science

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Humans are not good at thinking about the distant future. We are not alone in our short-sightedness. Living things, in general, are obsessed with the here and now and oblivious to what lies far down the road. There is a very good evolutionary reason for focusing on the present. Animals that succeed at surviving and protecting their progeny leave more young than other animals (in this case, hypothetical ones) preoccupied with what conditions might be like for their grandchildren and great-grandchildren. Animals that attend to their own survival and that of their offspring simply leave more offspring. Thus, natural selection can be said to favor animals that focus on the present — and animals within natural populations are chiefly descendants of parents and grandparents that cared for their own survival and that of their offspring. The short-term view makes sense evolutionarily.

Our very logical tendency to heed the here and now at the expense of the future has a limitation. Focus on the present adapts animals well to a stable environment, but leaves them poorly adapted to an environment that changes rapidly. Over evolutionary time, environmental change has generally occurred slowly enough to cause little problem for animals that live only for the present.

But humans have hastened environmental change. Anthropogenic changes have taken many forms, including introduction of invasive species, environmental degradation, and wholesale alteration of landscapes and vegetation. Perhaps surprisingly, many non-human animals have been able to keep pace with human impacts. In fact, some — crows, gulls and raccoons come to mind — have benefitted enormously from human activity. Others, of course, have become extinct, endangered or have seen their geographic ranges contract because of humans. We could quantify human impacts of each and every non-human species, if we cared to, and place each on a chart from least- to most-impacted.

Where on the chart would the common loon fall? Considering that loons are often viewed as the “voice of the wilderness”, one might suppose that they would suffer greatly from human encroachment. In fact, loons are hanging in there better than many other vertebrate animals. Knocked back in the middle of the 20th century, the common loon population has rebounded. Breeding populations are now generally stable or even increasing across most of the northern tier of United States. So loon populations appear to be hanging in there despite extensive shoreline development, entanglements with hooks and fishing line, and increases in methylmercury levels, among many other challenges.

A new anthropogenic threat now looms that is more extensive and unrelenting than others that loons have faced. Climate change has already caused many geographic ranges of North American animals to recede northwards. A recent study showed that bird species differed greatly in their northward shifts, but that, on average, breeding ranges are marching northwards by over 2 km per year. We have a bit of an apples and oranges problem here; the bird species included in the study varied greatly in their diets and habitats. Some, no doubt, are highly dependent upon temperatures (and related factors like vegetation) for their survival; others are not. So it is difficult to project precisely how the geographic range of the common loon might be affected. But do this: take a look at Audubon’s animated depiction showing the contraction of the loon’s breeding range.

Two patterns are immediately clear from the animation. First, the northern Wisconsin loon population (and abutting populations in Minnesota and Michigan’s Upper Peninsula) exist on an isolated “finger” that projects southwards from the heart of the range, which lies in Canada. Second, the model paints a very bleak picture of the future loon population in northern Wisconsin. According to the model, loons are projected to be much less abundant in northern Wisconsin by 2050 and gone altogether by 2080.

Now, a word of caution. Audubon scientists have attempted to distill the climate down to two main factors: temperature and precipitation. On the basis of these two climatic factors, the current distribution of the species relative to these factors, and the projected future climate based on the report of the Intergovernmental Panel on Climate Change (IPCC), they have produced the  animated graph that loon enthusiasts like us find so disturbing. Their projection is likely to provide a crude estimate of the impact of climate change on loons, not a precise one. That is, loons are likely to cope with climate change better than most other birds — as they have other environmental threats. Then again, loons might be especially sensitive to climate change and retreat northward more rapidly than the study predicts.

Like many other humans, I am obsessed with the day to day. I have studied loons as if they would be around forever. I have battled to obtain grants to keep my study afloat, to publish my papers in high-impact journals, to hire diligent field technicians who would collect reliable data. Now, forced by changing environmental conditions to glance towards the future, I can scarcely believe that the animals that I have learned so much about and grown so fond of might be well on their way to vanishing from Wisconsin in my lifetime.

 

 

 

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A lot of science is scut work. While I do ponder my findings, develop new hypotheses, and publish papers that might (slightly) change the way that others view the natural world, these activities are, in fact, only the most glamorous ones in the scientific profession. I spend far more time worrying that I am mistaken about a result. You see, scientists are nit-pickers who know from personal experience the difficulty of proving something is true. Scientists are skeptical of their own findings as well as those of their colleagues. We are always on the lookout for false assumptions, biased data samples, misleading correlations, and experimental results that are artifacts (false outcomes) of our methods. Thus, we spend a good deal of time poking and prodding our data, turning it this way and that, and making certain it is bullet-proof, before we try to publish or present it to colleagues. Scientists run many tedious and seemingly repetitive statistical tests aimed at testing a single hypothesis and ruling out alternative explanations for patterns we find in our data. If a flaw in our reasoning, an untested assumption, or a problem in experimental design weakens or invalidates our findings, we want to discover it ourselves in the solitude of our office — not have a listener at a talk or a reviewer of a grant proposal do so.

Scientists have a much higher threshold for accepting statements as fact than does the public at large. Indeed, flawed and misleading conclusions — which would bring harsh criticism to a scientist uttering them — are rampant in public discourse. The biased sample problem leads to many misleading conclusions. Following a political debate, TV commentators always tell us who won, based upon a sample of viewers. Unless one is very careful to control the political makeup of an audience, however, the outcome of such a poll is certain to be biased. Naturally, Fox News and CNN have audiences that differ greatly in their political leanings; in addition, people who watch debates on television or in person represent a biased sample of voters, not the population at large. Finally, viewers are more likely to see the candidate they favor as the winner of a debate, so favoritism towards one candidate will make that candidate more likely to be seen as the winner, even if their performance was worse that their opponent’s. That is, if 65% of all voters favor Ms. Sims over Mr. Peach ahead of the debate, and 55% of all voters say afterwards that Ms. Sims won the debate, Mr. Peach almost certainly performed better, because he beat his poll numbers.

I face the biased sample problem constantly in my analysis of loon behavior. For example, we have observed that loons shifting from a first to a second breeding territory tend to move a very short distance, often settling to breed on a new lake right next to their old one. It is tempting to surmise that loons that move between territories cover only a short distance in order to take advantage of their knowledge of the local area and ease their transition to the new breeding space. This sounds plausible but ignores the fact that shifters are not a random cross-section of the population. Instead, these loons are almost all old individuals with low fighting ability that have been evicted from first territories. Moreover, the new territories they shift into are not average breeding territories but new, untested ones with limited nesting habitat that seldom yield offspring. So old, worn out loons do not seem to be carefully choosing to settle in a new breeding space that they know well; rather, they are desperately setting up a new territory near their original one — and in a place that no other loon wishes to use — because it is not worthwhile trying to compete for a proven territory anywhere else.

mentions correlation

At the moment, I have turned a critical eye towards black flies and nest abandonment. I have “known” for decades that black flies cause high rates of nest abandonment in certain years, as they did in 2017. But it is one thing to know something is true, and quite another to convince other scientists of what you know. So I have gone back to field records from 1994 to 2017 and tallied occasions when field observers reported severe infestations of black flies on loons or around their nests during the early nesting period. Then I looked at the correlation between reports of severe black flies and rates of nest abandonment across years. The result, as shown in the figure above, is unsurprising. In years when black flies were reported to be abundant, nest abandonments were very common.  (By the way, that data point in the upper right corner is 2014.)

While I was certainly not on pins and needles during this latest analysis of black flies, it is a crucial piece of the puzzle. Lacking any direct data showing that black flies caused loons to abandon nests, my best evidence to support this conclusion was that cool springs lead to a high rate of nest abandonment. The strong correlation pictured above now implies a direct causal connection between flies and abandonments.

I breathed a sigh of relief at this finding. I am not sure how I would have responded if I had found that years of severe black flies were NOT correlated with rates of nest abandonment. Yet I cannot rest. I can imagine a scientific reviewer complaining that the correlation might have resulted from observer bias. For example, once an observer starts to notice that black fly population is high early in the year and possibly related to nest abandonment, he or she might be more likely to report severe black fly infestations on subsequent days. Such behavior by field observers might explain the correlation I found, at least in part.

In short, I am still uneasy about my analysis of black fly impacts on loon nesting. I am looking for additional statistical analyses that could help convince a skeptical audience of the link between flies and abandonments. That is what life is like for a scientist.

 

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A few months ago, a loon naturalist and photographer from New England told me I was wrong when I said that males choose the nesting site for pairs. For 15 straight years, he said, he had watched a female look at potential nest sites that her mates had selected during the pre-nesting phase and then choose to lay the eggs in one of her own favorite sites, ignoring her mates’ suggestions. Thus, he claimed to have an exception to the rule that males choose the nest location.

Now let me say right off the bat that he might be correct. The paper we published showing that males choose the site where eggs are laid demonstrates an overwhelming statistical impact of male identity on nest location. That is, male identity is clearly far more important to selection of nest location than is female identity, but we cannot exclude the possibility that an occasional female might turn the tables on her mate and lay the eggs in a site that only she prefers.

Let’s look more broadly at avian breeding behavior to examine the possibility that a female might buck the usual trend in nest-site selection. Hundreds of studies have shown us that reproduction in birds requires tight behavioral synchrony in mated pairs. Coordination in behavior, in turn, leads to harmonious hormonal profiles of males and females. In other words, mates must be on the same page — both behaviorally and physiologically — throughout courtship, copulation, nest-searching, egg-laying, incubation, hatching, and rearing of young. (Linda Grenzer’s beautiful photo from a few years back illustrates this coordination nicely.) If one pair member is out of phase with its mate — say, not ready to incubate the eggs after they are laid, or unprepared to rear the young — breeding fails.

The dependency of reproductive success on behavioral and hormonal coordination between mates puts enormous evolutionary pressure on pair members to conform to the normal breeding roles and patterns of the species. In general, a male or female that behaves differently from others of the species will not find a mate, or if it finds a mate, will not nest. Weirdos generally do not leave offspring, so weird traits — to the extent that they are genetically based — do not persist in populations. For this reason, I am skeptical that the naturalist has found a female loon that flouts the “males choose nest sites” rule. Based on previous research findings across many species, I would expect a female that laid her eggs in a spot not selected by her mate would be faced with a mate unwilling to share incubation duties.

The naturalist’s claim of an exception to the rule has a more fundamental flaw. It is based solely on observations of a single female and her mates. As someone whose data consists mainly of behavioral observations, I am keenly aware of the limitations of  behavioral data that are not analyzed rigorously, especially observations from one or a handful of animals. Countless times I have thought that loons were behaving one way, only to find, on closer scrutiny and with a larger sample, that they were behaving another. If your sole evidence for a conclusion is “I looked closely at an individual and it looks as though she is doing this”, as in this case, you are on thin ice.

The story of how we learned that males choose the nest site illustrates well the pitfall of trusting limited observation to reveal true behavioral patterns, so it is worth saying a bit about how that analysis unfolded. On the face of it, we thought, how could males choose the site where a mated pair lays their eggs? After all, females, not males, lay the eggs. In a very basic sense, females must always control where the eggs are laid. Therefore, I expected my analysis to show that females controlled nest site selection. However, egg-laying in loons occurs only after many days of nest-searching within the territory. So it was conceivable that males might somehow influence their mates to lay the eggs in one spot or another. In fact, our statistical analysis showed that males take the lead in nest-searching and spend much more time than females in looking for a nest location. And an additional set of statistical tests showed unambiguously that males control where the nest goes. Here is the essence of our finding. Nesting pairs comprising a male that bred previously on the territory and a new female unfamiliar with the territory tend to reuse the successful nesting site from the previous year. Indeed, pairs composed of an experienced male and a new female select nest sites identically to pairs wherein both pair members are experienced on the territory. In contrast, pairs made up of a female with previous breeding experience on the territory and a male without experience there ignore the successful nesting location from the previous year and instead select entirely new, untested sites for nesting. Such pairs show no more knowledge of good nesting sites than do pairs in which both pair members are new and unfamiliar with the territory.

I was — and still am — puzzled by these findings. It seems absurd that a veteran female breeder permits her novice mate to choose an untested nest site, when she “knows” the best place to nest, based on her past experience. As the egg-layer, moreover, the seasoned female would seem to have absolute control over where the eggs are placed. But loon behavior defies common sense in this case. The data are very clear.

One more point about “knowing”. The naturalist who insists that he saw a female choose nesting sites is quite confident in his report. That is, he contacted me to inform me of his finding, not to try and reconcile his interpretation with mine. He “knows” that he saw a female select the nest site in the territory he observed. As humans, we often make observations, puzzle over their meaning, and then settle on an explanation of what we have observed. Then we get stuck. We become so invested in our explanation that we are unwilling or unable to give it up. In fact, reluctance to admit errors is a great problem in science, as we often make findings, build our reputations on those findings, and are unwilling to admit — even in the face of overwhelming evidence to the contrary — that we were wrong. I made a great error of this kind a few years ago and took many months to admit my mistake.

Human stubbornness of this kind makes sense….to a degree. In a world where we encounter many people who try to fool us or influence us to serve their own interests, we should show a strong tendency to “stick to our guns”. In the age of information, though, we also have access to useful knowledge from skilled practitioners — people who have rigorously and critically tested ideas and considered alternatives before settling on a conclusion. If we can see no reason why they would benefit from misleading us, we would do well to listen.