Corydon sumatranus, Raffles, 1822

Gulson-Castillo, Eric R., Pegan, Teresa M., Greig, Emma I., Hite, Justin M., Hruska, Jack P., Kapoor, Julian A., Orzechowski, Sophia C., Shipley, J. Ryan & Winkler, David W., 2019, Notes on nesting, territoriality and behaviour of broadbills (Eurylaimidae, Calyptomenidae) and pitas (Pitidae) in Tawau Hills Park, Sabah, Malaysian Borneo, Bulletin of the British Ornithologists’ Club 139 (1), pp. 8-27 : 18-19

DUSKY BROADBILL Corydon sumatranus

Observed in groups of 8–12 individuals in the lowlands on eight occasions in 2012 (most in early July) and four times in 2013; also once on Gunung Lucia in 2013. We generally located them by their far-carrying calls, given consistently. Birds were observed both sides of the Tawau River in 2012, but in 2013 we generally saw them on the ridge west of the river. We usually saw flocks during the morning but also observed loud activity, including nestbuilding, well into the midday hours (although the species is reportedly crepuscular: Lambert & Woodcock 1996). One of the few times we saw the species in late afternoon was also the only time it was silent. On this occasion, on 2 March 2013, ERGC observed a small flock in a tall Macaranga hypoleuca tree with clusters of very small flowers. They sallied after insects while foraging and occasionally hovered immediately below a flower, but it was unclear if they were eating flowers or small insects. Groups of Dusky Broadbills mostly appeared to be accompanied by mixed-species flocks. The broadbills’ vocalisations were very audible over several hundred metres, making them the most obvious members of these flocks. The other birds consistently included species of Cuculidae and Picidae , including Raffles’s Rhinortha chlorophaea , Red-billed Zanclostomus javanicus and Chestnut-breasted Malkohas Phaenicophaeus curvirostris ; an unidentified small coucal Centropus sp. ; and Maroon Blythipicus rubiginosus , Orange-backed Reinwardtipicus validus , Checker-throated Chrysophlegma mentale , Crimson-winged Picus puniceus , Greyand-buff Hemicircus concretus , Buff-necked Meiglyptes tukki and Buff-rumped Woodpeckers M. tristis . Other species recorded sporadically near these flocks were Slender-billed Crow Corvus enca, Black Magpie Platysmurus leucopterus , Greater Racket-tailed Drongo Dicrurus paradiseus , Red-naped Trogon Harpactes kasumba and Maroon-breasted Philentoma Philentoma velata . We have found no mention of Dusky Broadbills associating with mixed-species flocks in the literature, but Norman (1964) reported a noisy flock at Kalabakan (near Tawau) in the company of Red-bearded Bee-eaters Nyctyornis amictus , unspecified hornbills ( Bucerotidae ) and Bat Hawks Macheiramphus alcinus . SCO also observed multiple Dusky Broadbills and Banded Broadbills in a clearing on the ridge west of the Tawau River on 7 March 2013. Both species vocalised frequently as they repeatedly flew back and forth across the clearing, but no interactions were observed. It was unclear whether Dusky Broadbill acted as a nuclear species in the flocks we observed, but it was certainly the loudest species and generally the only species that vocalised regularly. We twice encountered groups constructing nests (Fig. 7). Reports of Dusky Broadbill breeding behaviour are relatively common ( Lambert & Woodcock 1996), probably because the species is very Figure 7. Dusky Broadbill Corydon sumatranus nest

during early construction with an adult perched on vocal around nests, which they visit in large top (© Brian Magnier)

Dusky Broadbill nest visitation 29 June 2012

12:30 13:00 13:30 14:00

Time

groups. We found the first group building on 29 June 2012 and another on 15 July 2012. Both dates are typical for the species, yet late compared to other nests reported on Borneo ( Lambert & Woodcock 1996, Myers 2009). The first nest was suspended from a long rattan whip directly above the park’s main trail (c. 700 m from the headquarters), very close to the river. The second was in a low, swampy area off the trail, further to the east, near a Black-crowned Pitta territory.

Only the first nest was observed in detail ( Fig. 8 ). At this nest, a flock of c.8 birds worked amid a cacophony of constant calling. The birds generally took turns, bringing material one at a time, and added each piece of stick, vine, leaf or moss atop the growing pile, sometimes with a head-shaking motion similar to that used by Eurylaimus broadbills (see above). We observed the ‘winding’ behaviour described by Zubkova (2017), in which a flying bird latches the loose end of a fibre to the top of the nest, then spirals downwards while balanced on the side of the nest, to place the other end of the fibre near the base. However, we also frequently saw birds simply place a new piece of material atop the tangle of fibres (both behaviours visible in ML 471148). Young individuals, identified by their paler, smaller throat patches and paler bills, were present and called loudly with the others ( ML 471545–546). Although immatures did not actively participate in nest construction while we watched, their presence is consistent with suggestions that the species breeds cooperatively ( Lambert & Woodcock 1996, Zubkova 2017).

This nestbuilding attempt was abandoned the same day we discovered the nest, at c.14.20 h, after we began setting up a rope system for a hide in the trees nearby. Although they appeared unperturbed by our presence, the ropes we launched into the trees may have disturbed them sufficiently to abandon. The nest was still quite small and far from complete. However, the second nest, which was only observed by JPH, was also abandoned after just one day of building, and JPH did not disturb the birds in any way that would have obviously caused the birds to abandon.

Figures

Figure 8. Graphical summary of nest visitation by Dusky Broadbills Corydon sumatranus during the early nestbuilding period. X axis = time of day. The thin blue line represents a continuous nest watch, the thicker lines visits by broadbills. The colour of each visit alternates to illustrate visits with short intervening breaks, which would otherwise appear to blend into a single line; colour does not represent sex or individual. Red line represents disturbance. We watched the nest until 18:00 h, but no birds visited after 14:21 h.