Content originally published in Quail Call 2023
Arthropods are a staple food for northern bobwhite chicks, comprising much of their diet for the first two weeks of life. Arthropods provide chicks with the protein and energy required to maintain optimal growth rates. Management decisions influence arthropod abundance and accessibility through changes to vegetation structure and plant species richness. Seasonal disking of “brood fields” to promote ragweed and other arthropod-friendly plants is a common practice on managed quail lands throughout the Southeast.
However, as management costs increase, landowners are becoming increasingly interested in options to help offset various expenses. Agricultural leases are one option often used to achieve this goal, but understanding the extent to which various agricultural crops contribute to arthropod abundance could be important when combined with quail management. As part of a large-scale study on brood ecology, we investigated the effect of burning, disking fallow fields, and crop choice on local arthropod biomass and northern bobwhite broods’ diet.
We used a non-invasive molecular technique known as DNA metabarcoding to quantify the effect burning, disking of fallow fields, and agricultural crops had on the diets of bobwhite broods. DNA metabarcoding amplifies DNA and uses known references to identify organisms within a sample, in our case the droppings left by a brood while at roost. We collected a total of 188 fecal samples from brood roost-site locations at Livingston Place and Tall Timbers. We successfully amplified arthropods DNA from 126 (67%) of our samples.
Bobwhite broods consumed 16 taxonomic orders of arthropods, including mites and ticks, which may have been consumed either during preening or as a secondary prey (prey consumed by prey, or parasites of prey). The most frequently consumed groups at both sites were grasshoppers, spiders, and true bugs such as stink bugs, with grasshoppers occurring in over 85% of all samples. We found that bobwhite broods consumed grasshoppers, spiders and true bugs more than expected based on arthropod abundance, whereas they consumed ants, beetles, caterpillars, and flies less than expected (Figure 1).
If consuming certain arthropod groups provides a benefit to bobwhite chicks, such as increased growth rate, a management objective should be to increase the abundance and accessibility of those groups. We therefore sampled arthropod abundance bi-monthly throughout the breeding season on Tall Timbers and Livingston Place. Sampling occurred in burned and unburned uplands, fallow fields and planted agricultural crops (i.e., corn, cotton, grain sorghum, and soybeans), using pitfall traps and suction sampling. Five preexisting fields were split into equal parts and planted in corn, grain sorghum and soybeans, resulting in 15 fields of similar size (~3 acres).
We collected nearly 35,000 individual arthropods between the two sites. The arthropod groups consumed more than expected (grasshoppers, spiders and true bugs), were positively affected by recently burned uplands, burned between March and April, fallow fields, sorghum and soybeans, and negatively affected by corn and cotton (Figure 2). We found similar results for the arthropod groups consumed less than expected (ants, beetles, caterpillars, and flies). In addition, we found that the biomass of both sets of arthropods increased within corn and soybean fields as the breeding season progressed (Figure 2).
The development of Roundup Ready crops has resulted in clean agricultural fields, especially early in the summer. At the time of our study, Roundup Ready grain sorghum had not hit the market, thus, our results are applicable to traditional grain sorghum. It is important to note that the corn, grain sorghum, and soybeans planted for this project did not receive intense weed control. Weed growth within the crop fields likely attributed to the increased biomass over time.
We used the probability of broods consuming arthropods as a metric for accessibility. We found that the probability of consuming grasshoppers, spiders, and true bugs remained relatively high when foraging areas of radio-tagged broods consisted of 25% of either burned uplands, fallow fields, sorghum, or soybean fields. Consumption of these same groups drastically declined in foraging ranges consisting of 25% corn fields (Figure 3). We also found that consumption of the other arthropod groups was worse in foraging areas that consisted of corn fields compared to other field treatments (Figure 4). The consistent finding that corn fields negatively affected the probability of arthropods being consumed suggests that corn fields limit the diet choices of bobwhite broods.
The objective of this study was to better understand how various agricultural crops affect arthropod abundance and brood diet to improve our knowledge on the best management practices for existing fields. We found that keeping fields fallow was best due to a greater biomass of all arthropod groups through mid-August, when ~80% of broods will have hatched. However, we recognize there are numerous economic considerations when managing working lands for bobwhite. If you need to farm, consider crop type.
For example, we found grain sorghum to be the most beneficial crop to quail based on arthropod abundance and accessibility. However, the development of Roundup Ready grain sorghum may reduce the benefits during the early breeding season. Cotton had the lowest biomass of arthropods throughout the breeding season and, anecdotally, receives little use by radio-tagged birds at Livingston Place.
However, options to improve arthropod availability within croplands might include creating fallow field borders or fallow strips running through larger fields.