Fighter-pilot Parents Dataset

Description

These data were collected to test parental investment theory's predictions that parents should defend offspring based on offspring survival and recruitment potential and that future reproductive opportunities should impact decisions about the costs and benefits of defending current offspring. We studied eastern bluebirds (Sialia sialis) and tree swallows (Tachycineta bicolor), two species with similar nest defense behaviors and breeding habitat preferences, that nevertheless differ in their within-season re-nesting potential. We collected data on three nest defense behaviors (diving, alarm calling, and beak clicking), as well as and offspring age, number, weight and size. We elicited defensive behavior via human visits to the nest box at all stages of nesting over five consecutive breeding seasons Nestling weight and size were also measured over three of these breeding seasons. All three defensive behaviors were strongly correlated with each other, so we focused our analysis on dives, as we were able to measure this behavior as a count rather than as presence or absence only as we did for beak clicks and alarm calls. Both species increased diving as nests aged. Tree swallows dived more than bluebirds in all stages in accordance with our prediction that the species with the lower re-nesting potential would invest more in their current nest. However, we found no association between parental defense and nestling quality or brood size.

Steps to reproduce

We monitored nest boxes used by both focal species between mid-March and late August (the breeding season in our region) for 5 years. Monitoring consisted of visiting boxes at least 2, but up to 4, times per week and recording the species occupying the box, the stage of the nest, and the number of eggs or nestlings. Twice weekly visits were performed in the years when we collected behavior data only; more frequent visits were conducted during the years that we collected nestling measurement data, so as to more accurately standardize for nestling age. To collect defense behavior data, we approached the box and remained beside it for 1 minute while counting the number of dives the parent bird made toward us and noting whether we heard alarm calls or beak clicks from the parent. If more than one adult bird was present, the parent that first appeared or was more aggressive (if both present from the start) was observed. We knocked on the side of the nest box to alert parents to our arrival at the start of each observation, but did not force parent birds to leave the box if they did not choose to. When nestlings reached 11 days of age, we briefly removed them from the nest box to weigh, measure and band them. Weight was collected in grams by suspending the nestling ins a small mesh bag from a manual spring scale, and tarsus length, our measure of size, was collected using manual calipers. Nestlings were replaced in the nest box after the procedure was complete and we continued to monitor nests until nest completion (fledging - defined as being found empty after 14 (bluebird) or 15 (tree swallow) days post-hatching - or failure). We analyzed our data using R and RStudio (see README file for version and package details).

Institutions

• Radford University

  Virginia, Radford

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