Kangaroo:
John
Wh
tePhotos/Getty;
eggs:
Asta
rScott/A
amy;
fish:
Ke
vn
Atken/VWP
cs/A
amy;
eag
e:Er
cMedard/
naturepl.com; squirrel feeding: Andrew Mason/FLPA; squirrel on trunk: Mark Hamblin/2020VISION/NPL
H
oppingonthehindlegsis a defining
characteristicofthemacropod
marsupials:kangaroos,wallabies,bettongs,
potoroosandtheirkin.Eventreekangaroos
hopwhentheyfindthemselvesonthe
ground.It’sa highlyefficientmodeoftravel
thatemploysthick,stretchytendonstoabsorb
andreleaseenergy,likesprings.Whileother
animals require a huge muscular effort to
jump,macropodsquiteliterallybounce.
Atleastonefamilymemberdoesthings
differently,though.Themuskyrat-kangaroo
boundsaroundQueensland’srainforests
onallfourlimbs,placingitsfrontfeeton
thegroundandbringingbothhindfeetup
simultaneouslytomeetthem.So,eventhis
odditycouldbesaidtohop,albeitmorelikea
rabbit than a macropod.Stuart Blackman
T
itsareprodigiousegg-layers,
routinelyproducingclutchesof 10
to 12 withoccasionalrecordsofupto19.
Thesenumbersareimpressivewhen
comparedtosimilar-sizedspeciessuch
assparrows,whichtypicallylayfiveor
six.Thedifferenceis thattitstendto
produceonlyoneclutcha year,while
sparrowsgetonebroodfledgedthen
keepgoing,sothatthetotalfora year
is similar.Titsliterallyputalltheireggs
inonebasketinApril,takingadvantage
ofthesuperabundanceofcaterpillars.
Sparrows,ontheotherhand,relyona
widerrangeofinvertebratefood,often
workingintoautumntofeedsecond,
third or fourth broods.Amy-Jane Beer
Doallkangaroos hop?
Whydoblueand
greattitslayso
many eggs?
MAMMALS
BRITISH BIRDS
MARINEBIOLOGY
Y
es.Forair-breathingcreatureslike
ourselves,anabilitytoholdone’sbreathis
usefulshouldonefindoneselfsubmerged.But
coffinfish,too,routinelyholdtheirbreathinwater
- foruptofourminutes– eventhoughwater
is whattheybreathe.Assit-and-waitpredators,
coffinfishdon’textractoxygenastheyswimalong.
Instead,theymustactivelyinflateanddeflatetheir
gillchambers.Thesechambersareunusually
large,allowingthefishtoprocessa largevolume
ofwaterinonego,whichmayexplainhowthey
canaffordtobreathesoinfrequently.Butthere
couldbemoretoit.Inflationofthegillchambers
increasesbodyvolumeby 30 percent,whichmay
servetodeterpredators,inmuchthesameway
thatpufferfishesappearbigger by swallowing
seawater.Stuart Blackman
Canany sh
hold its breath?
Co nfishrespiration
- reallyquite
breathtaking.
Greattitsgo
largeonthe
laying.
Virtuallyall
kangaroos(here
westerngreys)can
be caught on the hop.
Q&A
84 BBC Wildlife December 2019