Caesar Kleberg News

TEXAS A&M UNIVERSITY-KINGSVILLE

The Booms and Busts of Quail

Can Rainfall be the Trigger for Bobwhite Nesting?

Article by LINDSEY HOWARD AND FIDEL HERNÁNDEZ

Photo by Tim Fulbright

Bobwhite populations are strongly influenced by rainfall. Is it possible that visual cues or rainfall itself be influencing their breeding? Spring arrived in Texas and with it, the familiar “bob-white” whistle heard throughout the Northern Bobwhite Quail’s range as adults call for mates. As the quail breeding season got underway, many managers and landowners began speculating how well quail populations would do this year, which started off very dry.

Bobwhite populations exhibit boom and bust dynamics that are characterized by drastic changes in population size from year to year. It is widely accepted that these fluctuations are related to rainfall, with years of high rainfall yielding larger quail populations than years of drought.

What is not known, however, is the exact cause of this relationship. Some have speculated it’s the higher abundance of insects, or better nesting cover, or cooler temperatures. Despite decades of research on this relationship, however, no one knows what specifically links rainfall to bobwhite population fluctuations.

Past research has focused on a variety of possible explanations, including heat stress and water deprivation, but a satisfactory conclusion has not yet been reached. Most hypotheses that are supported in captive or laboratory studies are disproven later during field studies.

In addition, much of this research has focused on the materialized effects of rainfall; that is, the habitat features that change because of rain. For instance, during the summer months, after sufficient spring rainfall, insects are abundant. This provides a good food source for both adults and chicks, promoting reproduction and survival.

Therefore, one might reason that the connection between rainfall and bobwhite populations is the increase in food. This line of reasoning, however, does not account for the time lag between when adults breed and chicks hatch. To ensure that chicks hatch when insects are most abundant, adults must have some prior indication of upcoming favorable conditions, to ensure they have time to breed, nest, and hatch chicks by the time those conditions arrive.

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Photo by Lindsey Howard

Brown, crisp vegetation, as occurs during drought, may provide a negative cue to bobwhites thereby inhibiting their reproduction.

Birds use a variety of information to anticipate favorable conditions and correctly time breeding. This information falls into two broad categories: predictive information and supplemental information.

Predictive information, such as day length, are long-term cues that can be relied upon from year to year. Such information triggers development of the reproductive organs and prepares the birds for breeding.

In unpredictable environments, however, long-term cues are not enough for adults to reliably tell when favorable conditions are near. In these cases, birds rely heavily on supplemental information. This is a type of environmental information, such as food availability or temperature, is specific to a local area and signals when actual breeding should begin.

Thus, once daylength results in the physical preparedness of the quail reproductive system, quail will hold themselves in a state of readiness, waiting until supplemental information triggers them to breed. We wonder if rainfall itself—and not the materialized effects of it—is providing an environmental cue triggering quail breeding.

Rainfall is an important supplemental cue for birds in desert and semi-desert regions. In places such as Australia, southwestern Africa, and the southwestern United States, breeding activities for various bird species have been documented to start during or shortly after rainstorms. As rainfall is the earliest indication that conditions will be changing, a rainfall event itself may act as a breeding cue.

In addition, factors closely tied to rainfall events, such as the rapid change in landscape appearance from dry, crisp, brown vegetation to lush, green vegetation may also be providing visual cues.

We will investigate this question in a two-year study conducted at the Caesar Kleberg Wildlife Institute at Texas A&M University-Kingsville. We will investigate whether vegetation color (during summer 2022) and rainfall (during summer 2023) act as reproductive cues for bobwhites.

Our first experiment will begin this summer, where we will house 20 bobwhite hens in aviary cages assigned to one of four different vegetation-color treatments: a brown treatment with dry vegetation; a green treatment with lush vegetation; a switch treatment in which vegetation color will change from brown to green mid-way during summer; and a control treatment with no vegetation.

To evaluate how bobwhites respond to color, we will monitor reproductive hormone levels and egg-laying rate throughout the experiment and compare these metrics among treatments. If vegetation color is a stimulus, then reproductive hormone levels should spike immediately following the switch from brown to green vegetation, as well as be higher in the green versus brown treatment. We will follow a similar protocol to test the influence of rainfall during summer 2023.

Our study will provide greater insight into what links rainfall with the boom and bust of quail populations. This information will help wildlife managers know how effective that management can be at mitigating the effects of unpredictable rainfall, as well as what can be done to prevent population lows. In addition, this study will increase our knowledge of avian reproduction in semi-desert environments, which is important for predicting consequences that climate change may have on desert birds.

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