Increasing reproductive productivity and population growth rates of the threatened Florida scrub-jay (Aphelocoma coerulescens) using a parasite removal experiment

Background/Question/Methods

As populations of Florida scrub-jays decline due to habitat loss, habitat degradation and associated lowered demographic performance, the threat of catastrophic disease and demographic impacts of chronic disease increase. It is likely that smaller populations of Florida scrub-jays are less genetically diverse increasing the risk of population wide mortality events and lowering the probability of survival. If habitats are degraded and Florida scrub-jays become increasingly “stressed” small populations are more likely to succumb to chronic diseases and parasites, reduce demographic performance, and probably suffer from the “Allee effect”. Furthermore, diseased individuals are more likely to be clinically ill reducing their ability to escape predators; exacerbating predation pressure.  In this study we identified a filarial nematode known to infect Florida Scrub-Jays. We measured the consequences of filarial nematode infection on survival and reproduction.  We attempted to remove the negative environmental pressure of filarial nematode parasitaemia by pharmacologically application of an anthelminthic, and monitored for improved condition and higher reproductive performance.  If positive results are found the technique could be applied to increase growth and stability of the at risk smaller Florida scrub-jay populations.

Results/Conclusions

We have identified the filarial nematode molecularly as belonging to the Aproctella genus, although previously the nematode was thought to be Cardiofilaria pavolovskyi. Although very understudied, it is likely that many parasites have their most negative effect on juvenile Florida scrub-jays as this is when first exposure occurs.  A high proportion (~60%) of Florida scrub-jays in our study population are infected by day 85 after hatching, and infection status (yes or no) is long-term with high repeatability. We found no effect on daily survival rates between fledglings known to be infected at day 85 compared to those that were not. Breeding birds that produce less young are more likely to be infected and have higher intensity filarid infections than those that produce 2 or more young.  Adults known to be parasitized with nematodes were just as likely to survive from one breeding season to the next compared to non-parasitized adults. We treated 20 breeding pair with the anthelminthic Ivermectin^© during the pre-breeding season January 2013. From February to July we are measuring reproductive metrics including, initiation of breeding, clutch size, brood size, fledgling success and survival to day 85 when young Florida Scrub-Jays become independent of parents.