All cavities are not equal

Come spring (late winter), the forests are bustling. Cavity-dwelling animals search for tree crevices and holes in which to lay their eggs and raise their offspring. Tree cavities provide a stable environment for successful nesting.

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Natural cavities are usually found in old wide trees, where the inner temperature of such cavities remains more stable than outside temperatures.

Only one problem remains. Cavities usually form in old or, at the least, decomposing trees, but forestry practices simplify forest cover composition. Fewer trees surpass forestry practice recommendation ages, so our forests have less large aging trees in which fungi can spread. More tree cavities are desperately needed. Nest boxes are our solution to this problem. The idea is simple: anyone can build a nest box and hang it on their own land (or somebody else’s with permission). This has helped boost the populations of certain cavity-nesters such as pied flycatchers (Ficedula hypoleuca) and great tits (Parus major).

It would be nice to think that we have solved the cavity problem, or that the problem will be solved if we raise the number of nest boxes to sufficient levels. But it’s not that simple. Several researchers have studied the functionality of nest boxes over the years. The microhabitats of tree cavities and nest boxes differ from each other in relation to temperature and moisture. Wroclaw University researchers were the most recent group to prove this distinction, but they also demonstrated that these functional differences drive the marsh tit (Poecile palustris) to choose natural cavities over nest boxes. Their study was conducted in two forests; the other had an unlimited number of tree cavities, while nest boxes were the only nesting option in the other forest. The marsh tits preferred natural cavities with thick walls buffering the holes from outside temperatures. And birds are not the only species that have been shown to prefer natural cavities, for example certain bats and the common brushtail possum (Trichosurus vulpecula) will settle in natural cavities due to their more stable microclimates.

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The common brushtail possum is an Australian mammal that nests in tree cavities. Picture: Wikimedia Commons. https://upload.wikimedia.org/wikipedia/commons/b/b4/Brush_tail_possum_4-colour_corr.jpg. By user:benjamint444 modified by Tony Wills [GFDL]

Nest box temperatures in the Wroclaw study fluctuated significantly more than the inner temperatures of tree cavities. Nest box temperature also changed at the same rate as outside temperatures. Nest box temperatures can therefore rise to dangerous levels during the summer, to where chicks are at higher risk of dying from excessive heat compared to broods in tree cavities. During the winter, nest box temperatures drop to lower levels than cavity temperatures, decreasing the shelter effect that many small birds utilize to survive the harsh cold.

Nest boxes also average lower air moisture levels compared to natural cavities. This may hinder mold from growing in the nest boxes, but concurrently lower moisture may encourage wasps (Vespidae) and tree bumblebees (Bombus hypnorum) to settle in nest boxes, making them inaccessible for birds. Fleas (Siphonaptera) may also increase in dry and warm conditions, so the number of competitors and ectoparasites may increase.

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Woodpeckers excavate cavities in decomposing trees and standing dead wood

To cap, nest boxes and natural cavities do not replace each other from a structural point of view and not all species will nest in boxes. The majority of nest boxes are so-called standard models, i.e. they are copies of each other in terms of dimensions and flight hole diameter. In real life, a standard model nest box is only accepted by a limited number of cavity dwellers. It is therefore imperative to conserve aging and decomposing trees, as their cavities are never of standard shape or size. If nothing else, decomposing trees in our yards should be conserved; trees can always be cut to a height that ensures they are of no danger to nearby buildings or people. Such standing dead wood is very rare in current heavily managed forests. With a standing birch dead wood tree it is even possible to attract the picky willow tit (Poecile montanus) to your yard.

The next best alternative is to ensure the structural heterogeneity of nest boxes, i.e. build boxes that are also suitable for species such as the common redstart (Phoenicurus phoenicurus), owls (Strigidae), treecreepers (Certhiasp.), and even certain mammals such as flying squirrels (Pteromys volans). This may require a little more trial and error, but it is the only way of maximizing the nesting alternatives in managed forests. Ideas for nest box designs abound online, Pinterest for example has a huge selection of box models. However, it is important to follow nest box construction instructions issued e.g. by the BTO and Audubon Society or these general safety instructions, to make sure that the boxes are as safe as possible for birds. Nest box positioning is also important; foliage has a protective effect, and the microhabitat of nest boxes positioned under foliage therefore remains more stable than in sun-exposed areas.

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Blue tits often utilize nest boxes.

Adding insulating materials to nest boxes is one way of adding to the inventiveness of nest box construction. To mimic the microclimates of natural cavities, a team of Australian researchers recently compared nest boxes that had been fitted with three types of insulating or heat-reflecting materials. Nest box temperatures remained most stable around the clock in nest boxes insulated with polystyrene foam. The inner temperature of one polystyrene-fitted nest box was nearly six degrees Celsius less than outside temperatures. Nighttime inner temperatures were also higher in the polystyrene nest boxes compared to non-insulated boxes when a heat-producing pillow was placed in the insulated and non-insulated nest boxes, to mimic the effect of birds spending the night in the boxes. The Australian study showed insulation had a more significant effect on nest box temperatures than nest box placement in a shady or sunny location. However, for the environment and breathability, it is probably better to use some type of natural fiber insulation in nest boxes. Also, insulated nest boxes are not enough to fill the void created by the disappearance of natural tree cavities, as the study showed that the temperature fluctuation of even the polystyrene-fitted nest boxes was greater that of natural cavities.

P.S. It is currently trendy to set up cool or “beautiful” nest boxes without thinking about their safety at all. Not a good idea! For example, ceramic bird boxes are much worse insulators than wooden ones, and painted boxes should use lead-free paint. https://www.telegraph.co.uk/news/earth/wildlife/12165505/Novelty-nest-boxes-putting-garden-birds-at-risk-warns-RSPB.html

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Helping out or avoiding risks

Social insects have numerous pathogens that can spread simultaneously in a densely packed colony. Mild exposure to one disease may not increase an individual’s risk of dying, but it does increase the individual’s risk of concurrently contracting another pathogen. Such double diseases are called superinfections, and they lead to death significantly more often than contracting one disease at a time does.

Preventing the spread of a pathogen within a colony is highly important for social insects. Other individuals can treat their sick counterparts either by helping them or by being aggressive. Help can come in the form of grooming, which serves to clean sick individuals of a potential pathogen, or spraying, where infected individuals are hosed off with antimicrobial chemicals. These chemicals are produced in the bodies of certain ant species, which spray the antimicrobials into their surroundings by increasing their internal pressure. On the other hand, aggression appears as biting and dragging of infected animals, which is done to prevent pathogens from spreading deeper into a colony by removing sick individuals from the colony.

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Ants are social insects. They live in colonies that can grow to tens of thousands of individuals © Sari Holopainen

To test how colony mates react to sick individuals, Austrian scientists conducted a study on Lasius neglectus ants. The scientists placed mildly sick ants, infected with one of two fungal pathogens, into a colony. The colony also housed healthy individuals used as controls. Sick individuals could therefore encounter healthy individuals, individuals with the same disease, or individuals suffering from the different pathogen. The controls on the other hand ran into other healthy ants or ants suffering from one of the two diseases. The researchers wished to see whether previous infection altered the behavior of the ants when meeting an infected individual. They were also interested in testing whether the ants reacted differently to individuals infected by the same pathogen as to individuals carrying the other pathogen.

The studied ant species is usually not aggressive towards its colony mates. However, during the experiment, infected individuals often began biting and dragging encountered individuals if they were also sick. Healthy individuals did not react to their diseased counterparts in the same way. Diseased individuals also sprayed other infected ants more often than healthy individuals did. Spraying was more common if the diseased individual suffered from the different fungus than did the sprayer. Grooming was most common when sick individuals with the same pathogen crossed paths.

In other words, infected ants are more aggressive towards other disease carriers, but concurrently they can alter their behavior according to the situation, and choose the safest decontamination method available. This is determined by whether the encountered ant is infected by the same or the other pathogen. Grooming requires individuals to be close to each other, but if both ants have the same infection, the risk of a new infection is minimal. Spraying can be done from a greater distance, in which case individuals don’t come into close contact. This helps sick individuals from contracting a superinfection, which would most probably be lethal.

The scientists were also able to determine that this risk aversion pays off, as mildly sick ants were successful at avoiding a superinfection. Both individuals therefore benefit from altering their behavior, also known as behavioral plasticity. This is extremely important for social insects in densely inhabited colonies, where sick individuals cannot be avoided.

Cleaning is not the only way in which colony insects help each other out. Another recent example comes from German scientists, who observed an African ant species (Megaponera analis) to tend to its injured individuals by licking. Their saliva is believed to contain antimicrobial substances that assist healing. The species often raids termite mounds, so an individual’s injury risk is great. Uninjured ants must make the choice of either helping injured counterparts back to the colony for medical assistance or not. Helping increases an uninjured individual’s risk of suffering injury. However, it is in the colony’s interest to treat as many individuals as possible.

A YouTube video showing uninjured ants tending to injured individuals

Hawks for hunting

Falconry is a centuries-old form of hunting in numerous countries around the world. It is considered an integral aspect of many cultures, and was therefore added to the UNESCO Lists of Intangible Cultural Heritage as a living human heritage element in 2010.

Falconry involves a trained bird of prey that is instructed by a falconer to hunt its natural prey species. The birds can be falcons, hawks, or eagles: even a few owl species have successfully been used. The falconer releases his bird once he has seen a potential prey animal. The bird flies after the prey, and pins it to the ground. The falconer follows, kills the prey, and gives the hawk a compensatory food reward. Falconry can be practiced during regular hunting seasons.

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Several cultures utilize birds of prey for hunting. Lotta the goshawk hunts in Finland. ©Markku Kallinen

Falconry is practiced in many Arab nations, European countries (e.g. Great Britain and the Czech Republic), and in most US states, to name a few examples. The International Association for Falconry (IAF) carefully regulates falconry. The association’s objective is to advance the protection and conservation of birds of prey through falconry and awareness raising.

Despite conservation efforts, many people harbor negative feelings towards falconry. And true problems do exist; certain countries allow the crossbreeding of species. If hybrid hunting hawks manage to escape from captivity, they can weaken the genetic purity of local birds. Alien species are also used in certain areas. For example, Britain has imported Harris’s hawks (Parabuteo unicinctus) into the country for pheasant hunting, but escapees have been reported nesting in the wild. The ethics behind captive wild bird species and breeding them in captivity also remains an issue. On the other hand, falconry has also managed to lessen prejudices that people have harbored against birds of prey in many countries, and falconry organizations further the conservation of both birds of prey and other bird species by e.g. raising awareness and campaigning against illegal animal trafficking.

At one time, falconry was also popular in Finland, where the goshawk (Accipiter gentilis) was the bird of prey most used. Falconry is technically legal according to Finnish hunting legislation, but actually obtaining a hunting hawk is not easy in practice. Goshawks are protected in the country, so a native bird cannot be captured. Therefore a bird must be brought in from abroad. The bird cannot be an alien species, and individuals brought in must also be sterile, as goshawks in other countries are of different populations than in Finland.

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Markku and Lotta mainly hunt mountain hare. ©Pia Kallinen

However, Finland certifiably has one pair of hunting goshawk and falconer. Markku Kallinen and Lotta the goshawk uphold an old hunting tradition that disappeared during the 1960s. Markku and Lotta mainly hunt mountain hare (Lepus timidus). See a video of Lotta feeding, filmed by Pia Kallinen.

Lotta’s activities can be followed (in Finnish) at https://www.facebook.com/haukkametsastys/

David and Goliath – a story of bark beetles

Bark beetles (Scolytinae) are small beetles a few millimeters in size. Their larva develop under tree bark eating the phloem, xylem, and cambium layers. Certain species cause extensive forest damage by killing healthy trees, while others only impact weakened individuals. The eating patterns (called galleries) and the trees’ defensive reactions cause disturbances in the nutrient and water cycling within the trunks. The trees literally dry to death.

Bark beetles can be detected by the gallery patterns they leave on tree trunks. These patterns are species-specific, and often very beautiful. The patterns can be used to recognize infestations and begin warding off the worst damage. Then again, the gallery patterns cannot be seen until the tree bark falls off.

Bark beetles also have a secret weapon: wood-staining fungi. This group of fungi includes several species that damage wood or cause serious diseases to trees. Bark beetles and wood-staining fungi have developed various relationships such as the ambrosia beetles that spread certain fungi species into their galleries to farm them for food. Wood-staining fungi benefit from the bark beetles transporting them to new trees, and have developed exceptionally sticky spores that attach to adult beetles as they are preparing to disperse. Bark beetles also benefit: the fungi weaken new tree individuals, giving adult bark beetles the opportunity to infest and lay their eggs in these trees.

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A possible wood-staining fungus is spreading beneath the bark of a birch infested by the birch bark beetle. ©Stella Thompson

It’s hard to believe that tiny beetles and even more minuscule fungi can kill gigantic trees. Situations where a bark beetle or fungi spreads to a new geographical region among lumber are particularly devastating. The new host trees have no immunity or defense mechanisms against this new organism and the alien species spreads like wildfire.

Dutch elm disease is a prime example of this. Ophiostoma ulmi, a fungus killing elm shoots spread from Asia initially to Europe and then, fueled by the post-World War I reconstruction boom, from Europe to North America in lumber. European elm species coped with the disease slightly better than their North American cousins. European elms also died, but the spread of the disease around Europe took several decades and finally the outbreak waned. 10–40% of the elms died, depending on the country in question. The situation was very different in North America. The American elm (Ulmus americana), a very popular urban and ornamental tree, formed large forests in the eastern areas of the continent. It narrowly escaped extinction through active eradication and education measures such as campaigns forbidding the transportation of firewood outside infected states. Unfortunately, a new, much more virulent fungus (Ophiostoma nova-ulmi) causing Dutch elm disease spread to Europe and North America during the 1940s. This fungus has caused the near annihilation of elms from several European countries. As of yet Finland has mostly been spared by the disease, but this may change with a warming climate that allows beetles belonging to the Scolytus genus that carry Dutch elm disease to overwinter in more northern regions. These beetles are already found on the northern coast of Estonia and in the Stockholm area of Sweden. The birch bark beetle (Scolytus ratzeburgi), commonly found in Finland, does not spread Dutch elm disease as it has specialized in solely utilizing birch trees.

However, the birch bark beetle spreads the Ophiostoma karelicum -fungus. Trappings

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The presence of birch bark beetles can be detected by their unique eating patterns. ©Stella Thompson

conducted during 2008 and 2009 for a study carried out in Norway, Finland, and Russia revealed the prevalence of O. karelicum: every single birch bark beetle individual carried the fungus, which was also found in each of the beetle’s galleries that were searched. The life cycle and ecology of O. karelicum is very similar to the fungi spreading Dutch elm disease, and the commonness of the fungus and the birch bark beetle means a very high risk of the disease spreading to e.g. North America. The birch species native to North America would most probably have no resistance to the disease.

On the other hand, pitch canker (Gibberella circinata) is a fungus spread by bark beetles, originating in North America, which has now spread to Europe where it causes pine mortality. The Scots pine (Pinus sylvestris), native to e.g. Finland, is especially susceptible, but the disease has not spread as far north as Scandinavia yet.

To make these dynamics even more complicated, several mite species have also been shown to transport or act as the primary hosts of wood-staining fungi. These mites are in turn spread by bark beetles. The relationships and interactions between these three organisms are still poorly understood.

The disease resistance of tree species can be increased through cultivation. American elm cultivars more resistant to Dutch elm disease have been found, and their disease resistance has been further enhanced through cultivation. These cultivars are most probably the reason that elm forests still exist today in North America, although the age and size composition of these forests has changed considerably with the death of the old and large trees. Biological and chemical disease control is also a possibility: fungicides can be injected into live trees to stop the spread of specific diseases. Six fungicides combating Dutch elm disease are currently on the market in the US.

Similar control measures can most probably be developed against O. karelicum. However, widespread injection campaigns are difficult to implement. In the US, Dutch elm disease is mainly controlled by injecting individual ornamental or urban trees. Injection control as an effective eradication measure requires more development before it becomes a feasible tool for preventing damage caused by alien species.

Crawlers and fliers – how to study forest insects

Studying insects is interesting yet challenging. Determining individuals to the species level

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The presence of birch bark beetles can be detected by their unique eating patterns. ©Stella Thompson

nearly always requires capturing them first, although some species, such as the birch bark beetle (Scolytus ratzeburgi), can be identified by the unique pattern they leave on tree trunks. However, it is almost always necessary to use various types of traps to capture individuals if identifying the insect species present at a certain site is the main objective of a study. For example, butterflies are trapped during the night using light traps, and the occurrence of certain protected species can be confirmed using feromone traps that use synthetic lures as bait. Traps can be dug into the ground, lifted high up into tree canopies, or attached to the insides of hollow tree trunks.

As my PhD research I am assessing how beavers affect forest beetle populations. I have several research questions:  do beaver-induced flood zones have different beetle species assemblages than other areas, do the increased moisture and sunlight conditions in the flood zone affect species assemblage, and do beaver areas advance or hinder potential forest pest or protected species. My research combines a game species with widespread effects on its surroundings and forest beetles, several species of which have become scarce and require protection. Beaver-induced flooding and the species’ habit of felling tree trunks may locally disturb forest owners, but my study is looking into whether beavers’ actions facilitate or disturb forest pests. Combining game and insect research is cool, and generates new information on which to base decision-making for future protection measures, beaver population management, and even for using beavers as a natural tool for restoring degraded wetlands and forests.

Window traps are widely used for determining the insect assemblages of sites. Window traps cannot be used to capture specific insect groups, because all sorts of invertebrates ranging from flies to pseudoscorpions and wasps to beetles creep or fly into them. Window traps are very simple: the trap is attached to a tree trunk or set to hang between two trees. Insects crawl or fly into the plastic plexiglas frame and then fall through the funnel into a liquid-filled container at the bottom. The container is filled halfway with water, dishwashing fluid, and salt. The dishwashing fluid prevents the insects from regaining flight, consequently drowning them. The salt helps preserve the insects until the trap is emptied out, which happens about once a month. I have 120 traps spread out at several sites, so every summer I collect about 600 samples.

Unfortunately other creatures may sometimes end up caught in the window traps. So far I have inadvertently captured a few common lizards and a bat. This is always disappointing, because an individual dying for nothing does not advance research or science in any way. In the same way it is frustrating if you unintentionally set up a trap on a tree trunk that an ant colony uses as its route. Hundreds or even thousands of ants may drown in the window trap. As my own study focuses on beetles, I cannot utilize the ants in any way. At least this does not happen very often.

After the trap container has been emptied the gathered sample is sifted through using tweezers and a microscope, to separate the insect groups that I am interest in. Next the individuals are determined to the necessary level. Sometimes determining the family level is enough, but if making conservation decisions or gaining new information on certain species is the goal, it is usually necessary to determine individual insects to the species level. How this is done depends on the order in question, e.g. beetles are often recognized by their ankles and genitals.

Occasionally you come across data deficient species, i.e. species that are not well known or understood. Species, genera, and families are determined using identification keys, which are sometimes incomplete. For example, currently the best key for identifying Finnish rove beetles is in German, and for several families the most complete keys are in Russian. So I’m currently kind of happy that I studied German in middle and high school. I guess next I should begin uncovering the secrets of Russian vocabulary.

Let’s ban lead shot!

The use of lead shot and sinks is a global phenomenon. Only the past decades has

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Grouse species also suffer from the harmful effects of lead shot. ©Stella Thompson

increased our understanding of the negative effects that toxic lead shot inflicts on ecosystems. As an example, birds die of lead poisoning after eating lead shot. They mistake the ammunition for sand or grit, which they use to aid their digestion. The birds’ gizzards and stomach acids dissolve the shot, causing lead to accumulate in their bones. As little as two lead shots is enough to directly cause the death of a mallard-sized animal.

During the 1980s, the US Fish and Wildlife Service (USFWS) conducted a study on the effects of lead exposure on water birds such as waterfowl. Diving ducks were found to be most susceptible, but lead shot was also commonly found in dabbling ducks, geese, and swans. Long-term monitoring by the USFWS also uncovered negative effects on bald eagle (Haliaeetus leucocephalus) populations, and since then, several studies have found harmful effects to numerous animal groups around the world, e.g. bears, deer, predatory birds, doves, loons, and frogs. International studies also associate lead shot with increased lead concentrations in people who regularly consume game.

A federal ban on using lead shot for waterfowl hunting was issued in 1991 in the US. Since then, 34 states have decreed tighter state-wide bans, e.g. California completely banned the use of lead shots in the home ranges of the California condor (Gymnogyps californianus), and by July 2019 California will completely ban lead shot in all forms of hunting, the first state to do so.

But what is the European Union’s game plan concerning lead shot? A total ban has been proposed, but the motion is currently only a thought, and we are still miles away from actual progress. Several countries in the EU have issued various types of bans, e.g. the lead shot has been prohibited in wildfowl hunting in Finland since 1996. The US also seems far from a federal ban.

So what’s the big deal, why are we not stepping up and pushing forward?

Not everyone has been satisfied with the disappearance of affordable, high quality, and gun-safe lead shot. The lead shot ban has caused a great deal of debate and criticism over the years. Many are hoping to weaken the ban in waterfowl hunting to only concern certain shallow wetlands or very important rest areas along migration routes. Those opposing the ban have based their arguments on several propositions formed in the 1990s, which have since been scientifically proven incorrect:

 

Claim 1: Lead shot is not dangerous, because it is believed to rapidly sink to the bottom of wetlands, where waterfowl cannot reach it.

After initiating the partial lead shot ban in 1991, the USFWS began long-term monitoring of its affects. Lead shot –induced mortality in mallards dropped by 64% in the six years following the ban. And this is a dabbling duck species, which according to studies should not even suffer the most from lead poisoning. The impacts that the ban has had on diving duck populations, which find their nutrition from the bottom mud layer of wetlands, or on small duck species are probably even more pronounced. Lead poisoning additionally causes e.g. reproductive problems, which can lead to long-term population declines even without directly killing all individuals. For example, a French research group found that female teals carry shot in their gizzards more frequently than males do, wherefore females had worse survival rates than males. A study in the US relates 17–46% of the mortality of loons directly to lead shot, while the same estimates for swans and bald eagles are 31% and 12%, respectively. The lead shot ban is estimated to annually save 1.4 million waterfowl in the States alone. In Canada, the lead concentrations found in the bones of water birds lessened by 50–70% following a ban. An although loons are not hunted as game, their population declines due to lead shot and sinks should be taken in to consideration when considering the fate of toxic lead shot.

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Both teal and mallards suffer from lead poisoning, which besides causing death also causes behavioural abnormalities. This makes individuals more susceptible to hunting. ©Veli-Matti Väänänen.

Claim 2: Alternative shot types (mainly steel, vismuth, and zinc) are inefficient and expensive.

A 2015 study in the US compared the effectiveness of lead shot and two types of steel shot in the hunting of mourning doves (Zenaida macroura). No differences were found in aim, the number of injured escapees, hunter satisfaction, or realized quarry numbers. Necropsies of shot doves revealed no differences in the numbers of through-body shots or average strike depths. Steel shot was therefore found to be accurate enough for dove hunting. A poll study found nearly 80% of US hunters to prefer steel to lead shot, or at least consider the two equally effective. Initially the steel shot sold in several countries tried to mimic the qualities of lead shot. The resulting low muzzle velocities and large ammunition size led to poor hunting success. Higher quality steel shot is currently widely available, but the damage caused by poor shot quality was immediate, and is the only reason why steel shot still carries a bad reputation. Many people tested steel shot once or twice, and returned to illegally using lead shot despite the bans.

Steel shot was additionally about four times as expensive as lead shot when the ban was issued in the US, but rising demand has caused their prices to drop significantly. The same would probably occur in many European countries, where demand to increase.

 

Claim 3: Hunting with alternative ammunition increases the numbers of wounded animals. This has been suggested to happen because of the ineffectiveness of non-lead shot and hunters being unaccustomed to lighter weight ammunition.

The USFWS annually conducts a poll inventorying e.g. the numbers of total hunted quarry and injured escapees. During the 1950s and ‘60s, the number of injured escapees was about 20%, but initially grew to about 24% after the partial led shot ban. However, a few years later numbers dropped down to initial levels, as hunters became used to the new shot. During the last years the level has dropped to 14%. The study conducted on mourning dove hunting success also did not reveal any differences in the numbers of injured escapees. So if European hunters are still performing worse after lead shot bans in their countries, they should perhaps consider looking in the mirror and wondering what’s wrong with their aim.

 

Claim 4: The lead shot ban has decreased realized duck quarries, e.g. because hunting and hunting success have lessened.

To date, there is no scientific proof to back either of these claims. But on the contrary, waterfowl populations have decreased markedly during this same time period due to disagreeable habitat change. Could this, by any chance, be the actual reason for diminishing quarry sizes? Especially as assessments and research show that hunters have in fact not obeyed the lead shot ban very widely. For example, 90% of Finnish hunters are still estimated to use lead shot in waterfowl hunting. About 70% of the ducks shot in Britain carry lead shot in their bodies. This means that the use of steel shot cannot have decreased duck quarries, because steel shot simply isn’t being used.

However, one actual problem is that steel shot cannot be used in certain older shotguns. This has probably slightly lessened the duck hunting enthusiasm of some elderly hunters.

 

Unfortunately, the European Commission wants to focus on only lessening the amounts of lead found in wetlands. The EU has ratified the UN’s Convention on the Conservation of Migratory Species of Wild Animals, so we should be rid of lead shots within three years. Therefore it is fairly questionable that a total ban is currently not being discussed in more detail. A few EU nations, e.g. Denmark and Holland, have executed a total ban, thus preventing the use of lead shot in any forms of hunting. Nothing appears to be happening in the US either. Despite the encouraging results on the number of lead poisoning incidents dropping dramatically, the effectiveness of partial bans is just too weak. An overview from 2015 by the University of Oxford estimates that 50 000 to 100 000 birds die annually from lead poisoning in Britain alone. According to the Finnish Food Safety Authority and the Finnish Museum of Natural History, every third white-tailed sea eagle (Haliaeetus albicilla) death is directly related to lead poisoning. Partial bans are ineffective and their execution cannot be properly monitored. A total ban would also create pressure to develop shot that would work well with older shotguns. Now is the time to finally completely ban lead shots.

 

Additional information

on lead poisoning occurring in several bird species

http://link.springer.com/article/10.1007/BF00119051

http://www.nwhc.usgs.gov/disease_information/lead_poisoning/

 

on the mourning dove study

http://onlinelibrary.wiley.com/doi/10.1002/wsb.504/full

 

on the effects of lead on teals

http://www.sciencedirect.com/science/article/pii/S0006320707001346

Golden eagles deter foxes, facilitate forest grouse

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Top predators can have surprising effects on ecosystems. Golden eagle @Sari Holopainen

The effects of top and mesopredators on lower levels of food webs have been researched from many perspectives, but less focus has been given to the roles that avian top predators play on mid-sized mammalian predators. The cascade effects of raptors, which concurrently affect several trofic levels, have also gained little attention. However, researchers at the University of Turku have observed how the golden eagle (Aquila chysaetos) affects pine marten (Martes martes) and red fox (Vulpes vulpes) populations, along with the cascade affects induced on black grouse (Tetrao tetrix) and hazel grouse (Tetrastes bonasia) populations.

Golden eagles hunt black grouse, red foxes, and pine martens. When the opportunity arises they will also catch hazel grouse, but because of their smaller size and habitat preferences (thick forests), hazel grouse are better protected from golden eagles, which prefer open territory when hunting. The researchers initially hypothesized that the golden eagle would locally lessen the numbers of red foxes and pine martens, thereby causing a positive affect on the two grouse species.

However, the truth is not quite as simple. Pine marten and red fox densities actually increase in areas with large numbers of golden eagle. One possible reason behind this surprising result could be the large prey populations available for all three predators in these areas, along with the partially overlapping habitat preferences of pine marten and golden eagle. On the other hand, pine martens avoid open territory, possibly because of the non-lethal deterrent effect that golden eagles exert on pine marten.

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Top predators can have surprising effects on ecosystems. Golden eagle @Sari Holopainen

But the story doesn’t end here: high densities of golden eagles still does have an effect, as larger numbers of young hazer grouse and black grouse are present at these sites. The golden eagle may therefore facilitate the grouse by lessening the numbers of mesopredators in their territories through the deterrent effect. This would lead to less predation and egg eating by the pine marten and red fox. In other words, red fox and pine marten avoid golden eagles so effectively, that the two grouse species benefit from their weakened predation performance. A similar protective effect has also been observed with the goshawk (Accipiter gentilis).

Increasing golden eagle territory and offspring densities cause decreasing numbers of black grouse, but this does not occur with hazel grouse. The small size of the hazel grouse most likely protects it from golden eagle predation. The black grouse, on the other hand, favors open territory. Golden eagles therefore appear to have a protective effect on juvenile hazel and black grouse individuals, while threatening adult black grouse.

Wetland_ecology_group_University_of Helsinki_black grouse

Black grouse lekking @Stella Thompson

The cascade effects directed at these grouse species do not appear to change with fluctuating pine marten and red fox densities. The presence of other mesopredators, e.g. raccoon dogs (Nyctereutes procyonoides) and the American mink (Neovison vison), has been suggested as the reason for this. The effects of these other mesopredators were not assessed during the study.

The golden eagle affects mesopredator behavior without affecting their population densities. A similar deterrent effect has previously been observed from white-tailed sea eagles (Haliaeetus albicilla) on the American mink, and golden eagles most probably also deter minks and raccoon dogs. The eagles additionally deter the movements of other potential egg thieves such as corvids.