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Good morning.  Many of you are away from home this weekend, congregating at some mysterious location on the western side of the continent.  Part of some top secret plan to take over the world or something.  Or have I said too much...

In keeping with the themes of travel and grouping together this week's Dawn Chorus will look at bird 'conventions'.

Birds are highly mobile animals and also generally highly social.  So you often find them in groups.  Or traveling to join groups.

Last week in her excellent diary lineatus showed us pictures from the Farallon islands.  Many of you were impressed by the number and density of seabirds on the islands.  Certainly some of the most striking wildlife spectacles on the planet occur in the areas where seabirds congregate to breed.

Here is the first seabird colony I ever saw, a large rock in the sea near the town of Homer Alaska (caveat - I have nothing to do with the video).

Seabird Colony - Homer, Alaska.  This colony contains large numbers of breeding kittiwakes and murres if I remember correctly and quite a few tufted puffins and pelagic cormorants.  Small numbers of a few other species.

This second video is of a seabird colony in the Farne Islands, in the North Sea off the coast of far northern England.  Common Murres again dominate and I also spotted cormorants (probably Great Cormorants), Fulmars, and an Atlantic Puffin.

So why are these birds all nesting so close together?  Follow me below the stylized Murre nest to find out.

Seabirds aggregate because suitable nesting sites are rare and highly clustered.  Being a seabird is great - you have this vast habitat full of fish and you can roam around until you find food.  It's great until you have to reproduce.  Then you remember you're a bird and you need a dry spot to lay your eggs.  And it has to be close enough to the coast that you can get out to the ocean and feed.  And it has to be safe from predators.

A few seabirds nest in remote hidden locations away from the ocean.  Most famously,  the Marbled Murrelet nests in coniferous forest.  Some other auks do the same as do some petrel species.  They nest in cryptic remote locations that are within flying distance of the ocean but are super difficult for anyone else, including ornithologists to find.

The majority of sea birds take a different approach.  They nest close to the water, in places that are difficult for terrestrial predators to access.  This usually means on islands or on cliffs (or both).  There are only a limited number of these places and so they end up being full of birds.

Unlike a songbird a seabird has completely separate feeding and nesting areas.  Songbirds defend a territory in which they nest and feed.  Seabirds feed in the ocean.  No territories there - how do you defend a school of fish?  Back on the island/cliff they defend just enough space to keep their nests safe from other birds.

Seabirds may also aggregate at sea if their food is also having a convention.  It is not uncommon to see this kind of feeding behavior in coastal waters in the winter here in Florida.

Pelican Feeding Frenzy

Now let's move onto land, at least somewhat.  Birds such as herons would have difficulty hiding their nests given their large size.  So breeding again occurs in protected areas (generally swamps).

More mysterious to me are the nocturnal roosts of many blackbird species.  Outside of the breeding season these birds form large nocturnal roosts, in some places reaching enormous numbers.  Presumably this is an anti-predator convention.

One kind of convention I find particularly interesting is the fishing group of mergansers.  I've been told that it is hypothesized that they hunt fish cooperatively underwater but this would obviously be very difficult to study.  The highly synchronized submersion and then return to the surface is suggestive of some sort of cooperative effort.  Socialist fisher ducks!!

One time a lot of terrestrial birds are not found in conventions is during the breeding season.  Then pairs or small groups defend an area and try and keep other members of the species at wing's length.  The dispersion of the birds through the habitat makes them harder to find although singing for territorial defense can help with location and ID

Territorial Song Sparrow and artificial playback

Some birds have an interesting variant on the territory called a lek.  In lekking species the territories defended by male birds are very small and close to one another.  Each male (or in some species pairs of males) is defending a small space in the lek with no resources for the female except for themselves.  The evolution of leks is a fascinating puzzle for evolutionary biologists.  These are particularly spectacular bird conventions as the males are often displaying like mad.

The Sage Grouse is probably the best known and most spectacular lekking bird in North America

A number of lekking species occur in dense forest.  The leks can be very impressive but difficult to capture on video.  This is, in my experience, an astonishingly good view of an Andean Cock of the Rock. The leks are quite impressive but it is difficult to get very lengthy looks at individual males as they pop in and out of the vegetation.

And I'm going to end this with a spectacular and somewhat baffling convention of Flamingos.  Given that they are filter feeders living in these fairly uniform habitats I have no idea of the purpose of this massive group display.  Maybe they just like it.

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