On the tenth day, lice were gone

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A total of 48 birds searched today, and NO LICE, if it hadn’t been for a Teal Anas crecca that was caught in the duck trap… It had several Anaticola and Anatoecus, as well as some Trinoton that I was too slow to catch.

Here are the numbers for the first ten days (# searched / # with lice):
Sparrowhawk Accipiter nisus (3 / 1)
Sedge Warbler Acrocephalus schoenbaenus (12 / 0)
Pintail Duck Anas acuta (1 / 1)
Teal Anas crecca (1 / 1)
Gadwall Anas strepera (1 /1)
Tree Pipit Anthus trivialis (16 / 0)
Treecreeper Certhia familaris (1 / 0)
Cuckoo Cuculus canorus (2 / 1)
House Martin Delichon urbicum (2 / 1)
Greater Spotted Woodpecker Dendrocopos major (2 / 2)
Pied Flycatcher Ficedula hypoleuca (15 / 0)
Red-breasted Flycatcher Ficedula parva (1 / 1)
Chaffinch Fringilla coelebs (1 / 1)
Icterine Warbler Hippolais icterina (3 / 0)
Barn Swallow Hirundo rustica (3 / 1)
Red-backed Shrike Lanius collurio (27 / 4)
Thrush Nightingale Luscinia luscinia (5 / 0)
White Wagtail Motacilla alba (18 / 0)
Yellow Wagtail Motacilla flava (2 / 0)
Spotted Flycatcher Muscicapa striata (22 / 0)
House Sparrow Passer domesticus (3 / 1)
Tree Sparrow Passer montanus (17 / 3)
Redstart Phoenicurus phoenicurus (16 / 0)
Wood Warbler Phylloscopus sibilatrix (2 / 0)
Willow Warbler Phylloscopus trochilus (71 / 0)
Winchat Saxicola rubetra (3 / 0)
Nuthatch Sitta europaea (1 / 0)
Common Tern Sterna hirundo (2 / 2)
Tawny Owl Strix aluco (1 / 0)
Starling Sturnus vulgaris (1 / 1)
Blackcap Sylvia atricapilla (3 / 0)
Common Warbler Sylvia borin (15 / 2)
Common Whitethroat Sylvia communis (19 / 0)
Lesser Whitethroat Sylvia curruca (47 / 0)
Wood Sandpiper Tringa glareola (1 / 1)
Fieldfare Turdus pilaris (1 / 1)
UNKNOWN HOST (found on bench) (2)

Thus, a total of 343 birds have been searched, with 22 having lice. So far, rather disappointing, but as expected for a catch that includes mainly long-distance migrants and insectivores. I hope this will change in September when we start catching short-distance migrants.

3 responses »

  1. Du får gärna utveckla “but as expected for a catch that includes mainly long-distance migrants and insectivores. I hope this will change in September when we start catching short-distance migrants.”, varför förväntar du dig detta mönster?

  2. The short answer is experience. In passerines, it seems to be much more common to find lice in short-distance migrants or non-migrants than in long-distance migrants, with some exceptions (swallows, larger migrants as shrikes and large warblers).

    As for an explanation of *why* this is the case, this is obviously much harder, because virtually no one does research on lice outside Domestic Pigeon. Some suggestions:

    1. Long-distance migrants are often long-distance migrants for a reason, and that reason is usually that there are no insects in the Northern hemisphere in the winter, so they have to migrate far south to be able to survive. This suggests that long-distance migrants have bills that have evolved to pick up insects, which is generally a good bill for preening. This may mean that long-distance migrants have fewer lice (both infestation rates and abundances) simply because they are generally insectivores. The fact that shrikes have higher infestation rates than e.g. warblers would suggest that this may be one influencing factor.

    Short-distance migrants include tits, sparrows, finches, buntings, and thrushes, and these are generally adapted to eating fruits, nuts, seeds, and so on. To be able to do so, their beaks may be evolved to be worse for preening but better for e.g. crushing seeds.

    2. It is also known that lice (and other parasites) have an actual deleterious effect on their hosts. Long-distance migrants will (in Europe) need to cross the Mediterranean and the Sahara on their way to the wintering grounds. Perhaps birds with lots of lice simply cannot cross these barriers, and thus at least some of the long-distance migrants have no lice simply because those that have lice don’t make it all the way to the wintering grounds.

    Short-distance migrants may face some such barriers (the Baltic, for instance), but these are not as substantial as those faced by the long-distance migrants, and more birds with lice survive these barriers, thus the infestation rates may be higher because of this.

    3. It may be a phylogenetic effect. Many of the long-distance migrants belong to taxa that are more speciose in their wintering grounds (flycatchers, “warblers”), while short-distance migrants generally belong to taxa that are more speciose in the Northern hemisphere (buntings, tits). It may simply be that there are fewer groups of lice on long-distance migrants than on short-distance migrants, and that this is reflected in the infestation rates.

    (On the other hand, shrikes s. lat. are more speciose in the tropics, but seem to have higher infestation rates than many other passerines…)

    4. Many short-distance migrants are more gregarious than long-distance migrants. It’s common to see flocks of tits and finches, for instance, while it is much less common to see flocks of warblers or wheatears. This would mean that lice on short-distance migrants may have many more opportunities to spread horizontally than those on long-distance migrants.

    5. There seems to be more lice recorded from long-distance migrants in Southern Europe than what I can find here. Maybe there are differences in breeding biology? Long-distance migrants in Southern Europe are likely in the breeding grounds longer, which may imply more opportunities for lice to spread horizontally in more southern populations than in more northern ones.

    6. It may also be that the northern populations are the ones that *can* fly longer, because they don’t have parasites, while southern populations have lice because they cannot fly much longer, and settle for a territory as soon after crossing the Mediterranean as possible. Short-distance migrants would not have that sort of dynamic, of course.

    7. Other reasons.

    But, as I said, there is NOTHING published on these things, so it is presently impossible to know. I hope I’ll be able to sue some data from this field work to ask at least some sorts of questions like this, but I think it would require collection in Southern Europe as well.

  3. Hur länge sitter en lus kvar? Det kan inte vara så att långmigrerande arter tappar* en större andel löss på vägen jämf med mer kortmigrerande arter o att det därför har färre löss kvar vid arternas breeding grounds?

    *expempelvis pga den fysiologiska ansträngningen är högre för de löss som ska färdas längre sträckor, jag tänker då framförallt på skillnader i temperatur? Eller är lössen skyddade från värme o andra påfrestningar av värdens fjäderdräkt?

    Du kanske kan fråga ifall Alfredo känner ngn i Spanien som kan samla in åt dig.

    Tack för det utförliga svaret! =) (svara bara på detta om du har tid)

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