Náttúrufræðingurinn - 2014, Blaðsíða 64

Náttúrufræðingurinn
64
óskyldra unga sem gæti hafa veikt
líkamlegt ástand hans og minnkað
áframhaldandi lífslíkur. Kostir og
gallir geta því verið við hjálp við
varp eins og hér er lýst.
Nefið á svartþrestinum var appel-
sínugult að lit en rannsóknir hafa
sýnt að því appelsínulitaðra sem
nef svartþrasta er, þeim mun betri
feður eru þeir. Þeir eru duglegri
að afla ætis fyrir unga og ungar
verða í betra líkamlegu ástandi.12
Má telja einsýnt að svartþrösturinn
hafi verið albúinn að takast á við
varpskyldur.
Gaman væri að heyra af fleiri til-
vikum af þessu tagi sem lesendur
kunna að hafa orðið vitni að meðal
íslenskra fugla.
Summary
A male Blackbird helper at
Redwing nests
Two inter-specific examples of helping
at two nests are described, involving
successive nesting attempts. European
Redwings Turdus iliacus nested in a gar-
den in the town of Garðabær, SW-
Iceland, in summer 2006 with a male
European Blackbird Turdus merula tak-
ing part in the breeding activities (Fig. 1).
Sometimes all three birds were observed
together at the nest and the two males
often seen fighting. One of the Redwings
turned out to be ringed (Fig. 2), at Höfn,
SE-Iceland on 15th April 2006, presumed
to have just arrived from abroad where
most Icelandic Redwings overwinter.3
That bird presumably was the female
since it did all the incubating, as is usual
in European Redwing.1
On hatching, the Blackbird fed the
young just as actively as the Redwing
pair itself, and mobbed potential preda-
tors (cats, humans) approaching the nest.
The chicks looked like ordinary Redwing
young. When they were about a week
old and still in the nest, the male Redwing
disappeared and was never seen again.
It is presumed to have died, possibly
killed by cat as one was seen trying to
reach the nest. To fend off cats a fine
meshed net was placed underneath the
nesting bush. When the five young left
their nest they stayed inside the fence
and were fed through the mesh (Fig. 3).
When the young were large enough the
fence was removed and the chicks
spread to nearby gardens. Nothing is
known about their existence thereafter.
On the 16th July, when the first brood
was about able to fly, had they survived
at all, another nest was discovered in
same garden containing one egg. The
nest was attended by only one Redwing
and a male Blackbird, assumed to be the
same birds as before. This was con-
firmed in the case of the Redwing since
this turned out to be the same ringed
bird from earlier. No other Redwing was
ever observed at the nest, but the four
chicks which later hatched looked like
Redwing chicks.
The male Blackbird showed similar
breeding behaviour as before, singing
and mobbing during the egg-laying pe-
riod, but keeping a low profile during
the incubation period. On hatching the
chicks were fed by the Blackbird. When
the chicks were about a week old the
ringed female Redwing was seen on the
lawn looking miserable. On closer look
the bird had an open wound on the thigh,
probably inflicted by a cat. It was never
seen thereafter, presumed to have died.
The Blackbird continued feeding the
chicks, which left the nest 10–11 days old.
The day after fledging the Blackbird was
seen mobbing three cats in a nearby gar-
den. The young were presumably nearby
but no further observations are available
on neither the brood nor the Blackbird.
These observations clearly indicate
cases of inter-specific helping at nest. It
is not certain if the male Blackbird actu-
ally ever paired with the female Red-
wing but this seems unlikely. On the
other hand the breeding attempts may
not have been successful in the chicks
leaving nest without the help of the
Blackbird, at least in the latter case.
Þakkir
Þeim Birni Þresti Axelssyni og Önnu Halldóru Karlsdóttur eru færðar
innilegar þakkir fyrir ábendingar um sérkennilegar samvistir þrasta. Er af-
skaplega gaman að fólk tekur eftir atburðum í náttúrunni. Slíkar athuganir
geta verið ómetanlegar eins og sannast í þessu tilviki. Sverrir Thorstensen
og Sólveig Bergs lásu handritið yfir og færðu margt til betri vegar.
Heimildir
1. Arheimer, O. 1978. Äggläggning, ruvning och kläckning hos rödvinge-
trast Turdus iliacus i subalpin ängsbjörkskog vid Ammarnäs i svenska
Lappland. Vår Fågelvärld 37. 297–312.
2. Fuglaathugunarstöð Suðausturlands. http://wp.fuglar.is/?page_id=26
3. Ævar Petersen 1998. Íslenskir fuglar. Vaka-Helgafell, Reykjavík. 312 bls.
4. Hannes Þ. Hafsteinsson 1986. Svartþrastarvarp í Reykjavík 1985. Bliki 5. 16–18.
5. Shy, M.M. 1982. Interspecific feeding among birds: a review. Journal of
Field Ornithology. 53. 370–393.
6. Riedman, M.L. 1982. The evolution of alloparental care and adoption in
mammals and birds. Quarterly Review Biology 57. 405–435.
7. Moore, M. 1973. Male Blackbird helping to rear young Song Thrushes.
British Birds 66. 366–367.
8. Erard, C. 1990. Aide au nourrissage chez le merle noir Turdus merula.
(Helper at the nest in the Blackbird Turdus merula). Oiseau et la Revue
Française d'Ornithologie 60. 56–58.
9. Skutch, A.F. 1935. Helpers at the nest. Auk 52. 257–273.
10. Skutch, A.F. 1961. Helpers among birds. Condor 63. 198–226.
11. Brouwer, L., Richardson, D.S. & Komdeur, J. 2012. Helpers at the nest
improve late-life offspring performance: Evidence from a long-term
study and a cross-foster experiment. PlosOne 7(4). e33167. doi:10.1371/
journal.pone.0033167
12. Préault, M., Chastel, O., Cézilly, F. & Faivre, B. 2005. Male bill colour and
age are associated with parental abilities and breeding performance in
Blackbirds. Behavioral Ecology and Sociobiology 58. 497–505.
um höfundinn
Ævar Petersen (f. 1948) lauk B.Sc.-Honours-prófi í
dýrafræði frá Aberdeenháskóla í Skotlandi 1971 og
doktorsprófi í fuglafræði frá Oxfordháskóla á Eng-
landi 1981. Ævar vann á Náttúrufræðistofnun Íslands
í 35 ár en er nú á eftirlaunum.
Póst- og netfang höfundar/Author’s address
Ævar Petersen
Brautarlandi 2
IS-108 Reykjavík
aevar@nett.is