Diel fledging patterns among grassland passerines: Relative impacts of energetics and predation risk

Ribic, Christine A.; Ng, Christoph S.; Koper, Nicola; Ellison, Kevin; Pietz, Pamela J.; Rugg, David

doi:10.1642/auk-17-213.1

Cited by 12 publications

(30 citation statements)

References 43 publications

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“…Ground-nesting grassland bird species tend to fledge in the morning (Pietz, Granfors, & Grant, 2012;Ribic, Ng, et al, 2018), a behavior also observed in many other songbirds (e.g., Chiavacci et al, 2015;Johnson et al, 2004;Lemel, 1989;Skutch, 1953). However, why nestlings of grassland birds exhibit this behavior is not well understood.…”

Section: Introductionmentioning

confidence: 98%

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

Ribic

Rugg

Ellison³

et al. 2021

Ecology and Evolution

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Although it is common for nestlings to exhibit a strong bias for fledging in the morning, the mechanisms underlying this behavior are not well understood. Avoiding predation risk has been proposed as a likely mechanism by a number of researchers. We used video surveillance records from studies of grassland birds nesting in North Dakota, Minnesota, and Wisconsin to determine the diel pattern of nest predation and fledging patterns of four ground‐nesting obligate grassland passerines (Grasshopper Sparrow ( Ammodramus savannarum ), Savannah Sparrow ( Passerculus sandwichensis ), Bobolink ( Dolichonyx oryzivorus ), and Eastern Meadowlark ( Sturnella magna )). We used the nest predation pattern as a surrogate for predation activity to test whether nestlings minimized predation risk by avoiding fledging when predation activity was high and preferentially fledging when predation risk was low. Predation activity was significantly lower starting 3 hr before sunrise and ending 3 hr after sunrise, followed by a transition to a period of significantly higher activity lasting for 4 hr, before declining to an average activity level for the rest of the diel period. There was little evidence that the four grassland bird species avoided fledging during the high‐risk period and Savannah Sparrow fledged at higher rates during that period. All four species had hours during the low‐risk period where they fledged at higher rates, but only Grasshopper Sparrow fledged preferentially during that period. Bobolink and Eastern Meadowlark had multiple hours with high fledging rates throughout the daytime period, resulting in no relationship between probability of fledging and predation risk. Given the species variability in fledging pattern seen in our study, it is unlikely that there is a universal response to any driver that affects time of fledging. Further study is needed to understand the complex interplay between species ecology and drivers such as physiology, energetics, and predation in affecting grassland bird fledging behavior.

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Section: Introductionmentioning

confidence: 98%

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

Ribic

Rugg

Ellison³

et al. 2021

Ecology and Evolution

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“…Young Cordilleran Flycatchers fledged at all times of the day, with almost half fledging in the late afternoon or evening, unlike young in many other species of songbirds that primarily fledge in the morning (Johnson et al 2004, 2013, Chiavacci et al 2015, Ribic et al 2018). The timing of fledging by young Cordilleran Flycatchers was also contrary to the maximum time hypothesis (Chiavacci et al 2015), which postulates that fledging earlier in the day may be a strategy that gives young fledglings more time to reach relatively safe locations before dusk.…”

Section: Discussionmentioning

confidence: 99%

“…Chiavacci et al (2015) attributed this pattern to the “maximum time hypothesis,” hypothesizing that predation pressure was the leading driver of the timing of fledging and that young fledged early in the day to have sufficient time to find safe locations before dark. However, Johnson et al (2004) and Ribic et al (2018) concluded that energetic considerations and sibling competition were the most important factors in determining the timing of fledging. All young in a brood typically fledge during a single day, but multi‐day fledging of some broods has been documented for many species (Johnson et al 2004, Chiavacci et al 2015, Ribic et al 2018).…”

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confidence: 99%

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

Darrah

Riper

2021

J. Field Ornithol.

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The behavior of young songbirds after fledging is one of the least understood phases of the breeding cycle, although parental provisioning rates and movement of fledglings are key to understanding life history evolution. We studied Cordilleran Flycatchers (Empidonax occidentalis) at two sites in southwestern Colorado, USA, from 2012 to 2017. We banded and sexed breeding adults to determine the relative contributions of males and females to nestling and fledgling care, and attached radio‐transmitters to nestlings to facilitate observations of brood behavior after fledging. Females made 60% and 78% of total observed feedings of nestlings and fledglings, respectively. Parental provisioning rates increased with nestling age, and per‐nestling provisioning rates increased with brood size. Parental provisioning rates declined just before fledging, then increased just after fledging. Fledging times of individuals in broods were asynchronous and concentrated during the late afternoon and early evening. Males stopped caring for fledglings before females even though this species is single‐brooded, with some late‐season broods being abandoned by males. Broods spent the first three weeks after fledging within 400 m of nests, after which they began to disperse. Most aspects of the breeding biology of Cordilleran Flycatchers in our study, including the duration of nestling and fledging periods, female‐dominated provisioning, and movement patterns of fledglings, were similar to those of other Empidonax species. However, the times when young fledged were not concentrated in the morning as reported in most other songbirds, and this result warrants additional study of the timing of fledging in ecologically and taxonomically similar species. The increased per‐nestling provisioning rate with increasing brood size was unexpected, and additional study is needed to determine if this increase results from a trade‐off between adult annual survival and productivity favoring increased provisioning of young in larger broods, or from the existence of high‐quality individuals where larger clutches and higher provisioning rates are linked.

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“…size hypothesis (NCH), in which parents and offspring are not in conflict and fledging is initiated by other factors only after offspring pass a developmental threshold (11,12). Perpetuating debate between these hypotheses are studies that focus on the proximate factors (parental and offspring behaviors) of fledging.…”

mentioning

confidence: 99%

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

Jones

Brawn

Ausprey

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Parent–offspring conflict has explained a variety of ecological phenomena across animal taxa, but its role in mediating when songbirds fledge remains controversial. Specifically, ecologists have long debated the influence of songbird parents on the age of fledging: Do parents manipulate offspring into fledging to optimize their own fitness or do offspring choose when to leave? To provide greater insight into parent–offspring conflict over fledging age in songbirds, we compared nesting and postfledging survival rates across 18 species from eight studies in the continental United States. For 12 species (67%), we found that fledging transitions offspring from comparatively safe nesting environments to more dangerous postfledging ones, resulting in a postfledging bottleneck. This raises an important question: as past research shows that offspring would benefit—improve postfledging survival—by staying in the nest longer: Why then do they fledge so early? Our findings suggest that parents manipulate offspring into fledging early for their own benefit, but at the cost of survival for each individual offspring, reflecting parent–offspring conflict. Early fledging incurred, on average, a 13.6% postfledging survival cost for each individual offspring, but parents benefitted through a 14.0% increase in the likelihood of raising at least one offspring to independence. These parental benefits were uneven across species—driven by an interaction between nest mortality risk and brood size—and predicted the age of fledging among species. Collectively, our results suggest that parent–offspring conflict and associated parental benefits explain variation in fledging age among songbird species and why postfledging bottlenecks occur.

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Diel fledging patterns among grassland passerines: Relative impacts of energetics and predation risk

Cited by 12 publications

References 43 publications

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

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

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

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

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