Growing Up Prairie: Cowbirds, Predators, and Baby Birds in Kansas Grasslands

When we think about human growth milestones – crawling, walking, teething – we know that every child is a little different. You may have started talking earlier or later than your siblings or your cousins, even though you are closely related. Maybe your older sibling got tall really quickly and was a star in youth basketball while you didn’t hit your athletic stride until you got into swimming in high-school; as humans we don’t expect these differences in individual development to ultimately affect our respective health and success as adults. Growing and developing at different speeds is something we observe in other animals as well. However, differences in the rate of development might be even more important in animals if they have to deal with dangerous or challenging environments.

Sarah Winnicki studies the growth and development of prairie songbirds as a Master’s student at KSU. Sarah participated in the Sunset Zoo Science Communication Fellowship Program and recently presented her research as a part of the Science on Tap series at Tallgrass Taphouse. The birds she studies at Konza Prairie Biological Station – Grasshopper Sparrows, Dickcissels, and Eastern Meadowlarks – all nest on or near the ground and develop astonishingly quickly. Bird species that nest high above the ground or in protected nest boxes or holes in trees typically leave the nest after 2 or more weeks. But the prairie species that Sarah studies can leave the nest after just 7 days!

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Sarah Winnicki and the prairie birds she studies: Grasshopper Sparrow, Eastern Meadowlark, and Dickcissel (top to bottom; photos courtesy of Sarah Winnicki).

So why do baby birds (nestlings) at Konza grow so quickly? And why within a single species or even a single nest do some birds grow faster than others? Sarah discussed some potential explanations. First, birds in a nest on the ground are especially vulnerable to predators. At Konza, nine out of ten nestlings are eaten by predators before they can leave the nest, many even before they hatch. Clearly, how quickly a bird can grow big enough to leave the nest and avoid being found by a hungry coyote or snake can make a big difference in how likely it is to survive. Second, food is an important factor in determining how fast birds can grow. Parent birds may not want to risk bringing food to the nest too frequently if there is a chance they could lead a predator to it. Alternatively, parents may not be good at finding high quality food, or there may not be much food in their part of the prairie; this lack of food may slow down the nestlings’ growth.

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A Grasshopper Sparrow with a meal for its young (left), and a speckled Kingsnake about to enjoy a meal from a Dickcissel nest (right). Photos courtesy of Sarah Winnicki.

Previous research explored how the presence of predators and the availability of food can influence growth and development of nestlings.  Sarah’s research, on the other hand, is highlighting a third factor that could affect how and when nestlings grow up. Brown-headed Cowbirds are a bird species native to the Great Plains that have adopted an unusual strategy for raising their young – they don’t! Female Brown-headed Cowbirds never make their own nests and instead lay their eggs in the nests of other species, including those that Sarah studies. The rightful parents of this nest then raise the large, hungry cowbird nestlings alongside their own hungry offspring. This strategy is known as brood parasitism. Competition with cowbird nestlings could shape the growth of the nestlings that belong in the nest. The nestlings that belong in the parasitized nest may grow more slowly if they are getting less food, or they may prioritize growth of certain body parts, speeding up development of their mouths or necks to improve their chance of getting fed.

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An adult Brown-headed Cowbird (left); A parasitized Dickcissel nest with both a cowbird nestling (white beak) and a Dickcissel nestling (yellow beak) begging for food (right). Photos courtesy of Sarah Winnicki.

Sarah and her extremely dedicated field crews have collected data to test these hypotheses over the last two summers at Konza. They work hard to find the very well-hidden nests of Grasshopper Sparrows, Dickcissels, and Eastern Meadowlarks in the tall, dense prairie grass and pay careful attention to the presence of Brown-headed Cowbird eggs. Once the eggs hatch they return to the nest every other day to monitor the growth of each nestling, taking over 30 different measurements including wing, leg, bill, and feather growth. They also set up camouflaged cameras at some nests to get footage of parents feeding the young and any visits from cowbirds or predators. With all of this data, Sarah teases apart how predators, food, and brood parasitism influence the growth and development of nestlings in grasslands. As the habitats that grassland birds depend on disappear, understanding why some nestlings are able to grow up successfully will be incredibly important for maintaining the diversity of the birds in our prairies.

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Sarah’s field crew drags ropes across the prairie to find nests by flushing birds off of their eggs as they approach – once a bird is seen flying away the crew stops and searches carefully for the nest. Photo courtesy of Sarah Winnicki.

This post is part of our series covering Science on Tap. This monthly event, a part of Sunset Zoo’s Behind the Science initiative, is a gathering at the Tallgrass Taphouse during which a featured scientist shares their research and engages with the audience in a lively conversation about the topic. Hopefully you are able to join in on the next conversation; if not, we’ll be here to provide a summary of the research that was shared!

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Sarah Winnicki presenting her research on brood parasitism and prairie birds at Tallgrass Taphouse.

 

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This post was written by Elsie Shogren. Elsie is a PhD student studying how the environment and sexual selection can interact to shape the behavior and morphology of birds in the Manakin family.

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