Αρχεία Ημερολογίου για Απρίλιος 2022

Απρίλιος 16, 2022

Distinguishing Between the Three Most Common Water Skink (Eulamprus) Species

Members of the genus Eulamprus, the Water Skinks, inhabit most of the east and south-east coast of Australia, including regions along the east end of the Victoria/New South Wales border, and around Adelaide. They often inhabit moist environments close to creeks and streams, but despite their name, they are regularly seen in locations away from water bodies, including around suburban residences, taking up residence under logs or under houses and so on. There are three commonly seen species, the Eastern Water Skink (Eulamprus quoyii), the Yellow-bellied Water Skink (E. heatwolei) and the Southern Water Skink (E. tympanum). There are, at the time of writing, two recognised subspecies of Southern Water Skink, (E. tympanum ssp. tympanum and E. tympanum ssp. marnieae), which I will not be addressing in this text. Furthermore, there are also two less frequently and more geographically restricted species, the Alpine Water Skink (E. kosciuskoi) and the Blue Mountains Water Skink (E. leuraensis), which are distinct enough to be identified easily.

Despite their frequent observation, many are having difficulty identifying which species of Water Skink they are looking at. There is quite a broad range of variety within each species, as well as overlap between species to add to the confusion. Here I will describe some of the diagnostic characters of the three most commonly seen, and frequently confused, species. At the end is also a dichotomous key I've written that may also be of assistance. The characters referred to is not a complete list of morphological features of each species, but those that help readily identify each one.

Eastern Water Skink (E. quoyii). https://inaturalist.ala.org.au/taxa/100709-Eulamprus-quoyii

The easiest and most reliable feature to identify Eastern Water Skinks is the clear, pale/yellow dorso-lateral stripe, which starts just above their eye-brow and extends down the length of their body, fading out by the time it reaches their hips. Unfortunately this feature can often be obscured by sunlight or camera flashes reflecting off the animals scales. Southern Water Skinks do not possess this stripe at all, but it can be observed in Yellow-bellied Water Skinks very faintly as a broken series of dots. Alpine and Blue Mountains Water Skinks also possess dorso-lateral lines, but are easily distinguished from Eastern Water Skinks by the overall dark, near black complexion of the Blue Mountains Water Skinks, and the Dark vertebral stripe of the Alpine Water Skink.

Yellow-bellied Water Skink (E. heatwolei). https://inaturalist.ala.org.au/taxa/38492-Eulamprus-heatwolei

In both Yellow-bellied and Southern Water Skinks, there is a mid-lateral division between their lighter lower lateral colour and the darker upper lateral colour extending down the length of their sides. This 'line' between the two intersects the tympanum (ear-hole). The pale colour hooks around the anterior and upper margin of the tympanum in Southern Water Skinks, whereas in Yellow-bellied Water Skinks it does not, and merely cuts straight across the ear-hole. Some specimens will have a pale coloured patch intersect the upper ear, providing the chance that E. heatwolei may be confused for a E. tympanum, usually there will be a dark division along the anterior margin of the ear to help make an identification.

Yellow-bellied Water Skinks also tend to have notably more dark banding over their eyes compared to Eastern or Southern Water Skinks.

Despite the name, the yellow colouring of the belly and of the legs is not unique to Yellow-bellied Water Skinks, and can be observed in the other species as well. I suspect it is likely breeding season colouration. The yellow can also be absent in Yellow-bellied Water Skinks to add to the confusion.

Southern Water Skinks (E. tympanum). https://inaturalist.ala.org.au/taxa/38483-Eulamprus-tympanum

In Southern Water Skinks, the snout appears to be proportionally shorter than the other species. They completely lack the aforementioned dorso-lateral stripe of the other species. The ventral colour hooks around the anterior margin of the tympanum, the upper posterior margin is dark.

Male vs. Female

I'm not aware of any morphological features that can be observed from a distance that distinguishes the sexes; however, the females can be identified when pregnant, as they will be noticeably wider than usual. The females give birth to live young rather than laying eggs like many other reptiles.

Key to Eulamprus:
1 Clear dorso-lateral stripe present
.......................................................................................................................................................................(Go to 2)
1* Dorso-lateral line absent or only marginally visible as a series of dashes or dots
.......................................................................................................................................................................(Go to 4)

2 Clear, dark vertebral line; yellow dorso-lateral stripe present, margined by dark colour on ventral side, presenting appearance of three dark lines running along the back
.......................................................................................................................................................................E. kosciuskoi
2* No vertebral line present
.......................................................................................................................................................................(Go to 3)

3 Very dark, near black, overall appearance, with yellow stripes/dots on lateral surface
.......................................................................................................................................................................E. leuraensis
3* Dark upper lateral region with light cream spots; lower lateral region has cream/pale coloured patching; cream coloured ventral surface; brass-brown to copper-brown dorsal surface with many to few dark spots; clear pale yellowish dorso-lateral stripe
.......................................................................................................................................................................E. quoyii

4 Pale ventral colour intersects, and hooks around the anterior margin of the tympanum (ear-hole), dark on the upper posterior margin (not to be mistaken with upper lateral patches that also may intersect ear-hole); no dorso-lateral line present; proportionally shorter snout
.......................................................................................................................................................................E. tympanum
4* Pale ventral colour intersects tympanum, does not hook around or border the margins of the upper half of the ear hole; dark eye-band usually present
.......................................................................................................................................................................E. heatwolei

Note: I would of liked to add annotated images for reference, but there doesn't appear to be an option to embed images into posts. I'm also happy to make corrections where necessary.

Posted on Απρίλιος 16, 2022 0800 ΠΜ by bwjone432155 bwjone432155 | 0σχόλια | Αφήστε ένα σχόλιο

Απρίλιος 24, 2022

Possible cases of hybridisation between Cracticus torquatus and C. nigrogularis

Cracticus torquatus (Grey Butcherbird) and C. nigrogularis (Pied Butcherbirds), including the juveniles, are generally easy to distinguish between. In the adult stages, Grey Butcherbirds have a white throat, a black cap, white lores (between the eyes and beak), an incomplete white collar, and grey plumage across the back. Pied Butcherbirds have a black throat, dark lores, a complete white collar, and black plumage on their backs. The juveniles are both shades of brown, with light coloured lores already visible in the Grey Butcherbird, while in Pied Butcherbirds, the dark throat/bib is faintly apparent as pale brown with a noticeable sharp transition to the lighter colour of the abdomen. Subsequently, there are very few misidentifications on iNat between the two species.

I've been rummaging through iNat observations for mis-id's and I've found some suspicious looking observations marked as Grey Butcherbirds (linked below), that seemingly possess most features that would identify them as Grey Butcherbirds. However, they also all have patches of black in the throat/bib area, with some having more black than expected on the back (obs - 4), and others with diminished lores (obs - 1, 2, 5). All observations are within the vicinity of Perth (19/09/2022 - Observation 18 is in western Victoria, if they are hybrids, it could indicate that hybridisation has occurred more than once between the two species). I've looked briefly on Google Scholar and the UNE library for any papers that discuss hybridisation between the species and found none so far. There's no mention of hybrids in any of the field guides I have either.

01 - https://inaturalist.ala.org.au/observations/65467072
02 - https://inaturalist.ala.org.au/observations/41440785
03 - https://inaturalist.ala.org.au/observations/40360665
04 - https://inaturalist.ala.org.au/observations/108492066
05 - https://inaturalist.ala.org.au/observations/67243862
06 - https://inaturalist.ala.org.au/observations/68597079
07 - https://inaturalist.ala.org.au/observations/127816336 (added 25/07/2022, pale back, white lores, patchy throat)
08 - https://inaturalist.ala.org.au/observations/127093449 (added 20/08/2022, another possible example)
09 - https://inaturalist.ala.org.au/observations/120294777 (added 20/08/2022, another possible example)
10 - https://inaturalist.ala.org.au/observations/106465823 (added 20/08/2022, another possible example)
11 - https://inaturalist.ala.org.au/observations/101399494 (added 20/08/2022, another possible example)
12 - https://inaturalist.ala.org.au/observations/105016159 (added 20/08/2022, another possible example)
13 - https://inaturalist.ala.org.au/observations/41440785 (added 20/08/2022, another possible example)
14- https://inaturalist.ala.org.au/observations/19490811 (added 20/08/2022, another possible example)
15 - https://inaturalist.ala.org.au/observations/23872139 (added 20/08/2022, another possible example)
16 - https://inaturalist.ala.org.au/observations/42152529 (added 20/08/2022, another possible example)
17 - https://inaturalist.ala.org.au/observations/14760326 (added 20/08/2022, another possible example)
18 - https://inaturalist.ala.org.au/observations/135641738 (added 19/09/2022, first example I've seen outside of the Perth area, spotted by @ricardosimao )
19 - https://inaturalist.ala.org.au/observations/142621160 (added 23/11/2022, spotted by @tristak87, thanks @george_seagull )
20 - https://inaturalist.ala.org.au/observations/146509601 (added 14/01/2023, first example in the list from the east coast, Brisbane)

It may be a case that this is variation within the species, differences in ontogeny between eastern and western populations, or I'm just outright mistaken; however, at the moment I'm curious about these observations and I suspect they may be hybrids between Grey and Pied Butcherbirds.

I've tagged a few people below that have identified a lot of Butcherbirds to see what knowledge and thoughts you fine people have.

@thebeachcomber @george_seagull @ratite @twan3253 @deborod @joshuagsmith @jadonald @louisb

References
Cayley, N.W. (1946). What bird is that? A guide to the birds of Australia (11th ed.). Australia: Halstead Press Pty Ltd.
Flegg, J., Madge, S. (1995). Reader digest photographic field guide to the birds of Australia. Australia: Reader's Digest (Australia) Pty Ltd.
Leach, J.A. (1926). An Australian bird book. Melbourne: Whitcombe & Tombs Ltd.
Menkhorst, P., Rogers, D., Clarke, R., Davies, J., Marsack, P., Franklin, K. (2021). The Australian bird guide (Revised ed). Australia: CSIRO Publishing.
Morcombe, M. (2000). Field guide to Australian birds. Australia: Steve Parish Publishing Pty Ltd.
Simpson, K., Day, N., Trusler, P. (1989). Field guide to the birds of Australia. Australia: Penguin Books Australia Ltd.

Posted on Απρίλιος 24, 2022 0418 ΠΜ by bwjone432155 bwjone432155 | 5σχόλια | Αφήστε ένα σχόλιο

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