Breeding biology of the White-winged Nightjar (Eleothreptus candicans) in eastern Paraguay

Robert G Pople

doi:10.1007/bf03544249

Abstract

Breeding biology of the White-winged Nightjar (Eleothreptus candicans) in eastern Paraguay. I present the first detailed description of the breeding biology of the White-winged Nightjar (Eleothreptus candicans), based on data collected over three breeding seasons during 1998-2001 at Aguara Nu, Canindeyu, eastern Paraguay. Male nightjars defended small territories situated on the upper slopes of ridgelines. Each territory contained one or more at which the male performed nuptial display flights. Aggregation indices confirmed that the primary display arenas of males were significantly clustered within the survey area. Within their territories, males apparently selected display arenas on the basis of their structural characteristics: mounds used as arenas were significantly lower and broader than random mounds. Males engaged in display activity from late August to early January. On average, males performed 0.54 ± 0.04 display flights per minute during nocturnal focal watches, but there was considerable intra-male variation in display rate. Following a burst of activity immediately after their arrival at display arenas at dusk, male display rate was best explained by ambient levels of moonlight. Males produced a previously undescribed insect-like tik call when inactive on their territories. Females made two nesting attempts per season, using a different site (360 ± 31 m apart) for each attempt. The clutch of two eggs was laid directly on the ground, adjoining a small access clearing, in either campo cerrado or wet grassland vegetation. The first egg was laid within two days of a full moon for all seven clutches for which laying date was confirmed. Incubation, brooding and chick provisioning duties were carried out exclusively by the female. The incubation period was 19 days and the nestling period c. 19-20 days. Overall, my data are consistent with polygyny - and even an exploded lek or landmark mating system - in this population of White-winged Nightjars.

Highlights

Owing largely to their cryptic plumage and crepuscular or nocturnal habits, the Caprimulgidae are comparatively under-studied
All data on nesting biology were obtained from females caught during the 1999 and 2000 breeding seasons
Aspect was not entered into the model, but univariate tests suggested that male territories were more likely to have a westerly than easterly aspect compared to random points (11 of 13 versus 5 of 13; G-test: G = 5.80, df = 1, P < 0.05)

Summary

Introduction

Owing largely to their cryptic plumage and crepuscular or nocturnal habits, the Caprimulgidae (true nightjars) are comparatively under-studied. Their breeding biology in particular is poorly known, and for many species the only published data are anecdotal or based on single nesting attempts. Studies of the better-known species show them to be generally ground-nesting, with clutches of one or two eggs, and an essentially monogamous breeding system (Cleere 1999, Holyoak 2001). Male White-winged Nightjars were found to perform ritualised display flights at small arenas – low anthills or termite mounds – located on the upper slopes of ridgelines in areas of open grassland. Display flights were accompanied by a dull “tk...grrrrrt” sound (recording in Ranft & Cleere 1998), perhaps produced by movement of air through the outer primaries

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