After a relatively mild and mostly snow-less winter, spring is well underway in the Highlands at this time. Leaves are reappearing on the trees, birdsong is abundant and the days are lengthening considerably now that we’re past the vernal equinox and are into the half of the year with more light than darkness. At the beginning of April I spent a Sunday out in Glen Affric and much of my time then was spent documenting some of the signs of spring.
I’ve been writing the latest in our series of Species Profiles that detail in words and photographs the features of many of the key species in the Caledonian Forest – this current one is on the goat willow (Salix caprea). I was hoping to get an image of some newly-emerged catkins to go in the Profile, so that was one of my goals for the day, and almost as soon as I reached the glen I spotted a relatively young tree beside the road with catkins just opening out from their buds.
The catkins were still at a very early stage of unfurling and were covered in fine silky, silver-grey hairs that are said to resemble the paws of a cat. This gives the tree its alternative common name of ‘pussy willow’. Goat willow is a dioecious species, which means that male and female flowers occur on separate trees, whereas most trees such as Scots pine (Pinus sylvestris), birch (Betula spp.) and oak (Quercus petraea) are monoecious, meaning they have both male and female flowers on the same tree. This tree was a female and it needs to receive pollen from a male tree, either by the wind or via an insect such as a bumblebee (Bombus spp.) for pollination to occur and seeds to be produced. I didn’t see any male goat willows with catkins visible nearby, but this tree, at the entrance to the National Nature Reserve, is at a lower elevation and in a more sheltered position than other goat willows in the glen, so was perhaps slightly ahead of the game in terms of flowering.
It would be at least a few more days before these female catkins were fully open and ready to be fertilised, thereby giving time for some males to begin flowering and produce pollen.
Moving on from the goat willow, I proceeded to the Dog Falls area of the Affric River, and when I got out of my car I heard a crow calling out overhead. I saw it flying around and land on a tree, then call again. I suspected it had a nest nearby, so I walked around to see if I could spot where it was. I didn’t have any success with that, but my path took me to the footbridge over the river, and I was immediately struck by the abundance of male catkins on an alder tree (Alnus glutinosa) right beside the bridge.
It was a wind-still morning and the catkins were hanging motionless over the water, so it was a rare opportunity to take some photographs of them, both in close up, and with a mirror-perfect reflection of the trees from the other bank of the river in the water below. Alder is another tree species, like goat willow and hazel (Corylus avellana), where the catkins appear before the leaves. The male catkins are quite similar to those of hazel, being pendulous and pale yellow in colour.
This tree was having a bumper year for flowering, as there were masses of catkins on its branches – more than I can recall seeing on it before. It was prime time for seeing them too, as most of the catkins were just opening fully, ready to release their pollen.
Alder is similar to hazel in another respect as well – it is monoecious, with male and female flowers occurring on each tree. The female flowers are smaller and much less conspicuous than the male catkins, so it’s easy to overlook them. However, many of the branches on this tree had female flowers, and, somewhat unusually, they could be observed at very close proximity, as they were on branches at eye level right beside the footbridge. The female flowers are bright red in colour and rather cone-like in shape.
Alder is pollinated by the wind, and fertilised female flowers develop into woody cones about 1.5 cm. in size, each containing a number of seeds. The cones ripen and open in October, releasing the seeds, which are able to float on water and are dispersed by both wind and water. The cones persist on the tree throughout the winter and usually fall off only when the new leaves appear the following spring. These female flowers were just at the beginning of that year-long cycle, as they awaited the arrival of pollen from some male catkins …
Although they are small, the female flowers are very intricate in their shape, and have great beauty to them. I spent some time photographing some with my high magnification macro lens, to reveal the remarkable and detailed works of natural art that they are. Again there is a similarity to hazel, as the female flowers of that tree are bright red and tufted – an example can be seen in one of my previous blogs here.
While I was photographing some of the catkins, I accidentally brushed against one of the branches, causing some pollen to fall out, so that inspired me to take a few photos with my flash, to capture the release of the pollen.
I took most of these photographs of the alder catkins from the footbridge, and at a certain point I noticed something moving on one of the wooden handrails. When I had a closer look I saw what I recognised as a nymph (i.e. the larval stage) of either a stonefly or a mayfly. Those are differentiated by the number of forks on their tails, and this one had a two-forked tail, but I couldn’t remember in the moment if that meant it was a stonefly or a mayfly. After photographing it I sent the specimen to Colin Plant, a specialist who helps me with identifications, and he replied that it was a final stage nymph (as the larval forms of aquatic invertebrates are known) of a common stonefly species (Isoperla grammatica). Stoneflies spend their larval stages, or instars, in fresh water, and this one had completed its development and emerged to undergo pupation and transform into an adult stonefly. It must have climbed up out of the water on to the footbridge, and its emergence like this was another clear sign of spring unfolding.
As is often the case for me, while I was photographing the stonefly nymph I noticed something else – an unusually-shaped rock formation beside the river.
It was one of those interesting moments in life, when I saw something for the first time (i.e. this rock formation). I’ve walked across that footbridge countless times over the years and had never noticed these shapes in the rock before. This day however, I spent more time there, and that enabled me to see more of the detail of the place than I’d previously been aware of. I wondered how many other places there are that I casually walk past, both in Glen Affric and elsewhere, which are similarly full of beauty, but which I haven’t yet taken the time to appreciate?
Still on the footbridge, I looked across to the other bank of the river, wondering if there were some comparable rock formations there. I didn’t see any close by, but I did notice some more mirror-like reflections in the still water. The Scots pines and birches on the cliffs above, plus the clouds in the mostly-blue sky, were all perfectly imaged in the water, where their fluid qualities contrasted with the solidity and permanence of the rocks that formed the river bank.
After taking a few minutes to savour the stillness of the water and the beauty of the reflections, I decided to move further up into the glen.
A couple of weeks previously when I’d been in Affric I’d stopped at the Dog Falls car park, as there’s a rock pool just below the bridge there where common frogs (Rana temporaria) breed each year, and I’d seen a lot of spawn in the water. I’ve seen them there in previous years at this time, and I featured some photos of the spawn in a blog I wrote last year. Now, I wanted to check on the progress of the spawn, as I suspected that the tadpoles would have begun to hatch from the eggs by this time.
At first glance, it appeared that there was still just a mass of eggs in the water, but as I looked more carefully, I saw that there were some very young tadpoles there too.
I suspected that they had only very recently hatched out, as they were very small and for the most part were motionless in the water. Some sections of the mass of frogspawn appeared to be more advanced in their development than others, for while there were lots of eggs in several areas, in others the young tadpoles were numerous and abundant. As in previous years, I also noticed some palmate newts (Lissotriton helveticus) in the rock pool, and they would be feeding on the frogspawn and the young tadpoles, which are very vulnerable when they are newly-hatched.
I wasn’t able to get any photographs of the newts, but I did get some brief video footage of one, and that features in the video clip at the end of this blog.
When a tadpole first hatches out from its egg, it has external gills – feathery structures protruding outwards from each side of its head. These enable the tadpole to absorb oxygen from the water, and are a characteristic feature of the larval stages of a number of amphibians – in some species of salamanders they are retained by the adults as well. However, with the common frog, the external gills soon disappear and are replaced by internal gills, which are inside a small slit on each side of the tadpole’s head. As the tadpole develops and then metamorphoses into a frog, the gills are replaced by lungs, so that the adult can breathe in the air.
After watching the tadpoles for a while, I continued further west in the glen, to an area on the north shore of Loch Beinn a’ Mheadhoin where there are a number of mature goat willows. The branches on those trees are too high to get close to any of their buds (which had not yet begun to open anyway), but I was interested in taking some photographs of the bark as well. Goat willow bark is smooth and grey or greyish-brown, with diamond-shaped lenticels on it, through which the tree exchanges gases with the atmosphere.
Over time, the lenticels develop into vertical fissures and old goat willows have a characteristic pattern of these on their trunks.
It strikes me that there’s a curious parallel between the lenticels on the goat willow and the external gills on the tadpoles. Both enable their respective organism to absorb oxygen from their environment, and both seem to be ephemeral, giving way to internal gills and then lungs in the case of the tadpole, and being replaced by fissures on the goat willow trunk.
By this time it was quite late in the day, so I began heading down the glen for the journey home. I hadn’t gone far at all though when I noticed the low-angled sun illuminating some old Scots pines on one of the islands in Loch Beinn a’ Mheadhoin, and I couldn’t resist taking a few final photos.
To finish this blog here’s a compilation of some video footage I took during the day – watch out for the palmate newt that makes a brief cameo appearance!