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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
ECOLOGY AND CONSERVATION
OF MEDITERRANEAN SEABIRDS
AND OTHER BIRD SPECIES UNDER THE BARCELONA CONVENTION
UPDATE & PROGRESS
Proceedings of the
13th Medmaravis Pan-Mediterranean
Symposium
Editors
Pierre Yésou - Nicola Baccetti - Joe Sultana
2012
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
Rat eradication at Yelkouan Shearwater Puffinus yelkouan
colonies on NE Sardinian islets:
success followed by unexplained re-appearance
Paolo Sposimo1, Giovanna Spano2, Augusto Navone2, Sara Fratini3,
Lapo Ragionieri4, Massimo Putzu2, Dario Capizzi4 , Nicola Baccetti5 & Barbara Lastrucci1
1NEMO S .r.l., P.z a M. D’Azeglio 11, I -50133 Fir enz e (FI), I tal y. sp os imo@nemoambiente.c om
2Cons or zi o d i G es tione A rea M arina Pr ot ett a Tavol ar a Punt a Cod a Cavallo, Via D ant e 1, I -07026
Olbi a (O T), It al y.
3Dipartiment o Biologia E voluzionis tic a, U niversit à degli Studi di Fi renze, Via Romana 17, I -50125
Firenz e (FI), It al y.
4Regi on e L azio, A genzi a R eg ional e P archi, Vi a del P es c ac cio 96, I -00166 R oma ( RM) , Italy.
5ISPRA, via Ca Fornac etta 9 , I -40 064 O zzano Emil ia ( B O), Ital y.
Summary: The Tavolara archipelago (NE Sardinia, Italy), which possibly holds over 50 % of the world
population of breeding Yelkouan Shearwaters Puffinus yelkouan, was infested by black rats Rattus rattus. An
action plan was developed in order to decrease the impact of rats. In October 2008, rat eradication of Molara
Island has been achieved by aerial distribution of poisoned baits while ground-based eradication was carried
out on three islets. Post eradication monitoring has shown that the operations were successful. However rats
were found again on Molara Island 21 months after eradication. Genetic analysis showed that they were from
the mainland population. Thus, most probably they have been intentionally introduced by man.
Key Words: seabird conservation, rodent eradication, Yelkouan Shearwater, Puffinus yelkouan, Rattus, Italy.
Introduction
The eradication of rodents on islands, aimed at the conservation of seabird populations and other
components of insular ecosystems, is becoming a common management practice. To restore
island ecosystems, rodents (mainly rats Rattus sp. and house mouse Mus musculus) are removed
according to standardized methods, including the spreading of poisoned baits by helicopter,
which enables access to large (up to more than 12,000 ha) or difficult-to-reach islands (Howald et
al. 2007, Veitch et al. 2011). In recent years eradication projects have been carried out on small to
medium-sized islands in the Mediterranean Sea (Genovesi & Carnevali 2011). The largest
Mediterranean islands where success has been confirmed are Lavezzi (73 ha) (Pascal et al.
2008), Zannone (103 ha) (Francescato et al. 2010) and Giannutri (240 ha) (Sposimo et al. 2008).
They were all treated by networks of bait stations placed on the ground. High predation rates by
black rats Rattus rattus on the largest concentration of colonies of Yelkouan shearwater Puffinus
yelkouan, potentially hosting more than 50 % of the species’ global population (Baccetti et al.
2009, Zenatello et al. this volume), suggested the urgent adoption of conservation measures in
the Tavolara archipelago which lies within the Tavolara – Punta Coda Cavallo Marine Protected
Area (NE Sardinia, Italy). An action plan for an overall decrease of the rat impact was produced
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
and operational strategies were evaluated for all different islands and islets of this area. Here we
report on the first actions that were put into practice, namely eradication of black rat from Molara
island (360 ha), achieved by aerial distribution (see Veitch 2002) in October 2008, and
ground-based black rat eradication on three islets.
Study area
Tavolara’s group (Figure 1) is
composed of 2 main islands,
Tavolara and Molara (600 and
340 ha, and 1900 and 1600 m
from the nearest point of the
Sardinia’s coast, respectively)
and some islets, 4 of which
have a surface between 2.2 and
13.6 ha and lie in an intermediate
position between the coast and
the main islands. The only wild
mammals inhabiting Molara and
the smaller islands were the black
rat (absent only from one islet)
and the house mouse (absent
only from Molara). Feral cats
were present on Tavolara, cows on
Molara and goats on both islands.
Materials and methods
Prelimary trapping
In March and September 2008 we performed two four-night trapping sessions (19-22 March; 2-5
September) on Molara, in order to estimate the relative abundance of rats.
Livestock protection
To avoid poisoning free-ranging livestock, two enclosures were built (total enclosures area: 1
ha) and ca. 50% of the goats and 80% of cattle were herded in.
Rat eradication on Molara
Bait was chosen according to the results of palatability and longevity tests. The selected product
was Brocum® (with 0.005% brodifacoum as the active ingredient). The formulation was 2g
cereal pellets. A spreader bucket for the aerial broadcast of pellet baits was purchased from
HeliOtago, New Zealand and a helicopter (Eurocopter Ecureil AS 350 - B2) was hired for the
operation. The pilot had no previous experience of similar works. Distribution trials for instrumental
calibration and pilot training have been conducted using non-toxic baits. Trials showed that, from
a height of 50m, in absence of wind, pellets were distributed on a radius of 45m, i.e. on 90m wide
Figure 1.Situation of Molara and surrounding islands.
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
transects. A transect map was drawn with GIS software and transferred on the helicopter's GPS.
Distribution transects were spaced 50 m from each other, for a total transects length of 53 km
(Figure 2). In October 2008 two aerial distributions of bait were performed, spreading 12.3 kg of
bait/ha on 1st October and 11.6 kg/ha on 21st October. The pilot’s assistant manually switched
the spread on and off. The two enclosures were excluded from aerial distribution. In these areas
bait was placed inside tamper-resistant bait stations, as a buffer area surrounding the enclosures.
A 20 m wide belt running all along the sea coast, larger in two areas (Figure 2), was baited by
hand. To assess the success of the rat eradication we placed and monitored 29 monitoring
stations, containing gnawing sticks, toxic and non-toxic wax blocks, six of which were located at
most likely landing places.
Rat eradication and control on other islands
Ground-based rodent eradication was performed on the three islets in winter 2009-2010. To
determine eradication units for future operations (also on Tavolara) and evaluate the risk of rat
reinvasion of Molara, rat specimens were trapped and collected for genetic analyses, in order to
test possible genetic flow between rat populations in the archipelago and on the adjacent
Sardinian coast. Genetic analysis was performed by genotyping 8 microsatellite loci (see
Abdelkrim et al. 2005 and 2009) in four black rat populations (Tavolara Is., N = 30; Molara Is.,
N = 30; Piana Is., N = 30, Sardinian mainland - Capo Coda Cavallo, N = 24). DNA was isolated from
rat tail tissues using the Puregene Kit (Gentra System), re-suspended in TE buffer and then
Figure 2. Flight route as planned over Molara island.
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
preserved at -20°C. Each individual was genotyped for 8 microsatellite loci already used on
Rattus rattus (see Abdelkrim et al. 2005 and 2009).
Results
Molara rat eradication
The relative abundance of rats on Molara was higher in late winter (0.75 ind/trap/night in March)
and much lower in late summer (0.38 ind/trap/night in September), suggesting that summer was a
critical period for rat survival. This evidence allowed us to identify the latter season as the best
period to carry out the rat eradication on Molara. A total of 7.4 tons of rodenticide bait was
scattered on the island. Several technical problems occurred during the operation. The most
serious of which was the malfunctioning of the spinner engine on both distributing sessions, so
most transects were covered by vertical dropping (see Micol & Jouventin 2002 for a similar
episode). Pellet distribution on the ground was found to be in 10 m wide stripes, alternating to
ca.40m wide empty stripes. The comparison of the helicopter tracks recorded by GPS and the
original planned transects showed marked discrepancies (up to 35m in some cases).
Nevertheless, in the first distribution only six areas, all smaller than 1 ha, were at distances
greater than 40m from the nearest treated point. Considering both distrubutions together, no areas
were left with a distance of more than 30m from the nearest treated point.
Starting two days after the first delivery, several rain showers were recorded, which steadily
degraded most fallen pellets. After 21 days, on the date of the second delivery, most previous
pellets already seemed considerably degraded. On the day following the second delivery, a heavy
and unpredicted rainfall (33 mm recorded by the nearest weather station) almost completely
degraded the newest pellets. If any rat had survived the first delivery, therefore, pellets from the
second one were available to them in adequate conditions only for a single night.
Carried out in a season when very few gulls (Laridae) are locally present, poisoning affected few
non target species. Corpses of two Barn Owls Tyto alba and two Ravens Corvus corax were
Islands Rat Breeding success n Year/remarks
Molara
(Sardinia)
Y 0 18 2006
Y 0 7 2007
C 0,67 3 2008
E 0,71 7 2009
E/R 0,86 7 2010
Tavolara
(Sardinia)
Y 0 22 2007; top of the island and in caverns with rats
N 0.78 9 2007; inside caverns inaccessible to rats
C 0,73 15 2009; in caverns with rats and local control
Table 1. Breeding success (number of fledged chick per pair; n=number of sampled nests)
of Yelkouan Shearwater according to the presence/absence of black rat (N= absent, Y=
present; C= controlled; E=eradicated; R=reinvaded); G. Spano & M. Putzu, unpubl. data.
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
found, both presumably dead after secondary poisoning. Livestock that could not be herded into
the enclosures was affected for an estimated one third of the goats while none of the 6-7 free
ranging cows died or showed any problems.
Despite these difficulties, the control of monitoring stations gave no sign of rat presence over the next
21 months, and thus the rat eradication was considered to have been successfully completed.
Yelkouan shearwater breeding success greatly increased after rat eradication on Molara, from total
failure before rat eradication to values reaching 0.71-0.86 fledglings per pair in 2009 and 2010 (Table 1).
After 21 months of an apparent absence of rats, signs of their presence were discovered in July
2010 along 1 km of the Molara coast facing the Sardinian mainland, 1600m far. These signs of
rats followed the appearance of several domestic rabbits (quickly captured and removed) in the
previous winter. We did not investigate who may have brought the rabbits to Molara and why.
Rat eradication from islets
Rats were easily eradicated from all three islets, but success was short lived. After 6 months they
were found again on the islet nearest to the mainland (Proratora, 4.6ha, 170m offshore), and also
at Cavalli (2.2ha, 300m offshore) after two years, although not yet present on adjacent Piana
(13.6 ha, 660m far from land and 530m from Cavalli).
Genetic analyses
All the analyzed loci are polymorphic, with a mean number of alleles equal to 10. The highest
values of genetic variability have been recorded for the Capo Coda Cavallo population, while the
lowest one is for the population of Piana (Table 2). Molara and Tavolara populations have similar
value of allelic richness, number of alleles and heterozygosity values. Piana and Tavolara
populations show evidence of heterozygosity excess. All four populations are characterized by a
high number of private alleles, a clear evidence of inter-population differentiation. Statistically, this
is confirmed by AMOVA that shows low levels of gene flow among our populations (Fst = 0.33,
P < 0.001), as well as by SAMOVA showing that the number of population groups that maximised
the distribution of genetic variation was k = 4. Moreover, the cluster analysis conducted with the
program STRUCTURE recorded the presence of four groups of populations (K = 4), each
corresponding to one of the four analysed populations. Finally, STRUCTURE indicates that the
genotypes of two specimens of R. rattus collected on Molara during the post-eradication monitoring
Population Na Ho He P
Piana Is. 2.36 0.352 0.355 P < 0.001
Tavolara Is. 4.22 0.510 0.554 P < 0.001
Molara Is. 4.42 0.488 0.545 P = 0.28
Capo Coda Cavallo 6.67 0.715 0.724 P = 0.03
Table 2. Genetics of black rat Rattus rattus from Molara and surrounding places (E. Sardinia,
Italy): mean allelic richness per locus (Na), observed heterozygosity (Ho), expected unbiased
heterozygosity (He) and the P- value of departure from the Hardy-Weinberg equilibrium (P).
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Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
cluster within the mainland population and not with the pre-eradication Molara population.
Discussion
Aerial bait distribution proved an efficient way to eradicate rats on Mediterranean mid-sized
islands, where a ground-based action could not be possible for technical and/or economic reasons.
The Molara operation represented the first case in the Mediterranean and Europe of using the
helicopter and bucket method. Problems with instruments (at least partially due to inexperienced
staff in their utilization) and the lack of a trained pilot made sticking to strict protocol (Cromartry
et al. 2002, McClelland 2011) impossible. On the other hand, failure of the spinner engine had
also occurred during the successful eradication of an island larger than Molara (Saint-Paul Island,
800 ha, Micol & Jouventin 2002), which prompted us not to suspend the flight. The experience
gained on Molara has thereafter helped two eradication projects carried out with the same bucket,
on Sa Dragonera (Balearic Is., Mayol et al. 2012) and on Montecristo (Italy, P. Sposimo et al. un-
pub.), where all instruments worked without noticeable problems.
The fact that the two rats collected during post-eradication monitoring on Molara Island clearly
clustered with the Sardinian mainland popul ation and not with the pre -eradication Molara
population strongly suggests that (1) a new population is present; (2) the eradication efforts had
been successful despit e the combined effects of inexperienced staff, heavy rains and
engine malfunctioning; and (3) the potential source for rat recolonization is the Sardinia
mainland population. Assessing whether re-colonization occurred spontaneously (which would
entail the largest sea crossing recorded for the species, 500 m being the maximum known; e.g.
Russell et al. 2005 & 2008; Russell & Clout 2005) or following intentional introduction is
unfortunately impossible to discern. Unintentional transportation is also possi bl e, but we
consider this as the most unlikely option. The concurrent, and definitely intentional, introduction of
rabbits represents an additional evidence of the intentional introduction option. However, the rapid
reinvasion of the islet nearest to the mainland (130 m), followed by that of the second nearest,
shows that re-colonization by swimming rats is a frequent phenomenon and confirms that a
careful evaluation of the risks of re-colonization is a fundamental measure before a rat eradication
project is carried out (see e.g. Capizzi et al. 2010).
References
Abdelkrim, J., Pascal, M. & Samadi, S. 2005. Island colonization and founder effects: the invasion of the
Guadeloupe islands by ship rats (Rattus rattus). Molecular Ecology 14: 2923–2931.
Abdelkrim, J., Pascal, M. & Samadi, S. 2009. Genetic structure and functioning of alien ship rat populations
from a Corsican micro-insular complex. Biological Invasion 11: 473-482.
Baccetti, N., Capizzi, D., Corbi, F., Massa, B., Nissardi, S., Spano, G. & Sposimo, P. 2009. Breeding
shearwater on Italian islands: population size, island selection and co-existence with their main alien predator.
Rivista Italiana di Ornitologia 78: 83-99.
Capizzi, D., Baccetti, N. & Sposimo, P. 2010. Prioritizing rat eradication on islands by cost and effectiveness
to protect nesting seabirds. Biological Conservation 14: 1716-1727.
Cromarty, P.L., Broome, K.G., Cox, A., Empson, R.A., Hutchinson, W.M. & McFadden, I. 2002.
Eradication planning for invasive alien animal species on islands – the approach developed by the New
Zealand Department of Conservation. Pp. 85-91 in Veitch C.R. & Clout M.N. (Eds.), Turning the tide: the
eradication of invasive species. IUCN, Gland, Switzerland and Cambridge, UK.
64
Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium
Genovesi, P. & Carnevali, L. 2011. Invasive alien species on European islands: eradications and priorities for
future work. Pp. 56-62. In Veitch C. R., Clout, M.N. & Towns D. R. (Eds.), Island invasives: eradication and
management. IUCN, Gland, Switzerland.
Francescato, S., Capizzi, D., Cecchetti, M., Forcina, G., Mastrobuoni, G., Noal, A., Sposimo, P. &
Zerunian, S. 2010. L’intervento di eradicazione del Ratto nero dall’Isola di Zannone. Pp. 37-110. In Zerunian
S. (Ed.), L’eradicazione del Ratto nero dall’Isola di Zannone. Ufficio Territoriale per la biodiversità di Fogliano,
Parco Nazionale del Circeo.
Howald, G., Donland, C.J., Galván, J.P., Russell, J.C., Parkes, J., Samaniego, A., Wang, Y., Veitch, D.,
Genovesi, P., Pascal, M., Saunders, A. & Tershy, B. 2007. Invasive rodent eradication on islands. Conserv.
Biol. 21: 1258-1268.
Mayol, J., Mayol, M., Domenech, O., Oliver, J., McMinn, M. & Rodríguez, A. 2012. Aerial broadcast of
rodenticide on the island of Sa Dragonera (Balearic Islands, Spain). A promising rodent eradication experience
on a Mediterranean island. Aliens: the Invasive Species Bulletin 32: 29-32.
McClelland, P.J. 2011. Campbell Island – pushing the boundaries of rat eradications. Pp. 204-207. In Veitch,
C. R., Clout, M.N. & Towns, D. R. (Eds.), Island invasives: eradication and management. IUCN, Gland,
Switzerland.
Micol, T. & Jouventin, P. 2002. Eradications of rats and rabbits from Saint-Paol Island, French Southerns
Territories. Pp. 199-205 in Veitch C.R. & Clout M.N. (Eds.), Turning the tide: the eradication of invasive
species. IUCN, Gland, Switzerland and Cambridge, UK.
Pascal, M., Lorvelec, O., Bretagnolle, V. & Culioli, J.M. 2008. Improving the breeding success of a colonial
seabird: a cost-benefit comparison of the eradic ation and control of its rat predator. Endang. Species
Res. 4: 267–27.
Russell, J.C. & Clout, M.N. 2005. Rodent incursions on New Zealand islands. Pp. 324-330. In Parkes, J.,
Statham, M . & Edwards, G. (Eds.), Proceedings of the 13th Australasian vertebrate pest conference .
Landc are Research, Lincoln, New Zealand.
Russell, J.C., Towns. D.R., Anderson. S.H. & Clout. M.N. 2005. Intercepting the first rat ashore. Nature
437: 1107.
Russell, J.C., Towns, D.R. & Clout, M.N. 2008. Review of rat invasion biology. Im plications for island
biosecurity. Science for Conservation 286, Wellington, New Zealand.
Sposimo, P., Capizzi, D., Giannini, F., Giunti, M. & Baccetti, N. 2008. Le cas d’étude de Giannutri (Archipel
Toscan, Italie) : la plus importante éradication de r ats en Méditerranée. Actes des ateliers de travail du
programme LIFE Nature 2003-2007 Conservation des populations d’oiseaux marins des îles de Marseille» du
12 au 16 novembre 2007 : 62-63. Marseille, CEEP.
Veitch, C.R., Clout, M .N. & Towns, D.R. (E ds.) 2011. Island Invasives: Eradicat ion and Management.
Proceedings of the International Conference on Island Invasives. Gland, Switzerland: IUCN and Auckland,
New Zealand.
Veitch, C.R. 2002. Eradication of Pacific rats (Rattus exulans) from Tiritiri Matangi Island, Hauraki Gulf, New
Zealand. Pp. 360-364 in Veitch C.R. & Clout M.N. (Eds.), Turning the tide: the eradication of invasive species.
IUCN, Gland, Switzerland and Cambridge, UK.
Zenatello, M ., Spano, G., Baccetti, N., Zucca, C., Navone, A., Putzu, M., Azara, C., Trainito, E., Ugo ,
M. & Phillips, R. 2012. Movements and moving population estimates of Yelkouan shearwaters at Tavolara,
Sardinia. This volume.
CITATION: The editors recommend that for references to this work the following citation should be used:
Sposimo, P., Spano, G., Navone, A., Fratini, S., Ragionieri, L., Putzu, M., Capizzi, D., Baccetti, N., & Lastrucci, B.
2012. Rat eradication at Yelkouan Shearwater Puffinus yelkouan colonies on NE Sardinian Islands): success followed by
unexplained re- appearance. (Pp. 58-64). In Yésou, P., Baccetti, N. & Sultana, J. (Eds.), Ecology and
Conservation of Mediterranean Seabirds and other bird species under the Barcelona Convention - Proceedings of
the 13th Medmaravis Pan-Mediterranean Symposium. Alghero (Sardinia) 14-17 Oct. 2011. Medmaravis, Alghero.