19 November 2011

Black-backed Water-Tyrant - a new bird for REGUA

On Saturday 12 November 2011, I found a Black-backed Water-Tyrant Fluvicola albiventer at REGUA, a private nature reserve located in the Serra do Mar mountains, in the municipality of Cachoeiras de Macacu, Rio de Janeiro state, Brazil. A vagrant to RJ state, this is the first record of this species at REGUA.

The bird was seen twice throughout the day, briefly in the morning and then again later in the afternoon. Initially picked up in flight, it landed in a bare dead bush at the water's edge on a small grassy island by post 300 of the Wetland Trail. With previous experience of this species in the Pantanal I knew immediately what it was. Although the bird was distant and remained fairly deep in cover, I managed to take a few record shots that show the key features: black upperparts including the nape and rear crown and black tail, white tips to the greater and medium coverts forming two faint broken white wing bars, a thin white band across the rump, white forehead and forecrown, face and underparts and black eye, bill and legs. After a few minutes it flew off and despite searching for an hour or so I couldn't relocate it.

Late afternoon, while on my way back from mapping a new trail, I refound the bird around the replanted tabebuia trees, just a short distance from the first sighting, and this time I was able to watch it for about 30 minutes. It was quite active, spending most of the time foraging from vegetation overhanging the surface of the water by just a foot or so, and sallying out over the water presumably to catch insects and frequently fanning the tail slightly and flicking it downwards. Unfortunately, it remained distant and tended to perch a little way into the vegetation, which prevented me from getting any good photos.

Black-backed Water-Tyrant, REGUA wetland, 12 November 2011. The tail, wing coverts, secondaries and tertials
are all rather worn - note the lack of any white tips to the tail, very faint white the wing bars and almost absent
white fringes to the tertials (just visible in the photo top right).

There are only two potential confusion species. Pied Water-Tyrant Fluvicola pica (its closest relative and sometimes considered conspecific), is found in northern South America is similar but shows white scapulars, no white wing bars, a completely white rump and white mottling on the mantle. In RJ state, female or immature White-headed Marsh-Tyrant Arundinicola leucocephala are superficially similar at first glance, but are easily separated by their slightly smaller size, more upright stance, much less contrasting demarcation between the grey/black upperparts (with no white on the wing coverts, tertials or secondaries) and greyish white underparts, as well as a largely orange-yellow lower mandible. They also rarely fan their tail.

Black-backed Water-Tyrant, Pantanal, Brazil, August 2006. Note the obvious white
wing bars, white fringes to the tertials and secondaries and tips to the tail.

Female White-headed Marsh-Tyrant, REGUA, November 2011. With poor or brief
views this is the only potential confusion species in RJ state, but note the greyish
mottling on the white underparts, the diffuse border between the underparts and
the pale grey on the crown, nape, mantle and edges to the scapulars and
orange-yellow on the lower mandible.

Black-backed Water-Tyrant is distributed throughout eastern South America, mainly in central and eastern Brazil south to northern Minas Gerias and north-west São Paulo states, as well as locally into eastern Bolivia, Paraquay, north-east Argentina and south-west Uruguay (click here for a map). It is resident throughout much of its range, but in the austral winter some migrate westwards into western Amazonia (western Brazil, north-west Bolivia, extreme southern Columbia, eastern Ecuador and eastern Peru). The nearest populations to REGUA are found approximately 600 km away, either to the north in northern Minas Gerais or to the west in central São Paulo state.

So is this a late overshooting spring migrant from Amazonia? Ricardo Gagliardi maintains the official RJ state bird list and he informs me that Black-backed Water-Tyrant is in fact spreading south into RJ state (a paper is currently in preparation) and there have been several recent sightings in the north of the state. However, he is surprised the species has already reached as far south as REGUA and writes that this record "indicates a continuity in the process of colonization of new areas for the species". The bird was still present the next day but hasn't been seen since.

Acknowledgments

Many thanks to Ricardo Gagliardi for kindly providing information regarding the status of the species in RJ state, and to Eric DeFonso for taking the time to find the bird the following day.

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