Do They Count Sheep To Go To Sleep?
Climate change puts the heat on Darwin's Chillingham cattle - Climate Change, Environment - The Independent
The Chillingham cattle, with their white coats, red ears and horns, currently number 85 animals, who roam freely around the grounds of Chillingham Castle, seat of the historically influential Grey family. They were once domesticated but now live wild and differ from most other UK mammals because they give birth throughout the year, not only during spring and summer. Over the past 60 years, more and more cattle have been born during the winter. When the record of births was cross-referenced with Met Office weather data, scientists found warmer springs nine months earlier were responsible.
As any farmer knows being able to count your stock is not only a basic requirement of the trade but also a legal necessity. So how do our brave researchers deal with counting up to 85?
The supporting data is online.
You guessed, they model the numbers.
State-space models have two main components; a process model and a data model. Observations of time-series data (e.g., census estimates of total population size) are assumed to arise from some ‘true’ unobserved state that represents the true dynamics of the population (Calder et al. 2003). The data model describes this relationship between the observed data and this true state by incorporating observation error. The dynamics of the true state of the population through time are described by the process model, which explicitly incorporates process variance.
The data model describes the relationship between the observed data, Yit, (the number of animals counted during census) and the underlying ‘true’ state of the population Nit (the total number of animals in the population including those animals that were not included in the count) by explicitly incorporating observation error. The relative population size within each of the six age/sex classes in year t is modelled using a multinomial distribution,....