Data and analysis code for Norton and DuVal - Causes and consequences of nest site fidelity in a tropical lekking bird: win-stay-lose-shift tactics are unrelated to subsequent success, but site-faithful females nest earlier
Data files
Apr 16, 2023 version files 202.59 KB
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Dataset1_across_yrs.csv
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Dataset1_w_nest_checks.csv
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Dataset2_w_nest_checks.csv
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Dataset2_within_yrs.csv
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Initial_timing.csv
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METADATA.csv
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README.md
Abstract
Nest site selection influences the survival of care-giving parents and their offspring, but search costs and site availability may limit site choices. Returning to previous nest sites may reduce costs and allow parents to better avoid local predators or access familiar resources. We investigated nest site fidelity in the Lance-tailed Manakin (Chiroxiphia lanceolata), in which long-lived females raise offspring without male assistance, and found that site choices are responsive to past success but do not predict future outcomes. We compared georeferenced nest locations for the same females detected in consecutive years (245 comparisons for 138 females) and females nesting repeatedly within a year (137 comparisons for 97 females). Females were faithful to nesting sites in 13.9% of comparisons across years and 10.2% within years, and were more likely to nest again in the same site if their offspring fledged. When switching sites, females moved farther if their previous nest failed. Nest-site fidelity was unrelated to mate fidelity or female age. We then assessed whether site choice related to subsequent female survival, nest timing, or nest survival. Contrary to the hypothesis that win-stay-lose-shift tactics improve subsequent nesting outcomes, we found females were no more likely to fledge chicks or survive to a later year after they reused nest-sites. However, across years, site-faithful females nested earlier on average than females that switched sites. Early nests were more likely to fledge chicks, and early-nesting females were more likely to renest when their first nesting effort was complete. Win-stay-lose-shift tactics may allow females to avoid areas where predation is likely, but new nest sites are not safer. Females that reuse nest sites benefit from early nest initiation, which both correlates with immediate success and creates potential for longer-term benefits of fidelity through increased opportunities to renest throughout the breeding season.
Methods
We used 19 years of information on the nest locations of individually banded female Lance-tailed Manakins to investigate why females renest at the same sites, and whether this behavior improves female survival or fledging success of the subsequent offspring. Lance-tailed Manakin females often have multiple nests in a single field season. Therefore, we examined effects of site-fidelity across years as well as within a year. When comparing a female’s nests across years, the most temporally adjacent nests were compared (e.g., a female’s final nest in 2010 was compared to her first nest in 2011). For nests in the same year, we used the lay date to determine which nest was active first.
Field methods: Nests were located by visual inspection of understory vegetation whenever a research team was present at the field site (usually March – early June annually). Nests were monitored every 2-4 days to determine dates of laying and hatching, as well as whether offspring successfully fledged. Fledging usually occurred around 16 days after hatching, and chicks that disappeared from the nest after 15 days with no signs of depredation were assumed to have fledged. Maternal identity was determined from the unique color band combination of females attending the nest, either by observation from a blind placed >10m from the nest, or by video recording. When females were unbanded, they were captured with mistnets at the nest and individually marked, as above. After offspring fledged or nest contents disappeared (and were presumed to be depredated), researchers recorded nest location with a GPS point (Garmin eTrex models, <6m accuracy). When lay date was not directly observed, it was inferred from hatch date by assuming an incubation period of 18 days. Starting in 2010, one egg of each two-egg nest was artificially incubated to ensure a genetic sample (Jones and DuVal 2019), and so lay date could also be inferred from embryo developmental stage in later years of data.
Distances between nests were estimated in meters, by applying the Pythagorean Theorem to nest pairs, with nest coordinates measured in UTMs. Nest-site choice was categorized as “faithful” if females moved less than 12 meters between consecutive nests. We chose the cutoff distance of 12 meters because distances were calculated from GPS locations with accuracy <6m. If the locations of two consecutive nests were recorded with maximal and opposite error, they could appear to be 12 meters apart when they were actually in the same sapling. Therefore, when nests were at least 12 meters apart, we were confident that the female was nesting in a new location. In practice, many instances of site fidelity occurred on a finer scale; researchers returning to search for nests in multiple years often noted that a specific nesting fork was reused, and such observations served as the initial inspiration for this analysis.