Blinded by the light: victims of the night

In late October, the municipality of Buenavista del Norte on the Canary Island of Tenerife, celebrates the day of the Virgin of Los Remedios, including, among other features, a big light display. As a child, Airam Rodríguez noticed that many shearwaters would also drop in (literally) for the festivities, attracted by the bright lights, but unable, in many cases, to get back in the air. Many of these shearwaters died from a variety of causes, including the impact of flying into the ground, dehydration, predation and poaching. As an adult, Rodríguez collaborated with researchers around the world to evaluate the scope of light-induced shorebird fallout.


Fallout victim: grounded Short-tailed Shearwater. Credit: Airam Rodríguez

The researchers began their work by searching a science citation index – the Web of Science – for articles on light-induced seabird mortality. They used references from these articles to find additional articles. In addition, they used the internet and social media to find programs in which citizens are encouraged to report grounded birds, and contacted people associated with these programs to get qualitative and quantitative data.

Rodríguez and his colleagues discovered light induced seabird fatality on 47 islands, three continental locations and across all of the world’s oceans. Of 115 species of burrow-nesting petrels, 56 have been reported as grounded by light. Several other groups of birds, including puffins, auklet and eiders also suffer from light-induced fallout, and it is very likely that more species are unreported.


Numbers of reported grounded seabird fledglings across the globe.  Circle size = numbers of birds  reported. Numbers = number of species affected. Circle color = IUCN (endangerment) category for each species as follows: CR = critically endangered, EN = endangered, VU = vulnerable, NT = near threatened, LC = least concern.

Of deep concern is that 24 species are globally threatened. In addition, fallout has been reported at sea, induced by lights used for fisheries and by lights on oil platforms. All of the studies of light-induced fatalities on land documented the highest mortality in fledglings that are grounded during their first flights from their nests toward the ocean.


Numbers of species of threatened seabirds that were rescued across the globe.  Numbers were not available for species with ? symbol.

Researchers don’t know why birds are attracted to lights. Perhaps birds view lights as a source of food; for example some species eat bioluminescent prey. Alternatively, as cavity-nesting birds, the only light these chicks see is from their burrow entrance, particularly when their parents bring in food, so the fledglings might confuse light with a food source. Lastly, artificial lights might override any celestial light cues the birds normally use for navigation, confusing them and causing them to crash to the ground. Supporting this hypothesis, seabirds generally don’t crash into lights, which might be expected if they mistook a light for bioluminescent prey.

Cory's shearwater fledgling at their nest at Tenerife Canary Islands. Photo by Beneharo Rodríguez

Fledgling Cory’s Shearwater first sees the light of day after emerging from its burrow at Arona on southern Tenerife Island. Credit: Beneharo Rodríguez

So what can be done about this problem? Accurate data are hard to come by, as many estimates of fallout-induced mortality come from relatively untrained volunteers, who are less likely to report dead birds. As one example, on Kauai, surveys from a general public rescue program for Newell’s Shearwaters identified 7.7% mortality, whereas later systematic surveys by trained researchers indicated 43% mortality. In some rescue operations, birds are banded and released, which, in theory, allows researchers to estimate the survival rate of rescue birds, but, in practice, these data are usually insufficient for accurate estimates

Rodríguez and his colleagues recommend a multipronged approach to combat seabird fallout. Individuals grounded by artificial lights can be rescued so they don’t succumb to the common causes of death – dehydration, predation and vehicle collision. In many cases the general public takes birds to designated rescue stations, where they are cared for until judged to be ready to release. The first rescue program was set up on Kauai in 1978; since then, people working for 16 rescue programs have released over 40,000 birds.

Release of a grounded shearwater. Photo Nazaret Carrasco (1)

Beneharo Rodríguez releases a Cory’s Shearwater from a cliff at Buenavista del Norte on Tenerife Island. Credit: Nazaret Carrasco.

The birds would be best served if humans behaved in ways that minimized fallout. Researchers need to learn more about why birds are attracted to artificial lights so engineers can develop outside lights that don’t attract them. Existing lights can be turned off when not needed, and dimmed when they are essential. Special accommodation can be made for unusual cases; for example in Cilaos, Reunion, Indian Ocean, streetlights are turned off during the fledging period of Barau’s Petrel. Lights can also be shielded so they illuminate an area for humans, but minimize the light visible to birds. Degraded nesting and breeding habitat can be restored to help compensate for birds that are lost to fallout. Lastly, conservation efforts should benefit the local economies so that residents will be more likely to support conservation initiatives, such as reduced evening lighting, that they might otherwise oppose.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Rodríguez, A., Holmes, N. D., Ryan, P. G., Wilson, K.-J., Faulquier, L., Murillo, Y., Raine, A. F., Penniman, J. F., Neves, V., Rodríguez, B., Negro, J. J., Chiaradia, A., Dann, P., Anderson, T., Metzger, B., Shirai, M., Deppe, L., Wheeler, J., Hodum, P., Gouveia, C., Carmo, V., Carreira, G. P., Delgado-Alburqueque, L., Guerra-Correa, C., Couzi, F.-X., Travers, M. and Corre, M. L. (2017), Seabird mortality induced by land-based artificial lights. Conservation Biology, 31: 986–1001. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Cat and fox: agents of Australian extinctions

Australia’s drylands are famous for their assemblage of ultra-cool mammals. As one example, it is difficult for us non-Australians to imagine a more endearing creature than the rock-wallaby pictured below.

Black-foted Rock-wallaby

Black-footed rock wallaby. Credit: Peter McDonald.

Unfortunately, numerous species of Australia’s dryland mammals are going extinct. Many of these extinct species weigh between 35 and 5500 grams – a weight range that researchers have described as the critical weight range (CWR). Peter McDonald and his colleagues wanted to know what was causing these extinctions, and why were they most prevalent in the CWR. They considered two hypotheses. First, perhaps the land was becoming less productive, either from habitat destruction by humans, or as a result of changing climate. Reduced plant abundance could cause herbivorous mammals to go extinct. An alternative hypothesis is that perhaps newly introduced predators, notably feral cats and red foxes, were killing the native mammals so effectively, that they were disappearing from the Ausralian drylands.

Previous research indicated that extinction rates were lower in areas that had more species living in trees and around rocks, leading McDonald to think that maybe habitat was influencing extinctions in important ways. In particular, he realized that rugged mountainous areas might have fewer predacious cats and foxes, and secondly that these two predators tend to go for prey within the CWR. Putting these ideas together, perhaps mountainous areas are refuges for Australia’s dryland CWR species, protecting them from predator-driven extinction. If so, mammal species richness would be highest in rugged, protected areas, and lowest in more open areas. If, on the other hand, mammals are going extinct because overall productivity is declining, we would expect overall species richness to be greatest in the most productive areas.
McDonald and his colleagues tested these two competing hypotheses by censusing mammals in four different types of habitats in Tjoritja National Park within the MacDonnell Range of central Australia. These were (1) mountain areas dominated by a sparse assemblage of shrubs and clumps of spinifex grass, (2) spinifex grasslands (with a more abundant cover of spinifex than found in the mountains), (3) Acacia shrublands, and (4) alluvial woodlands, which were most productive with richest soils.



Mountain refuge habitat_PeterMcDonald

Mountains. Credit: Peter McDonald



Spinifex grasslands


Acacia shrubland


Alluvial woodland

The researchers set up a variety of different mammal traps in 90 different sites representing these four habitats to capture and identify small mammals, and they detected larger mammals by searching for fresh scat at each site. The researchers estimated productivity with the normalized difference vegetation index (NDVI), which uses satellite imagery to measure the green-ness, and hence productivity, of a site or region.

In support of the predation hypothesis, more mammal species were found in the most rugged terrain.


Number of mammal species per site in relation to ruggedness of terrain. The curve is the fitted value of the regression equation.  The shaded area represents the 95% confidence interval.

In contrast to the productivity hypotheses, fewer mammal species were found in the most productive sites


Number of mammal species per site in relation to productivity of terrain as measured by the NDVI. The curve is the fitted value of the regression equation.  The shaded area represents the 95% confidence interval.

While it’s useful to evaluate both hypotheses by measuring current species richness, the researchers also needed to know how many species were actually driven to extinction in the time since cats and foxes invaded. They reconstructed historic species richness for each habitat based on subfossil remains (remains of organisms that are only partially fossilized), from indigenous knowledge supplied by aboriginal Australians, and from historical accounts in the early literature.

They discovered that CWR extinctions were most prevalent in alluvial (12/12 species) and acacia (7/7 species) habitats. Spinifex habitas lost 5/6 CWR species, while mountainous habitats only lost 2/6 CWR species. Importantly, species outside of the CWR have survived relatively well in all habitats, further implicating cats and foxes as the agents of extinctions.


Current (extant) and historic (pre-invasion by cats and foxes) mammalian species richness in the four habitats. The dots are the mean weight, and the lines are the weight ranges for each species.  The shaded area represents the critical weight range (CWR)

More support for the the predation-habitat link comes from recent research that indicates that red foxes are absent from the mountain habitat, while feral cats are substantially less abundant. Even when present, cats are much less efficient hunters in the mountain habitat because the complex rock structure affords more refuges to prey items.

Feral cat with fat-tailed antechinus_NTG

Feral cat captured on camera with a fat-tailed Antechinus. Credit Tony Griffiths.

Across Australia, many CWR species have gone extinct in regions colonized by cats and foxes. McDonald and his colleagues provide solid evidence that these introduced predators are responsible for these extinctions. They urge researchers to explore other mountainous regions in Australia to see if they too are acting as refuges for CWR mammals.

note: the paper that describes this research is from the journal Conservation Biology. The reference is McDonald, P. J., Nano, C. E. M., Ward, S. J., Stewart, A., Pavey, C. R., Luck, G. W. and Dickman, C. R. (2017), Habitat as a mediator of mesopredator-driven mammal extinction. Conservation Biology, 31: 1183–1191. doi:10.1111/cobi.12905. doi:10.1111/cobi.12908. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

River restoration responses

The Lippe River in Germany has been subjected to many decades of channelization, deepening, floodplain drainage, straightening and consequent shortening, with one result being that the modern Lippe is 20% shorter than it was two centuries ago. Beginning in 1996, conservation managers began reversing this trend by widening the river, raising the level of the river bed, constructing small islands within the river and terminating floodplain drainage operations over a stretch of 3.3 km. As a result of these activities, a small portion of the river looks much like it did 200 years ago.


A section of the Lippe River before (left) and after (right) restoration.

Over a 21-year period, researchers from Arbeitsgemeinschaft Biologischer Umweltschutz have conducted systematic surveys of fish communities at the restored and unrestored sections of the river. Researchers sampled the fish community with electrofishing – inputting a direct electrical current into the river – which causes the fish to swim towards the boat where they are easily collected with nets, identified by species, and returned unharmed into the river. A data set over this length of time in association with a restoration project is very unusual; oftentimes (in part due to funding issues) only one survey is conducted to assess the fish community response to river restoration.

About eight years ago, while a postdoctoral researcher at Senckenberg Research Institute in Frankfurt, Germany, Stephan Stoll was asked to analyze some river restoration outcomes, and, as he describes, “became hooked to the topic.” To evaluate the response of the Lippe River fish community to restoration, a group of researchers headed by Stephanie Höckendorff, a Master’s student with Stoll, first asked a very simple question – how did fish abundance and species richness (the number of fish species) compare in the restored and unrestored regions of the river.

The graph below shows several striking trends. Abundance peaked about 2-3 years after restoration, declined sharply the next year, and recovered in subsequent years to about three times the abundance found in unrestored sections. Importantly, abundance varied extensively year-to-year. For example, if you had done only one survey in 2000, you would have erroneously concluded that restoration had no effect, which is why the researchers emphasize the importance of collecting data over a long stretch of time.


Abundance of fish in restored (Rest-gray curve) and unrestored (Cont-black curve) sections of the Lippe River.  The gray vertical bar indicates the start of the restoration project in 1997.

Species richness increased sharply, but did not reach its peak until nine years after restoration. Again, there was extensive year-to-year variation in species richness.


Fish species richness in restored (Rest-gray curve) and unrestored (Cont-black curve) sections of the Lippe River.  The gray vertical bar indicates the start of the restoration project in 1997.

Höckendorff and her colleagues were intrigued by this delay in species richness, and turned their attention to understanding what types of species benefited most from the restoration. Their analyses indicated that colonizing species, such as common minnows and three-spined sticklebacks, tended to have short life spans, early female maturity, several spawning events per year and a fusiform body shape – a body that is roughly cylindrical and tapers at both ends. Interestingly, some of the most successful colonizers took quite a long time to get well-established within the community.


Common minnows, Phoxinus phoxinus. Credit: Carlo Morelli (Etrusko25)


The three-spined stickleback, Gasterosteus aculeatus. Credit: Ron Offermans

The restored habitat was highly dynamic, experiencing periodic flooding and the formation of temporary shallow bays and shifting sandbanks. These types of habitats tend to select for minnows, sticklebacks and other opportunistic species that are attracted to periodic disturbances. These opportunistic species were quick to move in, and continued to increase in abundance over time. Importantly, several rare and endangered species also colonized the restored habitat. However, large, deep-bodied, slow maturing and long-lived species did not benefit (at least over the 17 years of the survey), as these types of species are generally favored in less dynamic habitats, which are more stable and uniform.

Overall, these findings demonstrate the benefits of river restoration to the fish communities they harbor. But some species are more likely to benefit than others, and the time-scale over which recolonization occurs is highly variable. Surveys must be repeated over a long time-scale to tell conservation managers whether their restoration efforts are successful, and how they might change their future river restoration efforts.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Höckendorff, S., Tonkin, J. D., Haase, P., Bunzel-Drüke, M., Zimball, O., Scharf, M. and Stoll, S. (2017), Characterizing fish responses to a river restoration over 21 years based on species’ traits. Conservation Biology, 31: 1098–1108. doi:10.1111/cobi.12908. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.