Multistate modeling of Florida scrub‐jay adult survival and breeding transitions

Abstract

Adult nonbreeders are important for the stability and conservation of many species despite that their functional roles are often undervalued. Nonbreeders can buffer breeding population sizes and help their kin raise new generations of offspring, but in high numbers can compete and have negative effects. Long‐term studies are useful for elucidating relationships among nonbreeder population parameters, such as density, survival, and transitions to breeding status. Florida scrub‐jays are cooperative breeders where young delay breeding often for many years and are at risk of extinction across most of their range. Our objectives were to estimate how population covariates (pair density and mean family size) influenced Florida scrub‐jay adult nonbreeder survival and breeding transitions using long‐term data of uniquely marked birds and multistate capture–recapture models. The evolution and maintenance of Florida scrub‐jay delayed breeding has been attributed to living in crowded and sharply delineated habitat at Archbold Biological Station, the site of longest long‐term study. Contrastingly, most habitat we studied had a dynamic mixture of habitat quality with mean family sizes and pair densities much lower than the stable, optimal habitat at Archbold Biological Station. Despite having densities below carrying capacity, Florida scrub‐jays still delayed breeding. We found that greater mean family size was associated with greater breeder survival, possibly because nonbreeders contributed to predator detection and territory defense. Nonbreeder‐to‐breeder transitions increased with increased annual breeder mortality rates but were influenced little by population densities. Most Florida scrub‐jays became breeders by replacing dead breeders within occupied territories, and many male and female nonbreeders inherited their territories upon the death of their parents. Nonbreeders buffered changes in the breeding population supporting greater recognition of nonbreeder population roles within field and modeling studies.

Territory and population attributes affect Florida scrub‐jay fecundity in fire‐adapted ecosystems

“…Long‐duration studies and large sample sizes might be needed to target how the loss and formation of territories (thus population density of breeding pairs) is influenced by the complexities of habitat quality, breeder density, and sociobiology (e.g., mean family size, age, sex, relatedness among individuals). Nonbreeders generally fill annual vacancies associated with breeder deaths in occupied territories with little regard to territory quality and breeder population density (Breininger, Carter, Legare, Payne, Stolen, et al, 2022; Breininger, Stolen, et al, 2010), except in habitat unburned for many decades (Woolfenden & Fitzpatrick, 1984, 1991).…”

“…Here, we lumped all other habitat states as sinks because the scrub was too short or too tall or lacked enough scrub oak cover. As in the most recent studies, we classified the mid‐successional states in oak scrub as open‐medium (strong) or closed‐medium (weak) based on having ≥10 percent open sand within oak scrub patches (Breininger, Stolen, et al, 2014 ; Breininger et al, 2022 ; Eaton et al, 2021 ; Kent & Kindell, 2010 ). We hypothesized that strong had the greatest fecundity and that sink had the lowest when comparing territory quality states.…”

“…Dense Florida scrub‐jay populations have strong competition for space and possibly food (Fitzpatrick & Bowman, 2016 ; Mumme et al, 2015 ). Density represented the number of breeding pairs divided by the number of potential territories in the local population (Breininger et al, 2006 ; Breininger, Carter, Legare, Payne, Stolen, et al, 2022 ). Potential territories were 10 ha grid cells that were of sufficient quality that they could be occupied despite whether recruitment exceeded mortality (Breininger et al, 1998 ; Burgman et al, 2001 ; Carter et al, 2006 ; Duncan et al, 1995 ).…”

“…Each bird was classified as a nonbreeding adult, breeder, or juvenile based on behaviors described by Woolfenden and Fitzpatrick (1984). Individual breeder and nonbreeder detection probabilities are typically above 0.9 and almost all members of the family remain close together (Breininger et al, 2009, 2022). We observed that nonbreeding adults often fed young (nestlings, fledglings, juveniles) and aided breeders in territorial defense, spotting and mobbing predators (Woolfenden & Fitzpatrick, 1984).…”

“…We hypothesized that the presence of at least one nonbreeding adult in a territory (family) increased fecundity by increasing both survival of nests and individual fledglings. The presence of nonbreeders (potential helpers) for a breeder pair was recorded as whether there was one or more nonbreeding adults present in the territory during April, which was the peak of the nesting season (Woolfenden & Fitzpatrick, 1984, Breininger, Carter, Legare, Payne, Stolen, et al, 2022). Fitzpatrick and Bowman (2016) found that the fecundity increases at a greater rate with low numbers of helpers and that fecundity decreases with high numbers.…”