Providing evidence to improve practice

The journal, Conservation Evidence

Our online journal publishes research, monitoring results and case studies on the effects of conservation interventions. All papers include some monitoring of the effects of the intervention and are written by, or in partnership with, those who did the conservation work. It includes interventions such as habitat creation, habitat restoration, translocations, reintroductions, invasive species control, and education or integrated conservation development programmes, from anywhere around the world.

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Volume 5



Two translocations of silver-studded blue butterflies Plebejus argus (30 in 2006 and 72 in 2007) were made to an area of suitable unoccupied heathland from a nearby donor site. Monitoring of the 2006 release site in 2007 revealed the presence of only four butterflies. Several factors may have accounted for the low numbers. Poor weather (wet and cold) during the flight period may have been partly responsible, but the trend of earlier emergence of silver-studded blues may be a factor; over the last few years, there has been a trend towards earlier emergence and peak counts in June rather than July. Consequently, if the donor butterflies were collected later in the flight period after the peak count as was the case in 2006 and 2007, the proportion of fresh, actively-laying females may have been lower than in previous successful translocations conducted at other localities. In view of this, it is recommended that a further 30 fresh female butterflies are collected early in the flight period in 2008 and are translocated in order to enhance establishment success.

 

Cutting, removal and herbicide stump-treatment of dense grey willow Salix cinerea scrub from a 1 ha wet dune-slack was undertaken in a northwest England National Nature Reserve. This resulted, over the next two years, in colonisation by 139 vascular plant taxa. Of these, 11 are nationally or regionally notable, with 28 being new reserve records. The high proportion of ruderal plants in the first year was largely replaced by dune species in the second season after scrub removal.

 

In a 7-year field experiment undertaken in western Norway, the efficiency of four bracken control measures on a heathland was investigated: application of two herbicides i) Asulox®- and ii) Gratil®-with follow-up annual cutting; iii) annual cutting; and iv) biannual cutting. Assessments were also made as to what extent the characteristic species composition and vegetation structure of heathlands were restored, and effects of the herbicides on non-target plant species commonly found on heaths. Fastest reduction in bracken cover resulted from herbicide application, but cutting proved equally efficient in the longer term; Asulox and biannual cutting both reduced bracken cover from over 70% to below 10% in 2 years, while annual cutting achieved this in 5 years. Gratil failed to have long-term effects. Species composition progressed towards a desirable heathland vegetation community, but successional trajectories differed, and Asulox had minor unintended effects on a number of heathland plants, including heather Calluna vulgaris, several grasses, herbs and mosses. These effects could not be predicted by functional group or other simple species characteristics. However, any short-term detrimental effects of Asulox application were considered to be outweighed by the beneficial longer term effects of reduced bracken cover, which allowed re-establishment of the heathland flora.

As part of a larger project attempting to reduce predation pressure from introduced rats Rattus spp. on native fauna and flora on several islands off Pohnpei main island (Pacific Ocean), a rat eradication program was undertaken on the small island of Nahkapw (1.58 ha). Prior to commencement of eradication, a pre-treatment rat population assessment was undertaken; only a single female ship rat R.rattus was caught (subsequently fitted with a radio-collar and released) and wax indicator success was also very low, suggesting that the island hosted a very low density of rats. Bait-stations were positioned on the ground along two transects that ran the length of the island spaced approximately 20 m apart; the distance between the two transects varied but was never less than 10 m or more than 30 m. After 2-weeks of inactivity, these stations were supplemented with 22 bait stations attached to tree trunks adjacent to each ground-based bait station. These tree bait stations were maintained until the radio-collared rat died (25 days after initial bait placement). There was no evidence of non-target species being adversely affected by the bait.

As part of a larger project attempting to reduce predation pressure from introduced rats Rattus spp. on native fauna and flora on several islands off Pohnpei main island (Pacific Ocean), a rat eradication program was undertaken on the small island of Dekehtik (2.63 ha) where Pacific rats R.exulans were present. The island was systematically hand-broadcast with rodenticide bait at a pre-determined application rate of 50 kg/ha over one day. Radio-tracking revealed that rats spent a significant amount of time in the forest canopy. Therefore, to ensure that rats living in the canopy had a good chance of encountering bait, bait clusters (bolo baits) were fabricated and catapulted into one third of the palm trees on the island. Pre-bait application trap success (rat captures/trap nights) was 52%. Post-bait application trap success (as recorded 12-15 days after bait application) was 0%. Although rat chew marks were found on one wax indicator block 12 days after the bait application, subsequent monitoring detected no rats. No non-target species appeared adversely effected by the rodenticide bait.

As part of a larger project attempting to reduce predation pressure from introduced rats Rattus spp. on native fauna and flora on several islands off Pohnpei main island (Pacific Ocean), a rat eradication program was undertaken on the small island of Pein Mal (2.17 ha) where ship rats R.rattus were present. The island was systematically hand-broadcast with rodenticide bait at a pre-determined application rate of 50 kg/ha over one day. Radio-tracking revealed that rats spent a significant amount of time in the forest canopy. Therefore, to ensure that rats living in the canopy had a good chance of encountering bait, bait clusters (bolo baits) were made and catapulted into one third of the palm trees on the island. Mangrove forest surrounds the shore of Pein Mal where rats were also present. Throughout this habitat to ensure rat access to the rodenticide, a bait station grid was established with bait stations nailed to tree trunks approximately 2 m above the high water mark. Pre-bait application trap success (rat captures/trap nights) was 39%. Post-bait application trap success (as recorded 10-14 days after bait application) was 0%. Pre-bait application wax indicator success was 53%. Post-bait application wax indicator success was 0%; subsequent monitoring 6-months later detected no rats. No non-target species appeared adversely effected by the bait.

 

We report on the translocation of Seychelles magpie-robins Copsychus sechellarum, from the island of Frégate to the island of Cousin between 1994 and 1995. Prior to this translocation, the world population consisted of 47 individuals confined to Frégate . Five magpie-robins were translocated to Cousin and subsequently a new self-sustaining breeding population was established; this population increased almost 10-fold in less than 12 years to a high of 46 individuals in May 2006. It is now currently experiencing signs of regulation with a slight decrease in numbers with 31 birds recorded in June 2007. It is hoped that ongoing studies will identify the reasons for this decline, which at present are unclear.

 

Grasshoppers and crickets (Orthoptera) were monitored in the Mardyke River Valley in south Essex in July and August 2007. A standardised transect method was used to count Orthoptera in horse-grazed and ungrazed pastures. Sward height measurements were taken from each pasture. In ungrazed pastures Orthoptera were much more abundant (17.3 individuals/100 m) with greater diversity (7 species) than in grazed pastures (0.8 individuals/100 m; 4 species). The low sward height of the grazed pastures (< 6 cm on average) is considered to have afforded Orthoptera little shelter from inclement weather or avian predators. Based on additional observations, a reduction in the grazing pressure from 3.5 horses/ha (current grazing density to the south of the Mardyke) to less than 2 horses/ha would lead to a more heterogeneous and overall taller sward, which would be favourable for orthopterans and a wider range of other grassland invertebrates.

Great spotted woodpeckers Dendrocopos major predated nestlings from 14 out of 57 blue tit Cyanistes caeruleus broods by pecking through the sides of wooden nest boxes in 2005. Therefore, 31 nest boxes were covered with wire mesh prior to the 2006 breeding season. This action was largely successful, as nestlings from only 1 out of 48 broods of blue tits were predated in the 2006 breeding season. Therefore, covering nest boxes of this type with wire mesh appeared to be a simple and effective method of reducing woodpecker predation rates upon nest box breeding birds.

 

In August 2005, 20 North Island saddleback Philesturnus rufusater were translocated from Tiritiri Matangi Island to Motuihe Island in the Hauraki Gulf, New Zealand. Post release survival over the first year was high (70%). A minimum of 11 juveniles successfully fledged in the 2005/2006 breeding season bringing the population to a minimum of 25 birds one year after release. Assuming long term success this translocation brings the total number of island populations of North Island saddleback to 13 and contributes to the ongoing ecological restoration of Motuihe Island.

Arable field margins were established by natural regeneration or sowing with a legume seed mixture in 2001 on farmland at Romney Marsh in Kent. Establishment of bumblebee Bombus spp. forage plant species was monitored using frame quadrats from 2001-2004. Monitoring showed that the natural regeneration margins had low species richness of forage plants, and a sward dominated by creeping thistle Cirsium arvense or bristly ox-tongue Picris echioides, 'weed' species, which are unlikely to be favoured by the farmer or used extensively as forage plants by bumblebees. In the sown margins, the abundance of red clover Trifolium pratense and alsike clover T.hybridum was extremely high one year after margin establishment (almost 100% ground cover combined), but declined rapidly for T.hybridum two to three years after sowing. The subsequent invasion of the clover-dominated margins by perennial grass species in 2003 and 2004 suggests that legume swards may need to be re-sown every three years due to the poor persistence of Trifolium spp.

Renovation of historic buildings and measures to limit access by feral pigeons Columba livia var. domestica has a strong negative impact on some lesser kestrel Falco naumanni populations by reducing nest site availability thus lowering reproductive success. In order to test the efficacy of nest boxes as a means to mitigate for such loss of nesting sites, we studied the occupancy rate of roof-top nest boxes and compared their performance to that of 'natural' nests (i.e. located in cavities in bulidings and under roofs within buildings). Of 200 nest boxes provided, 16 (8%) were used for breeding in the first year (2007) and 35 (17.5%) in the second year (2008); it is expected that occupancy will increase substantially in subsequent years. In 2007, the number of fledged young produced/pair in nest boxes (1.82 young) was similar to that of attic nests (1.66 young), whilst those nest located with cavities (2.70) had a much higher reproductive output. In 2008 the number of fledged young produced/pairs in nest boxes was 1.54.

A small but important population of the endangered Java sparrow Padda oryzivora nests within crevices between stone blocks of an ancient temple complex in Java. In response to nest site losses due to temple restoration, and subsequently further damage to nest sites caused by a major earthquake, artificial nest sites (wooden nest boxes, sections of bamboo, and coconut shells) were provided. In the subsequent breeding season (2007), two pairs of Java sparrows successfully nested in these wooden boxes, one pair fledging seven young and the second pair two young. In 2008, three pairs again nested in the wooden nest boxes (located in different trees): one nest had nine eggs but failed as the parents were taken by a local birdcatcher; the second nest had 12 eggs, six of which hatched and subsequently fledged; the third pair fledged three young. A coconut shell was prospected by one pair but not used for nesting.

 

To mitigate for loss of a dyke supporting a population of the nationally rare grass-wrack pondweed Potamogeton compressus due to be infilled during flood defence works, a new section of dyke was excavated. Grass-wrack pondweed turions were collected prior to infilling of the old dyke and grown on, both indoors and outdoors, for transplanting into the new dyke once completed. The pondweed was also present within adjoining dykes potentially at risk to increased turbidity/siltation and/or water pollution, plus hydrological changes during construction works. Therefore, to reduce these risks, measures were implemented, including bunding of internal dykes and installation of 'silt curtains' to minimise such impacts. Finally, as the old dyke was infilled, the majority of the green material was removed by hand using grapnels, and sections of silt (including turions) where the plant was growing were sequentially removed mechanically and placed into the adjacent new length of replacement dyke. Monitoring of the new dyke in 2007 and 2008 (one and two years after creation) indicated successful grass-wrack pondweed establishment; in 2007 it was the dominant taxa. In 2008 its density was lower, however cover of other aquatic species had significantly increased. The results are consistent with those of another translocation, where good populations were present during the first 2-3 years of establishment, with populations tailing off as the new habitat is colonised i.e. the species is considered a primary coloniser.

 

Use of purpose-built hibernacula by great crested newts Triturus cristatus and other amphibians was evaluated at three sites (eight hibernacula in total) in autumn and a single site (two hibernacula) in spring. Autumn monitoring entailed regular checking under roofing felt tiles placed on the ground (these provide damp, dark refugia which are attractive to newts) in the vicinity of the hibernacula. Although no great crested newts were found under the tiles, six common frogs Rana temporaria and nine common toads Bufo bufo) were recorded at two of the sites. A combination of drift fencing and pitfall trapping was used during spring surveys; a total of 21 amphibians (six great crested newts, six smooth newts T.vulgaris, seven common toads, two common frogs) were caught in the pitfalls in the vicinity of the two hibernacula. In addition, one smooth newt and two toads were caught in a drift fence control situated away from the hibernacula but at a similar distance from the breeding pond. The results appear to demonstrate that the hibernacula are being used (at least in small numbers) by amphibians, including great crested newts at one site.

The netted carpet moth Eustroma reticulatum is one of the rarest moths in the UK where it now occurs only in a few sites in The Lake District of northwest England. In the late 1990's there was a decline in its larval foodplant, touch-me-not balsam Impatiens noli-tangere; a highly isolated netted carpet colony at Derwentwater almost certainly became locally extinct because of the extreme food shortages. Subsequently the balsam recovered and an attempt was made to reintroduce the moth to this locality by translocation of 30 larvae in September 2006. However, in September 2007 the site was surveyed for larvae, but none were found. The procedure was repeated (40 larvae translocated) in September 2007 but at an alternative site at this locality where the foodplant was more abundant and conditions were considered more favourable. In September 2008, surveys revealed four netted carpet moth larvae, considered progeny of the previous year's introduction; in order to bolster this initial success, a further 150 larvae were translocated. This movement of larger numbers of larvae was possible because of their unprecedented abundance found in the actively managed donor site. Monitoring is ongoing to ascertain the longer-term success of the translocations.

 

Waterfowl and breeding bird surveys were conducted at Abberton Reservoir Special Protection Area between 2004 and 2006 as part of a study related to an environmental impact assessment. A secondary finding of these surveys revealed a significant level of mortality in spring for mute swans Cygnus olor, and other waterbirds that were colliding with nearby overhead power lines. In the spring of 2004, nine mute swans were killed through collision with the 132Kv power lines, while in spring 2006, 21 were killed. In the summer of 2006, over 500 red flight diverters (320 mm long, 175 mm diameter) were installed at 5 m intervals along a 1.5 km length of the power lines. In the spring of 2007 only one mute swan was killed through power line collision, while in spring 2008 none were killed. The perpendicular distances over which bird carcasses were found on the ground from under the overhead power cables ranged from 10-351 m. This should be taken into account when designing future collision mortality surveys for similar power lines. It is recommended that appropriate bird flight diverters are fitted as routine best practise when installing any new overhead power lines.

A remote controlled camera proved a practical solution to survey a single, one-entrance outlying badger Meles meles sett in late January (outside the normal licensing period for disturbing badger setts), which was found to be present on the route of a proposed water pipeline. Upon ascertaining that the sett was almost certainly unoccupied, the sett was immediately taken apart and filled in following strict guidelines specified under the terms of the Natural England licence (supervised by the relevant authority), to allow pipe-laying activities to continue. Once the pipeline is installed and construction completed, badgers will be able to re-colonise the same area of ground.

 

Thinning of the woodland canopy by selective tree felling and removal of humus and nutrient-rich soil by scraping are techniques being used as a first step to regenerate heathland vegetation and associated insect assemblages at Norton Heath Common in southeast England. Two years subsequent to initial restoration activities, there has been germination and establishment of two heathland plant species, gorse Ulex europaeus and sheep's sorrel Rumex acetosella, in the tree-cleared and soil scraped areas, whilst the warmer microclimate created by tree felling has led to higher thermophilous insect species richness, particularly of butterflies. It is hoped that the continuation of felling and soil scraping will lead to the return of other characteristic heathland plants, especially heather Calluna vulgaris, and rarer species such as lousewort Pedicularis sylvatica.