BreedingofCory's shearwater Calonectris borealison Selvagem Grande and beneficial effects of removal of invasive mammals
F. ZIN O,
M.BIS C O I T O and A. BUCKLE
Abstract The largest colony of Cory’s shearwater Calonectris borealis nests on the island of Selvagem Grande in the north-eastern Atlantic. In 2002,a pro- gramme of eradication was conducted to remove two alien invasive mammals, the house mouse Mus musculus and European rabbit Oryctolagus
cuniculus.Preliminary studies recorded beneficial effects of the eradications for a variety of plant and animal species, including Cory’s shearwater. We recorded fledging rates of shearwaters for 1982–2001, prior to the eradication, and for 2002–2020, after the eradication, from two quadrats, each containing 134–329 nest sites. Although there was annual fluctuation in fledging rates in the quadrats, the mean rate of 40.74 ± SD 3.92 fledglings per 100 nest sites for the two quadrats combined prior to the eradication of mammals increased significantly, to 52.88 ± SD 5.03 per 100 nest sites, after the eradications. Because the two mammals were removed synchronously it is difficult to know which factors de- pressed fledging of Cory’sshearwatersonSelvagem Grande. However, the predatory behaviour of house mice on other oceanic islands, and the fact that increased fledg- ing was seen soon after the eradications occurred, suggest predation by house mice on shearwater hatchlings was the main cause of losses.
Keywords Alien invasive species, Calonectris borealis, Cory’s shearwater, European rabbit, house mouse, Mus musculus, Oryctolagus cuniculus, Selvagem Grande
Introduction T
he Cory’s shearwater Calonectris borealis colony on the Portuguese island of Selvagem Grande has been the
subject of study since the first scientific expedition to the island in 1963 (Pickering & Maul, 1965). Although catego- rized on the IUCN Red List as Least Concern (BirdLife
F. ZINO (Corresponding author,
orcid.org/0000-0001-9309-0786)
Freira Conservation Project, Rua Dr. Pita 7, 9000-089 Funchal, Madeira, Portugal. E-mail
fzino@netmadeira.com
M. BISCOITO (
orcid.org/0000-0002-9347-0823) Museu de História Natural do Funchal, Madeira, Portugal
A. BUCKLE (
orcid.org/0000-0002-5449-9279) School of Biological Sciences, The University of Reading, Reading, UK
Received 19 January 2021. Revision requested 6 April 2021. Accepted 5 May 2021. First published online 28 October 2021.
International, 2018), Cory’s shearwater is a Species of European Conservation Concern, category 2 (concentrated in Europe) with a threat status of depleted (BirdLife International, 2017). The Selvagem Grande population has been estimated to be 29,450 breeding pairs and therefore comprises the largest breeding colony of this seabird (Granadeiro et al., 2006). This is considerably less than the 130,000–150,000 breeding pairs formerly believed to have bred on the island (Mougin &Mougin, 2000). The de- clinewas caused by intensive culling of chicks and adults for meat, oil and feathers by local fishermen (Zino, 1985). To halt this culling, Paul A. Zino (father of FZ) bought the cul- ling rights in 1967 and built a small house on the island to support scientific study. This effectively turned the island into a wardened private nature reserve until it was made an official Nature Reserve by the Portuguese government in 1971, but wardening ceased and illegal killing resumed, with the indiscriminate slaughter in 1976 resulting in an estimated 8,000 breeding pairs in 1980 (Zino, 1985). Since 1981, Selvagem Grande has been wardened byMadeiran in- stitutions, including latterly the Instituto das Florestas e Conservação da Natureza (previously Parque Natural da Madeira). This has resulted in an increase in the population of Cory’s shearwaters of c. 5%per annum (Granadeiro et al., 2006). The breeding biology of Cory’s shearwater on Selvagem
Grande is well studied (Zino, 1971; Zino et al., 1987, 1991; Mougin & Jouanin, 1997; Mougin, 2000; Mougin et al., 2000; Mougin & Mougin, 2000) and the breeding cycle is consistent from year to year. Birds start to return to the is- land in early February, with numbers increasing through to March. Mating occurs mainly in April and egg-laying during late May–mid June (Zino et al., 1987; Thibault et al., 1997). Immediately after the female lays the single egg, the male takes over incubation but thereafter they incu- bate alternately. Incubation is 54 days and eggs hatch mid July–early August (Zino, 1971; Zino et al., 1987). Parent birds remain at the nest for 3–4 days after hatching, leaving chicks at risk of predation thereafter by the Madeiran wall lizard Teira dugesii selvagensis (Matias et al., 2009), yellow- legged gull Larus michahellis and, formerly, house mice Mus musculus (F. Zino, pers. obs., 1963–2008). Adults make long journeys, as far as the coast ofMauritania (F. Zino, unpubl. data, 1996), to obtain food for their young. Chicks reach maximum weight in September, which is when culling pre- viously occurred, some reaching almost double their adult
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Oryx, 2022, 56(6), 927–934 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321000661
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164
