Only long-term field data can capture nature’s stealthy rarities

 

A tiny crested tit snags a spider from under a twig, shaking the icy needles of a branch tip far above the ground. A lightning fast swoosh, smack! … a few feathers fall, drifting toward the snowy ground. A smug hawk finds a silent perch where it can pluck and eat its tiny prey, staving off winter’s hunger for another day. Predation events like this one collectively comprise a key selection pressure influencing animal populations, but they are difficult to quantify because of their brevity and the necessary stealth of predators. Over 35 years of field study of mixed-species flocks involving Paridae species in eastern Latvia, we documented nearly 200 instances of Eurasian Sparrowhawks (Accipiter nisus) attacking flock members. Roughly 10% of these attacks were successful, and successful attacks typically occurred in the lower canopy. It appears that the habitat distribution of members of these mixed-species flocks is associated with variation in predation, as only a few species composed the majority of the mortality observed.

 

 

This research was recently published in the Journal of Field Ornithology:

Krams, I.A., T. Krama, T.M. Freeberg, R. Krams, and K.E. Sieving. 2020. Attacks of songbirds in mixed‐species flocks by Eurasian Sparrowhawks: strategies of predators and potential prey. Journal of Field Ornithology. https://doi.org/10.1111/jofo.12350

 

Guest blog post by:

Indrikis Krams
Institute of Ecology and Earth Sciences
University of Tartu, Tartu, Estonia