Behavior of adult and young grassland songbirds at fledging

Abstract

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.

Diel patterns of predation and fledging at nests of four species of grassland songbirds

“…Although Ribic, Ng, et al (2018), andRibic et al (2019) suggested that nestling energetics were a primary driver for the timing of fledging for grassland birds, those studies lacked the context of the predator activity cycle. We now have that context.…”

“…While nocturnal predation does occur on grassland bird nests, the major predators of grassland bird nests are diurnal (Pietz, Granfors, & Ribic, 2012), so it was not unexpected that Ribic, Ng, et al (2018) did not find support for the predation risk hypothesis. However, as Ribic, Ng, et al (2018) and Ribic et al (2019) observed, predation may still shape grassland bird nesting ecology in other ways. For example, if grassland birds are able to determine relative predation risk (Ibanez-Alamo et al, 2015;Weatherhead & Blouin-Demers, 2004) and the relative pattern of risk is consistent over time, a result of evolution might be a pattern of preferentially fledging during times when predation risk was relatively low and avoiding fledging during times when predation risk was relatively high.…”

“…The second process is encounter response risk, that is, the risk that a fledgling's response to an encounter with a predator will fail to result in the fledgling escaping the predator. When encounter response risk is high, such as at the time of fledging when nestling locomotory ability is not well-developed (Heers, 2018;Jones et al, 2017;Ribic et al, 2019), we hypothesize that lowering predation risk becomes more dependent on reducing encounter risk and thus that fledging would occur during periods when encounter risk is lower. Therefore, a better understanding of predation pressures faced by fledglings in grassland ecosystems, and how those pressures change over the course of a day, would allow us to conduct a more robust assessment of the influence of predation risk.…”

Assessing timing of fledging in a cavity-nesting passerine using temperature data loggers

“…The two big advantages of this method over traditionally used frequent nest visitation are time and observer effort effectiveness and avoidance of disturbance of nestlings at the end of the nestling period when they might be provoked to leave the nest prematurely. Alternative remote methods such as radio-frequency identification technology (RFID) and video or trail cameras (Brandis et al, 2014;Iserbyt et al, 2018;Johnson et al, 2017Johnson et al, , 2013Johnson et al, , 2004Pietz et al, 2012;Ribic et al, 2019;Surmacki and Podkowa, 2022) allow precise determination of timing of fledging, and, especially in the case of RFID technology, also fledging order (Radersma et al, 2015;Schlicht et al, 2012). However, given the much lower cost and easier installation, iButton temperature data loggers may be a method of choice in many studies focusing on the identification of fledging age in altricial birds.…”

Parental benefits and offspring costs reflect parent–offspring conflict over the age of fledging among songbirds

“…Perpetuating debate between these hypotheses are studies that focus on the proximate factors (parental and offspring behaviors) of fledging. For instance, past studies have provided evidence in support of the PMH by documenting manipulative behaviors of adults, such as luring offspring with food or reducing their provisioning rates (5,13,14), but other studies have dismissed such observations as anecdotal or misinterpretations of adult behavior (2,15). Additionally, studies on these hypotheses have failed to acknowledge an apparent paradox with respect to fledging.…”