Interactions of Crows and Raptors
Introduc&on Kristina Haycock, Jack DeLap, John Marzluff •  Li#le to no informa.on about how American Crows interact with Osprey, closest is a study about House Crow and Osprey (Yosef 2012) •  Because Osprey are not predators of crows, there should be a difference in how they recognize (Marzluff et al. 2010) and react to (Hauser & Caffrey 1994) known threats such as hawks and eagles such as hawks and eagles Methods & Materials Results Red-­‐tailed Hawk (Buteo jamaicensis) Osprey (Pandion haliaetus) •  Natural observa.ons 1 of crows responding/not responding to wild raptors in Sea#le and other loca.ons around the US (OR, MN) •  Field experiments 2 , 3 placing each of two mounts (taxidermy Osprey and Red-­‐Tailed Hawk) in loca.ons where crows regularly or rarely encounter Osprey •  Trials conducted in the Sea#le area •  In order to make sure the observa.ons were independent, the order of birds was determined randomly •  Once a reac.on was shown, tests lasted 5 minutes •  Number of birds present and dives were recorded, with at least 1 hour between tests and tests were at random .mes of day •  Sta.s.cal analyses: we tested effects (main, interac.on, pairwise comparisons) using repeated measure generalized linear models in SPSS (2009); significance for all tests was evaluated at an α-­‐level = 0.05 1
Observa&ons of Crows & Wild Raptors 90% Crows Responding (% Cases) to Wild Raptors 2 Field Experiment: Do Crows Choose to Dive Equally? Mount Only 100% 80% 60% 40% 20% 0% 80%
60%
80% 70% 40%
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50% 0%
Osprey 40% 30% 20% 10% 0% Loca&on Only n = 11 n = 8 Osprey Red-­‐tailed hawk n = 6 n = 3 Eagles Other Red-­‐tailed hawk Looking solely at the mounts, Red-­‐tailed hawks elicited a stronger effect, however not a sta.s.cally significant one (x2 = 2.78, df = 1, p = .10) % Dive Responses by Mount/
Osprey, despite having the largest sampling (n = 11) had Loca&on by far the lowest percentage of 100% Scolding/mobbing events 80% However, pairwise comparisons of primary interest were significant: 60% 40% 20% 0% Shorelines Osprey Uplands Red-­‐tailed Hawk 4 In Osprey habitat, the response to Osprey was significantly less than to Red-­‐tailed Hawk (mean diff. =-­‐ 0.32, SE= 0.15, 1 df, p = 0.04) •  The response to Osprey was less in, rather than out, of Osprey habitat (mean diff. = 0.47, SE=0.15, 1 df, p = 0.00) •  The response to Red-­‐tailed Hawk did NOT differ with respect to Osprey habitat (mean diff. between habitat = -­‐ 0.23, SE= 0.145, 1 df, p=0.12) 2 0 0 Osprey Red-­‐tailed Hawk Looking solely at the mounts, crows averaged more dives (sta.s.cally significant) at Red-­‐
tailed hawks (x2 = 30.69, df = 1, p = .00; α-­‐level = 0.05) 20
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10 6 5 Within Typical Outside Typical Osprey Habitat Osprey Habitat (shorelines) (uplands) Loca&on Only 8 10 Results of chi-­‐square test on the effects of mounts and loca.on together was not in of itself significant (x2 = 0.57, df = 1, p-­‐value = 0.45) •
20 Mount Only 15 Crows chose to dive at the mounts we placed in uplands significantly more oden than at mounts placed in osprey habitat (47% of trials in osprey habitat versus 82% outside of osprey habitat; x2 =6.20, df = 1, p = 0.01). Field E
xperiment: W
hen C
rows D
ive, H
ow I
ntensely? 3 Mean Dives by Mount / Loca&on Within Typical Outside Typical Osprey Habitat Osprey Habitat (shorelines) (uplands) When Crows dove at the mounts, more dives were recorded at shorelines rela.ve to the uplands , but not significantly ( x2 = 1.00, df = 1, p = 0.32). Results of chi-­‐square test on the effects of mounts and loca.on together, which was not significant (x2 = 0.064, df = 1, p-­‐value = 0.801). Shorelines Osprey Uplands Red-­‐tailed Hawk Discussion •  We expected a mount effect and a difference in diving intensity at Osprey depending on loca.on, but because this effect was so striking it obscures the mount effect and makes the results sta.s.cally insignificant •  In order for the four-­‐way comparison to be sta.s.cally significant, Osprey dives would have to go up inland (which they did) but Red-­‐tailed Hawk dives would have to go down. This doesn’t follow common sense Future Direc&ons •  Figure out experience effect – is there a difference because crows in uplands aren’t used to Osprey fishing? •  Look at rela.ve experience of birds diving (scolding)Osprey -­‐-­‐ more young would suggests they are inexperienced and haven’t learned NOT to scold •  Be#er defini.ons for: “within” typical osprey habitat or “outside” – map actual Osprey territories Literature Cited •
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Hauser, M. D., Caffrey, C. 1994. An.-­‐predator response to raptor calls in wild crows, Corvus brachyrhynchos hesperis. Animal Behaviour. 48, 6, 1469-­‐1471 Marzluff, J. M., Walls, J., Cornell, H. N., Withey, J. C., & Craig, D. P. 2010. Las.ng recogni.on of threatening people by wild American crows. Animal Behaviour 79, 3, 699-­‐707. SPSS Inc. Released 2009. PASW Sta.s.cs for Windows, Version 18.0. Chicago: SPSS Inc. Yosef, R., Zvuloni, A., Yosef-­‐Sukenik, N. 2012. House Crow (Corvus splendens) A#empt to Coopera.vely Kleptoparasi.ze Western Osprey (Pandion haliaetus), The Wilson Journal of Ornithology 124 (2), 406-­‐408