Predators and isolation shape the evolution of 'island tameness,' providing conservation insights

Charles Darwin noted more than 150 years ago that animals on the Galapagos Islands, including finches and marine iguanas, were more docile than mainland creatures. He attributed this tameness to the fact that there are fewer predators on remote islands.

While "island tameness" is an old idea, there have been few rigorous studies of the phenomenon. Many aspects remain unclear, including the mechanisms behind it and the speed at which it evolves in island populations.

A new University of Michigan-led study of Aegean wall lizard populations on 37 Greek islands shows that island tameness is determined by both the diversity of the local predator populations and the length of time an island has been separated from the mainland.

 

The researchers found that as the diversity of predators on an island increases, so does the distance at which these small lizards start to flee when they are approached -- an anti-predator response which scientists call the flight initiation distance. In addition, they found that the longer an island has been isolated from the mainland, on average, the longer its resident Aegean wall lizards will wait before fleeing from a predator.

The results suggest that animals living on small, long-isolated islands face the greatest risk from introduced predators -- such as feral cats and rats -- and should therefore receive priority in conservation efforts, said U-M vertebrate ecologist Johannes Foufopoulos, co-author of a paper scheduled for online publication in the journal Evolution on Dec. 1.

 

"Being so fearless, these populations are extremely susceptible to any novel predator that's introduced. In fact, island tameness has caused numerous island-species extinctions at the hands of human-introduced predators and pets," said Foufopoulos, an associate professor at the U-M School of Natural Resources and Environment.

"Determining what factors lead to the loss of effective anti-predator responses is critical because it provides a fundamental understanding of evolutionary processes on islands and also helps conservation managers predict which island species are at most risk," he said.

The first author of the Evolution paper is Kinsey M. Brock, who conducted the lizard study for her graduate thesis at the School of Natural Resources and Environment. "This is the first study to systematically test for the ecological factors that drive island tameness and the rate at which it can occur," she said.

The study compared anti-predator responses of Aegean wall lizard populations on the Cyclades Islands in the central Aegean Sea to the composition of the predator communities and the isolation history of each island.

Site surveys were conducted to determine the resident lizard predators, which included rats; birds; vipers, sand boas and other snakes; feral cats; and stone martens.

Bathymetric data derived from navigation charts, targeted sonar measurements, and geomorphological reconstructions of past sea levels were used to determine how long each island has been separated from the Greek mainland. Some of the oldest islands have been cut off from the mainland for more than 450,000 years.

The researchers looked at how skittish the lizards were by measuring flight initiation distance, and they examined the likelihood that lizards will shed their tails by gently squeezing lizard tails between calipers in the laboratory. Tail-shedding, also know as tail autotomy, is a common but energetically costly anti-predator defense among lizards, who jettison the wriggling appendage when attacked and later grow a new tail.

 

Both the fear response and the propensity for tail-shedding were strongly associated with predator diversity on an island: The fewer predators present, the longer the lizards wait to flee and the weaker their tail-shedding ability.

"It would be evolutionary disadvantageous to shed your tail in a predator-free environment, as the fitness costs range from lowered social status to reduced locomotor ability and susceptibility to parasites," Brock said.

The study showed that not all predators were equally important in shaping behavior. Fast-moving predators, such as mammals and hawks, were much more influential than sit-and-wait predators, such as vipers, in driving the evolution of shy, flighty lizards.

"This makes sense, as shyness is going to be a much less effective response against sit-and-wait predators that remain hidden until the prey is within striking distance," Foufopoulos said. The researchers also found that because larger islands tend to support more diverse predator populations, anti-predator responses were most dramatically lost on small, predator-poor islets. And lizards on the oldest islands tended to be the most fearless.

"In summary, our results indicate that loss of anti-predator defenses is a serious problem for island organisms and suggest that small, long-isolated island populations stand at the highest risk from invasive predators and, as such, should receive priority in conservation efforts," Brock said.

The other authors of the Evolution paper are Peter Bednekoff of Eastern Michigan University and Panayiotis Pafilis of the University of Athens. The title of the paper is "Evolution of antipredator behavior in an island lizard species Podarcis erhardii (Reptilia: Lacertidae): the sum of all fears?"

The study received financial support from the School of Natural Resources and Environment, the U-M Museum of Zoology, the U-M International Institute and the SNRE Envoys.

Journal Reference:

1. Kinsey M. Brock, Peter A. Bednekoff, Panayiotis Pafilis, Johannes Foufopoulos. Evolution of antipredator behavior in an island lizard species,Podarcis erhardii(Reptilia: Lacertidae): The sum of all fears? Evolution, 2014; DOI: 10.1111/evo.12555

Cory's shearwater is able to provide immune protection to its offspring up to six years after being vaccinated

Cory’s shearwater is able to provide immune protection to its offspring up to six years after being vaccinated against a pathogen, research shows. Cory's shearwater (Calonectris borealis) is a seabird that breeds annually in remote islets and  islands. Characterized by long life expectancy, the species reaches sexual maturity after six years and its reproductive rate is very low (one chick per year).

A study published in the journal The American Naturalist indicates that Cory's shearwater is able to provide immune protection to its offspring up to six years after being vaccinated against a pathogen. The paper is signed by Raül Ramos and Jacob González Solís, from the Department of Animal Biology of the University of Barcelona (UB) and the Biodiversity Research Institute (IRBio), together with Romain Garnier, from Princeton University (United States), and Thierry Boulinier, from the Centre of Evolutionary and Functional Ecology in Montpellier (France).

Cory's shearwater (Calonectris borealis) is a seabird that breeds annually in remote islets and islands. Characterized by long life expectancy, the species reaches sexual maturity after six years and its reproductive rate is very low (one chick per year). "With these characteristics, the consequences of an infection outbreak on a colony of seabirds may be devastating; it may be a threat to the restoration and viability of the affected population," says Jacob González Solís.

The scientific team has studied seabirds' immune response to a vaccine against Newcastle disease virus. The researcher Raül Ramos, first author of the article, explains that "the study simulates a viral infection with a vaccine and examines the species' immune system in order to know how to act in case of real infection."

Immune response in chicks and females

The study was conducted in a Cory's shearwater colony in the island of Gran Canaria (Canary Islands) from 2008 to 2013. Authors evaluated the persistence of immunoglobulins or antibodies in mothers through time. The research has extended the results of a previous study developed by the same research team in 2011 which was focused on immunoglobulin persistence during chick growth.

To be exact, in 2008, researchers developed the first vaccination campaign in thirty females. Then, in 2010, they repeated it in a limited number of females to observe if a second exposure to the pathogen generated a quicker and more persistent response.

Chicks are protected six years after the vaccination

Results show that mothers are still able to transfer immunoglobulins to chicks six years after a vaccination, protecting their offspring against the pathogens that might infect the population. "Immunoglobulins are of female origin and maternal antibodies are transferred only when the egg yolk is formed," points out Raül Ramos. "In the case of chicks, the average lifetime of immunoglobulins is twenty-five days."

Besides extraordinary antibody persistence in vaccinated females, the study evidences a direct correlation between the amount of antibodies that the mother has when hatching and the amount received by the shearwater chick. In other words, the chick that is born during the year when the mother is vaccinated receives a great amount of antibodies. However, the chick of a female that was vaccinated years ago receives fewer antibodies and they are lost quicker during growth.

"Immunoglobulin levels in females are significant up to six years after the vaccination -- highlights Ramos -- , whether it is a double vaccination or not. Therefore, it would not be necessary to vaccinate again females to improve offspring's survival against infection outbreaks." According to experts, this mechanism of high antibody persistence in blood may be an evolutionary strategy to avoid reinfection in seabird colonies that always breed in the same colonies and are recurrently exposed to the same pathogens.

The study developed by the UB research group that studies immune response in Corey's shearwater populations is a key research to establish demographical models that facilitate the survival of world's seabirds against possible infection outbreaks. This happens, for instance, to the Amsterdam albatross (Diomedea amsterdamensis), a species that inhabits the islands of the Indian Ocean and is threatened by the avian cholera, an infectious disease caused by the bacteria Pasteurella multocida.

"Prevention is a key factor for these species, which are not generally exposed to predators. They are seabirds that breed in dense colonies, so a pathogen can easily spread if one individual gets infected. In the future, the experimental protocol will be used to study other seabird species of the order Procellariiformes (storm petrel, albatross, etc.) to observe if there is a similar pattern and compare it with species of other taxonomic orders, such as seagulls, cormorants or penguins," explain UB authors.

Journal Reference:

Raül Ramos, Romain Garnier, Jacob González-Solís, Thierry Boulinier. Long Antibody Persistence and Transgenerational Transfer of Immunity in a Long-Lived Vertebrate.    The American Naturalist, 2014; 184 (6): 764 DOI: 10.1086/678400

Plastic pollution: Another threat for seabirds

According to a study published on Marine Pollution Bulletin plastic ingestions affects around 94% of Cory's shearwaters on the Catalan coast. Jacob González Solís, from the Department of Animal Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona (UB), heads the research group that carried out the study. In the case of Yelkouan shearwaters and Balearic shearwaters, conclusions state that 70% of studied birds were affected by plastic ingestion. 

The paper is also authored by Marina Codina García, Teresa Militão and Javier Moreno, researchers at IRBio.

Plastic pollution is known to be a threat for marine ecosystems around the world, but it has not been much studied yet. Jacob González Solís explains that "this is the first assessment of plastic ingestion in Mediterranean seabirds. The Mediterranean Sea has been recognized as a singularly sensitive ecosystem because its coast is very industrialized, shipping activity is intense and it contains high density floating plastic areas."

Endangered Mediterranean seabirds

The scientific study is based on the analysis of 171 birds accidentally caught by longliners in the Catalan coast from 2003 to 2010. The UB research group studied plastic ingestion in nine particularly endangered seabird species: Cory's shearwater (Calonectris diomedea), Yelkouan shearwater (Puffinus yelkouan), Balearic shearwater (Puffinus mauretanicus), gannet (Morus bassanus); Audouin's gull (Ichthyaetus audouinii), Mediterranean gull (Ichthyaetus melanocephalus), yellow-legged gull (Larus michahellis), black-legged kittiwake (Rissa tridactyla) and great skua (Catharacta skua).

From civilization to seabirds' stomach

Floating plastic debris can produce entanglement, ulcers, infections and death to marine animals. They usually ingest them by mistake because plastic fragments resemble their natural food items (direct ingestion), but in other cases plastic comes from eating prey with plastic in the stomach (indirect ingestion). Ingested fragments are filaments, plastic spheres, laminar plastic and industrial pellets.

Results showed that 66% of seabirds had at least one piece of plastic in their stomachs. Cory's shearwaters were worst affected, with 94% of these birds containing plastic fragments (15 on average). In the case Balearic shearwaters and Yelkouan shearwaters, 70% contained plastic fragments.

"Results are alarming," emphasizes Gónzalez Solís. "All three of the worst affected are of conservation concern, particularly the Balearic shearwater, which is listed as critically endangered by the International Union for Conservation of Nature (IUCN). It is a Balearic endemic species; there are only around 3,000 breeding pairs in the world. We do not know its impact but it is necessary to study if it affects populations in a negative way."

Chicks, the most vulnerable

Seabird chicks are the most vulnerable to plastic ingestion as they cannot regurgitate as adults do. The lower occurrence of plastics in gulls probably results from their greater ability to regurgitate any hard remain. The study proves that plastic trash -- most of it from recreational activities -- enters oceans' food chain and may become a new threat for seabirds and marine ecosystems. Seabirds are among the most affected animals by plastic contamination, so they have been suggested as good as bioindicator species of the trends in plastic contamination at sea.

 

Sea isn't a rubbish bin

Accidental plastic ingestion is a global problem that affects as different species as the Laysan Albatros (Phoebastria immutabilis) in the Hawaiian Islands and the Northern Fulmar (Fulmarus glacialis rogdgersii).

"Plastic floats and is difficult to degrade," points out González Solís. "Eventually, all pollutants which are not destroyed on land arrive to the sea. The sea is not a rubbish bin. The control over plastic production and transportation at industrial level has probably improved, but there is an urgent need to develop stricter controls on waste dumping and prohibit ships' discharge into the sea."

González Solís is co-author of a study -- recently published on the journal PLOS ONE -- about the distribution of flavivirus -- viruses responsible for several infectious diseases that affect humans and other species -- among Western Mediterranean seabird populations. The study shows that yellow-legged gulls (Larus michahellis), widely distributed along the Mediterranean coast, may be potential reservoirs for these pathogens. Therefore, it is necessary to promote health surveillance on these seabird populations.

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Journal Reference:

1. Marina Codina-García, Teresa Militão, Javier Moreno, Jacob González-Solís. Plastic debris in Mediterranean seabirds. Marine Pollution Bulletin, 2013; 77 (1-2): 220 DOI: 10.1016/j.marpolbul.2013.10.002

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El Festival de las Grullas, interesante propuesta de educación ambiental y de democratizar el patrimonio natural.

Se reunirán 3.000 personas en el Festival, que ofrece un programa lleno de actividades abiertas a todo el público, entre las que se incluyen rutas senderistas, rutas de cicloturismo, un vuelo cautivo en globo para observar a las grullas, 20 talleres infantiles, cuentacuentos, paseos teatralizados o un “desayuno con grullas”.

El Festival de las Grullas en Extremadura organizado por la Dirección General de Turismo del Gobierno extremeño, nace con el fin de promocionar y divulgar una vez más la excepcionalidad de los recursos naturales de Extremadura y su condición de caso insólito en el contexto europeo a la vez que educar, conservar y sensibilizar hacia esta especie. Cultura, tradición, naturaleza, medio ambiente y turismo van de la mano en el elenco de actividades programadas para todas las edades y tipo de público durante el Festival. La organización y desarrollo de este evento ha supuesto la colaboración de entidades públicas y privadas relacionadas con la conservación y protección de la especie así como con la ordenación y promoción del turismo en la región.

El turismo de naturaleza en Extremadura tiene el reto de convertirse en uno de los ejes principales de desarrollo turístico de nuestra Comunidad Autónoma. El valioso legado natural de la región cumple todos los requisitos para convertirse en un foco de atracción de visitantes, en sintonía tanto con las demandas turísticas más actuales como con unos principios basados en la sostenibilidad.

 

Festivaldelasgrullas.com es un portal de ornitología y turismo. En las diferentes secciones de la web se puede encontrar toda la información disponible sobre las grullas en Extremadura, los diferentes núcleos de invernada y las mejores rutas para observarlas. Además se ofrece información turística relativa a empresas de guías especializadas en este tipo de servicios así como de alojamientos y restauración. Todos los componentes necesarios para la planificación de un viaje por los mejores espacios naturales extremeños en busca de una especie que, cada año, regresa a Extremadura para pasar los inviernos. 

Extremadura es la principal área de invernada para las grullas comunes europeas que realizan la migración siguiendo la ruta occidental. Unos 80.000 individuos eligen nuestra región para pasar el invierno, un 30-40% de la población europea occidental y más de la mitad de la población española, cifrada en algo más de 150.000 grullas.

La posibilidad de encontrar abundante alimento, unida a la existencia de numerosas zonas húmedas que sirven de refugio y a las temperaturas moderadas del invierno extremeño proporcionan a estas aves un hábitat óptimo para pasar los meses invernales.

 

Considerando conjuntamente las áreas de campeo, de alimentación y los dormideros, se estima que la superficie ocupada por esta especie estaría en torno a 1.835.000 ha, lo que representa el 44% de la superficie de la región. Se trata, por tanto, de una especie que puede observarse con facilidad en gran parte del territorio extremeño.

Las grullas son aves de tamaño grande y silueta estilizada, con cuello y patas muy largas y plumaje grisáceo. Pico pardo verdoso, más corto que el de garzas y cigüeñas. Patas oscuras. Ojo rojo. Longitud 114-130 cm y envergadura 200-230 cm. Peso entre 4 y 7 kg. Los machos son más corpulentos y de mayor talla que las hembras, aunque es difícil distinguirlos en campo (resulta más fácil cuando se observa un grupo familiar asilado).

El joven presenta un plumaje predominantemente pardusco, con la cabeza y cuello con tonos pardo rojizos. Carece del característico diseño rojo, negro y blanco en la cabeza. La falsa cola es menos aparente.

Grito muy característico (“kruu-kruu”) que puede escucharse a gran distancia y que emiten tanto en vuelo como posadas. La voz de los jóvenes es un silbido agudo y lastimero.

En migración es frecuente ver en grupos volando en forma de “V”.

Su dieta depende de los recursos disponibles en los hábitats donde se alimenta. Así, en las dehesas consumen principalmente bellotas de encina, en los cultivos de cereal de secano las semillas de trigo, cebada y avena, mientras que en los rastrojos de regadío buscan las semillas de arroz y maíz. En ocasiones también se alimentan en cultivos de leguminosas (habines) y de colza. Pueden consumir bulbos de especies silvestres (Arisarum, Arum, Biarum, Gynandriris, Hyacintoides, Romulea, Narcissus), tubérculos, tallos y brotes de herbáceas y de cereal, pequeños invertebrados, etc.

Merece destacar la especialización de las grullas en el consumo de la bellota, siendo de las pocas especies de aves que logran eliminar por completo su cáscara antes de ingerirla. En ocasiones aprovechan depresiones de terreno para colocar las bellotas y lograr picotear su cáscara con más facilidad. Los restos de las cáscaras pueden encontrarse bajo las encinas, apreciándose perfectamente las marcas y agujeros producidos por el pico. Del mismo modo, muestran una notable habilidad para desenterrar bulbos, apreciándose perfectamente las zonas donde han estado alimentándose, ya que el terreno aparece completamente removido por la actividad de su pico.

Las poblaciones de grulla común (Grus grus) utilizan dos rutas migratorias muy definidas a través de Europa. Por un lado, la “ruta occidental” sería la utilizada por las aves que nidifican en Europa continental, países ribereños del mar Báltico y escandinavos, que se desplazarían hacia el suroeste para establecer sus cuarteles de invernada en España, Portugal, Marruecos y Francia. Por otro, la “ruta oriental” implicaría a aves que nidifican más al norte y al este que las anteriores (gran parte de las poblaciones de Finlandia y del oeste de Rusia y ex-repúblicas), que se dirigirían al sur cruzando Estonia, Lituania, Polonia Hungría e Italia, para pasar el invierno en Túnez, Libia y Argelia. Otra variante de la ruta oriental se desplaza un poco más al este, bordeando el Mar Negro y el Mar de Mármara a través del Estrecho del Bósforo (Turquía), y alcanzando regiones situadas mucho más al sur, en Egipto, Etiopía y Sudán. Se han constatado casos de ejemplares que han utilizado indistintamente las dos rutas.

Ambas rutas han experimentado importantes cambios en los últimos años, ampliando sus zonas de invernada hacia el norte. En el caso de la occidental, ha aumentado notablemente la presencia de estas aves en países como Francia (por ejemplo en Lac du Der-Chantecoq, a menos de 200 km de Luxemburgo y Bélgica, prácticamente en el centro de Europa). Y con la oriental ocurre algo similar, constatándose una creciente importancia de la invernada en Hungría, Croacia, Serbia o Bosnia-Herzegovina, en detrimento de los cuarteles tradicionales próximos al Mar Rojo. Se asume que estos cambios están asociados al aumento de la disponibilidad de alimento (nuevos zonas de regadío, cambios en los cultivos), existencia de adecuadas zonas de dormidero (nuevos embalses, regadíos) y la disminución de las molestias (actividades cinegéticas) Por otra parte, las condiciones climáticas imperantes están propiciando inviernos menos adversos.

 

Las poblaciones de grulla común han experimentado un notable y progresivo aumento en sus áreas de reproducción durante las últimas décadas, hecho que se ha visto reflejado proporcionalmente en las áreas de invernada. En la década de los 80, la población invernante en la península ibérica no superaba las 55.000 aves, mientras que los censos más recientes (SEO/BirdLife, 2007) estiman sus efectivos en más de 150.000 aves.

La llegada de las grullas ocurre principalmente durante la segunda quincena de octubre, incrementándose progresivamente hasta alcanzar las máximas poblaciones entre diciembre y enero. Las llegadas más tempranas se producen en las primeras semanas de octubre (excepcionalmente en septiembre) y se pueden ver las últimas aves hasta principios de abril. Excepcionalmente hay ejemplares que no migran y que pueden permanecer aquí durante el verano, pero suele tratarse de aves débiles, enfermas o con alguna lesión.

Tradicionalmente se asocia esta especie a las dehesas de encinas, ya que la bellota es uno de sus principales alimentos durante el invierno. De hecho, casi todos los núcleos de invernada existentes en Extremadura integran en mayor o menor proporción zonas de dehesas, pero también pueden establecerse en áreas con cultivos de cereal (cebada, trigo, avena) o pastizales con árboles muy dispersos. Los cultivos de arroz y de maíz son intensamente utilizados por las grullas en invierno, puesto que en las fechas en las que llegan a Extremadura ya han sido cosechados y aprovechan la disponibilidad de alimento que ofrecen los rastrojos, donde encuentran con facilidad restos de semillas.

Las grullas mantienen rutinas muy marcadas, desplazándose a los comederos durante el día y volando al final de la jornada a los dormideros comunales, donde pueden llegar a concentrarse miles de aves. En ocasiones establecen predormideros en las inmediaciones de un dormidero principal, donde se agrupan antes de volar definitivamente a este último. Son especies eminentemente gregarias, pudiendo formar grandes bandos de varios cientos de ejemplares. No obstante, es frecuente también ver grupos familiares aislados, en los que los adultos acompañan a los jóvenes durante toda la invernada y pueden mantenerse al margen de los grandes bandos de alimentación.

Durante los vuelos migratorios los grupos se desplazan a gran altura adoptando una peculiar disposición en forma de “V”, a la vez que emiten su distintivo y sonoro canto. Al final de la invernada es relativamente frecuente observar bandos de grullas que comienzan su retorno hacia el norte. Entonces pueden verse grandes grupos de aves volando en círculos en busca de corrientes térmicas, hasta que alcanzan la altura suficiente para llegar planeando hasta su siguiente destino.