Tag: Otter

The jewel in the crown

The ‘Newcastle Diaries’ are intended as a new series of blog posts brought to life by a recent move to the city; inspired by a growing frustration at not being able to visit my regular, rural haunts half as often as I would like. While I assumed a move here would greatly decrease the time I spend in nature, quite the opposite has happened. And I find myself growing increasingly fond of the city and her wildlife. Heading back to this blog’s roots as a patch diary, I hope to share my experiences wildlife watching around my new, urban patch (the whole city, to be precise) with regular blog readers.

Diligently maintained by the Natural History Society of Northumbria since 1929, Gosforth Park Nature Reserve is, without a doubt, the jewel in the crown of the scant few wild places remaining in and around Newcastle. Indeed, when walking in the dappled shade cast by the sites many imposing trees, or engulfed in swaying growths of Phragmites, it is quite possible to imagine yourself elsewhen – in a time when nature still reigned supreme across the landscape. The sights and sounds of the city located a mere stone’s throw away drowned out entirely by nature – lost in a chorus of birdsong, creaking trunks and soggy, squelching footsteps. Truth be told, Gosforth is a rather beautiful site and one I was keen to explore in greater depth this week.

Walking the woodland tracks of Gosforth before noon, I was pleased to see that the intermittent bouts of rain tumbling from the heavens had not disturbed the wildlife. Mere moments after arrival, my eyes greeted by sight of a Great Spotted Woodpecker pair cork-screwing around the trunk of a denuded oak, clearly in the midst of some energetic, amorous pursuit. The male – as told by the conspicuous red blaze behind his head – clearly feeling somewhat frisky as the Spring draws ever closer. He was not the only one: a yaffling Green Woodpecker off to the East, a singing Goldcrest and the repetitive chanting of countless Great Tits likewise signalling the forthcoming shift from Winter to Spring.

While the birds of Gosforth gave plenty of hope for things to come, the woodland itself gave few. Trees, with the exception of a few intrepid, Catkin bearing, Hazels, still dormant; with scant botanical offerings on the ground to be seen. Still, the lack of cover appeared to work in my favour on this occasion – the characteristic white-rump of a Roe Deer easily picked out among from amid the trees. It’s owner – a doe – promptly joined by three more of her kin, all of whom preceded to wander, in a most un-deer-like fashion ever closer. Stopping, eventually, to ogle their admirers before ambling, with no sense of haste nor fear, back in the opposite direction. A memorable encounter, to say the least, and one which even gave rise to a few hurried photographs.

Evidently, the parks Roe Deer like to use the same time-honoured pathways utilised by human visitors – slot marks and, in some instances, droppings, visible for a good quarter-mile stretch of our journey. Made visible by the lack of lower-vegetation, and the gradual rot of the assorted leaves which once carpeted the ground.

Here too the tracks of Badgers were visible, rounded with distinct claw-marks, covering some distance and culminating in the familiar sight of broken-ground – doubtless where the mustelids foraged in search of forms sometime before our arrival. Badgers are not a species I expect to see within the city limits anytime soon; thus, for now, relics of their nocturnal activity will suffice.

Having departed the woodland temporarily, only after taking heed of a passing flock of Siskin, I soon found myself casting my eyes over a frigid and very empty lake. Almost beating a retreat after ten-minutes of expectant yet futile scanning. I am glad I did not, however, the sight of a rounded head surfacing on the fringes of the reeds, and the ensuing flick of a meaty tail as the creature dived, heralding the arrival of the Otter. A dog, to be precise, which fished for sometime around the frozen margins, appearing to break the crystalline film of ice as it rose and fell. Never once casting an eye in our direction. I’m sure it saw us, despite the screen – I was not exactly shy in my excitement.

At one point, marking perhaps the most comical yet exciting moment of the trip, the Otter departed the water entirely onto the ice.  Climbing out and showing himself in all his glory. That is before the surface gave way and he plopped head and front-paws first back into the water. Clearly, it was not so cold last night as to warrant a “proper” coating of ice.

I hate to use the same phrase twice – at least knowingly – but the sight of an Otter really was the jewel in the crown of an already enjoyable visit. A crowning glory, seldom seen and definitely an experience to savour.

Following our success at Gosforth, a brief jaunt to Newcastle’s rural fringe ensued leading us quickly to Prestwick Carr. A site I visit often which, once again, yielded superb views of Willow Tit – never to be taken for granted given the state of the wider population of these underrated passerines. Here too, Buzzards mewed overhead, a charming mixed flock of Yellowhammer and Reed Bunting fed among the amassed feet of some local goats, and a squadron of Golden Plover passed overhead, seemingly on route further inland. To their heather-clad breeding grounds, I suspect.

Willow Tit: not half as vibrant yet equally as charming

An Amateur Look at Otter Diet

In keeping with adaptation and evolution fish dominate the diet of L.lutra within freshwater ecosystems, though some localised populations occasionally differ from this trend (Webb, 1975; Jenkins et al, 1979; Carss, 1995). Among the fish species consumed otters show bias towards slower moving species where available (Erlinge, 1968) – a theory supported by the dominance of carp (Kloskowski, 1999; Cousins et al, 2011), eel (Britton et al, 2006; Chanin, 1981) and Italian barbel (Arca & Prigioni, 1987) at alternate locations across the otters range, while particular emphasis is given to eels as a preferred food source (Williams, 2000; Webb, 1975). It is, however, important to note that in accordance with Erlinge (1968) prey abundance may overrule individual bias when it comes to the selection of fish species by L.lutra; a theory supported by a preference for fast swimming Salmonids among some otter populations (Kortan et al, 2010; Ludwig et al, 2002). with Ludwig et al (2002) lending particular weight to the theory of abundance based prey selection by highlighting a distinct difference in diet between ecologically poor and rich habitats.

Small fish species are consumed in abundance, often more frequently that larger ones with species such as minnow, stickleback and bullhead all common place in the diet of L.lutra (Williams, 2000, Preston et al, 2006). Evidence in support of this theory comes from the popularity of bullhead among otters in South-West England (Britton et al, 2006) and stickleback amongst otters from Northern Ireland (Preston et all, 2006) though there is little evidence of smaller species wholly dominating otter diet at any location. These species do however have a relatively high frequency of occurrence, factoring in the diet of otters from populations in England (Copp and Roche, 2003), Denmark (Taastrùm and Jacobsen, 1999) and Finland (Ludwig et al, 2002) among others. This suggests that in keeping with Carss and Parkinson (1996) the proportions of these smaller fish species may have been underestimated as a result of flawed data analysis methods, implying that they could be of greater importance amongst certain otter communities. The small size of the bones within these species and the subsequent ease at which they are digested or overlooked are likely of paramount importance. A high dependence on smaller species and young individuals would further strengthen the theory of abundance based pretty selection given the tendency for these individuals to far outnumber larger species and mature individuals within the environment.

Though regarded as being of secondary importance  amphibian species may dominate otter diet in some locations (Erlinge, 1967; Carss, 1995) with a notable example coming from Jedrzejewska et al (2001) who revealed that frogs constituted 58% of otter diet in the Białowiza Forest, Poland. Where they are not the dominant food source amphibians are still a significant source of nutrition across much of Palearctic zone (Ottino & Giller, 2004; Krawczyk et al, 2011; Britton et al, 2006; Lanszki et al, 2001) with percentage frequencies of 17.1% or above seemingly commonplace (Britton et al, 2006).

It is argued that otter predation on amphibian’s shows a distinct temporal trend with the highest levels of predation recorded during the spring period when these species accumulate to spawn (Fairley, 1984; Weber, 1990). This is supported by some dietary assessments including those of Ottino & Giller (2004) and Britton et al (2010) both of whom noted increased predation rates during the spring period. Results from some studies contrast greatly with this temporal pattern, however, suggesting that amphibian species could be important food source year round with a frequency of occurrence of 16.5% during the month of January noted by Kloskowski (1999) echoing similar findings by Ludwig et al (2002). Both of these show amphibians to be an important food source outside of the spring period. As is the case with fish species it is, therefore, likely that amphibians are predated based on their availability in the environment rather than by preference (Jedrzejewska et al, 2001; Weber, 1990). Little preference is shown for individual species within the amphibian family though frogs and toads dominate across the Palearctic zone with newt and salamander species showing little prevalence in the literature with the exception of a single great crested newt (Triturus cristatus) noted by Britton et al (2006).

Alongside amphibians, birds are viewed as being of secondary importance in the diet of L.lutra with some stating seasonal abundance as the main catalyst for predation (Carss, 1995). Perhaps the most conclusive evidence in support of this comes from De La Hay (2005) who in his study of otters on Shapwick Heath, Somerset revealed a peak predation level of 60% during the month of July. This coincides with the known avian breeding season and suggests that otters are making clear use of the increased vulnerability of inexperienced fledgelings and brooding adults. This temporal exploitation of avian species was also observed by Lanszki et al (2001), Kloskowski (1999) and earlier by Chanin (1981) both of whom concluded that otter predation on birds peaked during this time.

Birds are however frequently consumed outside of the summer period and factor, to varying degrees, in the diet of otters in all seasons (Ottino and Giller, 2004; Clavero et al, 2003; Ruiz-Olmo and Palazon, 1997; Britton et al, 2006) highlighting their status as a regular but less significant addition to the diet of L.lutra in keeping with similar conclusions reached by Carss (1995). The sporadic predation of bird species and obvious ability to make use of seasonal gluts yet again shows the opportunistic nature of L.lutra with predation taking place based on both prey abundance and by means of chance encounters (Cousins et al, 2011). Among the avian species consumed by L.lutra water birds are the most frequently consumed in keeping with the shared habitat requirements of both predator and prey. Among these species, Ralliformes and Anseriformes predominate (Cousins et al, 2011; Chanin, 1981) though Columbiformes (Cousins et al, 2011), Passeriformes (Chanin, 1981) and Suliformes (De La Hey, 2005) have all been noted.

Mammals factor minimally in the diet of L.lutra and are generally thought of as insignificant when compared to more widely predated prey groups such as fish and amphibians (Jenkins et al, 1979; Carss, 1995). The available literature supports this assumption with mammalian species comprising only a fraction of otter diet across the Palearctic zone; a fact highlighted by low rates of occurrence in Poland (Krawczyk et al, 2010), England (Cousins et al, 2011) and Italy (Arca and Prigioni, 1987) among others (Britton et al, 2006; Remonti et al, 2007; Jedrzejewska et al, 2001). Though seemingly of little importance mammalian species are however a regular feature in otter diet occurring to a small degree in the majority of studies with the exception of Lanszki et al (2010) in their study of a Hungarian otter population. The regular occurrence of mammals throughout the literature further portrays the otter as an opportunist with the ability to exploit a prey source where abundant or when chance encounters make predation possible. Otters show little preference for individual mammal species,  apparent from the wide range of species consumed throughout the Palearctic zone. Of these, rabbits and smaller species are most frequently observed, likely due to their abundance in the wider ecosystem (Britton et al, 2006; Remonti et al, 2007; Cousins et al,2011). It should be noted however, that otters have  been known to prey on larger animals, most notably lambs (Harris, 1986) and hare (Conroy & Calder, 2000), though some incidences of otters consuming large mammalian prey are undoubtedly the result of carrion consumption such was the case with Lanszki et al (2001).

Further Reading

  1. Almeida, D., Copp, G. H., Masson, L., Mir, A, R., Murai, M. and Sayer, C. D. 2012. Changes in the diet of a recovering Eurasian otter population between the 1970s and 2010. Aquatic Conservation: Marine and Freshwater Ecosystems, 22 (1), pp. 26–35.
  2. Arca, G. and Prigioni, C. 1987. Food of the otter on the Fiora River(central Italy). Acta Theriologica, 32 (10), pp. 134–140.
  3. Britton, J. R., Pegg, J., Sheperd, J. S. and Toms, S. 2006. Revealing the Prey Items of the otter Lutra lutra in South West England Using Stomach Content Analysis. Folia Zoology, 55 (2), p. 167–174.
  4. Chanin, P. and Jefferies, D. 1978. The decline of the otter Lutra lutra L. in Britain: an analysis of hunting records and discussion of causes. Biological Journal of the Linnean Society, 10 (3), pp. 305–328.
  5. Cousins, L., Tansley, D. and Hepburn, L. 2011. Investigation into the Dietary Habits of the Eurasian Otter (Lutra lutra) in the Country of Essex. UCN Otter Spec. Group Bul, 28 (2), pp. 76-82.

Image Credit

  1. By Catherine Trigg – Flickr, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=2220697