5 eggs in the nest. And they also seem not be able to count their chicks otherwise brood mixing and adoption wouldn't be so frequent. Anyway, this is a fascinating topic and enough research to do for us in the coming years.

Some more hot numbers. The number of Least Tern nest that we have found has now passed 250. Apparently there are about 50 more in the making. The first chicks have now hatched which means there is stink bomb alarm whereever Least Tern chicks hang around in the salt works. Least Tern are bombarding intruders with their excrets if they get to close to their young. I have some sweet memories of being hit by something that consists of rotten/digested fish with freshly washed hair on late afternoon nest checking rounds. A lot worse than the diaper changes I have to do these days.