Boat-tailed Grackle, Antwerp

[AndyB]

Saw this photo posted just now in Euro Stop Press by Raymond De Smet. Haven't seen any other mention of it on the newsgroups. Is there an opinion that it might be a wild bird that hitched a ride in to port or is it a confirmed escape? :err:

http://www.surfbirds.com/cgi-bin/gallery/display.cgi?gallery=gallery11

[Jurij Hanžel]

It may be slightly off-topic, but I'd be interested to know what the Belgian RC made of the Grey Catbird that put in an appearance in Antwerpen in December 2006?

[Alex Lees]

If it isn't a confirmed escape and had turned up in the UK, then it would still fail to meet the criteria required by the BOURC (http://www.surfbirds.com/sbirdsnews/archives/bou/):

"That the species might be expected to arrive in Britain naturally and without ship assistance given favourable circumstances (i.e. the species is migratory and its migratory route matches that of other species believed to occur naturally)."

Boat-tailed Grackle is basically resident on the coastal fringe of the eastern US and Florida panhandle, with vagrants occurring north to New England. It is undergoing an impressive range-expansion, but unlike some highly migratory icterids e.g. Bobolink, I think the hypothesis that this bird could* make an unaided sea-crossing is untenable.

*obviously the fact that its right next to a major port means that it almost certainly did get there at least partially by boat.

The suite of Nearctic landbirds accepted as occurring as natural vagrants to Europe is dominated by long-distance Neotropical migrants, the most frequently occurring of which include a sub-set of abundant long-distance migrants which winter in the Amazon such as Blackpoll Warbler, Red-eyed Vireo and Grey-cheeked Thrush. These species predictably show up in Mid October, following the swift passage of deep Atlantic depressions and no one can doubt that most arrive unaided. The same could be said for many of the Caribbean winterers, they may have a slightly reduced flight capacity (in relation to the Amazonian winterers) and may also be numerically less abundant, which would explain their relative rarity in Europe (see Mclaren et al 2006 [attached]).

We get onto dodgier ground when it comes to Zonotrichia sparrows, which although migratory do not follow the expected pattern of occurrence shown by the longer-distance migrants - the absence of records from Scillies is very telling (IMO) and they also have an incriminating penchant for ports. Finally there are species that are either partial migrants or wholly resident - the BOURC admits Brown-headed Cowbird to the British List yet there are few extralimital records of this species, and it seems unlikely that this species would have the flight capacity to make a long sea crossing.

This leaves national rarities committees with an unenviable job; short of experimentation in a wind tunnel (with good sample sizes!), how do you decide what can and can't make it?

Alex

[WouterFaveyts]

Antwerp is one of Europe's biggest seaports so the chance of the bird being ship-assisted is rather big. In December 2006, A Grey Catbird was found in the harbor area as well, as mentioned bu Jurij. The Grackle has drawn a far smaller crowd than the Catbird, although their origin could very wel be similar (ship-assisted).

I don't recall it by heart and I don't find the info right away, but I believe the RC has not made a final decision yet on this bird.
More info on the Belgian RC can be found on this website, by the way: http://www.bahc.be/index.htm

[Alex Lees]

Antwerp is one of Europe's biggest seaports so the chance of the bird being ship-assisted is rather big. In December 2006, A Grey Catbird was found in the harbor area as well, as mentioned bu Jurij. The Grackle has drawn a far smaller crowd than the Catbird, although their origin could very wel be similar (ship-assisted).

I don't recall it by heart and I don't find the info right away, but I believe the RC has not made a final decision yet on this bird.
More info on the Belgian RC can be found on this website, by the way: http://www.bahc.be/index.htm

While we are on the subject of Mimids, the catbird is the most likely vagrant of the three on the British List to have occurred 'naturally' - whatever that means these days; given that it winters south to Colombia and has occurred as a vagrant right up into Alaska. The mockingbird is basically resident with some, short-range vagrancy and the thrasher is a partial migrant and only gets a sniff of the neotropics - vagrant to Cuba and central Mexico. Using the BOURC's own criteria it is debatable whether any qualify for admission.

So.... this leaves us with a dichotomy in dealing with putative transoceanic migrants:

1) admit anything

2) only admit long-range migrants

The first solution would obviously be distasteful for some as it means letting on grackles and even sheathbills (providing they are ignored - but what if they steal food from deckhands?) and the second solution sounds overly harsh. So what do you do?

Alex

[jamesg]

So.... this leaves us with a dichotomy in dealing with putative transoceanic migrants:

1) admit anything

2) only admit long-range migrants

The first solution would obviously be distasteful for some as it means letting on grackles and even sheathbills (providing they are ignored - but what if they steal food from deckhands?) and the second solution sounds overly harsh. So what do you do?


A good question. Obviously the current situation in the UK is in need of some overhaul - the constitution says that we only admit species deemed capable of arriving unaided, but as Alex says, several accepted species would almost certainly fail to meet this criterion (BH Cowbird, Brown Thrasher etc.).

In my opinion, these decisions about what can and can't make it are arbitrary and highly unsatisfactoy. No-one really knows the migratory limits of any given species, particularly given the massive variation in weather conditions over the Atlantic.

For me, it would be far more sensible to adpot Alex's option 1 - accept everything that arrives here on a boat. That way, there is far less ambiguity (aside the usual escape issue, which would be a problem regardless of ship assistance).

I think the BOURC still have a policy that birds are unacceptable if they are known to have been fed deliberately whilst on-board ship - again a pretty ridiculous idea IMO. By landing on a boat, the bird has already taken advantage of an entirely human-made habitat. Eating the food available onboard makes no difference to me. Would you accept a Red-tailed Hawk if it survived the whole crossing by eating all the moribund passerines on the deck?

It seems like the main reason committees adopt these silly rules is to avoid having to accept "ridiculous" species like Snowy Sheathbills. But why would it be so ridiculous? It is still a wild bird, one that is taking advantage of a human-made habitat. Is there any genuine difference between a dispersing Snowy Sheathbill hitching a ride on a boat, and a Cattle Egret taking advantage of entirely human-modified farm habitats to colonise new countries? Th sheathbill can jump ship any time it likes, in the same way that a Cattle Egret can turn around and head back to Iberia.

For me, I say accept the Sheathbill, the Grackle, the sparrows and stop worrying about what could and couldn't make it - we'll never know for sure anyway.

Boat-tailed Grackle - not exactly the most inspiring of vagrants, but would've been more exciting if it were a singing male - anyone who hasn't had a chance to hear the madness, check it out here (http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Boat-tailed_Grackle.html#sound).
James

[Alex Lees]

Just to drum this point home I've attached range maps (http://www.natureserve.org/infonatura/)for 1) a long-distance 'trans-oceanic' neotropical migrant* - Blackpoll Warbler (high potential for unassisted vagrancy) 2) a medium range intra-Nearctic migrant - White-crowned Sparrow (potential vagrant but still likely ship-assisted) and 3) a largely resident species - Northern Mockingbird (very unlikely 'natural' vagrant).

*these maps massively underestimate the winter-range of Blackpoll which has been recorded south to Argentina and is much more regular in the Eastern Amazon and the Atlantic Forest that the map suggests.

All three are obviously on the British List. I agree with James that the current system needs an overhaul, but I guess the purists will stand on the 'legal prerequisites of what constitutes a British bird paradigm'? What about a new category....

Alex

[AndyB]

Thanks for the maps.

It's a tough call on what's countable. By the way, a few weeks ago a probable Galapagos Mockingbird was seen well down near LA Harbor!