Sparrowhawk

We were able to establish baseline “norms” in the form of Shewhart charts for indicators that could be broadly categorised as indicators of change in:

(i) population demography because of altered recruitment, survival and mortality. Measures were:

  • proportion females;
  • proportion of first-year birds (having hatched in that calendar year or in the preceding calendar years);
  • proportion deaths from starvation or disease.

(ii) nutritional status measures were:

  • body weight;
  • fat score;
  • condition index.

(iii) physiological stress (fluctuating asymmetry)

Descriptions of how these indices are calculated can be found in the supporting PBMS report.

Where the health index reports as a proportion of the population (e.g. percentage of females) then for statistical reasons the index is presented as the Arcsine of the square root of the proportion. This value can theoretically range between 0 and 1.57, representing 0% and 100% of the population, respectively.

Proportions

The proportion of female and juvenile birds in each year's sample. Years where the value falls outside of the 95% prediction intervals may indicate change in the demographic structure of the species population.

Graph of year vs arcsin sqrt of proportion of female sparrowhawks
▲ Arcsin sqrt of proportion of female sparrowhawks

Graph of year vs arcsin sqrt of proportion of male juvenile sparrowhawks
▲ Arcsin sqrt of proportion of male juvenile sparrowhawks
Graph of year vs arcsin sqrt of proportion of female juvenile sparrowhawks
▲ Arcsin sqrt of proportion of female juvenile sparrowhawks

 

 

Figure legend

 

Body Weight

Median postmortem body weight of birds each year for different sexes and ages of birds. The sample size in any single year was at least 5 birds. Years where the value falls outside of the 95% prediction intervals may indicate change in the physical condition birds in that particular demographic which may indicate, in the case of years below the lower 95% prediction interval, that food availability may be restricted.

Graph of year vs median body weight of female adult sparrowhawks
▲ Median body weight of female adult sparrowhawks
Graph of year vs median body weight of female juvenile sparrowhawks
▲ Median body weight of female adult sparrowhawks
Graph of year vs median body weight of male adult sparrowhawks
▲ Median body weight of male adult sparrowhawks
Graph of year vs median body weight of male juvenile sparrowhawks
▲ Median body weight of male juvenile sparrowhawks

Figure legend

 

Putative cause of death

The proportion of birds that died of starvation or disease in each year. Years that fall below the lower 95% prediction interval indicates that there are fewer starved birds in the population (or demographic group), conversely an increase above the upper 95% prediction interval indicates there are more starved birds.

Graph of year vs proportion of female adult sparrowhawks that were diseased or starved
▲ Proportion of female adult sparrowhawks that were diseased or starved
Graph of year vs proportion of female juvenile sparrowhawks that were diseased or starved
▲ Proportion of female juvenile sparrowhawks that were diseased or starved
Graph of year vs proportion of male adult sparrowhawks that were diseased or starved
▲ Proportion of male adult sparrowhawks that were diseased or starved
Graph of year vs proportion of male juvenile sparrowhawks that were diseased or starved
▲ Proportion of male juvenile sparrowhawks that were diseased or starved

 

Figure legend

 

Fat score

The proportion of birds categorised as starved each year, based on their fat score.Years that fall below the lower 95% prediction interval indicates that there are fewer starved birds in the population (or demographic group), conversely an increase above the upper 95% prediction interval indicates there are more starved birds.

Graph of year vs arcsin sqrt of proportion of female adult sparrowhawks that starved
▲ Arcsin sqrt of proportion of female adult sparrowhawks that starved
Graph of year vs arcsin sqrt of proportion of female juvenile sparrowhawks that starved
▲ Arcsin sqrt of proportion of female juvenile sparrowhawks that starved
Graph of year vs arcsin sqrt of proportion of male adult sparrowhawks that starved
▲ Arcsin sqrt of proportion of male adult sparrowhawks that starved
Graph of year vs arcsin sqrt of proportion of male juvenile sparrowhawks that starved
▲ Arcsin sqrt of proportion of male juvenile sparrowhawks that starved

 

Figure legend

 

Condition

In the graphs below, years for which the average condition index (CI) is below the lower 95% prediction interval indicates that there are fewer birds with low fat reserves in the population (or demographic group), conversely an increase above the upper 95% prediction interval indicates there are more birds with low fat reserves. Low fat reserves means a bird is less likely to survive prolonged periods where they are unable to hunt successfully, or that the bird has starved. The condition index is used as a continuous measure of body condition, rather than categorical such as fat score. The mean condition of birds per year was calculated for different ages and sexes. The Condition Index is calculated as follows:

CI = (BW - GW) / SD

where:

  • CI = Condition Index
  • BW = whole postmortem body weight (g)
  • GW = Wet weight of gizzard contents (g)
  • SD = Sternum diagonal, which is the distance between the posterior point of the sternum keel plate and the distal point of the clavical (mm)
Graph of year vs condition index of female adult sparrowhawks
▲ Condition index of female adult sparrowhawks
Graph of year vs condition index of female juvenile sparrowhawks
▲ Condition index of female juvenile sparrowhawks
Graph of year vs condition index of male adult sparrowhawks
▲ Condition index of male adult sparrowhawks
Graph of year vs condition index of male juvenile sparrowhawks
▲ Condition index of male juvenile sparrowhawks

 

Figure legend

Fluctuating asymmetry

Higher levels of fluctuating asymmetry in feathers may indicate that birds in the population were subject to physiological stress during the period that those feathers were grown. The mean fluctuating asymmetry index per year in the weight of the 10th Primary feather is calculated for different ages and sexes of birds. The mean fluctuating asymmetry index is calculated as follows:

FA10w = 0.798 * SQRT( | FWl - FWr | - ME )

where:

  • FA10w = fluctuating asymetry index of 10th primary feather weight
  • FWl = weight of the left 10th primary feather (g)
  • FWr = weight of the right 10th primary feather (g)
  • ME = measurement error estimated from 2 repeat measures of the trait
Graph of year vs fluctuating asymmetry of adult sparrowhawks
▲ Fluctuating asymmetry of adult sparrowhawks
Graph of year vs fluctuating asymmetry of female juvenile sparrowhawks
▲ Fluctuating asymmetry of female juvenile sparrowhawks
Graph of year vs fluctuating asymmetry of male juvenile sparrowhawks
▲ Fluctuating asymmetry of male juvenile sparrowhawks

 

Figure legend

 

Photo: Saxifraga: Luuk Vermeer