Feral cats targeted to protect turtle hatchlings

Feral cats targeted to protect turtle hatchlings in Exmouth

By Angus Sargent 

http://www.abc.net.au/

Rangers and conservationists concerned for the welfare of turtle hatchlings have carried out a feral cat trapping program in Exmouth.

The Jurabi coastline, located on the point of the Cape Range National Park in Western Australia, is a major nesting ground for local turtle populations.

In a trapping program undertaken last week, seven cats were captured and destroyed using cages and soft jaw leg traps, designed to restrain the animals without causing any physical pain.

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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.

Adjustments to new predators in the Galapagos marine iguana

Berger, S., Wikelski, M., Romero, L. M., Kalko, E. K., & Rödl, T. (2007). Behavioral and physiological adjustments to new predators in an endemic island species, the Galapagos marine iguana. Hormones and behavior, 52(5), 653-663.

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.

Effects of feral cats on the evolution of antipredator behavior in the Aegean wall lizard

Li, B. (2012). Effects of feral cats on the evolution of antipredator behaviors in the Aegean wall lizard Podarcis erhardii (Doctoral dissertation, University of Michigan).

Exotic predators such as feral cats (Felis catus), have been the driving force behind the extinction of many endemic species of island mammals, birds and reptiles. Island endemics appear to be exceptionally susceptible to invasive predators because of small population size and frequent lack of anti-predator defenses. The goal of this study was to determine the impacts of feral cats on the island populations of Aegean Wall lizards (Podarcis erhardii, Lacertidae) in relationship to the expression of anti-predator behaviors. I estimated lizard population densities in areas with low cat density sites (LCD) versus high cat density (HCD) sites by conducting 100-m transect along dry-stone walls, on the island of Naxos, as well as on surrounding islets (Cyclades, Greece). Degree of expression of antipredator behaviors was determined by measuring flight initiation distance (FID) and rates of tail autotomy both in the field and in the lab for six populations in HCD, LCD sites and four satellite islets without cat presence. I also staged controlled encounters with mounted cats decoys and quantified escaping responses from lizards from these populations. I found that feral cats had a strong negative effect on lizard population densities. Lizards adapted their antipredator behaviors in response to cat predation by extending their FIDs, increasing their capacity for tail autotomy, and by staying closer to refugia. In laboratory predation simulations, lizards from cat-free islets had significantly shorter FIDs than LCD site lizards and in particular than HCD site lizards. Furthermore, some unique islet behaviors, presumably evolved in response to lack of predators and to ameliorate chronic conditions of food shortage, appear to render islet lizards strongly susceptible to cat predation. These behaviors include rarely utilizing available refugia, and moving towards anything new, including cat decoys. Nonetheless, I found that repeated exposures over three trials led to significant increases in FIDs for all populations, indicating at least some behavioral plasticity. My results suggest that although lizards may adapt their antipredator behaviors to cope with introduced predators, this offers at best only partial protection, so that there remains strong concern about their survival in the face of expanding feral cat populations.


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Study shows impact of feral cats on lizards in Greek Islands

 Male of Erhard's Wall Lizard (Podarcis erhardii) . 

Credit: Jeroen Speybroeck/Wikipedia

A team of researchers with diverse backgrounds from universities in the U.S. and Greece has conducted a study of the impact of feral cats on Aegean wall lizards living in the Cyclades (Greek islands). In their paper published in Proceedings of the Royal Society B: Biological Sciences, the team describes behavior adaptations they observed in native lizards to the presence of feral cats.

Feral cats are domestic cats that are living in the wild—reports over the past several years have implicated them in a number of extinctions and declines of other species, particularly birds. Another type of creature impacted by feral cats is lizards—cats are known to kill them whether they eat them or not. In this new study, the research team ventured to the Thera, Kea and Naxos islands in the Cyclades—where cats were introduced by humans approximately 9,500 years ago—to learn more about how the native lizards have adapted to the introduced threat.

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Cat eradication and the restoration of endangered iguanas on Long Cay

Mitchell, N., Haeffner, R., Veer, V., Fulford-Gardner, M., Clerveaux, W., Veitch, C. R., & Mitchell, G. (2002). Cat eradication and the restoration of endangered iguanas (Cyclura carinata) on Long Cay, Caicos bank, Turks and Caicos Islands, British West Indies. In Veitch, C. R., & Clout, M. N. (2002). Turning the Tide: The Eradication of Invasive Species: Proceedings of the International Conference on Eradication of Island Invasives,[University of Auckland, 19 to 23 February 2001] (No. 27). IUCN, 206-212.

Endangered Turks and Caicos rock iguanas (Cyclura carinata) are being displaced on Big Ambergris Cay
by an expansive development project. We chose Long Cay, Caicos Bank, as a relocation site for some iguanas because it: (1) is a large (111 ha), uninhabited, protected reserve, (2) previously supported iguanas but did not have a current population, (3) could support thousands of iguanas, and (4) had no native mammals, few scavenging birds, and no nesting colonies of scavengers. There was a small population of feral cats, well-known iguana predators. To restore the island, we conducted an intensive cat poisoning campaign using sodium monofluoroacetate (1080), in July 1999. In November 1999, a test-group of 25 iguanas was taken from Big Ambergris Cay to Long Cay. Since their successful establishment we have relocated more than 400. The first hatchlings were confirmed in January 2001. Occasional trapping may be necessary to maintain Long Cay free of cats. We have begun patrols and courtesy visits to vessels cruising the area, installed informative and cautionary signs, and produced public service announcements for TV to reinforce the importance of keeping domestic animals away from uninhabited islands.

Dog scavenging sea-turtle nests

Ruiz‐Izaguirre, E., Woersem, A., Eilers, K., Wieren, S. E., Bosch, G., Zijpp, A. J., & Boer, I. J. M. (2014). Roaming characteristics and feeding practices of village dogs scavenging sea‐turtle nests. Animal Conservation.

Village dogs are reported to prey on sea-turtle nests at various beaches worldwide. Sea-turtle species present in Mexico include six species, which are listed under the International Union for Conservation of Nature Red List. It is however not clear why dogs scavenge and how they enter nesting areas; this hinders effective management of dogs at sea-turtle nesting beaches. Hunger, for example, could be a driving factor for village dogs to scavenge sea-turtle nests. The aim of this study was to gain insight into roaming characteristics and feeding practices of dogs scavenging sea-turtle nests. Movements of 19 village dogs (9 nest scavengers and 10 non-nest scavengers) at Colola village and beach (an important nesting ground for the eastern Pacific green turtle: Chelonia mydas) were monitored through radio-tracking and direct observations. A prerequisite for nest scavenging is traveling to the beach. We computed ‘distance from home to beach’ and ‘the activity range’ of nest scavengers and non-nest scavengers. Furthermore, the dogs' owners were interviewed regarding feeding practices. Nest scavengers had a lower metabolic energy intake of their daily food corn tortillas (296 kJ kg⁻¹ BW^0.75) than non-nest scavengers (464 kJ kg⁻¹ BW^0.75) (two-sample t-test=2.67, P=0.017). Moreover, 39% of owners reported that they provided turtle eggs or egg shells to their dogs at least once. The activity range of nest scavengers was significantly larger than that of non-nest scavengers (F=11.64, P=0.007). Dogs were generally found at the beach at night (42%) and dawn (34%). Our findings have implications for the management of dogs at sea-turtle nesting beaches. We recommend that dogs' movements should be restricted between night (09:00 pm) and dawn (06:00 am) and that sufficient and adequate feeding of dogs should be promoted among dog owners.

Anti-cat behaviour in island reptiles

Li, B., Belasen, A., Pafilis, P., Bednekoff, P., & Foufopoulos, J. (2014). Effects of feral cats on the evolution of anti-predator behaviours in island reptiles: insights from an ancient introduction. Proceedings of the Royal Society B: Biological Sciences, 281(1788), 20140339.

Exotic predators have driven the extinction of many island species. We examined impacts of feral cats on the abundance and anti-predator behaviours of Aegean wall lizards in the Cyclades (Greece), where cats were introduced thousands of years ago. We compared populations with high and low cat density on Naxos Island and populations on surrounding islets with no cats. Cats reduced wall lizard populations by half. Lizards facing greater risk from cats stayed closer to refuges, were more likely to shed their tails in a standardized assay, and fled at greater distances when approached by either a person in the field or a mounted cat decoy in the laboratory. All populations showed phenotypic plasticity in flight initiation distance, suggesting that this feature is ancient and could have helped wall lizards survive the initial introduction of cats to the region. Lizards from islets sought shelter less frequently and often initially approached the cat decoy. These differences reflect changes since islet isolation and could render islet lizards strongly susceptible to cat predation.

Methods and strategies to control feral cats to protect Galapagos land iguanas

Phillips, R. B., Cooke, B. D., Campbell, K., Carrion, V., Marquez, C., & Snell, H. L. (2005). Eradicating feral cats to protect Galapagos land iguanas: methods and strategies. Pacific Conservation Biology, 11(4), 257.

A three-year programme to eradicate Feral Cats Felis catus from the island of Baltra in the Galapagos archipelago achieved good results by Initially poisoning with sodium monofluoroacetate (compound 1080) then trapping or shooting the remaining cats. The poisoning campaign removed 90% of the cats, its success being attributable to pre-baiting with unpolsoned baits to accustom cats to eating baits and placing enough baits to ensure that all cats encountered several baits within their home range. This, together with the use of metaclopromide (Pileran) as an anti-emetic, overcame a problem associated with poor retention of 1080 in thawed fish baits that limited the dose available to 1 mg 1080 bait, a quality insufficient to kill large cats. Removal of the remaining cats was delayed by a weather-induced irruption of Black Rats Rattus rattus and House Mice Mus musculus that enabled recruitment of kittens in 2002, but made cats more susceptible to trapping and shooting in 2003 when rodent populations collapsed. Since July 2003 no sign of a cat has been detected on Baltra despite extensive searching and monitoring throughout 2004. As cat abundance has decreased there have been more locally-bred juvenile iguanas (Conolophus subcristatus) seen during annual censuses. However, such recruitment may reflect the increasing maturity and higher fecundity of iguanas repatriated from 1991 onwards rather than being a direct result of reduced cat predation alone. More time is necessary to determine the benefits of reduced cat predation on the Iguana population.

Impact of introduced predators, including dogs and cats, on island reptiles

Case, T. J., & Bolger, D. T. (1991). The role of introduced species in shaping the distribution and abundance of island reptiles. Evolutionary Ecology, 5(3), 272-290.

Species interactions, as revealed by historical introductions of predators and competitors, affect population densities and sometimes result in extinctions of island reptiles. Mongoose introductions to Pacific islands have diminished the abundance of diurnal lizards and in some cases have led to extinctions. Through these population level effects, biogeographic patterns are produced, such as the reciprocal co-occurrence pattern seen with the tuatara and its predator, the Polynesian rat, and with the tropical gecko competitors Hemidactylus frenatus and Lepidodactylus lugubris in urban habitats in the Pacific. Although competition has led to changes in abundance and has caused habitat displacement and reduced colonization success, extinctions of established reptile populations usually occur only as a result of predation.

These introductions, along with many manipulative experiments, demonstrate that present day competition and predation are potent forces shaping community structure and geographic distributions. The human introduction of species to islands can be viewed as an acceleration of the natural processes of range expansion and colonization. The immediate biotic consequences of these natural processes should be of the same intensity as those of the human introductions. Coevolution may subsequently act to ameliorate these interactions and reduce the dynamical response of one species to the other. The role played by coevolution in mediating interactions between competitors and predator and prey is highlighted by the susceptibility of predator-naive endemic species to introduced predators and the invalidity of species-poor communities.

Dogs predating on green turtle nests

Fowler, L. E. (1979). Hatching success and nest predation in the green sea turtle, Chelonia mydas, at Tortuguero, Costa Rica. Ecology, 60 (5) 946-955.

Green turtle hatching success and nest predation were investigated at Tortuguero, Costa Rica, during July-November 1977. Forty-two percent of 350 study area nests and 57% of 237 beach survey nests produced emerging young; 38% and 24%, respectively, were destroyed by dogs, coatis, and vultures. The mean emergence percentage for the successful study area nests was 83%. About 13% of all eggs deposited did not hatch. A mean incubation period of 62 d and a mean clutch size of 104 eggs were recorded. Emergence success was not influenced by other recorded parameters (nest position on beach, rainfall, turtle's tag year, time of season, incubation period, and clutch size). Incubation period was related to nest position and clutch size. Dogs, coatis, and black and turkey vultures were the chief predators at Tortuguero; dogs did the most damage. Dogs and coatis found nests at all stages of development, but destroyed more nests containing hatchlings than nests containing unhatched eggs. Predation was related to nest position, but not to nest density. Nests were destroyed in equal proportion on the entire 35.4 km of beach. Predator activity was not consistent throughout the season; proportionally more nests were destroyed near the end of the nesting season than during the beginning.

Community turtle conservation in Costa Rica

Govan, H. (1998). Community turtle conservation at Rio Oro on the Pacific coast of Costa Rica. Marine Turtle Newsletter, 80, 10-11.

In June 1996, ADECORO started community-based management of the beach which involved both the participation of community members in controlling movements of their animals, and the removal of feral dogs which was carried out in conjunction with local authorities.

	Total Predated	% Predated
1994	417	15%
1996	292	9%

A marked reduction can be seen in predation levels subsequent to the commencement of this initiative. It is almost certain that the reduction of dog predation is the result of a combination of the activities of the beach patrols and general increasing awareness in the community. Increased public awareness is likely to have contributed to the decrease in the activities of human egg collectors. The number of nests collected by humans fell from 344(12%) in 1994, to 122 (4%) in 1996

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The iguana tragedy

Kutschera, U., & Kleinhans, S. 2013. Alfred Russel Wallace and the destruction of island life: the Iguana tragedy. Theory in Biosciences, 1-7.

The Galápagos Islands (Ecuador) are usually associated with the explorations and theoretical deductions of Charles Robert Darwin (1809–1882), but Alfred Russel Wallace (1823–1913) also investigated these islands and published several reports on the living world of this unique archipelago. In contrast to Darwin, Wallace described the destruction of natural ecosystems by humans and foresaw the resulting extinction of species. Here, we outline two case studies pertinent to Wallace’s prediction. First, we summarize the behavior of the predator-naive marine iguanas (Amblyrhynchus cristatus) on the Galápagos Islands, which are threatened by feral dogs and cats imported by humans. We also describe the unique life cycle of the spiny-tailed iguana (Ctenosaura bakeri) from the island of Utila (Honduras), a rare species whose populations are declining because of habitat destructions. In contrast to these threatened, endemic island species, the Green iguana (Iguana iguana) is still widely distributed, although, as a result of de-forestation, in some areas of South America local populations have disappeared. We conclude that Wallace was correct in his prediction that, because of human activities, numerous species of animals and plants will be driven to extinction, notably on islands.

Feral Dog with iguana Photo Galapagos Conservation Society

Farewell to the airport cats: Eradication of feral cats from Baltra island

A three-year program to eradicate feral cats, Felis catus,, from the island of Baltra in the Galápagos archipelago has achieved good results. With the objective of reducing the negative impact produced by the cats and restore a Galápagos ecosystem, the Galápagos National Park (GNP), with technical support from the Charles Darwin Foundation (CDF), began a project with the principal objectives of eradicating cats from Baltra island, and the restoration of its natural habitat. In addition, the project guarantees the survival of a population of repatriated land iguanas Conolophus subcristatus, a species made extinct on this island in the past, partly due to the presence of feral cats.

Eradication of cats was possible for various reasons: firstly, it is an island with a very small human population and therefore with a low risk or re-introduction of cats; its size is small (26km2) which helps control and monitoring; and lastly, the vegetation is sparse, with many open areas. Studies on feral cat behaviour and the most appropriate methods of control revealed that cats are active during the day and night. During the day, GNP staff looked for tracks and signs, and placed traps (Tomahawk and Victor types) and poison. At night, hunters removed cats with spotlights and rifles. With the objective of ensuring total eradication, in 2001, sodium monofluoroacetate (1080) in fish baits was placed over the entire island. The island was divided into 13 sectors and 350 bait stations were placed. This methodology was successful in controlling the cats. The population has slowly been reduced to the point of eradication. Removal of the remaining cats was complicated by a weather-induced eruption of rats Rattus rattus, and mice Mus musculus, that enabled recruitment of kittens in 2002, but made cats more sucseptible to trapping and shooting in 2003 when the rodent population collapsed. By the end of 2003 no sign of a cat was seen on Baltra despite extensive searching. Periodic monitoring on Baltra continues throughout 2004 to confirm the eradication of the feral cats, and the establishment of colonies of repatriated land iguanas. On reduction of the cat population there have been immediate increases in the numbers of locally bred terrestrial iguanas seen during annual censuses. However, this response may reflect the coincidental maturation of young produced by iguanas repatriated from 1991 onwards or climatic variations rather than resulting from reduced cat predation alone. It may be necessary to wait some years to see the full benefits of reduced cat predation. Currently the GNP is carrying out cat control programmes at two sites, Cerro Dragon and Cerro Montura, on another island in Galápagos, Santa Cruz. In addition, they are monitoring other islands to determine the areas where feral cats are threatening native species. 

Source: Galápagos National Park and the Charles Darwin Foundation.

Reptile decline due to cat predation

Bamford, M.J. & M. C. Calver. 2012. Cat Predation and Suburban Lizards: A 22 Year Study at a Suburban Australian Property. The Open Conservation Biology Journal, 6: 25-29

From observations conducted in a suburban property in Perth, Western Australia, over 22 years, it appears that a single pet cat may have exterminated a population (est. 40-50 animals) of the lizard Ctenotus fallens over two years, but with the greatest impact in just the first few months. C. fallens did not begin to recolonise the site until six years after the cat had moved away. The observations support the hypothesis that extinctions of wildlife in suburbia following the introduction of cats can be swift. They also suggest that C. fallens is a suitable species for reintroduction experiments into suburban Perth, comparing the success of reintroductions at sites where cats are confined with those where cats roam freely.

Cat predation on turtle hatchlings

Seabrook, W. 1989. Feral cats (Felis catus) as predators of hatchling green turtles (Chelonia mydas). J. Zool., Lond., 219: 83-88

In many parts of the world feral animals have been reported to have severe effects on marine turtle hatchling production. In this study, green turtle (Chelonia mydas) hatchlings were shown to be an important component of the diet of the feral cat (Felis catus) on Aldabra Atoll, Seychelles, and feral cat activity in the coastal areas was found to be concentrated on the beaches used most intensively by turtles for nesting. The impact of the feral cat's predation on green turtle recruitment could not be determined. However, despite cat predation, the size of the Aldabran green turtle nesting population has increased considerably since human exploitation ceased.

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. 

Dogs digging turtle's nest

Although dogs aren't the biggest predators of turtles, they take their share:

From http://biodiversitycatrice.wikispaces.com/Biodiversity

Impact of feral pets on island iguanas

Iverson, J. B. (1978). The impact of feral cats and dogs on populations of the West Indian rock iguana, Cyclura carinata. Biological Conservation,14(1), 63-73.

A population of rock iguanas, Cyclura carinata, inhabiting Pine Cay in the Caicos Islands was nearly extirpated during the three years following construction of a hotel and tourist facility. The decline, from an estimated adult lizard population of nearly 5500, was due primarily to predation by domestic dogs and cats introduced to the island simultaneously with hotel construction. Population declines on other nearby islands were also attributed to predation by these feral mammals.