Identifying predators of streaked horned lark fledglings in South Puget Sound

What eats streaked horned larks? This is one of the questions that CNLM is investigating in our efforts to help recover this species. This is important because one of the best approaches for increasing the number of streaked horned larks is developing conservation strategies that increase survival. In other words, if we know what eats larks, we can implement management techniques that decrease the abundance of lark predators.

This past breeding season, CNLM completed the second year of a three-year radio-telemetry study to identify mortality factors of larks during the post-fledging period. We focus on the post-fledging period (approximately the 8-week period from when young leave the nest until they reach independence) because previous research by CNLM indicated that this period is their most vulnerable life stage, with only 45% of fledglings surviving to independence.  

A streaked horned lark fledgling with an attached transmitter.

Over the past two years we have attached radio-transmitters to 37 nestlings and tracked them daily after they leave their nests. Field work has been conducted at two airfields and one native prairie site at Joint Base Lewis McChord Military base. Transmitters, which have seen dramatic advances in miniaturization and weigh about as much as a dollar bill, are attached using a fancy figure 8-loop harness that has been shown to have minimal impact on young birds. 

One of the transmitters and harnesses used to track lark fledglings.

CNLM’s Jerrmaine Treadwell tracking the lark fledglings.

The preliminary results have been interesting. Some (five) of the radios have fallen off and many (twenty-one) of the young have survived, but we have also observed one individual that died of natural causes and nine individuals that were killed by predators.  Forensic evidence suggests that most of the mortality seems to stem from other birds - most likely kestrels, harriers, or ravens.  In these cases, we usually find the transmitter next to a small pile of feathers, which indicates that they have been plucked.  The most surprising situation was finding a transmitter in coyote scat, clearly indicating predation by a coyote. 

So far, most of the predation has occurred at the native prairie site rather than at the airfields.  One possible explanation for this pattern is that airfield managers actively dissuade larger wildlife, like raptors or coyotes, from an airport due to the risk of wildlife-aircraft collisions, thereby reducing the likelihood of lark predation.  With another year planned for the 2018 breeding season, we look forward to finalizing our results and submitting our recommendations.


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