We got up for the aerial waterfowl survey of the Illinois and central Mississippi rivers on Wednesday, November 6th. Duck abundance was below the long-term average along both rivers this week, but especially low relative to LTA on the central MS River. I estimated ~298,000 ducks in the IRV on Friday, a 13% increase from last week but 14% below the 10-year average of ~346,000 ducks. Mallards continue to be significantly below LTA for the Illinois (-33%), while green-winged teal are 17% above their LTA and by far the most abundant species observed this week. I estimated ~271,000 ducks on the central Mississippi River, a 54% increase from last week but 30% below the 10-year average (~386,000). Though mallards are also below LTA along this river (-54%), we did observe an increase in most duck species this week, especially green-winged teal and northern pintail. The largest jump in abundance this week was observed on Swan Lake at Two Rivers NWR. Total duck abundance increased by 125% on this refuge, jumping from ~36,000 ducks last week to ~78,000 on Wednesday.
We had two “firsts” this week for our third field season of mallard and green-winged teal transmitter deployment. One was our first harvest of a 2024-marked bird, a green-winged teal shot on Thursday on a private property in Fulton County. Secondly, and somewhat surprisingly, we had the first departure of a 2024-marked bird. The surprising part was not the departure; it was the fact that it was a mallard. This is the earliest departure from our study area by a mallard during the 3 years of this project. In research, we are often concerned with “observer effects,” or how the methods we are using to investigate a question could potentially change the very thing we are trying to understand. Certainly, with transmitters, that question has been raised. After all, we are strapping 20g (and 10g) blocks of electronics+expoxy to the backs of these birds and wishing them the best of luck… all in the name of science. Could we be altering the birds’ movements, departure timing, survival, behaviors, etc., with these units? It doesn’t seem like it with this particular early-departing mallard. The mallard team at TN Tech shed some light on this question in a recent manuscript. They compared encounter reports of over 400 mallards fitted with GSM transmitters to birds captured during the same study, but only banded with USGS leg bands. They concluded that the two cohorts had similar harvest rates, winter dispersal distances, and harvest distributions, and that harness transmitters provide reliable information on wintering mallard ecology. The next step for researchers is evaluating these effects on other species and at different times of the life cycle. This week’s numbers are on the Aerial Inventories page.
