The behavior of adults and young at the time of fledging is one of the least understood aspects of the breeding ecology of birds. Current hypotheses propose that fledging occurs either as a result of parent-offspring conflict or nestling choice. We used video recordings to monitor the behavior of nestling and adult grassland songbirds at the time of fledging. We observed 525 nestlings from 166 nests of 15 bird species nesting in grasslands of Alberta, Canada, and Wisconsin, USA. Overall, 78% of nestlings used terrestrial locomotion for fledging and 22% used wing-assisted locomotion. Species varied in propensity for using wing-assisted locomotion when fledging, with nestling Grasshopper Sparrows (Ammodramus savannarum) and Henslow’s Sparrows (Centronyx henslowii) often doing so (47% of fledgings) and nestling Song Sparrows (Melospiza melodia), Common Yellowthroats (Geothlypis trichas), and Chestnut-collared Longspurs (Calcarius ornatus) rarely doing so (3.5% of fledgings). For 390 fledging events at 127 nests, camera placement allowed adults near nests to be observed. Of these, most young fledged (81.5%) when no adult was present at nests. Of 72 fledging events that occurred when an adult was either at or approaching a nest, 49 (68.1%) involved feeding. Of those 49 fledgings, 30 (62.1%) occurred when one or more nestlings jumped or ran from nests to be fed as an adult approached nests. The low probability of nestlings fledging while an adult was at nests, and the tendency of young to jump or run from nests when adults did approach nests with food minimize opportunities for parents to withhold food to motivate nestlings to fledge. These results suggest that the nestling choice hypothesis best explains fledging by nestlings of ground-nesting grassland songbirds, and fledging results in families shifting from being place-based to being mobile and spatially dispersed. Video clip data for this study are published at https://doi.org/10.2737/RDS-2018-0034-2.

中文翻译：

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成年和幼年草原鸣禽的雏鸟行为

成年和幼鸟在羽化时的行为是鸟类繁殖生态学中最不为人知的方面之一。目前的假设提出，羽翼丰满的发生要么是亲子冲突的结果，要么是雏鸟的选择。我们使用视频记录来监测雏鸟和成年草原鸣禽在羽化时的行为。我们观察到在加拿大艾伯塔省和美国威斯康星州的草原上筑巢的 15 种鸟类的 166 个鸟巢中的 525 只雏鸟。总体而言，78% 的雏鸟使用地面运动进行雏鸟，22% 使用机翼辅助运动。物种在羽化时使用翅膀辅助运动的倾向各不相同，雏鸟麻雀 (Ammodramus savannarum) 和 Henslow's Sparrows (Centronyx henslowii) 经常这样做（47% 的雏鸟）和雏鸟宋麻雀（Melospiza melodia），常见的黄喉鸟 (Geothlypis trichas) 和栗色领长马刺鸟 (Calcarius ornatus) 很少这样做（占雏鸟的 3.5%）。对于 127 个鸟巢的 390 次雏鸟事件，摄像机放置允许观察鸟巢附近的成鸟。其中，大多数幼鸟（81.5%）在巢中没有成鸟的情况下长大。在成虫在或接近巢穴时发生的 72 次羽化事件中，49 次 (68.1%) 涉及进食。在这 49 只雏鸟中，有 30 只 (62.1%) 发生在一只或多只雏鸟在成年接近巢穴时从巢中跳跃或跑出来喂食。当成年雏鸟在巢中时，雏鸟羽化的可能性很低，而当成年雏鸟确实带着食物接近巢穴时，幼鸟倾向于从巢穴中跳下或逃跑，这使父母保留食物以激励雏鸟羽化的机会最小化。这些结果表明，雏鸟选择假说最好地解释了地面筑巢的草原鸣禽的雏鸟的雏形，而雏鸟的雏形导致家庭从基于地点的转变为移动和空间分散。本研究的视频剪辑数据发布在 https://doi.org/10.2737/RDS-2018-0034-2。