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

Abstract

Fecundity, the number of young produced by a breeding pair during a breeding season, is a primary component in evolutionary and ecological theory and applications.Fecundity can be influenced by many environmental factors and requires long-term study due to the range of variation in ecosystem dynamics. Fecundity data often include a large proportion of zeros when many pairs fail to produce any young during a breeding season due to nest failure or when all young die independently after fledging. We conducted color banding and monthly censuses of Florida scrub-jays (Aphelocoma coerulescens) across 31 years, 15 populations, and 761 territories along central Florida's Atlantic coast. We quantified how fecundity (juveniles/pair-year) was influenced by habitat quality, presence/absence of nonbreeders, population density, breeder experience, and rainfall, with a zero-inflated Bayesian hierarchical model including both a Bernoulli (e.g., brood success) and a Poisson (counts of young) submodel, and random effects for year, population, and territory. The results identified the importance of increasing "strong" quality habitat, which was a mid-successional state related to fire frequency and extent, because strong territories, and the proportion of strong territories in the overall population, influenced fecundity of breeding pairs. Populations subject to supplementary feeding also had greater fecundity.Territory size, population density, breeder experience, and rainfall surprisingly had no or small effects. Different mechanisms appeared to cause annual variation in fecundity, as estimates of random effects were not correlated between the success and count submodels. The increased fecundity for pairs with nonbreeders, compared to pairs without, identified empirical research needed to understand how the proportion of low-quality habitats influences population recovery and sustainability, because dispersal into low-quality habitats can drain nonbreeders from strong territories and decrease overall fecundity. We also describe how long-term study resulted in reversals in our understanding because of complications involving habitat quality, sociobiology, and population density.

Impacts of increasing isolation and environmental variation on Florida Scrub-Jay demography

“…Unlike other studies (Breininger 2009; Breininger et al . 2022, 2023; Fitzpatrick & Bowman 2016), we did not find an association between fire history and variation in vital rates at the population-wide scale. This discrepancy is likely due to the low variation in the proportion of burned area observed across our study area during the study period.…”

“…Our results showing the importance of breeder survival and environmental fluctuations on population dynamics are largely consistent with previous work on the Florida Scrub-Jay (Breininger et al . 2022, 2023; Breininger & Oddy 2004; Woolfenden & Fitzpatrick 1984). The large contributions of variation in fecundity and population density both result from high temporal variation in fecundity, with high fecundity years frequently followed by low fecundity years (Woolfenden & Fitzpatrick 1984).…”

Survival of juvenile Florida Scrub-Jays is positively correlated with month and negatively correlated with male breeder death

“…The effect of habitat is not completely consistent with Breininger et al (2014) who found that yearling production was highest in optimal-open territories, in part because juvenile production is highest in optimal-open (Breininger et al 2023). The unexpected results of optimal-closed territories having the highest survival provide motivation for further investigation to better understand possible alternate management strategies for this declining species.…”

“…These classes differ in demographic performance (yearlings produced per pair-year). Territories with at least 10% of shrubs at optimal height among shorter shrubs and no more than an acre of taller shrubs together with 10%–50% ground cover as sandy openings (optimal-open) outperform optimal height territories without openings (optimal-closed; Breininger et al 2014, Lacy and Breininger 2021, Breininger et al 2023). Thus, 3 classes of habitat quality occurred in the study populations: optimal-open (source) outperforms optimal-closed (intermediate) which outperforms suboptimal (sink).…”

Evidence of a load-lightening helper effect in Florida Scrub-Jays: implications for translocation

“…two-thirds of helpers assist at the nests of their full parents, and 90% assist at least one parent, leading to high mean levels of relatedness between helpers and the young they tend (Woolfenden and Fitzpatrick 1984). Florida Scrub-Jay helpers may assist groups by reducing predation through sentinel duty, territorial defense, and by provisioning nestlings and dependent fledglings, which in turn increases reproductive success for the breeding pair (Woolfenden 1975, Mumme 1992, Mumme et al 2015, Fitzpatrick and Bowman 2016, Breininger et al 2023. Nest construction, egg-laying, and incubation are performed exclusively by the breeding female Fitzpatrick 1984, 1996), and breeders usually prevent helpers from tending nestlings until nestlings are about one week old (Rensel et al 2010).…”