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Rat eradication at Yelkouan Shearwater Puffinus yelkouan colonies on NE Sardinian islets: success followed by unexplained re-appearance

Authors:
  • Area Marina Protetta Tavolara Punta Coda Cavallo

Abstract and Figures

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.
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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).
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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.
... The success of these early operations was usually low, due to recolonization and inadequate evaluation of the consequences of the short distance from land (the exception was: La Scola, which will have to be treated repeatedly, see below). In the second half of the period, a similar fate was again encountered on two Sardinian islets, located 170-300 metres from land, and by a single failure (due to recolonization) on a large island, Molara (Sposimo et al. 2012). ...
... The case of Molara is different and more than 1000m offshore. Rats re-appeared there in 2010, two years after an otherwise successful aerial eradication, most probably due to a deliberate human intervention (Sposimo et al. 2012, Ragionieri et al. 2013, recalling 'recent genre fiction literature' (see e.g. Simberloff 2011). ...
... Francescato et al. (2010) Re-invaded MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated repeatedly MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated repeatedly MPA Tavolara and Regione SardaSposimo et al. Rouzeau F. & Vigne J.D. (1994). ...
... The success of these early operations was usually low, due to recolonization and inadequate evaluation of the consequences of the short distance from land (the exception was: La Scola, which will have to be treated repeatedly, see below). In the second half of the period, a similar fate was again encountered on two Sardinian islets, located 170-300 metres from land, and by a single failure (due to recolonization) on a large island, Molara (Sposimo et al. 2012). ...
... The case of Molara is different and more than 1000m offshore. Rats re-appeared there in 2010, two years after an otherwise successful aerial eradication, most probably due to a deliberate human intervention (Sposimo et al. 2012, Ragionieri et al. 2013, recalling 'recent genre fiction literature' (see e.g. Simberloff 2011). ...
... Francescato et al. (2010) Re-invaded MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated repeatedly MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated MPA Tavolara and Regione SardaSposimo et al. (2012) Eradicated repeatedly MPA Tavolara and Regione SardaSposimo et al. Rouzeau F. & Vigne J.D. (1994). ...
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CONSERVATION OF MARINE AND COASTAL BIRDS IN THE MEDITERRANEAN PROCEEDINGS OF THE UNEP-MAP - RAC/SPA SYMPOSIUM, HAMMAMET - TUNISIA - 20 TO 22 FEBRUARY 2015
... The success of these early operations was usually low, due to recolonization and inadequate evaluation of the consequences of the short distance from land (the exception was: La Scola, which will have to be treated repeatedly, see below). In the second half of the period, a similar fate was again encountered on two Sardinian islets, located 170-300 metres from land, and by a single failure (due to recolonization) on a large island, Molara (Sposimo et al. 2012). ...
... The case of Molara is different and more than 1000m offshore. Rats re-appeared there in 2010, two years after an otherwise successful aerial eradication, most probably due to a deliberate human intervention (Sposimo et al. 2012, Ragionieri et al. 2013, recalling 'recent genre fiction literature' (see e.g. Simberloff 2011). ...
Conference Paper
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A review of all the eradication projects involving Rattus rattus that have been carried out since 1999 on 14 Italian islands is presented. Data on different aspects related to the problem of rats on these islands are discussed, ranging from impact and benefit quantification, eradication methods and outcomes, to social problems such as lack of public awareness. A model aimed at identifying priority islands where eradication should be carried out was developed according to available budgets, an exercise that is worth extending throughout the Mediterranean.
... On the larger, more rugged islands of Molara (2008: Sposimo et al. 2012 ) and Montecristo (2012: Sposimo 2014 ) with foot inaccessible areas, such as steep areas or cliffs, bait was delivered by broadcast buckets suspended under a helicopter, and bait stations were used sporadically. ...
... Genetic analyses highlighted the difference between eradicated population and the new invaders, thus supporting the evidence of a successful eradication, and indicated that reinvasion may be caused by a rat exchange between the Molara Island and Sardinia mainland populations (Ragionieri et al. 2013 ). The considerable distance from the mainland (more than 1000 m) led us to exclude the possibility that rats may have reached the island by swimming (Russell et al. 2008 ), thus hypothesizing that reinvasion was probably driven by humans (Ragionieri et al. 2013 ;Sposimo et al. 2012 ). At Barrettini (Sardinia, distant 700 m from the nearest island), we recorded a black rat reinvasion at least 12 years after from its natural extinction (Baccetti, pers. ...
Chapter
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The black rat (Rattus rattus) is thought to be the most widespread mammal on Mediterranean islands. In recent years, many field studies have documented its detrimental impact on native species, communities and ecosystems. In order to restore island ecosystems by eliminating the impacts of black rat, several projects have been planned and implemented during the last 15 years on Italian islands. Although these projects were specifically aimed at protecting nesting shearwaters Calonectris diomedea and Puffinus yelkouan from rat predation, they were also planned in order to provide benefits to other island ecosystem components, species and communities. Rats were eradicated from small islands (about 1 ha of surface) to very large islands (over 1000 ha, i.e. Montecristo). Monitoring programmes showed that shearwater reproductive success increased after rat eradication. During these years, we obtained data on different aspects related to the problem of rat impact and control on islands: (1) rat impact on target species; (2) benefits for native species from rat removal; (3) field techniques and bait delivery methods; (4) impact of rodenticides on non-target species; (5) rat abundance, home range and movements and (6) rat reinvasion after eradication. Furthermore, we developed a model aimed at identifying priority islands where rat eradication should be carried out, and/or establish recommended actions.
... Parkes et al. 2011). È stato utilizzato un apposito bucket (distributore di esche), gentilmente fornito dall'Area Marina Protetta Tavolara -Punta Coda Cavallo, che lo aveva acquistato nel 2008 in Nuova Zelanda per l'eradicazione dei ratti nell'isola di Molara (Sposimo et al. 2012). È stato utilizzato inoltre un apposito sistema di controllo della distribuzione di esche GPS based, anche questo realizzato in Nuova Zelanda, che permette la distribuzione solo quando sono rispettati una serie di parametri (elicottero in movimento nell'area target, in corrispondenza o entro una distanza predefinita da uno dei transetti previsti nel piano di volo, purché non già percorso). ...
... effort on the island of Molara (Sposimo et al. 2012. Rat eradication at Yelkouan Shearwater Puffinus yelkouan colonies on NE Sardinian Islands: success followed by unexplained re-appearance. ...
Technical Report
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Eradicazione di componenti florofaunistiche aliene invasive e tutela di specie e habitat nell'Arcipelago Toscano Eradication of invasive alien plants and animals and protection of native species and habitats in the Tuscan Archipelago DOCUMENTI TECNICI
... The Sardinian key-site of Tavolara-Punta Coda Cavallo Marine Protected Area hosts the largest known breeding population of the species, estimated at 9,991-13,424 pairs (Zenatello et al., 2006) which, considering the most recent population estimates (Gaudard, 2018), could represent up to 55% of the global breeding population. Conservation actions in this area in the last decades consisted of rat eradication attempts on Molara island (Ragionieri et al., 2013;Sposimo et al., 2012aSposimo et al., , 2012b and in the successful deratization of Tavolara island (http://www.lifep uffin ustav olara.it) in 2008 and 2017, respectively. ...
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Pelagic seabirds are tied to their breeding colonies throughout their long‐lasting breeding season, but at the same time, they have to feed in a highly dynamic marine environment where prey abundance and availability rapidly change across space and seasons. Here, we describe the foraging movements of yelkouan shearwater Puffinus yelkouan, a seabird endemic to the Mediterranean Sea that spends its entire life cycle within this enclosed basin and whose future conservation is intimately linked to human‐driven and climatic changes affecting the sea. The aim was to understand the main factors underlying the choice of foraging locations during the reproductive phases. A total of 34 foraging trips were obtained from 21 breeding adults tagged and tracked on Tavolara Archipelago (N Sardinia, Italy). This is the largest and most important breeding area for the species, accounting for more than 50% of the world population. The relationships between foraging movements during two different breeding stages and the seasonal changes of primary productivity at sea were modeled. Movements appeared to be addressed toward inshore (<20 km), highly productive, and relatively shallow (<200 m) foraging areas, often in front of river mouths and at great distances from the colony. During incubation, the Bonifacio Strait and other coastal areas close to North and West Sardinia were the most preferred locations (up to 247 km from the colony). During the chick‐rearing phase, some individuals reached areas placed at greater distances from the colony (up to 579 km), aiming at food‐rich hotspots placed as far north as the Gulf of Lion (France). The need for such long distance and long‐lasting foraging trips is hypothesized to be related to unfavorable conditions on the less productive (and already depleted) Sardinian waters.
Chapter
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Introduced black rats (Rattus rattus) have decimated the seabird colonies on Saint-Paul Island (Southern Indian Ocean). Only six of the 13 seabird species originally breeding on Saint-Paul are now represented by only a few individuals confined to an islet located 150 m from the main island. This led us to believe that recolonisation was possible on Saint-Paul Island if all rats were removed from it. The Administration of Terres Australes et Antarctiques Françaises decided to eradicate rats and part of the funding was provided by the European Development Fund. Two preliminary trials were conducted in 1995 and 1996, and in January 1997 13.5 tonnes of brodifacoum bait (Pestoff Rodent Bait) were spread by helicopter. The island was intensively checked for rat presence during three months after the drop and during two more follow-up operations in late 1997 and early 1999, when respectively 48, 18 and five rabbits (Oryctolagus cuniculus) were killed. We are now confident that black rats are eradicated but eradication of rabbits still needs to be confirmed. Mice were not eradicated, presumably due to lack of good cover of baits, linked to spreader malfunction. The Saint-Paul Island project demonstrates the efficiency of the aerial technique against rats, but shows that rabbit eradication needs a more sustained effort. Breeding of endemic Macgillivray's prion (Pachyptila macgillivrayi) and of great winged petrels (Pterodroma macroptera) has already begun on Saint-Paul Island.
Conference Paper
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An ongoing monitoring programme allowed the re-assessment of the population size of Yelkouan Shearwater Puffinus yelkouan breeding at Tavolara (Sardinia, Italy), the largest world colony of this species. Results point at 9,991-13,424 breeding pairs, obtained by afternoon counts from land of birds approaching the colony and confirmed by the census of ground plots. Feeding areas of breeding adults, investigated with GPS loggers, stretch for some hundred kilometres and are mostly located at coastal gulfs of N and W Sardinia and SW Corsica, between Oristano, Ajaccio and the Maddalena archipelago. Counts from land suggest that the Orosei Gulf, in E Sardinia, might also be used.
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We review and update available information on the population size and distribution of Cory's Shearwater, Calonectris diomedea, and Yelkouan Shearwater, Puffinus yelkouan, in Italy. More than 90% of the population of these species rely on 64 islands, but the former breeds on twice as many islands as the latter. Some cases of local extinction were recorded. The analysis of distributions, along with that of island featu-res and presence of rats, showed inter-specific differences. The Yelkouan Shearwater tends to occupy larger and more offshore islands than the other species does. It's the only one that shows a clear positive correlation between abundance and island size. Finally, it is not present in rat-free islands, with a single exception of no quantitative relevance. Available data on the breeding success of both species are presented; comple-te failures where rats occur were recorded. Operations of rat control or eradication are presented and their consequences on seabirds' breeding success commented.
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In this paper, we review and analyse how three species of invasive rat (Rattus rattus, R. norvegicus and R. exulans) disperse to and invade New Zealand offshore islands. We also discuss the methods used to detect and prevent the arrival of rats on islands. All species of invasive rat can be transported by ship. However, rats can also swim to islands. Swimming ability varies greatly between individual rats, and is probably a learned trait; it is unlikely to be affected by variation in sea temperature in this region. Norway rats (R. norvegicus) are the best swimmers and regularly swim up to 1 km. Therefore, to prevent recurrent swimming invasions of islands, source populations may need to be controlled. Since islands differ in their attributes and individual rats differ in their behaviours, multiple devices need to be used to detect and prevent the invasion of islands, including poisons, traps, passive detection devices and trained dogs. In New Zealand, 85% of rat incursions have been successfully intercepted using traps and/or poisons. Any response should cover at least a 1-km radius around the point of incursion. If trapping, it is recommended that jaw traps are used. If using poison, it is recommended that hand-spread, short-life, highly palatable bait of the maximum permissible toxin concentration in small pellet form is used; if bait stations are used, large wooden tunnels that have a line of sight through them are recommended. To intercept invasions early, it is recommended that island surveillance is undertaken at least annually (preferably every 6 months).
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Breeding success of 5 Cory's shearwater Calonectris diomedea sub-colonies of Lavezzu Island (Lavezzi Archipelago, Corsica) was checked annually for 25 consecutive years from 1979 to 2004. Between 1989 and 1994, 4 ship rat Rattus rattus controls were performed in several sub- colonies. In November 2000, rats were eradicated from Lavezzu Island and its 16 peripheral islets (85 ha) using traps then toxic baits. We compare cost (number of person-hours required in the field) and benefit (Cory's shearwater breeding success) of control and eradication. The average breeding success doubled when rats were controlled or eradicated (0.82) compared to the situation without rat management (0.45). Moreover, the average breeding success after eradication (0.86) was signifi- cantly (11%) higher than after rat controls (0.75). Furthermore, the great variation in breeding suc- cess recorded among sub-colonies both with and without rat control declined dramatically after eradication, suggesting that rats had a major impact on breeding success. The estimated effort needed to perform eradication and checking of the permanent bait-station system during the year fol- lowing eradication was 1360 person-hours. In contrast, rat control was estimated to require 240 or 1440 person-hours per year when implemented by trained and untrained staff, respectively. Within 6 yr, eradication cost is lower than control cost performed by untrained staff and confers several eco- logical advantages on more ecosystem components than Cory's shearwater alone. Improved eradi- cation tools such as hand or aerial broadcasting of toxic baits instead of the fairly labour-intensive eradication strategy we used would dramatically increase the economic advantage of eradication vs. control. Therefore, when feasible, we recommend eradication rather than control of non-native rat populations. Nevertheless, control remains a useful management tool when eradication is not practicable.
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Tiritiri Matangi Island (220 ha) is 25 km north of Auckland City in the Hauraki Gulf. Pacific rats, or kiore, (Rattus exulans) were probably introduced to this island between 1100 and 1800 A.D. The impacts of Pacific rats on this ecosystem are not known, but from studies at other locations they were presumed to be detrimental to natural processes. Until 1984 the natural ecosystem was also degraded by removal of forest cover and pastoral farming. Restoration of the natural environment on this island began in 1984. Some 300,000 native trees have been planted and nine species of native bird translocated to the island. Pacific rats were removed in September 1993 with use of an aerial application of Talon 20P rodent bait. Specific actions were taken during this operation to protect identified potential non-target species where the population was considered at risk. Monitoring methods following the operation are de-scribed. There has been no rat sign found since the aerial operation.