Postfledging Movements and Survival of Juvenile Eastern Meadowlarks (Sturnella Magna) in Illinois

Abstract

<jats:title>Abstract</jats:title> <jats:p>The postfledging period is the least-studied stage of avian life cycles. Survival during this period has crucial effects on population dynamics. Survival of fledged young may be influenced by dispersal from their nest sites, because juveniles must cope with the hazards of novel environments. To better understand this important life stage, we used radiotelemetry techniques to study postfledging movements and survival of 50 juvenile Eastern Meadowlarks (Sturnella magna) at Prairie Ridge State Natural Area in Jasper County, Illinois, in 1999 and 2000. Juveniles began to move away from the nesting area in the third week after fledging. Most juveniles moved only 1–5 km from their birth site by the end of the study (90 days). Juvenile survival for the first 90 days after fledging was estimated as 56–69%. Mortality was greatest during the first week of the postfledging period, likely because of high rates of predation. Juvenile meadowlarks are flightless at fledging and thus are vulnerable to predators. We did not observe a second peak of mortality, as other studies have shown, at independence or when juveniles began to move away from their nest areas. The present study suggests that immediate postfledging movements may not be related to dispersal to future breeding sites, but rather occur in response to immediate needs for food resources and security from predators. Furthermore, the data suggest that presumed mortality patterns and estimated levels of juvenile survival are suspect; that interspecific variability of juvenile survival and postfledging movements may be considerable; and that detailed, longer-duration field studies are necessary to elucidate this important demographic period.</jats:p>

Habitat use and movement patterns by dependent and independent juvenile Grasshopper Sparrows during the post-fledging period

“…Predation is generally the primary cause of mortality during the post‐fledging period (Yackel Adams et al , Berkeley et al , Suedkamp Wells et al ), particularly within the first week for fledgling Grasshopper Sparrows (Hovick et al ). Because dependent birds are not foraging on their own, and are less able to escape predators because their flight feathers are not fully grown (Anders et al , Kershner et al , Suedkamp Wells et al , Hovick et al ), they may benefit from remaining in areas of greater vegetation cover. However, Jackrel and Reinart () found that snakes were more common in grassland areas with denser vegetation.…”

“…For the dependent‐age subset, one 6‐ to 8‐d‐old nestling from each nest ( N = 18) was selected at random for tracking. Only one nestling was tracked per nest to ensure independence of marked individuals (Kershner et al , Berkeley et al , Hovick et al ). For the independent‐age subset, previously banded nestlings ≥ 32‐d‐old were selected for tracking.…”

“…This period includes a dependent stage, when juveniles still receive parental care, followed by an independent stage. To survive and achieve independence, juveniles must become self‐sufficient at finding food and shelter and avoiding predators (Kershner et al , Berkeley et al , Hovick et al ).…”

“…Little is known about the post‐fledging ecology of grassland birds, particularly grassland‐obligate species. In addition, most research has focused on the dependent stage (Yackel Adams et al , Berkeley et al , Hovick et al ), with few studies conducted during the independent stage (Kershner et al , Suedkamp Wells et al ). These latter studies report increasing movement with increasing fledgling age, particularly for independent juveniles.…”

Long‐term coevolution between avian brood parasites and their hosts

“…Many altricial bird species have an extended period of post‐fledging care, and this period is often longer in brood parasites than in host fledglings (Soler et al , ). Despite its long duration and the fact that this period of care is critical for juvenile survival, because predation at this stage is very frequent (Naef‐Daenzer, Widmer & Nuber, ; Kershner, Walk & Warner, ; Grüebler & Naef‐Daenzer, ), the fledging period both of brood parasites and of hosts has not been sufficiently studied. Available information on relationships between brood parasites and their hosts during this period is very scarce.…”