Tuesday, 26 January 2016

African Wild Dogs: an energetics spat

As we were watching a Tasmanian Devil working its way through piles of chicken meat placed along the length of the verandah of our cabin at Loongana Mountain Retreat, I could not help thinking of a spat I had read about on the nutritional requirements of African Wild Dogs, Lycaon pictus (or Cape Hunting Dogs, as they were commonly known) and the effects of kleptoparasitism, i.e. big boys like hyenas stealing their food.

The reason why I thought of that was that this particular Devil was so full of food that it looked as if it might burst. The skin was stretched tight but it kept eating and even carried off a chicken breast and sternum as it waddled down the steps and disappeared into the night. But more posts on Tasmanian Devils later.

The spat on African Wild Dogs began with a paper in Nature in 1998 by Gorbman, Mills, Raab and Speakman2. They used isotope turnover methodology to determine energy demands in the wild from energy expenditure. Using those data, they then showed that an increase in kleptoparasitism to 25% of kills would require more than 12 hours of hunting per day—an unsustainable burden that could make the dogs susceptible to local extinction in areas where kleptoparasites are abundant. That calculation has been quoted widely (but not in the IUCN account of this species) in considering the survival of this, classified as Endangered, species. There is known to be an inverse relation between wild dog and hyena numbers.

In 2014, that view was challenged by Jongeling and Koetsier, writing in the African Journal of Ecology3.One of their arguments to support their view that kleptoparasitism is of no importance to survival was that packs of wild dogs often have attendant pups and, therefore, the amount of food that needs to be captured is greater than that needed to match the energy requirements of the adults. In response5, the authors of the 1998 paper concede this point but then calculate that their curve relating hours per day hunting required to percentage of food lost by kleptoparasitism would be shifted to the right such that for the unsustainable 12 hours of hunting, the level of kleptoparasitism would be 32.5 rather than 25%.

Jongeling and Koetsier’s second argument was that the dogs consume much more energy than the measured energy demand, and modelled mathematically a scenario in which the dogs eat one and a half to three times more than they need. If such a situation obtained the required hunting time at 25% kleptoparasitism drops to 6 hours per day. However, these authors in making such a claim, scored what can only be described as an own goal. In their rejoinder John Speakman and his colleagues soon pointed out that the first law of thermodynamics demands that the excess energy would have to go somewhere and that in two months a dog would put on 50 kg of weight!
They also made the case that it is very difficult to estimate intake in the field in observational studies.

Jongeling and Koetsier also used different values for the assumed energy content of prey. They quote the figures used by the authors of a book, The African Wild Dog1, to estimate the energy content of meat from Impala and Wildebeest which were those reported by the U.S. Department of Agriculture for low-grade beef carcasses (11.6 MJ per kg of flesh; 6.19 MJ per kg for viscera and skin); the value used by the authors of the 1998 paper was 5.2 MJ (which Jongeling and Koetsier’s claim was introduced ‘out of the blue’) but In the rejoinder there is no comment on this difference. I have to admit that I allowed myself a wry smile when I saw the figures that Creel and Creel are said to have used. The USDA figures matches that for dressed beef carcasses given in the food tables of McCance and Widdowson4. However, dressed beef contains much more fat than wild animal carcasses and the figure for lean beef is the same as that used by Gorbman et al, 5.2 MJ per kg.

So, apart from the point about hunting to feed attendant pups, Jongeling and Koetsier do not appear to have dented the case made for the putative effects of kleptoparasitism. There appears to me to be a lack of distinction between the weight of prey killed, the amount consumed by the dogs, the average daily energy expenditure and the amount of food eaten in a particular day. It is entirely possible for an animal to eat three times its daily energy requirement in one sitting without getting fat in the long term—if it does not then eat for three days. So observational intakes after a kill could be a fair estimate but unless the frequency of feeding is also known, the information is worthless in considering the energetics.

Having seen lions in Africa and India—and Tasmanian Devils—with stomachs so full that they could hardly move, it seems to me that the stomach in carnivores is used as a portable cache. The strategy seems to be: eat as much as you can as fast as you can, digest slowly, replenish reserves and then hunt again when hungry, i.e. when digestion is complete and the reserves are being drawn on. And, I ask, is that the pattern in the African Wild Dog?

Finally, I cannot help but point out that what happens to the lactating alpha female must be crucial for the survival of a pack and its individual members. With her increased energy requirement during lactation, a shortfall in food intake could be catastrophic for a local population.

Gorbman et al laid the foundations in their 1998 study on energetics in the wild. The time could be ripe for some simple observations and measurements in the now successful captive populations. That approach might now be more successful at shedding further light on energetics, food intake and the importance of kleptoparasitism in the survival of African Wild Dogs than any number of indirect studies and mathematical models of what might happen in the wild. Ecological physiology needs more physiology.

--------------------------------

1 Creel S, Creel NM, 2002. The African Wild Dog: Behavior, Ecology, and Conservation. Princeton University Press.
2 Gorman ML, Mills MGL, Raath JP, Speakman JR, 1998. High hunting costs make African wild dogs vulnerable to kleptoparasitism by hyena. Nature 391, 479-481.
3 Jongeling TB, Koetsier T. 2014. The predicament of the African wild dog, Lycaon pictus, is less precarious than claimed. African Journal of Ecology 52 466-470.
4 Paul AA, Southgate DAT. 1978. McCance and Widdowson’s The Composition of Foods. Fourth revised and extended edition. London: HMSO.
5 Speakman JR, Gorman ML, Mills MGL, Raath JP. 2015. Wild dogs and kleptoparasitism: some misunderstandings. African Journal of Ecology. doi: 10.1111.aje.12258

Monday, 18 January 2016

Pardalote. Spots before the eyes

It should have been obvious as we flicked through the book on Australian birds for the first time in 17 years. But it wasn’t. ‘It’s back to the land of the pardalote and other animals with strange names’. Even when the group saw its first pardalote at the Waterworks Reserve in Hobart, we still did not catch on. ‘Why pardalote—is it a French word for something?’ was one question.

There is one excuse why we did not twig immediately the derivation of pardalote. On previous trips to Australia in the 1990s we had previously seen only the Striated Pardalote—the same species as the pair seen in Hobart. When we later saw two other species, it should have been obvious why pardalotes are called pardalotes.

The genus Pardalotus was erected by Louis Jean Pierre Vieillot (1748-1831) and just as in Panthera pardus, the leopard, Leopardus pardalis, the ocelot, Geochelone or Stigmochelys pardalis, the leopard tortoise and Furcifer pardalis, the panther chamaeleon, it simply means ‘spotted’ in Greek and the Latin derived from Greek. So to answer the question raised above; it is sort of French.

The names of two species, both of which we saw later in Tasmania, actually refer to the spots: the Spotted Pardalote and the Forty-spotted Pardalote, providing pedants with the opportunity to point out that we then have a tautology.

Pardalotes are small, hardly-ever-still birds that feed on small invertebrates, lerp (the sugary excretion of sap-sucking psyllids) and manna.

The pair of Striated Pardalotes (Pardalotus striatus) we saw in Hobart were nesting in a hole between rocks at the side of the road, carrying food gathered from the surrounding trees. Using my extremely long focal-length lens, one of them was still just long enough to get a photograph.

Striated Pardalote. Tasmania
The next species we saw was the Forty-spotted Pardalotus quadragintus. Classified by IUCN as endangered, it is confined to southern Tasmania and there are calculated to be only 1000-1500 living individuals. Bruny Island is a stronghold of the species and we saw them in South Bruny (not included, surely erroneously, in the range in the map shown on Birdlife International) where at Inala, a special viewing platform has been constructed to view the colony there. They live in White Gum trees (Eucalyptus viminalis) exclusively. We were told they were colonial but territorial, one pair holding a feeding territory in one direction, a second pair in another direction and the third pair covering a further sector. A number of factors have been suggested as contributing to the decline, especially it would seem, clearance of White Gum. Recently, I have seen reports that the parasitic maggots of a fly are killing 75% of nestlings (a similar situation to that obtaining in the Galapagos with an introduced fly) together with the suggestion that nest infestation might be the cause of the decline from around 4000 birds in the 1980s. If that were the case then one could, of course, make the testable prediction that existing tracts of White Gum are not carrying as many Forty-spotted Pardalotes as they could.

The Forty-spotted Pardalote is the dullest looking of the four species. I had great difficulty getting a photograph and had only fleeting side-on views. They were constantly on the move, gathering food and being chased off by Honeyeaters (who defend the sources of lerp).

Forty-spotted Pardalote. South Bruny, Tasmania
Much more clearly marked and colourful is the Spotted Pardalote (Pardalotus punctatus) from Eastern and Southern Australia. We also saw that species in Tasmania, and it is then easy to see why pardalotes came by their name.

Thursday, 14 January 2016

Sightings of Thylacines: a Tasmanian coincidence

‘Just keep an eye out for the odd thylacine’, I reminded my wife as we travelled through Tasmania in November, ‘You gained your spurs as a leopard spotter in Botswana, now really show what you can do’. Alas, I have to report, she failed.

As sleet and snow fell and after high winds had knocked out the electricity supply, we admired the collection of thylacine photographs, many of which I had not seen before, in the restaurant of the lodge at Lake St Clair, and wondered whether any of the reports that the thylacine is not extinct were reliable. ‘I really hope so’, was the general conclusion. The conversation turned to reports made by people who knew nothing of the thylacine but who reported sightings that were compatible with their having seen one. And then it was back to U.K. where in my pile of accumulated post was the latest volume of Biographical Memoirs of Fellows of the Royal Society. As I started to look through it my eyes fell on the word Tasmania. This is what I then read:

…They were driving in a wilderness area on the western side of Tasmania when they saw an animal they did not recognize cross the road. At the next township they asked a woman what it was. They said they should not have seen such an animal as it was a Tasmanian tiger (ot Tasmanian wolf) and they are extinct! There have been many alleged sightings of the Tasmanian wolf. What distinguishes this one is that neither Professor nor Mrs Whitham knew that such an animal existed before they saw it in Tasmania that day.

Professor Whitham was Gerald Beresford Whitham FRS (1927-2014). the applied mathematician, lately of CALTEC.

The Thylacine skeleton in the Grant Museum at UCL
-----------
Minzoni AA, Smyth NF. Gerald Beresford Whitham 13 December 1927—26 January 2014. 2015. Biographical Memoirs of Fellows of the Royal Society 61, 557-577.