BDIgest Friday, 6 April 2018

This week, we take a look at a fascinating study on a migratory bird and how the authors teased out potential drivers of population trends. We also see an interesting experimental study about our tendency to redistribute wealth and our capacity for tolerating inequality. Finally, we look at three methods papers – one that tackles pseudoreplication, and two that address remote sensing.



Vermivora chrysoptera: Mark Peck 2013 (CC BY-NC-SA 2.0)

Birds of a feather don’t necessarily flock together

In a remarkable study reported (with commentary) in PNAS, we learned this week about “migratory connectivity” – a strong association between geographically-distinct breeding and nonbreeding areas. Kramer et al. (2018) determine the cause of population declines in one distinct breeding population of golden-winged warblers, by bringing together several lines of evidence. They used migratory data (70 individuals with geolocators), long-term (since 1966) citizen science population trend data, and land cover data for nonbreeding sites for two congeners, blue-winged and golden-winged warblers. These species are ecologically similar and migrate between approximately similar regions. This setup provided a good phylogenetic control. The breeding population of golden-winged warblers from the Appalachian Region appears to be in decline, while the other breeding populations of this species and breeding populations of the blue-winged warbler appear relatively stable. The blue-winged warblers exhibit weak migratory connectivity, with somewhat distinct breeding populations mixing in their nonbreeding area. The golden-winged warblers, by contrast, exhibit strong migratory connectivity with distinct breeding populations using distinct nonbreeding areas. The only declining population, from the Appalachian breeding site, was also the only population of either species to over-winter in northern South America, where it appears that habitat degradation (forest loss) may be linked to the population decline.

DOI: 10.1073/pnas.1718985115
With commentary:
DOI: 10.1073/pnas.1802174115

Ed: This study is quite unique in its breadth, depth, and use of phylogenetic controls. Deploying enough geolocators and recapturing 70 of the tagged birds after a year is phenomenal and provided a rich dataset on migratory movements in these two species. Having Breeding Bird Survey data going back to 1966 also provided a clear picture of population trends for both species, which, in turn, represented a neat phylogenetic control.




A little bit of Robin Hood doesn’t go enough of the way

Why do we struggle with inequality? Bechtel et al. (2018) try to answer that question using an experimental game played by a large number of German and United States study subjects (nearly 5000, in total). All participants were placed in random “pairings” whereby both participants recieved a “payout”. The pair partners were unknown to each other. The distribution of the winnings were such that the participant won either USD 25 (versus USD 75, i.e. disadvantageous inequality within the pair), USD 50 (versus USD 50, i.e. equality within the pair), or USD 75 (versus USD 25, i.e. advantageous inequality). Each participant was allowed to give to or take from their partner any sum they pleased. In general, participants tried to redistribute the winnings more equitably when they were in either inequality pairing: participants who received USD 25 took money from their USD 75 partners, and USD 75 participants gave money to their USD 25 partners. Even though the difference in winnings in the inequality pairings was USD 50, participants only gave/took USD 10 to/from their partners (on average). This would suggest that people try to apply some redistribution of wealth, but are generally quite comfortable with retaining relatively large inequalities – even when the starting point for both partners in a pair was essentially a luck-based lottery winning.

DOI: 10.1073/pnas.1720457115

Ed: Even though the dollar values in this study were somewhat trivial, this study still gives important insight into human behaviour with regard to tolerance of inequality and redistribution of wealth. Some of the study strengths include a very large sample of participants (who were representative of the adult voting public), and a “survey instrument” that allowed participants to both donate to and take from their partners.




Tetrao urogallus: David Palmer 2012 (CC BY 2.0)

Crying fowl over pseudoreplication

Individual variation in physiological responses to stressors, and individual variation in metabolism of circulating stress hormones are both relatively under-appreciated aspects of non-invasive hormone monitoring. Coppes et al. (2018) address this issue in an extensive study of faecal glucocorticoid metabolites in the capercaillie in Germany. The authors modeled (as the “full” model) the variability in the faecal glucocorticoids using several environmental parameters and animal sex (as fixed effects), and controlled for the individual variability using a random effect for animal ID. The authors then compared this model to a “naive” model that assumed each sample was independent and thus allowed for pseudoreplication (treating non-independent samples from the same animal as independent samples). The full and naive models differed in which parameters were considered significant and differed in how much variance was explained.

DOI: 10.1111/1365-2664.13140

Ed: Although treating repeated measures from individuals is an important step in analysis, as the authors highlight, the broader issue that this study exposes, is the problem of pseudoreplication. By removing the random effect for individual ID in the “naive” model, the authors were actually incorrectly increasing the effective sample size by assuming that the multiple samples from a given individual all contained unique information. Naturally, this would change how much variance could be explained by the model, and it could allow additional variables to be selected as significant, simply by inflating the sample size. The important take-home message here might be that researchers need to think clearly about pseudoreplication during study design (incorporating sufficient spatial or temporal separation in sampling to reduce pseudoreplication) and during statistical analysis (for example by using a random effect in a random effects or hierarchical model).




Sixth sense

Remote sensing offers the promise of being able to monitor biological populations in areas that are difficult or dangerous to reach, with ease, speed, and costs that might outperform traditional human observers. However, to date, remote sensing has mostly been used successfully when counting large animals across a relatively small spatial scale when the background substrate is relatively homogeneous. As this review in Methods in Ecology and Evolution shows, there are still a number of obstacles to overcome before remote sensing can play a larger role in monitoring biological populations. Some of these obstacles include the cost of high-resolution data, and the ability to automate the organism detection and counting process, which is currently still subject to error.

DOI: 10.1111/2041-210X.12973

Ed: This is a field ripe for further development and improvement, both in counting animal populations and plant populations (not addressed in the review).




Drones for clones

As an example of one of the scenarios where remote sensing may prove helpful in counting animal populations, Hodgson et al. (2018) performed rigorous ground-truthing for drone-based remote-sensing of a seabird colony. The authors created replicas of seabirds of known number so that they could compare the accuracy of ground-based counts by human observers with counts based on drone imagery processed manually or with a semi-automated process. The drone-based counts were more accurate than the ground-based counts.

DOI: 10.1111/2041-210X.12974

Ed: This study demonstrates an important aspect to any remote sensing study – the need for rigorous ground-truthing. The drone method appeared to work well in this contrived example, but, it should be noted that the background substrate – beach sand – was homogeneous and the replica birds on nests represented large detection targets. If a drone-based count is going to work for any animal population – this would probably be it.






Every dog has its … picture painted

This week’s conservation art profile:

Depicting 4454 wild dogs all individually hand painted. Caitlin O’Gorman’s representation of what is left in the wild. Oil on canvas. 2m x 1.8m

Caitlin grew up mostly in Ireland, and completed her final years of schooling in KwaZulu-Natal. She has sketched and painted for as long as she can remember. Our lives are full of accidental stories which take us in unexpected directions. One of the happiest accidents in Caitlin’s life was discovering the Michaelis School of Fine Art at the University of Cape Town. In 2018, she is in her fourth and final year as an undergraduate, and a key component of the year is a display of what drives and inspires the people in her class. For Caitlin it is conservation and therefore, she plans to work in collaboration with the Landmark Foundation to discover the inspiration for her project. Watch this space.

From Caitlin:

I am a fine art student currently in my fourth and final year of studying. I have always had a strong passion for wildlife and my art has resulted in always taking the shape of that subjectivity. In my practice in recent years, I attempt to convey to the viewers the emotions that I feel about wildlife and it’s current state. Although there is a lot of good happening with wildlife conservation, there is dramatic negative activity happening and I attempt to portray this human-wildlife co-existence in a way that challenges the viewer and engages them with a more emotive and connected response. As a visual representation of statistical information, I hope to allow the viewer to truly see the stats rather than read, and in turn to draw the viewer in to empathize with the subject.




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Lacewings at Little England, Beaufort West

Nesoleon boschimanus. Photo credit: Les Underhill (2018)

Report by Les Underhill

Lacewings are not one of the charismatic groups of insects, and have been poorly studied. They consume aphids and do pollination, so they are one of the key ecosystem service providers, and deserve better attention than what they have received to date. There is only one entomologist in South Africa who has focused on lacewings, Dr Mervyn Mansell, at the University of Pretoria. He says that, in South Africa, there are currently 415 described species in 14 families of lacewings. There are many taxa that await description, and he reckons that we should eventually end up with about 500–550 species for South Africa. For the whole of Africa, it is likely that there will prove to be 1000–1500 species.

On three trips to the Landmark Foundation’s farm at Little England in the Karoo north of Beaufort West a total of 18 lacewing have been photographed and uploaded to the LacewingMAP section of the Virtual Museum ( 13 have been identified to species level, three to genus and, for one, the photo was only good enough for the ID to be done to family. The number of species so far is a paltry six! But it is a start. These are the first ever records for this grid cell.

Mervyn Mansell, who does the identifications for LacewingMAP, reckons that we could expect at least 50 species in that area. “It is actually an extremely rich area for lacewings. Lots of fieldwork needs to be done here.”

The first six species for this grid cell are listed below. The species notes were written by Mervyn Mansell in his comments on the identification. The number of records to date is given, as well as the link to the record in LacewingMAP with what is currently the best available photo of the species in the grid cell. The distribution map for each species, based on the LacewingMAP database, is also provided. The take home message from these maps is plain: Our knowledge of the distributions of the lacewings is weak.

Systematic list of lacewings recorded on the farm Little England

Centroclisis maligna. Photo credit: Les Underhill (2018)

Centroclisis maligna (Myrmeleontidae)

This species is fairly common and widespread in the drier western parts of southern Africa. It is readily distinguished form other Centroclisis species by its reddish colour. The large robust three-toothed larvae live freely in sand and do not construct pitfall traps.

One record:


Creoleon mortifer. Photo credit: Les Underhill (2018)

Creoleon mortifer (Myrmeleontidae)

A common and widespread species, occurring throughout most of southern Africa and northward. It is highly variable, often with black streaks in the wings that have led to numerous synonyms. Rests with wings wrapped around the body. Larvae live freely in sand.

Two records:


Myrmeleon doralice. Photo credit: Les Underhill (2018)

Myrmeleon doralice (Myrmeleontidae)

This species is common and widespread throughout southern Africa, particularly in the drier areas. Larvae construct pits and are pinkish in colour. Although the adults are fairly common, the larvae are not frequently encountered, although they are pit builders, and usually occur in open exposed situations.

Three records: m


Nannoleon michaelseni. Photo credit: Les Underhill (2018)

Nannoleon michaelseni (Myrmeleontidae)

This species is widespread in South Africa and Namibia, and is fairly common in the drier western parts of the subregion. It is currently the only species in the genus, although another undescribed species is also known. It is characterized by the broad clear wings and long clavate antennae. Nothing is known of its biology.

Two records:


Nesoleon boschimanus. Photo credit: Les Underhill (2018)

Nesoleon boschimanus (Myrmeleontidae)

This species is widespread in South Africa and Namibia, and is fairly common in the drier western parts of the subregion. It is currently the only species in the genus, although another undescribed species is also known. It is characterized by the broad clear wings and long clavate antennae. Nothing is known of its biology.

Three records:


Dichochrysa tacta. Photo credit: Les Underhill (2018)

Dichochrysa tacta (Chrysopidae)

Another of the “brown” “green lacewings”. Fairly widespread and common in the drier western parts of South Africa. Not known from neighbouring countries. Larvae live freely on vegetation, where they are active predators.

Two records:


We are grateful to the Landmark Foundation for their warm hospitality at Little England. Mervyn Mansell’s role in doing the identifications and writing the comments is crucial to the success of this project.

The data were extracted from the LacewingMAP section of the Virtual Museum (Animal Demography Unit (2018). LacewingMAP Virtual Museum. Accessed at on 2018-04-02)


Bird ringing report – Paardeberg 2018/03/28

Cape robin-chat (Cossypha caffra). Photo credit: Dieter Oschadleus (2018)

Cape robin-chat – Virtual Museum record

Report by Dieter Oschadleus

The Paardeberg stands out as a mountainous island in an agricultural landscape between Paarl/Wellington and Malmesbury in the Swartland region of the Western Cape. Very little bird ringing has taken place here, so Les Underhill and I had a ringing session on Bowwood Farm on Wednesday.

The top species was Cape White-eye (n=22), followed by Southern Masked Weavers (n=8), where 2 of the latter were males in partial breeding plumage. The ring of one bird has been recovered in the Paardeberg area, a Cape Weaver ringed with ring 231054 in Tygerberg.

Thanks to Julian and Bridget Johnsen for hosting us!

Streaky-headed seedeater (Serinus gularis). Photo credit: Dieter Oschadleus (2018)

Streaky-headed seedeater – Virtual Museum record

Karoo prinia (Prinia maculosa). Photo credit: Dieter Oschadleus (2018)

Karoo prinia – Virtual Museum record

Cape weaver (Ploceus capensis). Photo credit: Dieter Oschadleus (2018)

Cape weaver – Virtual Museum record

Southern masked-weaver (Ploceus velatus). Photo credit: Dieter Oschadleus (2018)

Southern masked-weaver – Virtual Museum record

Olive thrush (Turdus olivaceus). Photo credit: Dieter Oschadleus (2018)

Olive thrush – Virtual Museum record

Cape white-eye (Zosterops virens). Photo credit: Dieter Oschadleus (2018)

Cape white-eye – Virtual Museum record

BDIgest Friday, 30 March 2018

In this week’s digest of research that caught our attention, we look at socio-economic and development issues associated with background climate oscillations and anthropogenic-driven climate change. We also look at climate change mitigation and biodiversity conservation, artificial selection pressures on a large carnivore, and methods of estimating population density in an elusive carnivore species.



Bet the farm – rolling the climate dice

Food security around the world is closely linked to climate variability, but in a recent article in Nature Communications we learn just how extensive the problem is. Crop productivity on two-thirds of the world’s cropland is significantly affected by three climate oscillations: El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the North Atlantic Oscillation (NAO). The areas affected by the three oscillations are inhabited by approximately 4 billion people and contribute two-thirds of global food crop calorie production.

DOI: 10.1038/s41467-017-02071-5

Ed: Against this background, the implications of adding variability and unpredictability of anthropogenic-driven climate change would suggest that risk in crop farming and food security will only increase for half the world’s population.




Photo credit: CDC Global 2012 (CC BY 2.0)

The carbon sins of the rich shall be visited upon the poor

The world’s population is becoming increasingly urban, and recent rapid urbanisation has resulted in a proliferation of informal urban settlements or slums, which are home to > 800 million people. Some of this urban migration may be due to food security risk associated with climate variability (such as described in the article above). A compelling article in Ecological Indicators provides an important example of the social science required for assessing climate change vulnerability in these at-risk urban communities. In the particular slum community studied, overall vulnerability to climate change was high, there was a high information barrier (and hence low awareness of climate change impacts). As might be expected, for coping strategies, financial and food support were deemed important, followed by information support.

DOI: 10.1016/j.ecolind.2018.03.031

Ed: Interestingly, technological support was deemed least important for coping with climate change in slum communities, yet much attention is focused on technological interventions and relatively little attention is given to practical information and resource distribution.




Photo credit: Bobulix 2010 (CC BY-NC-ND 2.0)

Picking winners and losers – conserving carbon or biodiversity

Although the net impact of climate change is likely to be negative for biodiversity, there will be some taxonomic groups that benefit from climate change. Carbon conservation – specifically, conserving above-ground carbon stocks in tropical forests – is seen as one of the ways to combat climate change. Contrary to the putative net effects of climate change, it is tacitly assumed that this form of carbon conservation will promote biodiversity. A thought-provoking article in Science Advances suggests that the relationship between above-ground carbon stocks and biodiversity differs for different taxonomic groups, and may also differ in re-growth forests compared to old growth forests (within a taxonomic group). Thus, among the taxonomic groups studied, the relationship between carbon stocks and biodiversity could vary from positive to negative and could appear linear or non-linear. Choosing a single climate change mitigation strategy, such as conserving tropical forests to maximise carbon stocks, will inherently include trade-offs in biodiversity in certain taxonomic groups. A similar article in Science Advances from 2017 about using fire suppression in savannas to maximise carbon sequestration came to similar conclusions. Thus, more nuanced, integrated approaches that consider both carbon conservation and biodiversity conservation (across multiple taxonomic groups) may be required as we try to mitigate anthropogenic-driven climate change.

DOI: 10.1126/sciadv.aar6603

Ed: This is going to be a tricky concept to grapple with. Climate change in general is leading to population declines, geographic range shifts (and expansions or contractions). When biodiversity is already a climate change concern, how will we weigh the biodiversity benefits of mitigating climate change against the potential biodiversity costs (in some taxa) of maximising carbon conservation? As a species, we will need to become much better at assessing risks, attributing value, and optimising trade-offs.




Photo credit: Karlafg 2010 (CC-BY-SA-3.0)

Survival of the … slowest?

Typically, in harvested populations, the selection pressure of hunting or harvest should select for accelerated life history traits. However, research on a hunted population of brown bears in Sweden, published this week in Nature Communications, shows that when hunting regulations prevent the harvest of mothers with cubs, selection pressure may favour slower life history traits. Mothers that exhibit longer maternal care receive a survival benefit. Interestingly, this survival benefit cancels out the loss of reproductive opportunities associated with the slower breeding strategy, such that net fitness for the slower breeding females is similar to that of females following a “normal” maternal care strategy. Over the last 30 years, the proportion of litters in the population raised over 2.5 years has increased measurably relative to the proportion of litters raised over 1.5 years.

DOI: 10.1038/s41467-018-03506-3

Ed: A great demonstration of artificial selection at work … and over a relatively short time-frame for a long-lived large mammal.




Photo credit: Lukas Kaffer 2007 (CC-BY-SA-3.0)
Leopards are contagious too,
Be careful tiny tots,
They don’t give you a temperature
But lots and lots of spots
(Spike Milligan)

Spotty spotting of the spotted

A major issue in biodiversity research revolves around how to count animals in a population or estimate their population density reliably. This is particularly problematic for “cryptic” species that have low detection probabilities. Solitary felids often fit into this category, including leopards (Panthera pardus), which are largely nocturnal and have coat patterns that provide good camouflage. In a great study reported in the African Journal of Ecology, leopard density was estimated across a broad geographic region in South Africa (the Eastern Cape Province and Western Cape Province). The authors used movement data of collared animals and “captures” from remotely-triggered cameras to estimate density using two different techniques – which provided surprisingly similar final density estimates. These density estimates of approximately 1 leopard per 100 sq km are low compared to published estimates for populations elsewhere in the leopard’s geographic range (published, for example, here). Even within this region, density estimates varied greatly among sites (from 0.24 to 1.89 leopards per 100 sq km).

DOI: 10.1111/aje.12512

Ed: This study produced great congruence between two different methods of estimating leopard density, suggesting that the reported densities for the region are quite reliable. The study also opens up interesting questions about what drives variability in leopard population density (both within this geographic region, and across the leopard’s geographic range).






I can’t believe it’s not butter!

This week’s conservation art profile:

Malachite Kingfisher (oil painting … not a photo!) by Tanya Scott.

Tanya has recently completed an MSc at the University of Cape Town using the data from the bird atlas project in South Africa (Birds along a transect across KwaZulu-Natal: altitudinal preference and altitudinal migration). She represented South Africa in the half-marathon at the 29th Summer Universiade in Taipei City in 2017. Her last formal art education was at Westerford High School in Cape Town where the art teacher was Mr Anthony Cain.


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