The story of Coastal Douglas-fir forests: All about owls

As the worst fire season in Canadian historyーdriven by climate change, ecosystem fragmentation, and long-term land-use mismanagementーdecimates forests across the country, species-at-risk biologist Jared Hobbs reflects sadly on the dramatic decline of Northern Spotted Owls and Western Screech-owls across British Columbia. Habitat loss is central to this story. Old-growth logging has reduced the number of Northern Spotted owls in the wild in BC to a single individual, while species like Western Screech-owls battle to find adequate nesting structures in monoculture tree plantations. Meanwhile, generalist species like Barred owls have been able to infiltrate new territory due to anthropogenic habitat conversion and are outcompeting, and predating upon, native species. 

According to Hobbs the way forward is clear: Stop logging old growth and protect maturing forests for the future.

What are some of the common owl species you might expect to encounter within the Coastal Douglas-fir Biogeoclimatic (CDF) zone?

Northern Saw-whet (Aegolius acadicus), Western Screech- (Megascops kennicottii), Great Horned (Bubo virginianus), Northern Pygmy (Glaucidium gnoma), and Barred (Strix varia) owls are all common to the CDF. Barn (Tyto alba), Long-eared (Asio otus), Short-eared (Asio flammeus), and Snowy (Bubo scandiacus) owls are unlikely to be found in the CDF, but do occur in the lower mainland, so they are within the geographic range of interest to this interview. In addition, both Great Gray (Strix nebulosa) and Northern Hawk (Surnia ulula) owls can be irruptive in this general region. 

The other species that would have once been common to the CDF, but is today virtually extirpated from BC, largely due to ongoing habitat loss, is the Northern Spotted owl (Strix occidentalis caurina, referred to as “Spotted owl” throughout this interview). Tragically, the loss of this species from the CDF is not unique to this region. There is only one Spotted owl left in the wild in British Columbia, and her days are likely numbered. Currently, there is  a group working to mobilize an emergency order to halt old growth logging within the range of the owl, but progress is not happening quickly enough. 

What sorts of habitats on the Gulf Islands and Southern Vancouver Island are most vital to maintaining healthy owl populations?

The most important habitat for most forest-dependent owl species almost anywhere, is mature forest, and the older the better. Most smaller owls are secondary cavity nesters: they depend on primary excavators, like woodpeckers, to build cavities for them and owls move in when woodpeckers move out. In older forests there is a legacy of these cavities created by primary excavators that owls can use. In the CDF, the Northern Flicker (Colaptes auratus)ー fortunately, one of the more common woodpeckers in the regionーbuilds some of the best cavities with about a 3~3¼” diameter, which is the preferred size for Northern Saw-whets and Pygmy owls. Western Screech-owls also often use cavity nests. 

Barred and Great Horned owls (among others like Great Gray and Northern Hawk owls) are a little different. Because they are large they cannot use cavities. Instead, they look for tree deformities, like a broken top that forms a chimney-like structure (called a “chimney nest”). On average these trees are around 300 years old when they break and it takes another 200 years of rot for the chimney to form, so they are typically 500 years old. These are not structures that can be easily recreated. Once cut, they are gone forever. 

In the absence of an appropriate chimney nestーand that absence is becoming more common as large, old trees are being logged in BCー there are few other options for larger owl species. Mistletoe infections can be an adequate substitute and abandoned or usurped Northern Goshawk (Accipiter gentilis) and Red-tailed Hawk (Buteo jamaicensis) nests are another alternative.  However, these are only options for species who are willing to use them like Great Horned or Barred owls. Other species, like Spotted owls, will only very rarely use anything but broken tops and that exclusive preference is contributing to their population decline. 

Western Screech-owl is another species that prefers to nest in broken top trees but can also occupy hollows created by large limb snaps. As a fairly brittle softwood species, black cottonwoods (Populus trichocarpa) are highly prone to snapping and as a result are common nesting trees for this species.

Unfortunately, there are not a lot of human-made solutions for providing adequate nesting sites beyond conserving natural habitats. Some species like Barn owls do sometimes use flat platforms built in barns and there are a few recorded instances of a Screech-owl nesting in a barn, but this is extremely rare.

Nest boxes are an option for some species (e.g., Screech- and Saw-whet owls) but they are only really helpful in areas where the only missing habitat requirement is a proper nesting structure. In such cases, multiple nest boxes should be installed as owls like variety and will switch boxes once they are dirty (i.e., from juvenile defecation and dropped bits of prey) because the parasite load gets too high for continued occupation. Over time, owls will return to these nest boxes, but they will typically wait a year or more to ensure any parasites have died off. 

However, even multiple boxes are a stop-gap at best. To use a simple analogy, imagine your home: it does no good to put a bed in a building if there is no way to cook and store food, no heat or water, and no place to use the bathroom. Likewise, because owls need habitat elements like edges to forage in, and forests to ensure appropriate thermal regimes, nest boxes are inadequate in meeting all of an owl’s needs and thus should not be considered a solution to habitat loss.

Is population decline a significant worry in this region? If so, are there any species of particular concern? What are some of the major drivers of population decline?

Population declines are always a concern for any biologist. Speaking in very broad terms, there are some species that are generalists, for example, deer, who tend to cope well with anthropogenic influences on the landscape like habitat loss, and their populations are stable or increasing. It is the specialists that really suffer from change. Specialists are species that have evolved over millennia to maximize their efficiency at surviving in a stable environment. When humans change the habitat this can have a profound impact on specialist species. 

Old growth forest-dependent species in BC, for example, are in a category of great risk due to the amount of logging that has occurred on the landscape. By some estimates,  less than 3% of the historic extent of old growth remains intact in BC, but the amount lost varies between Biogeoclimatic zones. In the CDF zone there is less than 1% remaining. This is too much change. Any species that has evolved to be an expert at surviving in an old growth CDF forest is in big trouble. There are many old-growth forest dependent species recognized to be in decline on the federal Species at Risk Act (SARA) or BC’s red-list.

Generalist vs. specialist owl species

When invasive species arrive in a new area, native species, being naive to the influence of the new arrivals, can often struggle. Generalist Northern Barred owls, for example, are relatively new to BC and have had a significant impact on local populations of Spotted and Western Screech-owls.

Male Western Screech-owls sing in their territory to advertise their prowess and secure a mate. The volume and length of his call is a fitness signal (i.e., demonstrates how strong he is). This is an effective strategy if it occurs in territories that are occupied by species that Western Screech-owls have co-evolved with over time such as Pygmy, Northern Saw-whet, and Great Horned owls. Because of this co-evolution, the Screech-owl knows 1) that Pygmy and Saw-whet owls are too small to be a threat and 2) if he hides n dense vegetation or a den while singing, he will be safe from predation by Great Horned owls. 

However, expansion of commercial logging activities has increased forest fragmentation in boreal forest ecosystems, while fire suppression has converted grasslands to forestland in the prairies, creating an intermittent network of “stepping-stone” habitats for Barred owls. Over the past five to six decades, these landscape modifications have allowed Barred owls to skip their way across Canada. Now the Barred owl, an eastern species, is replacing Western species like the Northern Spotted Owl or Strix occidentalis caurina (occidentalis quite literally means “to the west”).

As a novel owl on the scene in the guild of 15 British Columbia owls (there are 16 species in total in Canada, with the Eastern Screech-owl (Megascops asio) being the 16^th) the Barred owl is still relatively new. When it arrived on the west coast, native owls were not prepared. The Western Screech-owl’s usual defense strategy of calling from thick brush does not work against Barred owls who will enter even the tightest of situations and attack them.

Likewise, the dietary requirements of Spotted owls that were once a competitive advantage became a weakness. In a 2008 paper “Barred owls eating worms and slugs: The advantage in not being picky” (Livezey, Elderkin, Cott, Hobbs, &  Hudson), the dietary difference between Barred and Spotted owls was explored. It explained that as generalists, Barred owls are able to switch between multiple prey items and persist in a changing landscape. Conversely, millennia of evolution has taught Spotted owls that they must stay focused on the highest reward prey items, which includes two species: pack rat (Neotoma cinerea, 98% of Spotted owl diet) and flying squirrel (Glaucomys sabrinus, 2% of diet). As a result, Spotted owls will ignore everything else to focus on these two prey items.

In a stable environment, this evolutionarily-driven prey strategy will allow Spotted owls to outcompete all other species. But when the landscape is altered because of activities like logging, the whole prey-base changes. Suddenly generalists, like Barred owls who will eat anything they can fit down their throats, start to outcompete. They will eat and deplete the Spotted owl’s preferred, higher-reward prey and then switch over to lower-reward prey items when pack rats and squirrels get too scarce, leaving Spotted owls with nothing. 

Ultimately, both Barred and Spotted owls have a body mass of about 600 grams, both have basic metabolic requirements (BMR) of 54 grams of protein per day averaged through the year to survive and to carry them through their logical stages of breeding. But because the Barred owl is a generalist it can meet these requirements much more readily than the Spotted owl can, particularly in disturbed (i.e., unstable) habitat. 

Together these examples demonstrate how landscape change can allow generalist species to enter a new ecosystem and alter long standing dynamics by outcompeting native species. 

Coupled with habitat loss, the arrival of non-native species is a major driver of population decline among owl species as illustrated in the pop-out box above. Some native species have been readjusting their evolutionary dynamic in response. On the west coast, there are two subspecies of Western Screech: the more coastal Megascops kennicottii kennicottii and the more interior-associated, Megascops kennicottii macfarlanei.  Both these subspecies evolved without Barred owls, but the macfarlanei subspecies encountered Barred owls soon after they first arrived in the Flathead River Valley in the 1950s or 60s. This means that interior Screech-owls have been exposed to Barred owls for around six decades. Relative to members of the coastal kennicottii subspecies, who have only had two or three decades of exposure, there have been some noted behaviour changes among macfarlanei owls.

To give an example, Screech-owls on the coast tend to fledge young between June 8 and 12 on average. In the Flathead, it’s closer to mid-July, so it is not only later, but it is asynchronous to the Barred owls’ breeding season, reducing the influence of predation. That is, the Barred owls are focused on their young and not so focused on hunting, giving the macfarlanei owls a bit of relief.  Note that, there could also be other influences at play like weather and snowpack persistence; more research is required. 

Another, very distinctive difference between macfarlanei and kennicottii is that individuals of the former subspecies are much more secretive. On the coast, a person could quite literally walk right up to a kennicottii owl without them moving away. They are fairly tolerant of human presence. Whereas on the Flathead, if so much as a twig cracks the macfarlanei owl will quickly depart. It is likely that this wariness is a product of five plus decades living with an efficient predator (i.e., the Barred owl). With that kind of selective pressure, the surviving macfarlanei owls seem to have learned quickly to be wary. The hope is that the coastal kennicottii owls will learn to evade predation from Barred owls in the same way.  

As one might expect, coastal Screech-owl populations are lower where Barred owls occur alone; however, Barred owls do not persist well alongside Great Horned owls who predate upon them. As an example, 67% of avian predation on Northern Spotted owls is attributed to Great Horned owls, and there is likely a similar influence on Barred owls who are of similar size. Great Horned owls are owl hunters, but as mentioned above, they do not generally hunt Screech-owls as these smaller owls tend to hide in thick brush. Recent findings suggest a high correlation between good numbers of remaining Screech-owls in territories also occupied by Great Horned Owls as Barred owls are being kept away. 

There is a similar relationship between Ospreys (Pandion haliaetus) and Great Blue Herons (Ardea herodias). Ospreys are very territorial and defensive of their nests, they will aggressively chase away any threatening species, including Bald Eagles (Haliaeetus leucocephalus). Bald Eagles tend to predate on Herons, so over time Herons have learned to establish their breeding colonies around Osprey nests. Often an Osprey nest can be found in close proximity to a Great Blue Heron colony in the interior. It is possible that over time, coastal Screech-owls will learn to select territory and nesting sites based on the presence of Great Horned owls  to avoid predation by Barred owls, the same way Herons select sites for their breeding colonies based on Osprey presence to avoid predation by Bald Eagles. 

Have there been interruptions to owl species’ lifecycles in this region due to habitat loss? Are owls able to adapt quickly enough to changing landscape conditions to increase the chances of species survival? 

What defines an owl as being an adult is acquisition of territory. Owls who have claimed territory are known as “residents”. Once an owl becomes a resident they work to attract a mate, which generally takes a year, after which owl pairs are monogamous. If the female owl dies, the surviving male will typically stay in the same territory and call for a new mate to join him. When this happens, the male will call or sing to attract a female and if/when she arrives, the male owl will often show her the available nesting cavities and other features of the territory to prove that he can provide for her and their future young. Conversely, if the male owl in a breeding pair dies, the surviving  female is more likely to move on to seek out a male in a new territory. 

This is at odds with the basic ecology of mammalian mate selection. Because mammalian females carry the young and thus are more valuable (or are “the resource”), the males take on the dangerous job of roaming around looking for females. Among owls (and many bird species) it is the opposite. The female lays an egg and the male provisions the female and the young, so it is not the female that is the resource, it is the territory and it is the male’s job to provide the food.

Once an owl pair has bred, their young hatch in summer (typically around June) and leave the nest (i.e., fledge) just a few weeks later to enter what is called the post-fledging area (PFA). Over the next one to three months, depending on the species and the preference of the parenting pair, the young are cared for by their parents and taught to hunt within their occupied territory. By mid-August to early September, the parents stop tending to their juveniles.

Reproductive cycle: coastal Western Screech-owl

Based on extensive data from numerous nest sites, research has found that coastal Screech-owls typically  begin courtship sometime in late March in BC. Eggs are generally laid within two weeks (i.e., in early April) and are incubated for an average of 30 days. The hatchlings will stay in their nest for about 30 days before fledging sometime between June 8 and 12. 

While some researchers theorize that juveniles are driven away by parents, this is not true. There is no aggression, there is passive disassociation. That is, the parents stop feeding them and after a while, the young owl realizes that it is time to start seeking prey independently. However, they also recognize that they will not be able to outcompete their parents who are experienced hunters, so they must move out of the PFA to find their own territory. The act of leaving natal territory (or PFA) is called dispersal. 

The juvenile then spends late fall and most of winter roaming around trying to acquire territory and find a mate. If all goes well this process is complete by spring. However, the allee effect (not to be confused with the allele effect, which is genetic depression) has had great influence on owls particularly, Spotted and Screech-owls.

Both species rely on a social cue (i.e., calls) to acquire territory, so they will roam around until they hear an unpaired adult owl of the opposite sex calling. But if potential mates are missing from the landscape (and this is becoming an increasingly frequent reality due to habitat loss resulting in population-wide declines on the landscape), young owls will keep searching and that is when they die. The more fragmented the landscape, the further the owl will move. But there is a high energetic cost associated with moving around. Traveling long distances is at odds with the natural life cycle of these resident species who have evolved to occupy a given territory. Moving also renders the owl’s primary defenseーto sit still and/or be camouflaged against the bark of a treeーineffective, thus making them susceptible to predation by Great Horned or Barred owls.

Further in this prolonged search for a mate, young owls are likely to have less energy available as their habitat falls around them making prey scarce. Yet, this is when they need that energy most. It takes at least 120 years for forests to achieve adequate structural heterogeneity to support owls and the prey-base many species depend on. It is unlikely owls will be successful in meeting their basic metabolic requirements in clearcuts or regenerating monoculture forests that are between 10 and 40 years old (and this is especially true for specialists like Spotted owls). 

To go back to the beginning: the length of time it takes an owl to be considered an adult depends on the condition of the landscape. That is, the more degraded the habitat, the longer the dispersal process, and the more time passes before an owl becomes a reproductively capable adult (if ever). In some populations the impact of habitat loss has been tremendous. In BC, there was a 100% mortality rate documented (by Hobbs) among dispersed Spotted owls. One was hunted by a Great Horned owl, but all others starved. Normally, the mortality rate in raptors is about 50%. Over the past 20 years in BC, Spotted owl survival rates in BC have plummeted. It is tragic to watch all these young owls fledge and die. In response, the province started a captive breeding program, but at present the wild population of Spotted owls in BC is down to a single resident female.

The same is likely happening with Screech-owls, though the population is less well researched and the numbers are higher. By continuing to damage the landscape, humans have created the conditions for Barred owls to move into a Screech-owl’s territory and interrupt the Screech-owl’s life cycle. It is nearly a certainty, without any published literature behind it, that Screech-owls are experiencing a much higher mortality rate coupled with a much lower recruitment rate than they would have in an unmodified landscape.

When an owl is miraculously able to become a resident adult, most species breed just once every two years, but this is only a very general rule as it differs between species and there are a number of factors that might influence fecundity. For example, there was one pair of Spotted owls that reproduced five years in a row, but that was a record-breaker (i.e., the most productive owl ever found in North America), so highly unusual. More typically, owls skip a year to retain a healthy body condition before reproducing again. 

The longevity of owls is difficult to determine, and there is some debate around it as it is challenging to conduct rigorous long-term studies. Monitoring owls in captivity doesn’t really work because, being isolated from predators and starvation, longevity is amplified. The current thinking is that Screech-owls live from 3 to 5 years on the low end and 10 to 12 on the upper end.  Spotted owls can live up to 17 years, but in a perfect example of the longevity provided by captivity, one Spotted owl lived to be 31 so there is a massive range. 

What are your recommendations for conserving owl numbers and diversity in this region? Is there anything individuals can do to help stabilize populations in decline? 

STOP LOGGING OLD GROWTH.

It is a ridiculous notion that logging old growth has been considered acceptable for so long. We know better. We know we’re in a biodiversity crisis that logging practices are exacerbating, so why are we still doing it? Mostly to line the pockets of corporate shareholders.

Multinational corporations love operating in BC. They can take advantage of very weak, diluted environmental protections that do not comply with SARA or with provincial policies. On the surface there is some pretense of protection, but ultimately decisions to protect habitat are made by politicians, not scientists.

 In BC, forest licensees can log without pre-surveys (for any species, including species-at-risk), and there is no requirement for population-level monitoring in response to logging practices. Licensees also seem to disregard the BC Wildlife Act and the Migratory Birds Convention Act. They log during the breeding period and they do it all the time. Licensees capitalize on the relatively weak environmental protections in place and thus have a massive advantage in the global marketplace. 

Taxpayers subsidize the construction costs for logging roads and the province all-too-frequently waives their stumpage fees making generous allowances for salvage logging in areas of beetle kill or fire damage. Logging in BC continues with no consideration to the financial cost to the province in lost environmental services (i.e., greenhouse gas emissions), or to increased recovery costs for species-at-risk that are badly affected by logging. Logging results in biodiversity loss, and leaves taxpayers with the bill of recovering those species that have been impacted. How do politicians get away with allowing multinational companies to come in and destroy local ecology, subsidized by taxpayer dollars, only to take corporate profit elsewhere?

The single answer to the question how can we do better for owls and just biodiversity in general is screamingly evident: stop logging old growth forests. 

These are special ecosystems where a myriad of animals have evolved in stable conditions to outcompete the generalists. The second we start logging, we tip the scales in favor of the generalist and against the specialist. Consequently, the species listed under Schedule 1 of SARA are all specialists.

Individual actions to help stabilize biodiversity and better protect declining species like owls are much more enigmatic and potentially irrelevant compared to changing the way forests are logged in this province. The best way to contribute to this change is to vote out politicians who support old growth logging, write to locally elected representatives, and support a transition in BC’s logging industry. Though timber is, of course, an essential resource, there are ecologically-informed approaches to timber harvest that could be adopted. Logging old growth is never acceptable under any circumstances. 

Another easy contribution to protecting owls and other bird species is keeping pet cats indoors. Outdoor cats account for up to 300 million bird deaths a year in Canada alone, so one of the biggest impacts a single person can have to protect local avian populations is to keep their cat indoors.

In the CDF zone, where there is so little old growth remaining, what sorts of habitat should be targeted for protection to ensure there is adequate habitat for local owl populations in the future? 

There is a technical advisory committee currently working on exploring and implementing the recommendations made by Al Gorley and Garry Merkel in their strategic review of old growth forest management in BC. They have tried to target and map areas where there is a high biodiversity emphasis, but this is not a new game. Twenty years ago the government was working on something called “high biodiversity area options” that it tried to map, so this is a long-overdue task and argument. But, basically, the older a forest is, the more valuable it is. This means, anything age class eight (141–250 years) or nine (250 years +) needs to be protected. To take a longer-range view, one might recognize that forests remaining in the eight/nine age class is a fractional percentage of historical extent, so saving some forests in the six (101-120 years)/seven (121-140 years) range to eventually recruit eight/nine would also be prudent. Then we need time. In other words, even if forests are not old yet, we need to let them become old–only then will the habitat that specialist species require be available to them. 

First we need to stop logging and eroding our recovery options, then we need the passage of time. – Jared Hobbs

As noted earlier in this article, the CDF in particular has very little old growth remaining. In these habitats it is not only important to protect the tracts of old growth that remain, but also to protect individual old trees. This will both maintain habitat and also retain genetic diversity for the forests of the future. 

Further reading and references

British Columbia. (n.d.).  Dwarf Mistletoes. Forest insects and pathogens. https://www2.gov.bc.ca/gov/content/industry/forestry/managing-our-forest-resources/forest-health/forest-pests/dwarf-mistletoes

Curk, T. McDonald, T., Zazelenchuk,D., Weidensaul, S., Brinker, D., Huy, S., Smith, N.,  Miller, T., Robillard, A.,  Gauthier, G., Lecomte, N., & Therrien, J.-F. (2018). Winter irruptive Snowy Owls (Bubo scandiacus) in North America are not starving. Canadian Journal of Zoology, 96 (6). 553-558. DOI: 10.1139/cjz-2017-0278

Gorley, A. & Merkel, G. (2020). A new future for old forests:  A Strategic review of how British Columbia manages for old forests within its ancient ecosystems. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/forestry/stewardship/old-growth-forests/strategic-review-20200430.pdf

Livezey, K.B., Elderkin, M.F., Cott, P.A., Hobbs, J, &  Hudson, J.P. (2008). Barred owls eating worms and slugs: The advantage in not being picky. Northwestern Naturalist, 89 (3), 185-190. DOI: 10.1898/NWN08-04.1

About Jared Hobbs

Jared Hobbs is a registered professional biologist and a registered Polar guide living on Pender Island, BC. Throughout his career he has focused on conservation of species-at-risk in BC, Yukon, Alberta, Northwest Territories, Kauai, Alaska, Australia, and Antarctica. He has authored and co-authored a number of academic articles and books and has received awards for his dedication to conservation. In addition to his work as a biologist, Jared is a professional wildlife photographer and mobilizes his work to raise awareness, increase empathy, and strengthen species conservation. His photos have been used by many publishers, government agencies, and  environmental advocacy groups worldwide. 

You can help

Raincoast’s in-house scientists, collaborating graduate students, postdoctoral fellows, and professors make us unique among conservation groups. We work with First Nations, academic institutions, government, and other NGOs to build support and inform decisions that protect aquatic and terrestrial ecosystems, and the wildlife that depend on them. We conduct ethically applied, process-oriented, and hypothesis-driven research that has immediate and relevant utility for conservation deliberations and the collective body of scientific knowledge.

We investigate to understand coastal species and processes. We inform by bringing science to decision-makers and communities. We inspire action to protect wildlife and wildlife habitats.