Unusual nest sites of Réunion Stonechat Saxicola tectes high in trees - a response to increased predation of ground nests?

2009·3.1 MB·

by  Markus Handschuh

Unusual nest sites of Reunion Stonechat Saxicola tectes
high in trees—a response to increased predation risk
of ground nests?
MarkusHandschuh
—
Des nids duTraquetde laReunion Saxicola tecteshautdans des arbres unereponseaune
augmentation du risque de predation au sol? En decembre 2003, des Traquets de la Reunion
Saxicola tectes ont ete observes occupant des territoires dans la plupart des habitats a haute alti-
tude dans le nord de Tile. Cinq nids ont ete trouves, dont deux juste au-dessus du sol sur des
m m
talus, deux a une hauteur d’environ 9 et 12 dans des arbres du genre Cryptomeria et un
m ,
a environ 7 dans une fougere arborescente Cyathea sp. L’emplacement du nid a une hauteur
elevee au-dessus du sol est inhabituel pour le Traquet de la Reunion, une espece endemique
commune de File de la Reunion, et le genre Saxicola en general. Des emplacements pareils sont-
ils communs quoique restes inapenpas jusqu’a present? Ou sont-ils dus a Fabsence locale de sites
de nidification typiques, a un niveau localement elevee de derangement, ou a une augmentation
du risque de predation des nids au sol par des mammiferes predateurs introduits? Cette derniere
hypothesesembleetrelaplusplausible. Des etudes plus pousseessonttoutefois necessairesafinde
determiner si Futilisation d’arbres comme site de nidification est un phenomene de plus en plus
frequent, ce qui pourrait avoir des implications pour la conservation.
Summary. In December 2003, territory-holding Reunion Stonechats Saxicola tectes a common
,
Reunion endemic, were encountered in most habitat types at higher elevations in the north of
the island. Five nests were found, ofwhich two were lowabove the ground on banks, whilst two
were at c.9 m and c.12 m in Cryptomeria trees, and one at c.7 m in a tree fern Cyathea sp. Nest
sites high above the ground are unusual for Reunion Stonechat and the genus Saxicola in gen-
eral. Potential explanations include such sites being a more common but to date overlooked or
unpublished traitofReunion Stonechat, alocallackoftypicalnestsites, alocallyhighlevelofdis-
turbance, or increased predation risk ofground nests by introduced mammalian predators. The
latterexplanation seems most likely. However, more detailedstudies are required to investigate if
tree nests are an increasingly frequent phenomenon with potential conservation implications.
R
eunion Stonechat Saxicola tectes is endemic Methods
to the 2,500 km2 island of Reunion, an During a visit to Reunion in December 2003, I
overseas department of France in the Indian located five nests ofReunion Stonechat (seeTable
Ocean. The species is described as very common, 1 for details) and made unsystematic observations
typically at higher elevations of the island (e.g. on the species’ habitat and nesting.
Barre 1983, Barre et al. 1996), and currently
is not considered globally threatened (BirdLife Results and Discussion
International 2009).
Although Reunion Stonechat is relatively Habitat
conspicuous and easily observed, its breeding Along a hiking track from the village Le Brule
biology is not well known, and few detailed towards the protected forest of La Roche Lcrite
accounts of its nesting have been published (altitudinal range: c.700-1,500 m) in the north
&
(see Milon 1951 in Urquhart Bowley 2002, ofReunion, territory-holding Reunion Stonechats
Cheke 1987 and Probst 2002; a line drawing were encountered in most habitat types except
illustrates a typical nest in Barre et al. 1996). dense, single-species plantations of introduced
Here, I provide details on five nests found in Japanese Cedar Cryptomeria japonica bereft of
December 2003. undergrowth. At lower altitudeswith mostlyexot-
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Captionstofiguresareonpage206
largely native, more open, mixed evergreen forest
at higher altitudes, I found stonechat territories
arranged linearly along the hiking track, with a
territorial male every 100-300 m. However, I did
not search for stonechats awayfrom the trail.
Compared to other Saxicola Reunion
,
Stonechat occupies a broader range of habitats
&
(Urquhart Bowley 2002). According to Barre
et al. (1996) and Cheke (1987), it can be found
icsecondarygrowth,stonechatterritoriesappeared almost anywhere from the lower extent ofthe for-
I clumped around openings and clearings. In the est at 300-800 m up to the highest elevations at
j
UnusualnestsitesofReunionStonechat:Handschuh BullABCVol16No2(2009)-205
&
c.3,000 m. Probst (2002) adds that in parts ofthe 1951 in Urquhart Bowley 2002, Barre et al.
south itstilloccursdowntosealevelandalsomen- 1996, Cheke 1987, Probst 2002). Although Barre
m
tions a nest at 3,030 on the Piton des Neiges. et al. (1996) mention that, occasionally, nests
Cheke (1987) notes that the stonechat is the only are located in trees, on the lower branches or in
m
Turdidae on the island and therefore takes advan- a trunk cavity 1-2 above the ground, I have
tage ofall the ‘small thrush’ niches open to it, i.e. found no account ofthe species nesting higher up
open ground as well as closed-canopy forest, in in trees.
addition to the scrub habitat typical ofthe genus Nest sites high above the ground are also
Saxicola. unusual for the genus Saxicola in general, as its
members typically nest on or near the ground in
Nestsites the cover of the field layer (Urquhart & Bowley
Table 1 gives details ofthe five nests found. Two 2002). There are several potential explanations for
were on banks (Fig. 3), whilst the otherthreewere the high nestsites reported here. (1) Tree nests are
high above the ground: two at c.9 m and c.12 m, a more common but to date overlooked trait of
respectively, in Cryptomeria trees (Fig. 1), and one Reunion Stonechat. This explanation is unlikely,
c.7 m high in a Cyathea tree fern (Fig. 2). The as the nestingofReunion Stonechathaspreviously
nestsites several metres above ground are unusual. been studied systematically and in greater detail
&
Reunion Stonechats normally nest on the ground (Milon 1951 in Urquhart Bowley2002, Cheke
under a tussock or in a tuft ofground vegetation, 1987, Probst 2002), and available information on
or on vegetated banks along forest tracks (Milon the birds ofReunion has been collected and com-
&
piled (Barre etal. 1996, Barre Barau 1982), but
not a single nest high in a tree has been reported.
Captions to photos onpage205 Ifit is a regular trait ofthe species, then it would
Figure 1. NestsiteofReunion StonechatSaxicolatectes most likelyhave been noted before.
c.12 m abovetheground inJapaneseCedar Cryptomeria (2) Local lack oftypical nest sites. This is also
japonicatree, Reunion, 17 December2003. Thearrow unlikely, as in each ofthe three cases reported here
indicates the location ofthenest (Markus Handschuh) potential typical nest sites were readily available
Sitede nidificationduTraquetdelaReunion Saxicola both in thevicinityand in thewider surroundings
tectesdans un Cedrejaponais Cryptomeriajaponicaa ofthe nestingtrees. Atthepicnicsite thesewerein
environ 12 m au-dessusdusol, Reunion, 17decembre the form ofareaswith awell-developed field layer,
2003. La fleche indique l’emplacementdu nid (Markus
such as patches of rough grass, vegetated banks
Handschuh)
and margins of roads and tracks, and root plates
cFD.ie7gcumermeabb2e.orvNe2e0st0th3e.sigtTrehoouefnaRdreriunonwitroiennedifScetarotnneesCcythahatethelSaoac,xaiRtceiouolnnaiotofenct,tehse17 oinffnaaltlievnetrfeoerse.stFuwratshelromcoarteed, othnelynecs.t20i0n amtrfeerofmerna
nest (Markus Handschuh) typical bank nest in the same habitat.
Sitede nidification duTraquetdela Reunion Saxicola (3) Locallyhighlevelsofdisturbance. Frequent
tectesdans une fougerearborescente Cyatheaaenviron and / or heavydisturbance maycause birds to nest i
7 m au-dessusdu sol, Reunion, 17decembre2003. high above the ground. Fiowever, the two nests
La fleche indiquel’emplacementdu nid (Markus on banks were located directly on the edge of a
Handschuh) narrow, well-used hiking trail (during my obser-
Figure 3. Typical nestsiteofReunion StonechatSaxicola vations several people passed the nest <2 m from
tecteson avegetated bank, Reunion, 17 December2003. the incubating female, without it leaving the nest)
Thearrow indicates the location ofthe nest (Markus and a small road (with cars passing at a distance
Handschuh)
of <3 m), respectively. According to A. S. Cheke
Sitede nidification typiquedu Traquetde la Reunion (pers. comm.), stonechats have successfully nested
Saxicolatectesdans un talus herbeux, Reunion, 17
decembre 2003. La fleche indique1’emplacementdu nid alongside the same trail for decades. Also, almost
(Markus Handschuh) all of the Reunion Stonechats I encountered
seemed relatively unwary of people, independent
Figure4. Nest and eggsofReunion StonechatSaxicola
tectes, Reunion, 17 December 2003 (Markus Handschuh) ofwhether they had an active nest or not.
Nid etoeufsduTraquet de la Reunion Saxicolatectes, (4) Predator avoidance / locally increased pre-
Reunion, 17decembre 2003 (Markus Handschuh) dation riskofground nests. The mostlikelyreason
206-BullABC Vol16No2(2009) UnusualnestsitesofReunionStonechat:Handschuh
.
Table 1. Detailsoffive nestsofReunion StonechatSaxicolatectesfound in December2003.
123= Forphotograph ofnestsitesee Figs. 1-3, respectively.4= Forphotographofnestand eggssee Fig. 4.
*=Ageestimated, basedon nestling developmentofEuropean Stonechat S. torquatusrubicola (pers. obs.).
Tableau 1. Donneessurcinq nidsduTraquetde la Reunion Saxicolatectestrouvesen decembre2003.
123= Pourune photode (’emplacementdu nid, voirFigs. 1-3, respectivement.
4= Pourune photodu nid etdesceufs, voirFig. 4.
*= Estimation de I’age baseesurledeveloppementdesjeunesduTarierpatre S. torquatusrubicola (obs. pers.).
Nestno I1 2 32 43,4 5
Date 17December2003 17December2003 17December2003 17December2003 18December2003
Locationand NorthReunion,Mamode Asnest1 NorthReunion,along c.200mfromnest3along NorthReunionnearvillage
heighta.s.1. Camp,c.1,200m hikingtracktoLaRoche track,c.1,500m Hell-Bourg,c.1,400m
Ecrite,c.1,500m
Habitat Relativelyflat,park-like, Asnest1 Steepterrain,mesothermic Asnest3 Rivervalleywithmostly
publicpicnicsite,withsingle evergreenforestwith steeptopographyandwoods
JapaneseCedarCryptomeria denseundergrowth,short ofexoticpinePinussp.and
japonicatreesandvarious vegetationandbaresoil broadleavedtrees
artificialverticalstructures,
surroundedbyopen
JapaneseCedarplantation
withgrassyundergrowth
Nestsite c.12mabovegroundin c.9mabovegroundin Belowtrack,c.7mabove 0.7mabovegroundin 1.1mabovegroundon
>20-mtallJapaneseCedar c.20-mtallJapanese groundinc.9-mtalllive semi-cavityondensely vegetatedrockfacenext
treenexttominorpaved Cedartree;nestentirely Cyatheatreefem,entirely vegetatedbankwherethe tominorpavedroad;cavity
road;nestconcealedin concealedatbaseoffirst, concealedincavitycreated pathhadbeencutfromthe behindclumpofmoss;nest
broomofdenseshort dense,1-mlongbranch, bydeadvegetationhang- slope;nestconcealedby entranceconcealedbytuft
branchesattrunk,darkspot invisiblefromground ingfromthetrunk,invisible overhangingmoss.Extent ofgrass,onlysmallhole
andsomenestingmaterial fromoutside andshapeofnichesug- visiblefromoutside.Niche
visiblefromground gestthatitmayhavebeen mayhavebeenenlargedby
enlargedbythebird. thebird.
Nestdescription Outerwallsmainlyofdry Asnest1 Notexaminedclosely Outerwallsmainlyofmoss, Asnest4
grassanddryleaves,con- resemblingmoss-domi-
taininghardlyanymoss.Nest natednestsofEuropean
cuplinedmainlywithfine RobinErithacusrubecula.
plantmaterialandsomeani- Nestcupasnest1
malhairandsmallfeathers.
Entrancefaces north-west east south-east west south
Nestcontents* Threenestlingsc.9daysold Twonestlingsc.6daysold Nestinconstruction Presumablycomplete Presumablycomplete
clutchoffoureggs,female clutchofthreeeggs,female
incubating incubating
for high nest sites may be a (locally) increased potential nest predators is likely to be higher at
&
predation risk of ground nests by introduced locations frequented by humans (see Cheke
mammalianpredators.Although thespecies is still Hume 2008), such as the picnic site, e.g. due to
common on Reunion (A. S. Cheke pers. comm.) waste andleftoverfood. However, because atleast
and there is no published evidence that it suf- Black Rats have been abundant in the forests of
fers from high nest predation, which could cause Reunion at all elevations for centuries (see Cheke
birds to nest higher in trees, this may be a recent & Hume 2008), feral cats are a more likely cause
phenomenon that has not been noted in earlier ofa significant change in nest site selection (A. S.
&
studies (Milon 1951 inUrquhart Bowley2002, Cheke pers. comm.).
Cheke 1987, Probst 2002).
Both Black Rats Rattus rattus and Norway Nestcontents
Rats R. norvegicus as well as feral Cats Felis catus I found clutch sizes of three (nest 4) and four
have been introduced to Reunion (pers. obs.; (nest 5) eggs, and brood sizes oftwo (nest 2) and
Cheke & Hume 2008). The density of these three (nest 1) nestlings. Both incubating females
UnusualnestsitesofReunionStonechat:Handschuh BullABCVol16No2(2009)-207
.
were sitting tightly at around midday and were the submitted draft which greatly improved this note,
thereforepresumedto havefinishedtheirclutches. and Ron Demeyforprovidingthe Frenchsummary.
Of 12 completed clutches that Milon (1951 in
Urquhart & Bowley 2002) recorded, 11 com- References
&
prised three eggs and one four eggs. In 1973-74, Barre, N. Barau,A. 1982. OiseauxdelaReunion. St.
Cheke (1987) found eight nests containing three Denis: ImprimerieArts Graphiques Modernes.
eggs andsixwitheggs, andassumedtheclutchsize Barre, N. 1983. Distribution et abondance des oiseaux
to be 2-3 eggs. However, Barre & Barau (1982), terrestres de file de La Reunion (Ocean Indien).
Barreetal. (1996) andProbst (2002) reportclutch Rev. Ecol. 37: 41-&85.
sizes of2-4 (most commonly three) eggs. Barre, N., Barau,A. Jouanin, C. 1996. Oiseauxdela
Reunion. Paris: Les Editions du Pacifique.
Conclusion BirdLifeInternational. 2009. Speciesfactsheet: Saxicola
Nests of Reunion Stonechat high above the tectes. www.birdlife.org (accessed4July2009).
Cheke,A. S. 1987. Theecologyofthesurvivingnative
ground in trees merit further investigation to land-birds of Reunion. In Diamond, A. W. (ed.)
determinewhethertheyare (a) arare, irregularand StudiesinMascareneIslandBirds. Cambridge, UK:
local occurrence, or (b) more common and wide- Cambridge UniversityPress.
spread but previously overlooked, or (c) a recent Cheke, A. S. & Hume, J. P. 2008. Lost Land ofthe
and perhaps increasingly frequent and widespread Dodo: An EcologicalHistory ofMauritius, Reunion
phenomenon. Ifthe latter is the case, it should be andRodrigues. London, UK:A. & C. Black.
established which factors cause tree nesting and, Probst, J.-M. 2002. Faune indigene protegee de llle
in particular, whether the phenomenon is related de la Reunion. Le Port: Association Nature et
to predation of ground nests and therefore has Patrimoine.
potential implications for the conservation ofthis Urquhart, E. & Bowley, A. 2002. Stonechats:A Guide
insular endemic passerine. to the Genus Saxicola. London, UK: Christopher
Helm.
Acknowledgements
POBox93 054, SiemReap, Cambodia. E-mail:Markus.
I am grateful to the Durrell Wildlife Conservation [email protected]
Trust and the Mauritian Wildlife Foundation, in par-
ticular DavidJeggo and CarlJones, for mytwo-month Received 13 December 2008; revision accepted 4June
secondment to Mauritius, from where I also visited 2009.
Reunion. I thankAnthonyChekeforhis commentson
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