PS 47-126 - Caught on camera: effects of invasive grasses and brood parasitism on Dickcissel food provisioning and reproductive success

Background/Question/Methods

Grassland birds are declining more rapidly than any other avian group in North America. To work toward the conservation of these species, it is important to understand reproductive behaviors. To this end, we evaluated relationships between invasive plants, brood parasitism, nestling condition, begging behaviors, and provisioning behaviors observed on Dickcissel (Spiza americana) nests on high-definition cameras in the Grand River Grasslands of southern Iowa. We searched for nests using behavioral monitoring techniques on 4-6 sites in 2015, 2016, and 2021, and monitored nests until they fledged or failed. We filmed each nest between nestling day 4-6, and measured nestling condition on day 6. For each nest filming session, we collected data on, presence and number of brood parasites, nestling begging behaviors, provisioning rates, and size and identity of arthropods provisioned.

Results/Conclusions

We collected video data during the breeding season in 2015 (n=68 filming sessions), 2016 (n=105), and 2021 (n=34). The mean number of hours filmed per filming session was 2.1 in 2015-2016 and 6 hours in 2021. The most frequently provisioned arthropods were Orthopterans (large, medium and small respectively), followed by medium Lepidopteran larvae.Our preliminary analyses suggest a small negative effect of invasive grass cover on provisioning rates and nesting success. Moreover, we found reduced nestling condition in areas highly invaded by invasive grasses. We also found that increasing numbers of brown-headed cowbird nestlings led to increased rates of begging, and higher nest failure. These results show the importance of invasive grasses and brood-parasitism in Dickcissel reproduction and highlight the potential benefits of using high-definition cameras for monitoring and managing populations for conservation.