The dog and cat population on Maio Island, Cape Verde

Antunes, A. C. L., Ducheyne, E., Bryssinckx, W., Vieira, S., Malta, M., Vaz, Y., Nunez, T. & Mintiens, K. (2015). The dog and cat population on Maio Island, Cape Verde: characterisation and prediction based on household survey and remotely sensed imagery. Geospatial Health, 10(2).

The objective was to estimate and characterise the dog and cat population on Maio Island, Cape Verde. Remotely sensed imagery was used to document the number of houses across the island and a household survey was carried out in six administrative areas recording the location of each animal using a global positioning system instrument. Linear statistical models were applied to predict the dog and cat populations based on the number of houses found and according to various levels of data aggregation. In the surveyed localities, a total of 457 dogs and 306 cats were found. The majority of animals had owners and only a few had free access to outdoor activities. The estimated population size was 531 dogs [95% confidence interval (CI): 453-609] and 354 cats (95% CI: 275-431). Stray animals were not a concern on the island in contrast to the rest of the country

Cats as predators of endangered bats

Rocha, R. 2015. Look what the cat dragged in: Felis silvestris catus as predators of insular bats and instance of predation on the endangered Pipistrellus enmaderes. Barbastella 8 (1) .

This note reports the predation of a threatened Madeira pipistrelle bat by a domestic house cat. This represents the first confirmed record of cat predation upon a Macaronesian bat and adds to an increasing body of evidence suggesting that free-ranging cats pose a strong negative impact to native insular vertebrate populations.

Cat predation on Zino's petrel

Zino, F. (1992). Cat amongst the freiras. Oryx, 26(03), 174-174.

A further threat to Pterodroma madeira was identified in 1991 when feral cats killed 10 petrels on a single ledge

Indirect dispersal of seeds by lizard-preying cats

Nogales, M., Medina, F. M., & Valido, A. (1996). Indirect seed dispersal by the feral cats Felis catus in island ecosystems (Canary Islands). Ecography, 19(1), 3-6.

In this paper we present an unusual incidence of an introduced Camivora Felis catus as indirect seed disperser of plants that produce fleshy fruits in different ecosystems in the Canary Islands. Four hundred and twenty six seeds from at least 8 fleshy fruit plant species have been identified in the analysis of 1047 scat groups, the majority of them being found in the lower habitats (<600 m a.s.l.) of the Canary archipelago. Seeds from two plant species were significantly matched with the presence of lizard prey, and fruits of Juniperus phoenicea, Neochamaelea pulverulenta and Withania aristata were directly consumed by the cats. Passing through the gut of the Gallotia galloti(Lacertidae) and Felis catus apparently does not damage the seeds. At the moment, the phenomenon studied in this paper does not seem to have a great quantitative importance in the natural regeneration of the plants if we compare the direct vs indirect seed dispersal.

Conservation of Zino petrel

Zino F. et al. (2001) Conservation of Zino's petrel Pterodroma madeira in the archipelago of Madeira. Oryx, 35, 128-136.

Birds restricted to islands are susceptible to extinction, and burrow or ground-nesting birds are particularly vulnerable to introduced mammalian predators. Human intervention has also played a vital part. Birds have been used as a source of food, and in more recent times the rarer species have suffered from specimen and egg collection. The island of Madeira and its resident species, which include the endemic Zino's petrel or Madeira freira Pterodroma madeira, are no exception. From subfossil evidence, this bird was once abundant. It was first recorded in 1903, and was already limited to the high central mountain massif of Madeira. By the middle of the century it was considered extinct, but a relict population was rediscovered in 1969. By 1985, all known breeding attempts were disrupted by introduced rats, to the extent that no young fledged. In 1986 the Freira Conservation Project was founded with the aim of increasing the population of Zino's petrel, by controlling rats and human interference, the principal perceived threats to the species. This control was extended to cats after the disaster of 1991, in which a cat(s) managed to get onto one of the breeding ledges and kill 10 adult birds. The results of these efforts have been positive and the small colony is making a slow, but steady recovery. To maintain this success, a conservation strategy for the future is suggested.

Cat diet in Macaronesia (Atlantic Ocean)

More than a dozen of papers describing the diet of feral cats on most of Macaronesian islands (Cape Verde, Canary Island and Madeira), Atlantic Ocean.
Although exotic mammals represent an important proportion of their  diet, native species suffer a strong impact from cat's predation.

Macaronesia

1 Medina F. M., Oliveira P., Menezes D., Teixeira S., García R. & Nogales M. 2010. Trophic habits of feral cats in the high mountain shrublands of the Macaronesian islands (NW Africa, Atlantic Ocean). Acta Theriologica 55: 241–250.
Feral cats Felis catus Linnaeus, 1758 have contributed to the extinction of numerous native species on islands, which are clearly sources of global biodiversity. We studied the diet of this introduced predator in the Madeira and Cape Verde archipelagos, which harbour important colonies of endangered sea birds in the high mountain habitats, and compared the results with those obtained in the same habitat in the Canary Islands, Macaronesian archipelago. On Madeira, 461 prey were iden ti fied from 143 scat groups. Mammals, over all mice, constituted the basic diet appearing in 95% of cat scats. On Fogo (Cape Verde), 657 prey items were obtained from 145 scats, and mammals were also the most important prey, reaching a frequency of occurrence of 88%. Although introduced mammals were the main prey category on all Macaronesian islands, we observed variation in feral cat diet among these is lands. Birds were more frequently consumed on Madeira, lizards on Tenerife (Canaries) and invertebrates on Fogo. No specific differences were observed in relation to La Palma.We suggest that the diet composition on these islands varies according to the respective availability of the different prey types.

Canary Islands

2 Nogales, M., A. Martín, G. Delgado & K. Emmerson. 1988. Food spectrum of the feral cat (Felis catus L., 1758) in the juniper woodland on El Hierro (Canary Islands). Bonner Zoologische Beiträge 39: 1-6.
The diet of feral cats inhabiting a juniper woodland on the island of El Hierro (Canary Islands) has been studied by analyzing 248 scats. A total of 1029 prey items have been identified indicating that the introduced mammals (Oryctolagus cuniculus, Mus sp. and Rattus sp.) constitute the basis of the diet appearing in 88.3 % of the samples and representing 85.4 % of the consumed biomass. Mus sp. is the most frequently captured prey but in terms of biomass. Mus sp. is the most frequently captured prey but in terms of biomass, Oryctolagus cuniculus is the fundamental bais of the diet as has similarly been found in other areas studied. Birds can be regarded as alternative prey resources of some importance though they only account for 8 % of the biomass with Cory's shearwater (Calonectris diomedea), contributing practically half this value. Reptiles appear in 44.3 % of the scats but only represent 5.9 % of the biomass, Gallotia galloti caesaris being the most frequently captured species (64.1 %). Insects, (mainly Orthoptera & Coleoptera), despite their high frequency of apparition (45.5 % of scat groups), are insignificant due to their small size, though worthy of note is the large number of larvas of Pimelia laevigata.

3 Nogales, M., M. Abdola, C. Alonso & V. Quilis. 1990. Premiêres données sur l’alimentation du chat haret (Felis catus L., 1758) du Parc National du Teide. Ténérife (Iles Canaries) Mammalia, 54: 189-196. 

Le régime alimentaire du chat haret (Felis catus) est étudié à partir de 221 groupes d'excréments (environ 600 excréments) collectés dans le Parc National du Teide (Ténérife), apportant ainsi des données sur les proies capturées, leur fréquence d'apparition dans les groupes d'excréments et leur biomase. De l'étude de ce matériel on dégage que le régime se compose surtout d'Oryctolagus cuniculus, qui représente une biomasse de 64,4% et une fréquence d'apparition de 53,8%, et de reptiles (Principalement de Gallotia galloti, lézard endémiques des iles Canaries occidentales) avec 74,2%, une fréquence d'apparition en groupes de 74,2% et une biomasse de 20,6%.

In this paper we present preliminary data concerning the food spectrum on the feral cat in the Teide National Park on Tenerife. After having analysed 221 scats, 523 prey items have been identified. Rabbits (Oryctolagus cuniculus) are the fundamental base of the diet (frecuency of apparition 53,8% and biomass 65,4%) as has been similarly found in other areas studied. Also, reptiles (principally Gallotia galloti, an endemic lizard on the Western Canary Islands) was frequently captured, appearing in 74,2% of the scats groups and representing 20,6% of the total biomass.

4 Nogales, M., J.L. Rodríguez, G. Delgado, V. Quilis & O. Trujillo. 1992. The diet of feral cats (Felis catus) on Alegranza Island (North of Lanzarote, Canary Islands). Folia Zoologica 4: 209-212.
The diet of feral cats on Alegranza has been studied by analyzing 110 scats. A total of 199 prey items have been identified indicating that introduced mammals (Oryctolagus cuniculus and Mus sp.) constitute the basis of the diet appearing in 100 of the samples and representing 99,5% of the consumed biomass, Fortunately, it appears that breeding seabirds are not represented in their diet. However the species constitutes a potential threat to the birds if its present prey declines in number.

5 Nogales, M. & F.M. Medina. 1996. A review of the diet of feral domestic cats (Felis silvestris f. catus) on the Canary Islands, with new data from the laurel forest of La Gomera. Zeitschrift für Säugetierkunde 61: 1-6. 

In this study we present a review on the diet of the feral cat on the Canary archipelago, providing the first data from the reliet laurel forest (Garajonay National Park). Among the 403 prey items identified in this habitat, rats were most numerous followed by reptiles. A total of 1.047 scat groups has been studied in the lat eight years from the main habitats of the Canaries. Most of the 2.963 prey items identified represent introduced mammals (rabbit, Oryctolagus cuniculus; mouse, Muscf. musculus and rat, Rattus sp.). These prey were commonly captured in most habitats with the exception of high mountain scrub. In this habitat, reptiles were taken instead introduced mammals. They were also more commonly included in the diet from open ground and open forest than from the denser forest. Birds were more frecuently consumed in the forest than in open areas. Anthropods appeared in significant proportions in the scats from habitats where these items reached high numbers. The results indicate that the diet of feral cats clearly varies according to the different habitats.

6 Medina, F.M., R. García & M. Nogales, 2006. Feeding ecology of feral cats on a heterogeneous subtropical oceanic island (La Palma, Canarian Archipelago). Acta Theriologica 51: 75−83.
We found a total of 987 prey in the 500 scats of feral cats Felis silvestris catus Linnaeus, 1758 analyzed in the present study. Introduced mammals (rabbits, rats and mice) constituted the most important prey both in percentage and biomass. Reptiles were the second most important prey, being more frequent than birds and inver te brates. Mammals were the most frequently eaten group in all five main habitats of the island, being more frequent than the remainder of prey in the laurel forest. Rabbits appeared more often in the temperate forest, rats in the laurel forest and mice in the high mountain. Birds were more frequently captured in the three higher habitats (laurel and pine forest, and high mountain) than in the two lower ones (xerophytic shrub and temperate forest). Reptiles were preyed on less in the laurel forest than in the other main habitats. Morisita index indicates a high trophic overlap among the different habitats with the exception of the laurel forest which shows important differences from the other habitats. Levin’s niche-breadth was broader in the xerophytic shrub and narrower in the temperate forest, reaching in ter mediate levels in the other three main habitats. The results obtained in the present study evidence a general pattern in the trophic ecology among similar habitats in the different subtropical Canarian islands. However, some important differences exist that could be a function of the differential prey availability and composition in each ecosys tem.

7 Medina, F.M. & R. García. 2007. Predation of insects by feral cats (Felis silvestris catus L., 1758) on an oceanic island (La Palma, Canary Islands). Journal of Insect Conservation 11: 203-207.

Predation of insects by feral cats (Felis silvestris catus) on a heterogeneous oceanic island (La Palma, Canary Islands) was studied. A total of 127 invertebrates were identified in the analysis of 500 scats (100 from each habitat of the Island). Invertebrates appear in 18.00% of the scats, representing an insignificant percentage of the total consumed biomass by feral cats on La Palma Island (0.05%). Insects were the most common invertebrate prey both in percentage of occurrence (90.6%) and invertebrate biomass (93.53%), with a total of 115 prey items. Orthoptera, Lepidoptera and Coleoptera were the main prey groups. Among the five main habitats present in La Palma Island, the temperate forest shows the lowest consumption of invertebrates, although insect consumption did not show statistical differences. However Orthoptera and Lepidoptera were more frequently preyed on in the pine forest and in the xerophytic shrub, respectively. Moreover, applying the Simplified Morisita index, a different insect composition of the diet was observed among habitats. Although, none of insects predated by feral cats are threatened, the identification of invertebrate component of the feral cats’ diet is an important tool for the correct understanding of predation significance and to prevent damage to endangered insect species.

8 Medina, F.M. & M. Nogales. 2009. A review on the impacts of feral cats (Felis silvestris catus) in the Canary Islands: implications for the conservation of its endangered fauna. Biodiversity and Conservation 18: 829-846.
Feral cats have been directly responsible for the extinction of numerous species on islands worldwide, including endemic species of mammals, birds and reptiles. The diet of feral cats in the main habitats of the Canary Islands, as generally occurred on oceanic islands, is mainly composed of introduced mammals, and native species of birds, reptiles and insects. The impact of feral cat upon the endangered species was assessed by evaluating their relative abundance in the cats’ diet and by considering their current conservation status. A total of 68 different preys were identified at species level in all studies carried out in the Canary Islands (5 mammals, 16 birds, 15 reptiles and 32 invertebrates). From all the species preyed by feral cats in the Canary Islands, only four of them are considered threatened by the IUCN Red List of Threatened Species: one endemic bird Saxicola dacotiae and three endemic giant lizards, Gallotia simonyi, Gallotia intermedia, and Gallotia gomerana. Although some efforts on management control have been carried out, it is necessary to enforce these conservation activities on those areas of Tenerife, La Gomera and El Hierro where giant lizards are still present. Furthermore some local areas where endangered bird species are highly predated should be protected. Nevertheless, it is important to take into account the presence of other introduced species such as rats, mice or rabbits in order to avoid problems derived from the hyperpredation process and mesopredator release effect.

9 Nogales, M. & F.M. Medina. 2009. Trophic ecology of feral cats (Felis silvestris f. catus) in the main environments of an oceanic archipelago (Canary Islands): An updated approach. Mammalian Biology 74: 169-181. 
The diet of feral cats in the main habitats of the Canary Islands is composed of introduced mammals, birds, reptiles and insects. However, introduced mammals constitute the main source of biomass consumed, followed in importance by reptiles and birds. PCA analysis of biomass revealed the ordination of three different groups, corresponding to the diet in the laurel forest (La Gomera), thermophilous forest (El Hierro) and one large group that include the rest of habitat types. A similar pattern was observed when these habitats were analyzed in a single island (La Palma). Oryctolagus cuniculus was an important prey in practically all habitats, while Rattus rattus was frequently captured in the laurel forest, Mus musculus domesticus in the open shrubs (both xeric and high mountain), reptiles (mainly lizards genus Gallotia) in the open habitats of Tenerife, birds play a relative role in forest habitats, and large invertabrates (basically Orthoptera and Coleoptera) in the three forest habitats and in the xerophytic shrub of Fuerteventura. Morisita’s index of similarity of diet showed maximum differences between the forest habitats (pine and thermophilous vs. laurel forest), indicating an important heterogeneity in the diet of feral cats in these environments. Shrub habitats showed smaller values of Levin’s niche breadth than those from the forest habitats, showing a broader diet in the latter. Lastly, the diet of feral cats on the Canary Islands follows the general pattern of other islands located at similar latitude and mainly composed by rabbits and mice. However, specific preys such as lizards, rats or birds, play an important role in particular habitats in which they are abundant.

10 Medina, F.M. & M. Nogales. 2007. Habitat use of feral cats in the main environments of an Atlantic Island (La Palma, Canary Islands). Folia Zooliga 56(3): 277–283

In this study we assess the habitat use of feral cats in the five main habitats represented on La Palma Island in the Canary Islands. We determined habitat use by the presence of faeces. Faeces persistence time was significantly different between habitats, being clearly lower in the laurel forest (the wettest) than in the other habitats. This humid environment promotes the high presence of invertebrate decomposers such as Isopoda and Diplopoda. Once the effect of differential persistence times for faeces among the different habitats was controlled for, data obtained indicated that feral cats showed no differences in the use of the five main habitats present on La Palma Island. Although cats selected closed habitats more frequently than open ones, because they prefer cover for hunting, no statistical differences were found in the island habitats studied.

11 Medina, F. M., M. López-Darias & M. Nogales. 2008. Food habits of feral cats (Felis sylvestris f. catus, L. 1758) in insular semiarid environments (Fuerteventura, Canary Islands). Wildlife Research 35: 162-169.
In this study, we present the first data on diet and impacts of feral cats on a semiarid island (Fuerteventura, Canary Islands). A total of 614 prey was identified in the 209 scats analysed. Introduced mammals, specially rabbits and mice, were the most consumed vertebrate prey and constituted more than 90% of biomass. Barbary ground squirrels, Algerian hedgehogs, and rats were preyed upon less even though they were abundant on the island. Invertebrates, mainly Orthoptera, Coleoptera, Hymenoptera and Odonata, were the second most important prey items (in terms of actual numbers) but they contributed only minimally with respect to biomass (<1.1%). The presence of terrestrial molluscs in the diet was interesting because they are a rare prey in an insular context. Birds and reptiles occurred at a low frequency. A total of 677 seeds was counted, mainly belonging to Lycium intricatum (Solanaceae) and two unidentified plant species. Levin’s niche breadth was narrow due to the high consumption of mammals. Morisita’s index showed a similar trophic overlap in diet with respect to the other xeric habitats of the Canarian archipelago. Considering that more than 90% of biomass corresponded to introduced mammals, we conclude that feral cats are not having a large direct impact on the native prey species.

12 Medina, F.M. y M. Nogales. 1993. Diet of the feral cat (Felis catus L.) in the xerophytic zone of the Macizo de Teno (Northwestern Tenerife. Doñana Acta Vertebrata, 20 (2): 291-297

The diet of the Feral cat (Felis catus) was studied in the xerophytic zone of Tenerife, by analyzing 200 scats. A total of 477 prey items were identified. Mammals (Oryctolagus cuniculus, Mus musculus and Rattus  sp.) constitued the basis of the diet occurring in 86% of the samples and representing 85,4% of the consumed biomass. Reptiles occurred in 57% of the scats and representing 13,6% of the biomass. The lizard (Gallotia galloti), endemic of the western Canary Islands, was frequenetly captured, occurring in 54% of the scat groups and representing 13% of the total biomass. This percentage is very importan in the world context of the diet. Birds and insects (frequence of occurrence less than 5%) were insignificant in the diet.


Cabo Verde
13 Medina, F. M., P. Oliveira, P. Geraldes, J. Melo & N. Barros. 2012. Diet of feral cats Felis catus L., 1758 on Santa Luzia, Cape Verde Islands. Zoologia Caboverdiana 3 (2): 67-73.

The diet of feral cats Felis catus on Santa Luzia, Cape Verde Islands, was studied. A total of 147 prey items were identified during the analysis of 26 scat groups collected during the summer of 2010. House mouse Mus musculus was the most important prey, both in percentage of biomass and number of preys consumed (89.7% and n= 117, respectively). Reptiles were the second most important prey, represented by one skink species (Chioninia stangeri) and an unidentified gecko species. The remainder of the identified prey consisted of one bird species (Passer iagoensis) and one undetermined Tettigoniidae species (Insecta). No endangered species were identified in scats of this introduced predator, but future surveys must be carried out to further avoid threats to the island’s biodiversity. 

Estimating feral cats density on Corvo island (Azores)

Oppel, S., , Hervias, S., Oliveira, N., Pipa, T., Cowen, H., Silva, C., Geraldes, P., 2012 Estimating feral cat density on Corvo island, Azores, to assess the feasability of feral cat eradication. Airo, 22: 3-11.

Feral cats have had negative effects on native biodiversity on many islands worldwide. Eradicating feral cats from islands is often feasible, and can yield great benefits to native biodiversity, especially for seabirds. Corvo Island (Azores) is an important island where feral cats limit the distribution and abundance of breeding seabirds. To assess whether the eradication of feral cats on Corvo would be feasible we used camera traps to estimate the density of feral cats. We deployed 24 camera traps at 253 locations around the island for 14 months, and identified cats detected by camera traps individually based on the coat colour. We then used spatially explicit capturere-capture models to estimate cat density for Corvo. Cat density in the uninhabited upland part of Corvo, which is dominated by cow pastures, was 0.036 (95% CI 0.025–0.054) cats/ha. The lowland part of Corvo, which is inhabited by humans and contains domestic cats, had an estimated cat density of 0.734 (0.581 – 0.927) cats/ha. Overall, we estimated that the cat population on Corvo during our study period included 163 (123 - 228) individuals. The estimated cat densities are within the range of cat densities from other islands where cats have been successfully eradicated, and we conclude that feral cat eradication on Corvo would be technically feasible. However, the co-existence of feral and domestic cats would create operational challenges, and the current lack of a legal framework to ensure that all domestic cats are sterilised would increase the risk of a feral cat population becoming re-established after eradication.

Impact of alien predators on seabirds on Corvo island (Azores)

Henriques, A. C. M. (2010). Impacto dos predadores introduzidos na ilha do Corvo no sucesso reprodutor das populações de cagarro (Calonectris diomedea borealis) (Doctoral dissertation, Universidade Técnica de Lisboa) (in Portuguese with English abstracts).

In the Corvo island, Azores, there are important species of seabirds classified as prioritary by the Annex I of the Bird Directive, for example Cory’s Shearwater Calonectris diomedea borealis, is one of the species that represents in terms of number and density the biggest expression in this archipelago in an European level. One of the major threats for the birds that reproduce in islands is the presence of predators, like rats, so, in this context, we analysed the variables that could explain the distribution of rodents, identified the accessible places of nesting of Cory’s, monitored the reproductive season and tried to understand the causes of fail in the egg and chick phase. The results point out a positive relation between rat abundance and reproductive success of Cory’s. The characteristics of the reproductive season are similar to those described for Berlengas and Selvagens, but they differ in the hatching success and chick success. We verified that in the first days of life of the chicks the predation is very significant and other variables should be taken into account, for example the predation by cats.

The Corvo Island has unique features, in terms of endemic fauna and flora, numbers of human population, introduced predators, size of the island, among others, that gave to this island the status of Biosphere Reserve. Additionally, there are important species of seabirds that only reproduce in restricted areas of Europe, and are classified as prioritary by Annex I of the Birds Directive. Nevertheless, the populations of some species are still to confirm (e.g Pterodroma feae, Oceanodroma castro) and others need more research in terms of numbers and localization of the colonies (e.g Puffinus puffinus, Puffinus assimilis). 

The more conspicuous of the seabirds here present is Cory’s Shearwater, Calonectris diomedea borealis and has the biggest expression in terms of numbers and densities in the Azores archipelago which represents 60-70% of the world population. The Corvo population is one of the major ones but the nidification areas and the actual size of the population is still not well known. One of the major causes of the decline of the seabirds, besides the fisheries, specially those ones who reproduce in cavities on the soil, are the introduced predators in islands, places that originally yield millions of seabirds. The biggest problem is that they evolved in environments that were predator free and lack defense mechanisms to face the predation of eggs and chicks by rats and cats. This causes the reproductive collapse in some species and could force the nesting places to sub-optimal conditions, that can compromise the viability of the populations. Last year, SPEA started a LIFE+ project “Safe islands for seabirds” to assess the impacts of the predators on seabirds and prepare the restoration of habitat, by ways of predator and invasive plants control and reforestation with endemic species. This project has an important ecological relevance as it can represent a important step in the developing of protocols for exotic species eradication in islands with human population, with both cats and rats as the major predators. 

The objectives of this thesis were to quantify the influence of rodents in the reproductive success of Cory’s Shearwater. We analyse the distribution of three species of rodents (Rattus rattus, R. norvegicus and Mus musculus) in different habitats and their dependence with some environmental variables. The method chosen was by means of tracking tunnels in two different seasons, one in April-May and the other in September-October, that wanted to express different food availability and different stages of the reproductive period of Cory’s in Corvo. For this analysis we decide do use an algorithmic model Random Forest for the software R 2.9.2. Our results point out the dependence of the presence of rodents with introduced anthropogenic characteristics as roads, exotic vegetation and distance to village. Also we noticed some differences between the house mice and the rats in terms of abundance and selection of habitat. 

We were able to identify different accessible colonies of Cory’s Shearwater in the island, and monitor almost 200 nests, once a week, in eight different places of Corvo. We analysed and compared times of hatching, fledging, incubation period and breeding success, with other islands (Berlenga, Selvagem Grande and others from Azores, such as Graciosa) where Cory’s shearwater reproduces, and finally we tried to understand which are the main causes of failure using the model Nest Survival for the program MARK. This program is an important ecological tool for testing different factors and the correlation between them that could influence the weekly nest survival. Also give us the weight of the model for explaining the data. 

Our results point out the synchronization of times of hatching and fledging among the different places in the Atlantic, but there’s a major difference in the hatching and fledging successes. Surprisingly the causes of failure don’t seem to be related with rat abundance, as the majority of the studies point out, ant the time with less survival probability seems to coincide with the first days after hatching when the chick is more vulnerable. Our assumption is that there is a third variable that wasn’t account for, that is influencing the abundance of rats and the reproductive success of Cory’s. This variable is the presence of cats. 

The analyse of the Life Table demonstrate the big resilience in fluctuations of the population of Cory’s Shearwater in Corvo Island, a characteristic of long lived species. 

We recommend that for the planning of the eradication protocol both cats and rats should be target of control at the same time, incorporate prioritary areas of control for rodents and to study more accurately the causes of fail that influences the seabirds success. 

Multiple predators on Corvo island

Hervías, S., A. Henriques, N. Oliveira, T. Pipa, H. Cowen, J. A. Ramos, M. Nogales, P. Geraldes, C. Silva, R. Ruiz de Ybáñez & S. Oppel. 2012. Studying the effects of multiple invasive mammals on Cory’s shearwater nest survival. Biological Invasions, DOI 10.1007/s10530-012-0274-1

The most common invasive mammals—mice, rats, and cats—have been introduced to islands around the world, where they continue to negatively affect native biodiversity. The eradication of those invasive mammals has had positive effects on many species of seabirds. However, the removal of one invasive mammal species may result in abundance changes of other species due to trophic and competitive interactions among species. Understanding the overall impact of several invasive species is a key challenge when evaluating the possible effects of eradication programmes. Here we assess the influence of the three most common invasive mammals on nest survival of Cory’s shearwater (Calonectris diomedea). We monitored six breeding colonies over 3 years and measured the activity of mice, rats and cats to examine the influence of invasive mammals on nest survival. We found that nest survival showed a similar temporal trend in all years, with lowest weekly survival probabilities shortly after chicks hatched.Cats were identified as major predators of chicks, but no measure of colony-specific cat activity was able to adequately explain variation in shearwater nest survival. Nest survival was on average 0.38 (95 % confidence interval 0.20–0.53) and varied among colonies as well as over time. We found a small positive influence of rats on nest survival, which may indicate that the presence of small rodents as alternative prey may reduce cat predation of chicks. Our findings suggest that the eradication of rodents alone may exacerbate the adverse effects of cats on shearwater nest survival.