Introduction Objectives Methods Preliminary results ...

Breeding ecology of rough-legged hawks (Buteo lagopus) in the High Arctic: are nesting structures vulnerable to climate change? A. Beardsell1,4 , G. Gauthier1,4 , D. Fortier2,4 and J. Bêty

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Département de Biologie, Université Laval, Québec, G1V 0A6 2 Département de Géographie, Université de Montréal, Québec, H2V 2B8 Département de Biologie, Université du Québec à Rimouski, Québec, G5L 3A1 4 Centre d’Études Nordiques

Introduction

Objectives

Rough-legged hawks is a common migratory bird of the Arctic

1. Map nest locations of rough-legged hawks and determine their spatial distribution. 2. Determine the frequency use of these nests over the years. 3. Characterise breeding sites and their surrounding habitat to assess features that may affect their use and reproductive success. 4. Assess the vulnerability of breeding sites to mass movement processes.

I Long-lived, top predator I They nest → in large bowl of sticks I Nests are located on cliffs, hoodoos, rocky outcrops, steep hillside and bluffs overlooking river banks in the tundra

Preliminary results

Methods Study area

Fig. 1: Rough-legged hawk nests, Bylot Island.

Nest distribution I Closely associated with the occurrence of cliffs and bluffs [3]. I These features affect the availability and suitability of nesting sites [1].

Nest reuse I Same structures can be reused for many years I Reduces the time + energy required for nest building I Advantageous when the breeding season is short as in the Arctic I May increase nest quality over the years due to addition of new material.

Habitat use Physical and biological features may influence : I The use of a nesting site I The reproductive success of the pair using it

Nest collapse A major factor affecting breeding success ↓ 18-25 % of nest failures are due to collapses and or slope failure [2, 3] Nesting on steep escarpments thus provides benefits but also entails some risks. Can these risks be enhanced by climate change?

Bylot Island (73◦ N 80◦ W), Nunavut→ ∼ 500km2 of tundra (see Fig.2)

Climatic data Obtained from a local weather station (temperature, precipitations, wind speed, etc.)

Nest monitoring I Nest searches are conducted by foot I Detection facilited by the alarm calls and the aggressive behavior of adults I Each nest is revisited 2 times minimum to assess: I If the nest is use I The reproductive success I Data available for the period 2007-2014.

Fig. 2: Map of 59 known rough-legged hawk nesting sites on Bylot Island visited in 2013. 43 were still intact (green circles) and 16 had collapsed or were buried nests (red circles).

Nest site characterization Habitat features of each nesting site will be characterized Table 1: Habitat variables measured at two spatial scales around nests (in a ∼100 m and ∼1 m radius). Surrounding environment

Nesting-site

Geomorphological setting Substrate type Slope gradient Soil water content Soil particle size Height of escarpment Active layer thickness Presence/absence of running water

Nest dimensions Exposure of nest to bad weather Accessibility to predator Presence of overhang Orientation Nest height from bottom of escarpment Altitude Distance to the nearest-neighbor nest (Inactive and active) Dominant plant species nearby

References and Acknowledgements [1] Newton I., Population Ecology of Raptors,1979. [2] Potapov Eugene R., Oikos, 78(2):pp. 362–376, 1997. [3] Swem T. R., Master’s thesis, Boise State Univ., 1996. Many thanks to Marie-Christine Cadieux, Audrey Robillard and Jean- François Therrien.

Fig. 3: Nest collapse that occurred between 14 June and 30 July 2013.

Data analysis (yet to come!) I Link between number of years of reuse and breeding success will be examined with logistic regression. I Differences in habitat features between used/unused nests and successful/failed nests will be examined with ANOVA. I Effect of geomorphological characteristics and climatic variables on nest persistence over time will be examined with proportional hazard regression.