Goldilocks Is Dying

Given today’s high debt ratios, supply-side risks, and ultra-loose monetary and fiscal policies, the rosy scenario that is currently priced into financial markets may turn out to be a pipe dream. Over the medium term, a variety of persistent negative supply shocks could turn today’s mild stagflation into a severe case.

Nouriel Roubini

NEW YORK – How will the global economy and markets evolve over the next year? 

There are four scenarios that could follow the “mild stagflation” of the last few months.

The recovery in the first half of 2021 has given way recently to sharply slower growth and a surge of inflation well above the 2% target of central banks, owing to the effects of the Delta variant, supply bottlenecks in both goods and labor markets, and shortages of some commodities, intermediate inputs, final goods, and labor. 

Bond yields have fallen in the last few months and the recent equity-market correction has been modest so far, perhaps reflecting hopes that the mild stagflation will prove temporary.

The four scenarios depend on whether growth accelerates or decelerates, and on whether inflation remains persistently higher or slows down. 

Wall Street analysts and most policymakers anticipate a “Goldilocks” scenario of stronger growth alongside moderating inflation in line with central banks’ 2% target. 

According to this view, the recent stagflationary episode is driven largely by the impact of the Delta variant. 

Once it fades, so, too, will the supply bottlenecks, provided that new virulent variants do not emerge. 

Then growth would accelerate while inflation would fall.

For markets, this would represent a resumption of the “reflation trade” outlook from earlier this year, when it was hoped that stronger growth would support stronger earnings and even higher stock prices. 

In this rosy scenario, inflation would subside, keeping inflation expectations anchored around 2%, bond yields would gradually rise alongside real interest rates, and central banks would be in a position to taper quantitative easing without rocking stock or bond markets. 

In equities, there would be a rotation from US to foreign markets (Europe, Japan, and emerging markets) and from growth, technology, and defensive stocks to cyclical and value stocks.

The second scenario involves “overheating.” 

Here, growth would accelerate as the supply bottlenecks are cleared, but inflation would remain stubbornly higher, because its causes would turn out not to be temporary. 

With unspent savings and pent-up demand already high, the continuation of ultra-loose monetary and fiscal policies would boost aggregate demand even further. 

The resulting growth would be associated with persistent above-target inflation, disproving central banks’ belief that price increases are merely temporary.

The market response to such overheating would then depend on how central banks react. 

If policymakers remain behind the curve, stock markets may continue to rise for a while as real bond yields remain low. 

But the ensuing increase in inflation expectations would eventually boost nominal and even real bond yields as inflation risk premia would rise, forcing a correction in equities. 

Alternatively, if central banks become hawkish and start fighting inflation, real rates would rise, sending bond yields higher and, again, forcing a bigger correction in equities.

A third scenario is ongoing stagflation, with high inflation and much slower growth over the medium term. 

In this case, inflation would continue to be fed by loose monetary, credit, and fiscal policies. 

Central banks, caught in a debt trap by high public and private debt ratios, would struggle to normalize rates without triggering a financial-market crash.

Moreover, a host of medium-term persistent negative supply shocks could curtail growth over time and drive up production costs, adding to the inflationary pressure. 

As I have noted previously, such shocks could stem from de-globalization and rising protectionism, the balkanization of global supply chains, demographic aging in developing and emerging economies, migration restrictions, the Sino-American “decoupling,” the effects of climate change on commodity prices, pandemics, cyberwarfare, and the backlash against income and wealth inequality.

In this scenario, nominal bond yields would rise much higher as inflation expectations become de-anchored. 

And real yields, too, would be higher (even if central banks remain behind the curve), because rapid and volatile price growth would boost the risk premia on longer-term bonds. 

Under these conditions, stock markets would be poised for a sharp correction, potentially into bear-market territory (reflecting at least a 20% drop from their last high).

The last scenario would feature a growth slowdown. 

Weakening aggregate demand would turn out to be not just a transitory scare but a harbinger of the new normal, particularly if monetary and fiscal stimulus is withdrawn too soon. 

In this case, lower aggregate demand and slower growth would lead to lower inflation, stocks would correct to reflect the weaker growth outlook, and bond yields would fall further (because real yields and inflation expectations would be lower).

Which of these four scenarios is most likely? 

While most market analysts and policymakers have been pushing the Goldilocks scenario, my fear is that the overheating scenario is more salient. 

Given today’s loose monetary, fiscal, and credit policies, the fading of the Delta variant and its associated supply bottlenecks will overheat growth and will leave central banks stuck between a rock and a hard place. 

Faced with a debt trap and persistently above-target inflation, they will almost certainly wimp out and lag behind the curve, even as fiscal policies remain too loose.

But over the medium term, as a variety of persistent negative supply shocks hit the global economy, we may end up with far worse than mild stagflation or overheating: a full stagflation with much lower growth and higher inflation. 

The temptation to reduce the real value of large nominal fixed-rate debt ratios would lead central banks to accommodate inflation, rather than fight it and risk an economic and market crash.

But today’s debt ratios (both private and public) are substantially higher than they were in the stagflationary 1970s. 

Public and private agents with too much debt and much lower income will face insolvency once inflation risk premia push real interest rates higher, setting the stage for the stagflationary debt crises that I have warned about.

The Panglossian scenario that is currently priced into financial markets may eventually turn out to be a pipe dream. 

Rather than fixating on Goldilocks, economic observers should remember Cassandra, whose warnings were ignored until it was too late.

Nouriel Roubini, Professor Emeritus at New York University’s Stern School of Business, is Chief Economist at Atlas Capital Team and CEO of Roubini Macro Associates. He is a former senior economist for international affairs in the White House’s Council of Economic Advisers during the Clinton Administration. He has worked for the International Monetary Fund, the US Federal Reserve, and the World Bank, and was Professor of Economics at New York University's Stern School of Business. His website is, and he is the host of

The AUKUS squad

The strategic reverberations of the AUKUS deal will be big and lasting

A profound geopolitical shift is happening

Just occasionally, you can see the tectonic plates of geopolitics shifting in front of your eyes. 

Suez in 1956, Nixon going to China in 1972 and the fall of the Berlin wall in 1989 are among the examples in living memory. 

The unveiling last week of a trilateral defence pact between Australia, the United Kingdom and the United States (introducing the awkward acronym of aukus) is providing another of those rare occasions.

Aukus envisages a wide range of diplomatic and technological collaboration, from cybersecurity to artificial intelligence, but at its core is an agreement to start consultations to help Australia acquire a fleet of nuclear-propelled (though not nuclear-armed) submarines. 

One consequence of this is Australia cancelling a contract, worth tens of billions of dollars, signed in 2016 with France for diesel-electric submarines. 

In announcing aukus on September 15th with the prime ministers of Australia and Britain, Scott Morrison and Boris Johnson, President Joe Biden stressed that it was about “investing in our greatest source of strength—our alliances”. 

However, America’s oldest ally, France, has reacted with understandable fury. 

Jean-Yves Le Drian, its foreign minister, called it a “stab in the back”. 

On September 17th President Emmanuel Macron withdrew France’s ambassadors from Washington and Canberra (though not London).

The powerful reverberations of aukus show what a profound shift it represents. 

For America it is the most dramatic move yet in its determination to counter what it sees as the growing threat from China, particularly the maritime challenge it poses in the Pacific. 

Not only is America sharing the crown jewels of military technology, the propulsion plant for nuclear submarines, with an ally for only the second time in 63 years (the other time being with Britain). 

It is also robustly signalling its long-term commitment to what it calls a “free and open Indo-Pacific”.

Many countries in the region which share the sense of threat from China welcome that. 

Aukus will now provide a potent backdrop for the first in-person meeting of leaders of the Quad—America, Australia, India and Japan—in Washington, DC, on September 24th. 

Last month, amid a chaotic withdrawal from Kabul, there was talk of America’s lack of staying power and a loss of faith among its allies. For all the anger in Paris, aukus changes that narrative. 

“The larger significance of this is that the United States is doubling down on its allies, and its allies are doubling down on the United States,” says Michael Fullilove of the Lowy Institute, a think-tank in Sydney. 

“Unfortunately, France is collateral damage.”

In Australian eyes the developments that led to aukus were largely made in China. 

It was the heavy-handed pressure that China has applied on Australia, the most striking recent example being the response to its call for an independent investigation into the origins of covid-19, that led to urgent interest in ways to push back. 

Ditching the submarine contract with France was a bold move. 

Although the deal with Naval Group, a company in which the French state has a majority stake, had run into difficulties over its escalating costs and delays, and had few friends among politicians or the press, it was nevertheless one of the largest contracts in the history of Australia and was widely thought to be too big to dump. 

That the government has done so, despite the prospect of hefty penalties, reflects both the scale of its bet on America as an ally and the attractions of the submarine technology it will obtain: far stealthier and with far longer range than the diesel-electric ones.

Britain may be the least important of the aukus trio; certainly, its role is belittled in the French decision not to recall its ambassador to London (Mr Le Drian called Britain the “third wheel” in the deal). 

Even so, for Mr Johnson the pact illustrates his country’s changing role in the world. It conveniently chimes with the post-Brexit effort to promote “Global Britain” (henceforth to be energetically championed by a new foreign secretary, Liz Truss). 

And it gives substance to the “tilt to the Indo-Pacific” that was embraced in a comprehensive review of foreign and defence policy published in March.

For the French, too, aukus crystallises what they view as profound realities in international relations, notably the idea that Europe needs more “strategic autonomy” so as not to depend excessively on America. 

However the muted reaction among France’s European partners casts familiar doubt on how serious such autonomy can be. 

After news of the aukus deal emerged, a German official called for “coherence and unity” among Western powers, which he said would require “a lot of effort” to bring about. 

France has concluded that it will struggle for fair treatment in the face of the reflexes of Anglophone allies to club together (the trilateral deal comes on top of the “Five Eyes” intelligence-sharing alliance that involves the same three countries plus Canada and New Zealand). 

But French fury, especially against Australia, is also driven by a personal sense of betrayal.

That goes beyond the loss of a giant contract, painful as that is. 

France sets great store by its role in the Indo-Pacific region, where it keeps some 7,000 troops and has nearly 2m citizens, including in its island territories such as New Caledonia and French Polynesia. 

It has been assiduously building what it thought was an ever-closer relationship with Australia. 

As recently as August 30th the communiqué from high-level Australian-French ministerial consultations spoke of “the strength of our strategic partnership” across many areas, and stressed “the importance of the Future Submarine programme”. 

Yet neither at that summit nor at the many others over the months when aukus was in the works was France given any notice of it. 

The “six months of secrecy” was “quite a performance,” says François Heisbourg, a French foreign-policy expert who through his think-tank had for years been involved in cultivating connections with Australia.

The fallout in France is one of several caveats to what otherwise appears to be a strategic coup for the three partners in aukus. 

The administration’s idea of working together with allies to check China makes sense. 

But a major split with a key ally—one with serious Indo-Pacific interests—hardly helps. 

Creative efforts will now be needed from the aukus squad to try to mitigate the damage.

Second, there is what this says about American diplomacy. 

The French were bound to be upset, but the handling of them was graceless. 

That comes on top of the Biden administration’s poor handling of the withdrawal from Afghanistan. 

One example of foreign-policy incompetence looks unfortunate; two in quick succession look like a pattern. 

That is not a good omen for the management of the relationship with China, which involves elements of military competition, economic laissez-faire and collaboration over, say, climate change and arms control.

Third, American foreign policy has often been criticised, including by Mr Biden, for placing too much emphasis on the military dimension and not enough on diplomacy and other tools. 

The nuclear-submarine initiative is a big move on the defence front, but China is increasingly powerful in the region on the economic and financial fronts. 

China responded to aukus by criticising its “cold-war mentality”. 

The next day it applied to join the cptpp, an 11-country transpacific trade pact that America helped to instigate as a way to limit China’s influence, but then abandoned.

There is no quick fix for America’s mistakes in economic policy. Indeed, the rivalry between China and America, together with its allies, will play out across many areas over many years. 

It is the defining geopolitical challenge of the 21st century. 

And now in aukus it has acquired a new landmark. 

In a precarious labour market, universal basic income isn’t the only solution

History shows that improving the future of work takes more than letting employers off the hook

Sarah O’Connor

© James Ferguson

On November 9 1830, a hundred farm labourers descended on a farm in Kent in the south of England and destroyed a threshing machine with saws, hatchets and axes. 

At Burnham Overy in Norfolk, workers destroyed another machine as they shouted: “It keeps an honest man from getting work.” 

The country was in the throes of the Swing riots, where farm labourers smashed threshing machines, burnt barns, sent threatening letters to farmers and demanded higher wages. 

By the last 10 days of November, write historians Eric Hobsbawm and George Rudé, “virtually all of Southern England seemed in flames”.

The workers were responding to transformations in the world of work which had left them desperate. 

New threshing machines saved labour by a factor of five to 10, displacing many workers who usually relied on manual threshing jobs to keep them going in winter. 

Farm employment had become more casual and precarious. 

“It is cheaper to hire day labourers . . . than to maintain servants in the house, especially as they are always sent home on a rainy day,” one contemporary observer wrote.

We are at another moment in history where work is becoming more uncertain and insecure, at least for some. 

Last year, Amazon Flex drivers were hanging their smartphones in trees outside pick-up sites in an apparent attempt to try to win a split-second advantage as delivery tasks went to those closest by. 

On some farms in Scotland, raspberry pickers were being sent to sit in their caravans unpaid when it rained or when their productivity rate fell too low.

The idea of a universal basic income — a policy where the state pays everyone a monthly sum without conditions — is often pitched as a solution to these problems. 

If technology is set to make work more scarce, unpredictable or precarious, advocates say, we need to give people a base level of income that is independent of the labour market. 

Otherwise, they might end up just as angry and desperate as the machine-breakers of the 1830s.

But a UBI wouldn’t just be a response to the changing labour market, it would also shape it in ways that are hard to predict.

In the case of the Swing riots, some historians have argued that a well-intentioned welfare system actually helped to exacerbate the plight of farm labourers. 

In the mid-1790s, magistrates in Speenhamland in Berkshire decided on a local system of poor relief that would top up the wages of the low paid to a minimum income based on the price of bread. 

The system spread, but according to economic historian Karl Polanyi it was a “fool’s paradise” because it encouraged farmers to pay lower wages in the knowledge that public funds would make up the difference. 

When the cost of the system rose, its generosity was cut sharply. 

“[The] ‘right to live’ eventually ruined the people whom it was ostensibly designed to succour,” he wrote.

It’s important to stress this isn’t the only version of the story. 

Other historians dispute the notion that the Speenhamland system impoverished people. 

They say the system of poor relief, which varied widely between parishes, is better seen as an insufficient remedy to the problems of the age rather than a contributor to them.

Nonetheless, it is worth considering how employers today would respond to the introduction of a UBI. 

We know that employers do react to welfare changes. 

One academic paper suggests the UK’s “working families’ tax credit”, introduced in 1999, led employers to reduce wages somewhat for recipients of the top-up, with a spillover effect on to those who weren’t receiving the benefit.

If a UBI let employers off the hook entirely from the idea that a job should be something a person can live on, it could make it easier to hire people for fewer hours on a casual or fleeting basis. 

Campaigns for a “living wage” and “living hours” might lose steam. 

Even minimum wages could come under philosophical assault. 

You might argue that would be no bad thing if it gave employers more flexibility while people still had income security. 

But variable income isn’t the only problem with an unpredictable job: it also affects your ability to arrange childcare, plan a life outside work and maintain relationships.

On the other hand, UBI’s supporters argue it could have the opposite effect. 

People with a solid income floor to rely on would be able to walk away from jobs that are badly paid or don’t fit around the rest of their lives. 

Employers would be forced to compete for staff by offering attractive pay and conditions.

Which of these scenarios would be more likely would depend on the generosity at which the UBI was set and the macroeconomic context in which it operated. 

Sadly, pilot schemes such as the one in Finland can’t help us much with this question, since they are too small to affect employer behaviour.

In the meantime, there are other things we can do to improve the future of work. 

The first step should be to recognise that not every problem is the result of technological change. 

The raspberry pickers who are sent back to their caravans without pay when they pick too slowly, for example, are not the victims of an algorithm or machine. 

The farmers treat them this way because the law allows it.

UBI is worthy of more debate. 

But there is a danger in seeing job insecurity as an inevitability to which we must adapt, when in some cases it is simply a regulatory failure to which we should respond.

The Case for a Food Systems Stability Board

The absence of a Food Systems Stability Board is a notable gap in the global governance architecture needed to bolster sustainability and resilience. By agreeing to launch consultations regarding the creation of such a body, governments could contribute to a better future for hundreds of millions of highly vulnerable people.

Sandrine Dixson-Declève, José Antonio Ocampo, Felia Salim

LONDON – The COVID-19 pandemic, rising rates of global poverty and inequality, persistent conflict, and the escalating climate and biodiversity crises are shocks and stresses that together contribute to increasing hunger, as well as growing food and nutrition insecurity. 

To help tackle this urgent problem more effectively, and make the global food system more stable and resilient, governments should consider establishing a new, multilateral, United Nations-led Food Systems Stability Board (FSSB).

Today, between 720 million and 811 million people – about 10% of the world’s population – go to bed hungry every night, and at least 2.4 billion lack access to a healthy and nutritious diet. 

Absent major international action, these trends are likely to persist. 

The latest report by the Intergovernmental Panel on Climate Change demonstrates that global warming’s effects have left no region untouched, with significant implications for the food system over the coming decades.

Food systems underpin the security of the global economy, as well as national security in many countries: hunger and lack of access to food have historically driven civil unrest. 

These systems are also among the principal drivers of ecosystem loss and climate change, with agriculture and land-use change responsible for a quarter of global greenhouse-gas emissions. 

At the same time, ecosystems such as forests, mangroves, and the ocean are central to humanity’s efforts to adapt to the climatic changes already underway.

Ensuring the long-term resilience of the global food system will require a significant multilateral collaborative effort. 

This should build on existing structures and institutions such as the Committee on World Food Security, the Food and Agriculture Organization, the World Food Programme, and the World Bank. 

It will also demand concerted attention from heads of state and government, ministers of finance, and the leaders of multilateral financial institutions.

A quartet of international meetings – the UN Food Systems Summit in September 2021, the G20 summit in October, the UN climate conference (COP26) in November, and the Nutrition for Growth Summit hosted by the Japanese government in December – offer a rare opportunity to focus international attention on the hunger and food-security crisis, and its links to the changing climate. 

Each of these gatherings could pave the way for the creation of an FSSB of national governments and international organizations working to address this issue. 

This could be part of a broader global effort to enhance food governance and achieve – in the words of the government of Indonesia, which will hold the G20 presidency in 2022 – a “just and affordable transition toward net zero.”

Moreover, there is an encouraging precedent for such a body. 

The Financial Stability Board (FSB), established by G20 finance ministers in April 2009 with the aim of preventing a repeat of the 2008 global financial crisis, has positively contributed to global macroeconomic stability and is now an authoritative, independent, and well-respected body. 

Its findings directly influence the decision-making of G20 finance ministers, as well as that of the heads of the International Monetary Fund, the World Bank, and the regional development banks.

In a similar fashion, an FSSB, if established, would be charged with promoting the health and resilience of the global food system, including by addressing issues such as price stability, trade, strategic reserves, and the effects of climate change on production. 

The board would fully respect national sovereignty, and not issue legally binding recommendations. 

Rather, it would give credible advice to governments on how to build a food system that is better prepared to withstand future shocks and ensure greater global access to nutritious food.

While governments would decide the precise scope, structure, and composition of an FSSB, we believe the body could play a helpful role in several ways. 

For example, it could analyze early-warning systems and risk-modeling data on hunger, agriculture, and climate, including from the existing Agricultural Market Information System database. 

It could also advise the World Trade Organization and national governments on food-related trade policies, while helping countries respond to changing market dynamics and a volatile climate.

Additionally, the FSSB could support and enable countries to submit voluntary five-year food system risk assessments and resilience plans. 

It could also gather and share knowledge about global food-trade vulnerabilities, such as those relating to climate change, conflict, lack of crop diversity, pollinator loss, and other threats, and identify and review the regulatory, supervisory, and voluntary measures needed to address them.

The FSSB could support contingency planning for cross-border crisis management, especially with regard to systemically important food crops or areas particularly affected by climate vulnerability, biodiversity loss, and/or future pandemics. 

Lastly, the board could collaborate with the IMF to include more consideration of risks related to climate, biodiversity, and food and land-use systems in the Fund’s regular Article IV consultations with member countries.

The FSSB could comprise relevant national representatives from ministries of agriculture and rural affairs, trade and commerce, health, environment, and finance, as well as international standard-setters and leading scientists in the field of global food-system risks. 

As with the FSB, the institution’s audience would be member states, including heads of government, finance ministers, and other portfolios.

The current absence of an FSSB is a notable gap in the international governance architecture required to bolster the sustainability, equity, and resilience of the global food system in the twenty-first century and beyond. 

At the UN General Assembly and UN Food Systems Summit – both taking place in September – governments could agree to initiate a one-year consultation process to explore the creation of such a body. 

By doing so, they could contribute to a better future for hundreds of millions of vulnerable people – and ensure access to food and security for all.

Sandrine Dixson-Declève is Co-President of the Club of Rome. 

José Antonio Ocampo, a former finance minister of Colombia and United Nations under-secretary general, is a professor at Columbia University, Chair of the Independent Commission for the Reform of International Corporate Taxation, and an ambassador of the Food and Land Use Coalition. He is the author of Resetting the International Monetary (Non)System and co-author (with Luis Bértola) of The Economic Development of Latin America since Independence.

Felia Salim, Chair of the Board of Directors of the Partnership for Governance Reform, is an ambassador of the Food and Land Use Coalition. 

Hummingbird cross-dressers

Some female hummingbirds have evolved to look like males

Intriguingly, that makes mealtimes less stressful

MALE BIRDS are often colourful and ornate. 

These embellishments demonstrate the wearer is a suitable candidate for fatherhood and is not to be trifled with by other males. 

Why females are sometimes colourful too is more of a mystery.

One idea is that if the sexes co-operate to raise their young—which birds often do—males as well as females must be choosy about their mates. 

But Jay Falk of the University of Washington has another explanation. 

In a paper in Current Biology he suggests it is a way for females to avoid being harassed when they are feeding.

Plumage transvestism, known technically as female-limited polymorphism, is especially common in hummingbirds. 

Earlier work involving Dr Falk, who was then a PhD student at Cornell University, showed that it has evolved independently in all nine big groups of these birds and is found in nearly a quarter of hummingbird species. 

This makes them ideal for studying it. 

But that work was done on museum specimens. 

Mr Falk, as he then was, wished to take the question into the field.

His reason for doubting sexual selection as the explanation for female-limited polymorphism in hummingbirds was that males of this group do not help raise the young. 

He therefore tested an alternative—that male-like plumage in females confuses real males. 

To do so, he decamped to Panama, and spent four years studying a species called the white-necked jacobin.

He started by collecting and recording the details of a lot of birds, eventually fitting some with tiny transponders so that he could follow and identify individuals. 

Over the course of the study, he captured 436 jacobins, of which he managed to recapture 135 in at least one subsequent year.

Sexing hummingbirds is hard. 

As with most avians, the males have no penis. To work out a bird’s sex, he took a blood sample. 

This showed that nearly 30% of females had male-like colouration. 

A jacobin’s age, though, is easy to estimate from its beak. 

Younger birds’ beaks have more serrations. 

On this basis, he discovered that all young jacobins, regardless of sex, sport male-like plumage. 

Only later in life do some females develop distinctive muted colouration—a fact confirmed by some of the recaptures, which had changed plumage in the intervening period.

This is the reverse of normal for sexual selection, in which there is no point in immature individuals pretending they are mature, nor mature females pretending to be males. 

So he carried out experiments at hummingbird feeding stations filled with sugarwater to try to find out what benefits adult-male-like plumage brings.

First, he put pairs of stuffed hummingbirds by these stations—mixing males, females with male plumage, and females with female plumage—and recorded how they were treated. 

A clear pattern emerged. 

As might be expected, stuffed females in female plumage received a lot of sexual attention from males, whilst those in male plumage were spared. 

More surprisingly, they were also on the receiving end of more aggression, perhaps because males see females as easier to drive away from contested food sources. 

Both courtship and hostility, though, distract from the serious business of feeding, and are therefore harmful.

He then started varying the amount of sugar in the sugarwater, while measuring the frequency and length of visits to feeders. 

Female birds with male-like plumage, he discovered, fed more frequently and for longer than those with muted colours. 

At feeders with higher sugar concentrations, the difference was yet more pronounced—probably because, the stakes being higher, birds with muted colours were experiencing more harassment.

And that, perhaps, explains why hummingbirds as a group have evolved female-limited polymorphism so often—for, of all known vertebrates, they have the highest metabolic demand per gram of body weight. 

Anything detracting from feeding will get short shrift from natural selection. 

If looking like an adult male while actually being juvenile, female or both gets the job done, such plumage will evolve.

The remaining puzzle is why some adult females, having adopted the disguise as juveniles, then go on to abandon it. 

Perhaps the muted female colours make them less conspicuous to predators, especially at their nests. 

But polymorphisms of this sort are normally maintained because each option is advantageous when rare in a population, and disadvantageous when common. 

The details of how such a trade-off—between access to food and protection from predators—would work in this case remain unclear. 

Dr Falk has therefore only half-answered the question he set out to investigate. 

Answering the other half might require another trip to Panama.