Did Barred Owls Move into Western Forests in the Last Century? New Genetic Evidence Suggests Not

We were discussing whether the migration of barred owls had been influenced by humans. It reminds me a bit of the wildfire and climate thought experiment. If it were 10 percent humans, would we manage differently than 60% humans? What if it’s difficult or impossible to know for sure (it usually is..)?


Then I ran across this interesting paper  from May of this year (2021)  which suggests a different history, plus also has interesting observations on hybrids.

Geographic distribution of samples. Sampling locations of the 51 individuals in our study. Putative identities of samples categorized with sampling locations, morphology, and vocalization are shown: SOs (Strix occidentalis), BO (S. varia), and hybrids. Putative hybrids are shown as “unknown.” For locations with a high density of samples (e.g., Humboldt County and Siskiyou + Shasta County in California; Lane + Benton County in Oregon), the distribution of sampled individuals is visualized in pie charts. The size of circles and pie charts correspond to the number of samples. The range of BOs is shown in green. The ranges for NSO and CSO are shown with red and orange lines, respectively. Sampling locations of EBO in figure 2C were shown: Kentucky and Ohio (KY/OH), New York, Massachusetts, and New Jersey (NY/MA/NJ) and Indiana (IN).


Then I ran across this interesting paper  from May of this year which suggests a different history, plus also has interesting observations on  hybridization.

Unexpectedly, we found substantial differentiation between WBO and EBO that is inconsistent with a separation time of between 80 and 130 years ago. There are two plausible explanations for this observation: First, we do not know “where” this divergence may have occurred. Given our limited sampling of EBO individuals, it is possible that there is a substantial amount of genetic variability within EBO, and that there exists an unsampled EBO population that is directly ancestral to extant WBO individuals. Work by Barrowclough et al. using mitochondrial data (Barrowclough et al. 2011) suggested that there is substantial variation within EBO. Although we confirmed that our samples included the population structure observed with mtDNA, it is still possible that our data do not fully cover the range of EBO diversity (Supplementary MaterialsSupplementary Material online, mtDNA analyses). Based on figure 2C, we suspect that further sampling in or near Indiana may be fruitful in identifying a putative EBO “source” population for WBO. Second, it is possible that BOs were actually living in western North American forests before the earliest recorded observations. Our estimate of the population split time overlaps with the predicted time of recovery of forests that connected the eastern and western parts of North America after the last Ice Age (Adams 1997). Given this expansion of the possible habitats together with the weak signals of a founder effect in WBO, the migration of large numbers of BO to the new western habitat accompanying the recovery of the forests is a plausible explanation for the differentiation between WBO and EBO. It would not be very surprising if BOs, which maintained a large effective population size even during the last Ice Age, have lived for a long time in Canadian forests with cold temperatures. Additional BO sampling in both central North America and these northern forests will be crucial for distinguishing between the remaining hypotheses. Regardless, our data clearly refute a scenario in which the WBO samples are very recently derived (i.e., within the past 130 years) from a panmictic population of EBO (as encapsulated by the 12 EBO samples examined in this study). Since our analyses focused on BO-specific variants, we believe that this ambiguity in BO population history can only be explained by distinct evolutionary histories of the sampled WBO and EBO individuals. An older divergence time between WBO and EBO populations is also more consistent with the observed variability in EBO versus WBO plumage (cf. fig. 1Hanna et al. 2018). Finally, we would like to emphasize that the results of our methodology are insensitive to unknown facets of WBO population history, such as any potential population bottleneck associated with the founding of WBO populations. This is because WBO demographic events that occur after the EBO–WBO split do not affect the distribution of coalescence times between EBO and WBO samples, nor the expected number of mutations on any WBO-specific branches of the genealogy.

(my bold)

These findings on evolutionary and demographic history of BOs are also important for conservation of SOs since little was known about the history of their “invasive” species, BOs. So far, it has been believed that the habitat loss in the eastern part of the North America caused the migration of BOs to the west. But if BOs have lived in Canadian forests for a long time, their recent invasion to the range of SOs might be due to different reasons, such as the recent loss of boreal forests caused by the climate change and human activities (Gauthier et al. 2015).

Or perhaps they started moving south during the Little Ice Age (1800s) and it took awhile? Lots of possibilities. And we might be collecting data on, and arguing about, the answer, farther into the future than any investment we would be making in controlling barred owl populations.

It would be ironic if Homo sapiens, who hybridized with and displaced Neanderthals (are we the Barred Owls of the hominids?) determined that other species shouldn’t have the have the same prerogatives.

“For one reason or another, the ancestors of modern humans in Africa start expanding in population, and as they expand their range, they meet with these other hominins and absorb their DNA, if you will.”


5 thoughts on “Did Barred Owls Move into Western Forests in the Last Century? New Genetic Evidence Suggests Not”

  1. The findings of these studies hardens my long-held unease about the Western Barred Owl control program. Why do humans have this compulsion to manage the destinies of other species? We have proven ourselves unable to manage our own.

  2. Sharon – GREAT POST – Only adds to the number of reasons to let evolution handle this non-problem at no further wasted cost to the taxpayer. The tally of scientific reasons for and against human intervention to save the SO is NEGATIVE versus SOME REALLY SIGNIFICANTLY LARGER POSITIVE NUMBER 🙂 :-). It would be nice if we could save the petite and cute SO. But, not if it requires destroying a species that has significantly more chance of survival in the future. I think it is time for the misinformed Pied Pipers to recognize the damage that they have done to the environment through their unscientific, emotionally driven efforts to remove, as much as possible from OUR federal forests, the use of renewable forest resources provided by sustainable forest management. The alternative is continued use of extracted non-renewable resources.

    Mac – Nice Thought – I wonder if some believers in the Darwin Theory understand that they are guilty of self contradicting logic when their actions show, no matter what they say, that they don’t believe in Evolution. I speak of those who want to eliminate the BO in spite of it’s OVERWHELMING SURVIVAL ADVANTAGES, and no disadvantages, compared the SO. It only gets worse if these same people are intolerant believers in global warming. For, then they compound their faulty logic when they want to kill off the species that, of the two, has the best chance of survival no matter what the future holds for the environment.

  3. “If it were 10 percent humans, would we manage differently than 60% humans?” Neither NFMA nor ESA make that kind of distinction.

    Barred owls have a wider dietary range and are more tolerant of disturbance (they are found in suburban eastern tracts) than spotted owls. It shouldn’t be surprising that they would do better than spotted owls in forests fragmented by development or logging, or therefore that we are seeing them increase recently in western forests that have become more fragmented.

      • I agree with Matthew’s logic there. If fragmentation outside the park allows barred owls to get established closer to the spotted owl refugia, then the barred owls are more likely to encroach on them. That’s kind of the nature of fragmentation – it doesn’t just affect the disturbed sites.


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