Buckthorn berries and Bohemians

Common Buckthorn (Rhamnus cathartica) berries

While out walking the other day I came across a single, lonely buckthorn shrub-tree along one of our fencelines. It stood out from the other woody vegetation because it was the only one in the row that bore any berries. We have so few berry-bearing bushes on our property, I went up for a closer look and some photos.

Buckthorn isn’t native to North America; it’s originally from western Eurasia, and was introduced to North America early in the 1800s. Given the right conditions (which includes disturbed land), buckthorn can be very invasive. It leafs out earlier than many of our native plants, giving it a longer growing season, and plants are very hard to kill – like willows, they’ll resprout from roots and stumps. One site I’ve read also suggests that the shallow, spreading root system outcompetes those of other understory plants. I’ve been to a few places where the shrub has spread and established itself over a wide area. Not a lot of fun when you have to walk through it! The name does actually refer to little hawthorn-like thorns that grow at the ends of the stems.

Common Buckthorn (Rhamnus cathartica) berries

When freshly ripe, those berries look like they ought to be tasty, but they’re actually poisonous. A handful of berries will give you abdominal pain and diarrhea; a bowlful can cause serious problems. The amount of poisonous chemical contained within the berries decreases once they’re ripe – probably a strategy the plant evolved to keep animals from eating the berries before they were ready to be dispersed.

This can cause some problems for wildlife in areas where the plant has been introduced. In its native range, berry-eating birds know not to eat the berries before they’re ripe, but birds not familiar with the plant don’t have that knowledge. They may eat the berries while they’re still toxic, and suffer the consequences.** (Edit: Reader Julie of the Rouge River Bird Observatory in Michigan comments that the author may have jumped to conclusions with the article I linked to at the **. Julie’s own research on avian use of non-native fruits has shown no such toxicity of buckthorn berries to birds. Julie knows a thing or two about a thing or two, so I’m inclined to believe her.) However, if the berries make it past ripening and into the fall, they’re an excellent source of winter nutrition for our birds. Clumps of buckthorn are great places to check out when you’re birding in the winter, because more often than not there will be waxwings or robins or bluebirds or other berry-eaters flitting about the shrubs.

Bohemian Waxwings

Many species will feed on buckthorn, but of particular interest to me are Bohemian Waxwings. The winter specialty of Bohemians is mountain-ash, also called rowan (Sorbus americana), which bears bright orange berries. In years that mountain-ash crops in the north are poor, Bohemians will move farther south looking for food. Once they reach southern Ontario the mountain-ash crops might have improved, but their diet can also be supplemented with the berries of the widespread buckthorn (by the time they make it down here, of course, the berries are well past ripe and entering shriveled).

I saw a flock of Bohemians, 40 of them, while I was out this afternoon. I spotted them before I heard them; they were being unusually quiet for waxwings. I had neither my binoculars nor my long lens, but the way they were all clustered at the top of a couple of trees is, from my small amount of experience, typical of the species, as was their completely unconcerned attitude as Raven and I approached to stand a short distance away. A few birds were calling, which confirmed the ID even if I couldn’t see them well. I stood and watched for several minutes before they all began to call and then abruptly departed.

One buckthorn bush isn’t enough to keep them occupied for the winter, nor is our neighbour’s single crabapple tree. Still, I hope they might linger, that I might meet them again.

Bohemian Waxwings

**As per this article. Some websites are very anti-buckthorn, others are pro-buckthorn, at least in terms of its benefit to wildlife.

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Bohemian redux

Bohemian Waxwings

Dan took Raven out for her exercise today. When he came back in, he called up to me to say that there was a large flock of Bohemian Waxwings down near our little pond. He said they seemed to be sticking around, so I grabbed my camera and he was kind enough to take me back to where he’d seen them.

Bohemian Waxwing tracks

When we got back there, they were gone. We paused and listened, wandered around a bit, but there was no sign of them. The only evidence of their passing were little footprints in the snow where they had been coming down to the ground. They’d apparently been doing this while Dan was watching them, but it wasn’t really clear what they were interested in. Today was a somewhat mild day and snow fleas were out in force, so I wonder if they might have been plucking the springtails from the surface of the snow. Although their diet in the winter is mostly fruit, this is primarily because insects are hard to find, and they haven’t adapted to eating seeds.

Bohemian Waxwings

We wandered back through the woods along the edge of our fields, popping back out near the house. As we started to cross the meadow, Dan paused, thinking he might have heard something. All I heard were feeder birds, tree sparrows, and we took a few more steps before Dan decided no – those really were waxwings he was hearing. Sure enough, a flock – the same ones? – had alighted in a tree on the far side of the house. There were fewer than when he first saw them, so if they were the same, who knows what happened to the rest.

Bohemian Waxwings

I snuck up to their tree and watched them for a while, taking a few shots from underneath. Then I went back to the house to see if Dan’s video camera was handy, as I wanted to try to record all the noise they were making. Turned out the battery wasn’t charged, so I couldn’t get any video, but when I went back out they’d left the treetop anyway, and were swooping down to the ground on the neighbour’s property.

Bohemian Waxwings feeding on fallen apples

When I got back over there I could see what they were feeding on. Fallen fruit, probably apples judging from the size of them. They were actually digging them out of the snow and then pulling pieces off once they’d got them to the surface. The ones scattered on the snow have already been pulled out.

Bohemian Waxwings

They were somewhat flighty, never seeming to stay on the ground more than ten or fifteen seconds at a stretch, but they didn’t go far, just flying up to the top of the apple tree they were feeding under.

Bohemian Waxwings

I got much better looks at them this encounter than I did last time I saw them (I wonder if these might even be the same group?). Normally they hang out high in the crown of a mature tree, and you’re always looking up at their underside. That’s where we first found them. But of course, when they come down to the ground to feed they’re at eye-level, and even at some distance away it’s still a better view. You can see their yellow lightning stripes much better in these photos.

Bohemian Waxwings feeding on fallen apples

They’ll probably be here for another month or so, perhaps sticking around into April before they start making their way north to their breeding range. The tundra and northern taiga where they nest will still be frozen well into May. The waxwings won’t start nesting there till late May or early June, by which time some of the birds around here, such as robins, might already be fledging a brood. There’s no rush for the waxwings to be heading back, in any case, so they’ll stay till the snow starts melting here and then follow the melt north.

Since they showed interest in the neighbour’s apples, they might hang around till the fruit are gone. I’ll have to keep an ear open for them.

Bohemian Waxwings feeding on fallen apples

Wandering winter waxwings

Bohemian Waxwings

I went out late to take Raven for her afternoon walk today. It was nearly four by the time I finally got the skis strapped on (with the mild weather, all the snow was wet and stuck to the snowshoes when I hiked out, making my feet feel uncomfortably heavy). The skis make more noise than the snowshoes, and I had to watch where I was going because the trail out had gotten a little rough with the melt and certain un-snowshoed travelers making holes in the track. So I was nearly halfway out along the first field before the sound of the birds registered. I stopped, looked up. And there, at the top of the trees just ahead, was a huge flock of Bohemian Waxwings, all chirring in their high-pitched bell-like call. I hadn’t brought my camera. I hadn’t even brought my binoculars, figuring it was so late in the day. What to do?

I struggled only a moment before turning back and skiing as fast as my clumsy rustiness and bumpy trail would let me, glancing once or twice over my shoulder to make sure they hadn’t flown. The way I figured it, if they flew before I came back out with the camera, I hadn’t lost anything, but I most definitely would not be getting a photo if I didn’t go back for it. I grabbed the camera, switched out the lenses to the telephoto, called in to Dan that there was a flock of Bohemians (“How many?” “Oh, dunno… twenty? Twenty-five? Fairly large.”), hurried back out, strapped on the skis again, and started back down the trail.

Bohemian Waxwings

They’d stayed. Whew! Thank you, birdies! I would’ve been disappointed not to get a photo, but not upset; it was a thrill just to discover them. I realized on going back out that the group was larger than my initial hurried estimate. In fact, when I sat down to count the individuals in the top photo of this post, I came up with a total of 85 birds. That’s a pretty good-sized flock!

I can count on one hand the number of times I’d seen Bohemians prior to this (twice). They’re an irruptive species that breeds in the far north, from the Hudson Bay of Northern Ontario, west through the boreal into Alaska, and south through the Rockies to about the Canada-US border. The closest breeding population of Bohemian Waxwings to us here in eastern Ontario would be the Hudson Bay population, some 1200 km (700 miles) away as the waxwing flies, and even there their numbers are thin.

In the recent Ontario Breeding Bird Atlas the species was detected in just 16 of about 85 100-square-km squares surveyed, with a probability of observation of just 6% (that is, the percent chance that you’ll detect the species in any given square in the region within the first 20 hours of field work – the method of data standardization used in the atlas). The first documented nest of the species in Ontario was only found in 2003.

Bohemian Waxwings

Bohemian Waxwings feed primarily on mountain-ash berries in the winter. When crops of these berries are good in the north they rarely roam very far south. However, when crops are poor they may travel farther in search of food. Ontario birder Ron Pittaway writes a “winter finch forecast” every year where he consults naturalists from across Ontario and other parts of the country to assess tree seed crops in various regions. Knowing how food supplies are distributed about the northern forests helps him to make a prediction on what northern species might irrupt south and in what numbers. He’s usually pretty accurate. This year he indicated that mountain-ash berries are in good supply through much of the north, and so there will be low numbers coming south this year.

He also notes that while spruce, hemlock and birch crops are poor in northeastern Ontario, they’re good in northwestern Ontario and crossbills and redpolls will mostly move in that direction rather than come south this year. I haven’t seen a single redpoll yet this winter.

Bohemian Waxwings

Slightly larger than Cedar Waxwings, they can easily be told apart by their grayer bellies and rufous undertail coverts. This is good, because when you’re looking up at a group of waxwings perched at the top of a tree, it’s often hard to see the other diagnostic marking, the white-and-yellow patterns on the wings. I pished to try to draw them down a bit closer, but they just tipped their heads and laughed at me. Yeah right, they seemed to say, we saw you walk up here, and your black wolf isn’t helping make you any more convincing.

They hung around just long enough for me to run off a couple dozen shots, and then, in one decisive movement, they all took off and departed for places west. I was pretty surprised to see them in the first place, really. Neither the 30 acres behind the house or the 100-acre woods down the road have much in the way of berry bushes, that I’ve seen, and even early on in the winter I’d noted to myself that we probably wouldn’t be seeing any waxwings as a result. So I was delighted they decided to swing by to say hello!

"Bohemian Waxwing / Jaseur boreal" by Eric Bégin on Flickr -- A closer encounter than mine! Taken in Québec last April.

The birds we counted

Black-capped Chickadee on sumac

I had this written and ready to go yesterday evening, but WordPress suffered a glitch and wouldn’t let me post or save anything. The good guys at behind the scenes got it fixed promptly, however, and hopefully there won’t be any further hiccups!

It had been my original intention to make the post about our CBC as just a single entry, but I found when I got home and started going through my photos, and thinking about what I wanted to say, there was just too much to cram into a single post. Yesterday I talked about the history and purpose of the CBC; today I’ll elaborate on the results of our own outing.

Generally CBCs are quiet affairs, at least compared to summer surveys. In the summer a survey of an area that large could easily turn up 70 or 80 species, or even more if you’re in an area of diverse habitats. In the winter, at least here in the northeast, you’ll be lucky to get a few dozen with a good bit of hunting and the whole day at your disposal. We didn’t have the whole day, and the frigid temperatures meant we weren’t really into hunting, so we took what we could get. This is one of the pitfalls of the CBC, that there is no rigorous sampling method so effort varies from year to year according to the number of people available and how many hours they’re able to put in. Weather also plays a factor – the day is selected randomly in advance, usually for a weekend, and the count goes ahead rain or shine. A year with excellent weather is probably going to produce more birds than a year with heavy precipitation, for instance. These variables are all recorded so that they can be factored in in future analyses, and generally for monitoring surveys like this the data are looked at with a wider lens rather than on a year-by-year basis.

Black-capped Chickadee on winterberry

Because we only had a few hours available to us before the snow started falling and the roads got cruddy, and because we limited the amount of walking we did outside because the cold and wind could peel the skin from your cheeks if you stayed out too long, we had a small list, with just 16 species. Some of the species that were included on the list were star additions that we were pleased to see, though nothing exceptionally rare. Most, though, were common birds. Black-capped Chickadees were, unsurprisingly, the most common with 54 individuals counted. Part of this was because we made a few stops near bird feeders, which always draw in a crowd. But they’re also the most frequently encountered species in the winter woods, especially in evergreen stands. Evergreens, because they’re good cover, often have birds in them, compared to deciduous woods or open fields that are more often than not empty, so we made a disproportionate number of stops in coniferous patches. The above individual was part of a flock that were moving through a stand of young pines, bordering an open wetland filled with winterberry bushes sporting their bright orange berries.

Waxwings

We also had many of the usual suspects: Blue Jay, Hairy and Downy Woodpeckers, Red- and White-breasted Nuthatches, crow and raven, Red-tailed Hawk, Dark-eyed Junco. In addition to these were some less common though expected species: Brown Creeper, for instance, and Common Redpoll, the latter with 50 counted in three flocks, all flying overhead. We were pleased to find two small flocks of White-winged Crossbill, an irruptive species that is moving south in large numbers this year, being found in many areas south of the border that only get to experience them infrequently. We’ve been hoping to have some come to our feeder this winter, but so far haven’t seen any.

The most exciting birds to find, however, at least in my opinion, was a huge flock of waxwings. Dan discovered them during one of our leapfrog stops. He hustled back to find me (I was finishing up the person 1 segment) and grab his video camera from the car. There was an amazing number of birds in the flock, too many to get a precise count as they joined and departed the main body of birds perched in the tree beside the road. I made a quick estimate by eyeballing groups of fives to figure there were some 80 birds in the flock. Cedar Waxwings are not a species I see regularly in the winter, so finding such a large group of them was exciting.

Cedar Waxwings on buckthorn

They seemed to be feeding from buckthorn bushes that were growing between the road and a little patch of wetland. Common Buckthorn (Rhamnus cathartica) is an introduced species that’s become pretty well established through much of northeastern North America. It’s originally from western Eurasia and was brought to the New World as an ornamental garden plant. Though it can be invasive in some habitats, and causes problems for soybean farmers as it is the other plant host in the two-host cycle of soybean aphids, but it’s a great winter food source for birds, who feast on the shrub’s juicy black berries.

There is some misconception that because a chemical in the berries actually acts as a laxative in humans, the birds must therefore be unable to obtain sufficient nutrition from the berries and in the long-term could actually suffer or die from a diet composed mostly of them. Of course, that wouldn’t make much sense; shrubs produce berries for the purpose of attracting animals to eat them and thereby spread the seeds. Killing the animal who is spreading your seeds for you would be counterproductive, you’d be out of a courier in no time fast. Similarly, the parent plant “wants” the bird to take the seeds far from the parent plant, so including a laxative is likewise not a great idea. Bootstrap Analysis goes into more detail on the argument. She also points out that they’re a non-native plant so they’re not the top choice for planting in your garden, and provides a list of alternatives. But the fact that they do offer a viable food source for birds in the winter means that even though they’re displacing native plants, it’s not all bad.

One of these things is not like the other

When the waxwings weren’t feeding on the berries they were perched up in the tree, conserving energy or just digesting, I’m not sure. It was difficult to see the birds in the bushes very well, but the ones in the trees were conveniently out in the open. In scanning the flock, we discovered that about five of the birds were conspicuously different. They were bigger, grayer, and had reddish undertails. They were Bohemian Waxwings. This was an extremely pleasant surprise; the Winter Finch Forecast by Ontario Field Ornithologists’ Ron Pittaway had predicted this irruptive species to stay north this winter, as it specializes on mountain-ash berries in the colder months and the berry crops up north were good this year.

Bohemian Waxwings

The birds were all perched up near the crown of the deciduous tree they were sitting in, which made it difficult to get good photos as they were not only backlit by the grey sky, but also tucked behind criss-crossing branches. And the photos I did get were all mostly of their undersides, which does highlight their nice rusty undertail coverts, but doesn’t show much of the rest of their plumage, including some fabulous lightning bolts running down the wingtips. These were only the second group of Bohemians that I’ve seen, since they’re an irregular, uncommon irruptive, and tend to move around a lot. I didn’t get great photos of the first group, either. I’ll admit that I’ve never tried super hard to track them down, though.

Cedar and Bohemian Waxwings

Bohemians breed in extremely small numbers in Ontario, restricted to the Hudson Bay Lowlands up north. The second Ontario Breeding Bird Atlas suggests that they’ve been expanding eastward a bit since the last atlas. Most of the species’ range is further north and west, however, including the northern part of Manitoba, Saskatchewan, and Alberta, up through the territories, over to Alaska, and south through the Rocky Mountains. It could be these were Ontario birds, but they could just as easily have come southeast from the main portion of their range, as they depart the northern part of their breeding range and will wander as far east as Newfoundland looking for winter food sources. Either way, these birds have made a long trip, and it was really nice to get to see them.

Winter bird irruptions

Common Redpoll

I have more to add to the winter colours theme of the last couple of posts, but feel like a change of pace today. I haven’t done any posts yet about birds, which is a little surprising given that birds are really my primary interest in nature (first birds, everything else second). So here’s a post on birds.

This winter, southern Ontario, and indeed most of northeastern North America, is enjoying a phenomenon called “irruption”. An irruption is similar to migration in birds, but takes place irregularly, usually every two to four years (depending on the species), rather than every year. Most irruptions are the result of food shortages in the areas where the birds usually spend their winters. Because the birds can’t find sufficient food there, they start to move south in large numbers. In many of these species, small numbers may be seen every winter, but an irruption is marked by a great abundance of the species south of its usual range. This winter seed crops, especially of deciduous trees, did very poorly in much of the north, resulting in low food availability for most seed-eating species.

The above photo is of a Common Redpoll, named for the red cap on its head, a regular irruptive species that usually comes south into southern Ontario and the northeastern states every couple of years. On their wintering grounds, redpolls feed primarily on the catkins of birch and alder trees. In a year of poor catkin production, redpolls will begin to move out of their regular range in search of an area with good food availability. In the south, this is often in the form of bird feeders. Redpolls love nyger seed (thistle seed), and will swarm nyger feeders in large numbers. They’re rarely seen in small numbers or individually, and flocks can reach 40 or 50, to upwards of 100 birds. This year is a bigger year for redpolls.

PISI1

Another frequently seen irruptive species is the Pine Siskin. This year they seem to have carried on through southern Ontario to places further south, but in some years they can be just as, or often more, numerous at the feeders than the redpolls. Siskins depend on evergreen cone seeds, but are also enthusiastic visitors to nyger seed feeders. Although they’re not very flashy, they can be distinguished from some other brown, streaky finches by their sharp, narrow beak (not well seen in this photo), and the yellow tints to their wing feathers.

Pine Grosbeaks and Bohemian Waxwings have also been reported in large numbers this winter. I haven’t had a chance to go out to look for either, yet, unfortunately. The last time I saw a Pine Grosbeak was some four or five years ago, and the only ones I’ve seen in Ontario were at the University of Guelph, back when I was a student there. They’ve been reported there again this year. That gives you an idea of the frequency of their irruptions this far south. I’ve never had the luck to see a Bohemian Waxwing, although I’ve gone looking for them.

RBNU4

These aren’t the only species that come south in years of low food availability. Red-breasted Nuthatches are seen periodically in larger numbers, and this year they moved out early in the fall, to destinations further south. My parents have one coming to their feeder this winter, however, and they’re usually gone by mid-fall. Black-capped Chickadees are usually year-round residents on their territories, but in years of good breeding success (that is, lots of babies!) coupled with poor winter food supply, large numbers of primarily young birds will move south looking for food. Chickadees moving through in the fall was slightly elevated this year, but 2005 was the biggest movement over the last few years. Blue Jays will also irrupt in larger numbers some years than others. We had a moderate movement this year, but the best year since I’ve been keeping track was probably 2003.

Northern Saw-whet Owl

Seed-eaters aren’t the only group of birds that undergo periodic irruptions. The seed shortages that cause birds to move also affect rodent populations in those areas, which depend heavily on seeds as their food source. In years of poor seed crops, rodent populations suffer sharp declines (often called “population crashes”). This year rodent populations had an especially severe crash, as last year’s seed crop had been good, encouraging a good breeding season this summer. That breeding success was followed by this fall’s seed shortage, causing a precipitous decline in numbers.

Birds that prey on rodents, such as owls, tend to follow their population cycles fairly closely. Because rodents were so abundant, owl populations, particularly the Northern Saw-whet Owl (pictured above), had a very successful breeding season. When rodent populations crashed this fall saw-whets began moving south in huge numbers. Saw-whets usually follow a four year cycle, where every fourth year their rodent prey, Red-backed Vole, peaks in number and so does their population. Saw-whets are naturally migratory and will move south every year, but the numbers encountered in the south vary according to the size of the movement. The combination of high saw-whet numbers due to this year’s breeding success and the low prey availability because of poor seed crops resulted in a larger-than-normal movement of saw-whets this fall.

GGOW

Great Gray Owls follow a similar pattern, although they usually only move as far as they need to to find food, which means they don’t often make it as far south as most human communities. A bird of northern Ontario, they often just move to another part of the north when prey shortages occur, since such shortages are often regional in nature, although small numbers are usually seen as far south as cottage country every winter. A few years ago, in the winter of 2004-5, a huge movement of these beautiful northern owls occurred in southern Ontario, and I had the opportunity to get out and see several. They’re the only ones I’ve seen.

Another species of owl that comes south every year, but can move in larger numbers some years, is Snowy Owl. There’s usually one bird that winters at Tommy Thompson Park (home of the research station, and as close to a backyard as I have here in the city) every year, although I haven’t seen reports of it this year. However, in years of larger movements, such as 2005-6, many Snowy Owls can be seen in a relatively small area (of suitable habitat, of course). The photo below was taken on Amherst Island, near Kingston, where we had up to 13 individuals during one day.

SNOW3