I was reading in the paper this morning about measures being taken to preserve the few remaining wild Spotted Owls in BC. In the article Barred Owl (BO) was described as an “Invasive species” and may need to be culled. Although I have heard of the Northern Spotted owl (NSO) and its conservation, my cursory research suggests that the BO is not what I would consider ‘invasive’, but is merely extending its range. Then I read that the two species can hybridize. Does anyone have any information/thoughts on this matter that might help me understand this issue. Are they essentially one species with variants, or are they considered completely different?
I do not want to get into the politics or ethics of logging, although I do know it is part of the picture.
I have heard of this issue with BOs before, but I think invasive is a strong term. It is more expansion of range which just happens to intersect with the range of the Spotted Owl. I also think that culling the BOs is not the best idea, and I am sure there are other non-lethal methods that would also work.
Different species, same genus.
Northern Spotted Owl is a subspecies of the Spotted Owl - Strix occidentalis
Barred Owl is a separate species - Strix varia
Looking at conservation policy in the US, a lot of national agencies define “natural” ranges as historic ranges prior to European colonization of the Americas. Therefore, range extensions due to climate or anthropogenic land use in the last 569 years count those species as nonnative in their new range.
How that definition was made is socially problematic and also leads to some really strange policy today.
The range expansion of barred owls may have been helped by humans. Here’s a paper that discusses that, but you might have to buy it to read it: https://bioone.org/journals/the-american-midland-naturalist/volume-161/issue-1/0003-0031-161.1.49/Range-Expansion-of-Barred-Owls-Part-I--Chronology-and/10.1674/0003-0031-161.1.49.short.
Spotted owls depend on specific type of habitat- old-growth coniferous forests- while barred owls can survive even in suburban areas as long as there are enough trees. Because of this, barred owls are much more adaptable and can outcompete spotted owls. They can also hybridize with each other (called a sparred owl). This just adds even more pressure onto the spotted owls affected by habitat loss, especially since barred owls
displace spotted owls, disrupt their nesting, and compete with them for food.
https://www.fws.gov/oregonfwo/articles.cfm?id=149489615
The USFWS is currently conducting an experiment to see whether culling barred owls helps the spotted owl population:
Across all study areas, barred owl removal appears to have stabilized spotted owl populations, though at low levels, on the removal areas compared to continuing declines of spotted owls where no barred owl are removed. There is evidence that barred owl removal has substantially improved the apparent survival rate of spotted owl on the Hoopa study area, though the total spotted owl resident population remains relatively low and is not increasing significantly yet.
My understanding is that the only reason the Barred Owl has been able to expand so far west is because of human changes to the landscape. The leading theory is that the Great Plains were an impassable barrier for the owls, but with tree planting and urbanisation, the owls have been able to move west. This does not seem all that different to a Brown Tree Snake being enabled to reach islands by human commerce and shipping. If it were a benign species, Barred Owl wouldn’t be classed as invasive, but as it is, studies suggest that it will over time wipe out the Northern Spotted Owl. How to prevent this is a really tricky ethical question. There’s an article that gives more information here: https://www.nationalgeographic.com/science/article/140717-spotted-owls-barred-shooting-logging-endangered-species-science
Worth noting that the westward range expansion of Barred Owl was guided if not caused by anthropogenic modification to the landscape. It’s very likely the species would be nowhere near the Pacific Northwest if people didn’t establish towns and cities to “guide them out”.
Thank you all so far (I’m sure there will be others). So my takeaway so far is that while they can hybridize, they are different species. Human activity has allowed the BO to expand its range, but it is technically not an invasive species.
Correct?
I agree with all, but I think that the last point “it is technically not an invasive species” depends on your definition of “invasive species”.
Under some definitions, it would be classified as invasive. But this is a notoriously squishy and disputed concept.
They can hybridize because they’re different species - if they weren’t, it would just be called breeding ;)
And as cthawley said, it depends on how you define ‘invasive species’, but it’s important to note that species can be any combination of invasive/non-invasive and native/non-native. There are non-invasive non-natives, and invasive natives.
Also, looking at ‘native’ status on a scale as large as a continent isn’t really meaningful. Another example of a species that is native to North America and also invasive is the Red-Eared Slider: it’s native to parts of the United States, where as far as I’m aware it isn’t invasive, but it is also invasive in many parts of the US (and the rest of the world) where it is not native and it has only come to as a direct result of humans.
Sounds like a similar situation to California Tiger Salamander and Barred Salamander, USFWS is I believe ‘removing’ hybrids from the population where pure CTS is found in an effort to preserve their genetic diversity.
Apparently the hybrids are one of the rare cases of combined hybrid vigor (when offspring are more fit than either parent) along with maintaining their fertility/ability to reproduce, representing a threat to the native populations. Side note, there’s no name for the hybrids that I can find, which is surprising since they’ve been interbreeding for over 50 years!
With climate change, who knows? Maybe all these hybrids are actually good news in disguise, since the genetics of an endangered species are somewhat preserved, and maintained in situ, though it would depend on what we imagine the future of a pure native would be in the presence of climate change.
Since we’re also already on the edge/start of the 6th global extinction event (Anthropocene/Holocene extinction) with a rate of species extinction in the 10-10000x background extinction rate after humans diversified/spread globally, it’s harder for me over time to worry about hybrids versus outright extinction, but maybe this is an overly cynical attitude?
The larger question of when or how to define a species as invasive is really intriguing, made more so by climate change and some of the management recommendations in the face of climate change. For instance, I’ve been in conferences where recommendations have been made to insure landscapes are permeable and connected in order that species can move as needed in response to habitat change. However, it seems obvious that an entire vegetative community and the many vertebrate and invertebrate species that inhabit that community are not going to move in lockstep, together, across a permeable landscape. One or more species will inevitably move more quickly than the rest, or permeability will be achieved for one species much sooner than others, allowing it to respond sooner, and when that happens is that species to be considered invasive? Like the mountain pine beetle in the Rockies http://www.climatehotmap.org/global-warming-locations/rocky-mountains-co-usa.html, of which millions of dollars are being spent to control https://www.cbc.ca/news/canada/edmonton/mountain-pine-beetle-alberta-mountains-trees-forestry-1.4285846. Apparently that is a negative result of a landscape being made permeable. And the definition would seem to get murkier with concepts like Assisted Migration https://www.fs.usda.gov/ccrc/topics/assisted-migration. Regarding hybridization, there is the example of “genetic rescue” as a result of hybridization, such as in the Sierra Nevada red fox, so possibly not all hybridization should be considered negative: https://academic.oup.com/jhered/article/110/5/559/5475287?login=true as brought up by @yerbasanta, how does one determine if hybrization is negative or positive, and in what time frame?
Regarding barred owls, i agree that barred owl removal is not a valid longterm solution to the barred owl-spotted owl concern (a concern not limited to the northern spotted owl, but now also to the California spotted owl). But is society willing to watch one species replace another, possibly to the extinction of the species being replaced? If barreds replace spotteds throughout much of the spotted owl range, are we willing to embrace barred owls?
All great responses which have taught me a lot. Another question, perhaps more controversial (and I stress that I have no ‘agenda’ here) - if humans are part of the landscape, is it not inevitable for some species to go extinct and others to thrive? Or should we strive, by whatever means, to preserve a species? There are probably no clear cut answers, but I would be interested to hear what folks think.
iNaturalist itself doesn’t consider barred owls invasive. An interesting comparison is when humans built bridges, coyotes moved on from the west to the east. They are not an invasive species, but simply took advantage of human’s actions.
Taking advantage of human actions (such as the intentional or unintentional introduction of a species) is part of many definitiions of invasive species. Specific to barred owls, here are almost 300 p on the California spotted owl; ,https://www.fs.fed.us/psw/publications/documents/psw_gtr254/psw_gtr254.pdf
You can do a word search for invasive, or go to the barred owl sections. Or a paper from over 20 yrs ago: https://watermark.silverchair.com/auk0050.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAApswggKXBgkqhkiG9w0BBwagggKIMIIChAIBADCCAn0GCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQM0w2H1R_CFZpKoVcXAgEQgIICThRi5fP6plZUgxL3m-TnAbjWRIwx11Bxw6l6KbKTz8tpN3uT8PncvguA3EMc4ZUFI65Bvo7cc3x5mYFdlqpZosPaH9LspLkVKVMHD6UbXeIzeBQoHzYs1ZSbggVqUe-p4BEFjczK89i9cI3eImtrtVD3hs6rldlLdE4gceaLfRxxspA67h1kWFDuOwq58jp943vZEf8ir7YBiI6cSnNDj2TWARWqzHJVlSFGQm5x8WCeRJZVYD32l6SIegs9GSPk8O7Vfgys576rctZQNeAMM4PVkR6IlQ7Lendatodm-vGFroX5KzCJvRrJ6cTR_On7fex0qabYP80Ur2Doa-aNZIzlO9jQzjdCdU32zGXdn35-so9H8PEreRMCqfSALNJ39gtgARfKFDxDgNzzIwdEvwloPBOJ7GZOFe_BpD0cSICHZqzx0GcUk0iV7yxVpAfAs2cmvWPKS7ohtcZ1RVCHOpgWBgSxV3IcOtLAW8ZhWVuMlJI0SW1MgMqrrt0j7zNjCkCnU3SFI65_gzuCq5exy_m-3NPw9XH-9Jaq-E5Sbik7Pp_Mru5-yL0-495N_lYqGCfSY0f1cXn9z8zxZLjnyYx8eYuByM4Aq5qwsodi_Tnfou8q5B2ZQ6L9Es92ZJzjQy7tXKzPikVXTJTnCLPYmCX-nnV7oW_OW2OPmftGDbRg7ngF8N5oSjS2l8pKT8L42empez9RePGTEFXf8sQ6hIphDckMhzxQU40azZj1-hTrJWyZRU8iWUj0citkANNfA18uiNTYjq-17wPFH8if
Or another from 2020: https://academic.oup.com/condor/article/122/1/duz058/5670813?login=true
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iNaturalist only tags things as ‘introduced,’ not invasive.
Amen to that. Cardinals and cormorants are great examples. Everybody loves cardinals on the Canadian landscape, even though the first record of cardinals was in 1901. They have since expanded to the point that they have put in appearances in places like Moosonee, just south of James Bay. You will never see them on a list of invasive species. Double-crested cormorant has gone through a significant range expansion relative to 19th Century baselines as a result of aquaculture practices in their winter range and (probably) invasive species (one deliberately introduced) provisioning nesting birds in the Great Lakes. This “problem” has been addressed by legislating removal from the protections of migratory bird conventions and legislation, primarily at the instigation of anglers. Meanwhile millions of non-native fish are introduced to the same waters every year by government agencies and angling groups for the entertainment of anglers. It’s a bizarre policy framework, and that’s the polite version. Shooting barred owls, on the other hand, is easy as pie.
Yes, that’s the official state of the taxonomy. I would argue that it speaks to the issues with species concepts that have been discussed in other topics.
That is a pretty rough approximation that depends on a bunch of assumptions, the largest of which is that we have an overarching definition of species that everybody agrees on. That assumption is demonstrably false.
As well, the “hybrids” have been shown to be fertile and to produce viable offspring in backcross matings. By some widely accepted definitions of species that means they are not reproductively isolated and therefore not separate species.
I think the hybridization is a bit of a red herring when talking about one species or two in this situation. It is not so much a case that barred owls and spotted owl DNA is homogenizing through hybridizing, rather spotted owls are being displaced and the remaining small populations of spotted owls are breeding with the only mates they can find: barred owls. There has not been much evidence of widespread gene flow between the two species and what is being found is only from spotted owls to barred owls.
None of that constitutes a red herring. Barred owls are abundant and widespread relative to spotted owls. Spotted owls were greatly reduced in abundance and range by the time barred owls arrived on the scene. The paucity of mates for spotted owls is primarily an artefact of processes that predate the arrival of barred owls on spotted owl habitat. As well, the larger size of barred owls strongly suggests that standard Darwinian mate selection pressures will favour barred owls. The fact that hybrids are viable and fertile in backcrosses flatly contradicts the various flavours of the biological species concepts’ criteria for species. There are other species concepts and some of them make at least as much sense as the biological species concept but the statement about hybrids that I quoted in my earlier post doesn’t force the conclusion that there are 2 species as has been suggested.
I agree that existing definitions of invasive species are all over the map and useless for informed discussion. Part of that hinges on defining invasive. More challenging is the part that hinges on defining species, which is a much slipperier concept than most people suppose. I’m not necessarily against removing barred owls if there’s a longterm possibility that it will lead to restoration of spotted owl populations but barring some pretty major interventions on the habitat side does anybody see that happening? Everything I’ve seen suggests that shooting barred owls will have to be a permanent activity. Official culls will almost certainly encourage vigilante culls which will almost certainly lead to spotted owls being shot. I mean, think about how many 5 foot tall, bright white, red-headed whooping cranes of which there are almost none have been shot by imbeciles hunting for geese.
People need to stop making categorical statements about what is obvious in situations like this. Every conceivable approach is fraught with uncertainty and internal contradictions. That needs to be acknowledged, not denied, if any meaningful, sustainable progress is going to be possible. These are wicked problems in every sense. They cry out for some sort of Structured Decision Making process but the leadership to get the conflicting perspectives to the table is missing in action almost everywhere.
Since the topic of species status came up for these species, it turns out that despite their hybridization and their similar appearances, the genomes of these species are millions of years diverged (Their mitochondrial DNA is about 11% different (https://pubmed.ncbi.nlm.nih.gov/29038757/). If they evolve at the usual bird rate of ~2% divergence per million years, that would put them in the ballpark of 5 million years diverged. For reference, most species pairs of boreal birds (eg, Townsend’s vs Black-throated Green Warbler, Chestnut-backed vs Boreal Chickadee, etc) are only a million years or two diverged, so these two owls are quite distant as far as hybridizing species pairs go.)
In birds it is very common for first-generation hybrids to be viable even between very distant species, while the species barriers act on the later generation offspring of those hybrids. It wouldn’t be surprising if the first generation Sparred Owls were perfectly healthy, while their offspring were less fit - I don’t think it is known how fit the later generation Sparred Owls are yet except that they can backcross.
I’m hoping that if the Northern Spotted Owl goes extinct, at least some of their best genes can be rescued by hybridization into a new lineage of owl that will persist in the changing environment. At least it is better than no owls at all. Millions of years of unique adaptation will be lost, but maybe some of it will be salvaged.