Is Hen harrier (Circus cyaneus) breeding success in Bowland linked to the egg laying date?

Storton, R (2008) Is Hen harrier (Circus cyaneus) breeding success in Bowland linked to the egg laying date? [Dissertation]

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The Hen harrier (Circus cyaneus) is a rare breeding bird in England with less than twenty
pairs breeding in recent years. It’s preference for breeding and hunting on heather
moorland used for grouse shooting brings it into direct conflict with man.
Bowland in Lancashire is the most successful breeding site for hen harriers in England
due to a partnership between the RSPB and United Utilities who are a large land owner in
the area. Whilst working for the RSPB through the breeding season of 2006 & 2007 the
author was able to study the species closely and realised that nests were failing each year.
The hypothesis for the project was ‘Is hen harrier breeding success linked to egg laying
date’. If a relationship between egg laying date and the success of the nest could be
proven then this would then help to identify the nests more likely to fail.
All harrier nests on United Utilities land in Bowland over 2006 & 2007 were found and
monitored and data for egg laying and nest success collected and analysed. Also rainfall
data from a gauge on the breeding grounds was analysed to see if rainfall affected
breeding success. The data for the nest data (figure 3) proved that date did affect nest
success with a peak around the 23rd April with the most successful nests grouped around
this date and the further from this date eggs were laid the less successful the nest.
However, the data for rainfall data in Bowland (figure 4) showed no connection between
amounts of rainfall and nest success.

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