LEGOUAR P, SCHEKKERMAN H, JEUGD H VAN DER, NOORDWIJK A VAN, STROEKEN P, HARXEN R VAN & FUCHS P (2010) Survival and dispersal in Little Owls Athene noctua in The Netherlands based on 35 years of ringing data. LIMOSA 83 (2): 61-74.

The breeding population of Little Owl in The Netherlands has decreased by 50-70% over the past 50 years. Loss of suitable habitat and a reduction in breeding success have been indicated as the main causes of this decline. Here, we analyse ringing data from the period 1973-2007 (Fig. 1) to evaluate whether low or declining survival may have contributed as well. We used multi-state mark-recapture modelling to jointly analyse live recaptures and dead recoveries of a total of 25,759 ringed Little Owls (of which 3,812 were reported back at least once), taking into account spatial variation in ringing and recapture effort between and within two main regions (Fig. 2).
      Adult annual survival rate was on average 75.3% (95%-CL 69-82%), did not differ between regions and showed no long-term trend but was usually high with markedly lower values in about 25% of all years (Fig. 5a). Poor survival years seemed to occur regularly with a period of three to four years but were not associated with variation in the abundance of voles, winter severity index or duration of snow cover. They were associated with lower than average mean annual temperature and rainfall (Fig. 6), which may have affected availability of arthropod prey and earthworms. While adult mortality was spread throughout the year with a slight peak during the breading season, mortality of juveniles peaked shortly after fledging (Fig. 3). Collision with road traffic was the most frequently reported cause of death (Fig. 4). First-year survival was on average 25.8% (95%-CL 22-30%) and declined from 30% in the beginning to 18% at the end of the study period (Fig. 5 lower panel). This decline was not well explained by variation in mortality of nestlings after ringing, an increase in road traffic, variation in weather conditions or vole abundance. We hypothesize that a general deterioration of feeding conditions may have played a role, which may also underlie the decline in breeding success reported by Stroeken et al. (2009). Both reduced first-year survival and declining productivity will have contributed to the observed population decline over the past 20 years, while an earlier strong decline in the 1970s was probably mainly caused by direct loss of nesting habitat through land consolidation and country-wide destruction of orchards.
      Data on dispersal distances, corrected for the spatial distribution of observer effort, confirmed the Little Owl's highly resident behaviour, with 76% of adults breeding at the same coordinates as (i.e. within c. 1 km from) the previous year and 15% of young recruits settling within this distance from the natal site. Natal dispersal (95% within 10 km) was more prominent than breeding dispersal (95% within 4 km), and females recruited further away than males (Fig. 7).

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