Postfledging survival and local recruitment of a riparian songbird in habitat influenced by reservoir operations

Abstract

ABSTRACT. The impact of anthropogenic activities on breeding bird populations are typically assessed using nest success despite the importance of the postfledging period and juvenile survival for the population dynamics of many birds. Using a combination of radio telemetry data collected between 2012 and 2014, and long-term monitoring data collected between 2005 and 2016, we evaluated whether postfledging survival of Yellow Warblers (Setophaga petechia) is affected when their riparian nesting habitat becomes inundated by the Upper Arrow Lakes Reservoir in the Columbia River Valley near Revelstoke, British Columbia, Canada. Thirty-eight percent of radiotagged fledglings (n = 26) survived for at least 21 days after leaving the nest. Radio-tagged birds that fledged from nests in territories that were inundated by water tended to be have lower survival than those that fledged from nests in territories that were not inundated by water. Local recruitment was low (6.4%, n = 438). Local recruitment was nevertheless positively affected by nestling condition prior to fledging. Fledglings from territories that were not inundated by water also tended to be more likely to recruit locally than those that fledged from territories that were inundated by water. In both cases, we estimated that reservoir operations that flooded habitat reduced postfledging survival or local recruitment by approximately 50%. Our study emphasizes the importance of considering the postfledging period when developing mitigation measures or management plans aimed at minimizing the impact of anthropogenic activities on bird populations. Survie des jeunes après l'envol et recrutement local d'un passereau ripicole nichant dans un habitat touché par la régulation du niveau d'eau d'un réservoirRÉSUMÉ. Les impacts qu'ont les activités anthropiques sur les populations d'oiseaux nicheurs sont habituellement évalués à partir du succès de nidification, malgré l'importance de la période suivant l'envol des jeunes et la survie juvénile dans la dynamique de population de nombreux oiseaux. En combinant des données de radiotélémétrie obtenues entre 2012 et 2014 et des données provenant d'un suivi réalisé de 2005 à 2016, nous avons évalué dans quelle mesure la survie après l'envol des jeunes de Paruline jaune (Setophaga petechia) était affectée lorsque leur habitat de nidification se trouve inondé par le réservoir Upper Arrow Lakes dans la vallée du fleuve Columbia près de Revelstoke, Colombie-Britannique, Canada. Trente-huit pourcent des jeunes munis d'un émetteur (n = 26) ont survécu au moins 21 jours après avoir quitté le nid. La survie des jeunes ayant pris leur envol de nids situés sur des territoires ayant été inondés était généralement plus faible que celle des oiseaux ayant pris leur envol de nids situés sur des territoires n'ayant pas été inondés. Le recrutement local était faible (6,4 %, n = 438). Néanmoins, le recrutement local était positivement lié à la condition des jeunes avant l'envol. Les jeunes ayant pris leur envol dans les territoires non inondés ...

Rusty Blackbird Habitat Selection and Survivorship during Nesting and Post-Fledging

“…We observed low mortality rates for rusty blackbird fledglings in the first week after fledging (3%) compared to those reported for other songbirds, e.g., 21-81% for ovenbird [2], 11% for worm-eating warbler [8], and 90% for rose-breasted grosbeak (Pheucticus ludovicianus) fledglings [7]. All observed fledgling mortality took place in the first four days of a yellow warbler (Setophaga petechi) study [58]. Our high rusty blackbird fledgling survival contrasts with virtually every other songbird post-fledging study.…”

Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird

“…Rising water levels do, however, coincide with the three-week post-fledging period when juveniles are dependent on their parents. Studies show this is a period of high mortality for songbirds [ 32 ], and we have shown that the survival of radio-tagged fledglings and the recruitment of colour-banded fledglings from inundated territories are lower than the survival and recruitment of fledglings from territories not inundated by water [ 17 ]. Our individual-based model estimates that under current reservoir operations rising water levels that extend into yellow warbler habitat (the riparian shrub zone at > 435m a.s.l.)…”

“…Females can nest multiple times during a breeding season (maximum = 3) and may renest after both failed and successful nesting attempts. Fledglings are independent of their parents after approximately 21 days [ 17 ].…”

“…We used the model output from Scenario 2 because 11 of the 12 years of observational data were collected in “early fill years”. We were unable to compare predicted and observed productivity (average number independent young produced/female/year) because we only used radiotelemetry to quantify the post-fledging survival of a subset of young in three years (see [ 17 ] for details of the radiotelemetry study).…”

“…Studies that monitor nests can document flooding (e.g. [ 15 ]), but need to evaluate the extent to which flooding reduces nest success that may also fail for other reasons [ 16 ], allow for the possibility that individuals of multi-brooded species can re-nest, and incorporate reservoir operation effects on the survival of fledglings [ 17 ]. Long-term monitoring studies of species of concern can sometimes document changes in annual productivity associated with variation in the management of reservoir water levels (e.g.…”