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Analysis of Observations

ZipcodeZoo analyzes changing populations, based on changes in observation rates.

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For more information about the statistics used on these pages, click here.

Changing Observation Rates

This chart shows observations for the period 1860-2006 from the ZipcodeZoo database of observations. The curves show the number of observations reported per year. The number of observations per year has substantially increased since 1940, and particularly in the last two decades.

While the curves for plants and animals are similar, they are not identical, suggesting that changing interest in the geographical distribution of plants and of animals has followed different courses.

There are currently 127,715,643 observations in our database, for the 2,646,497 species on this web site. These observations are not evenly distributed across species... instead, for many species, there are no recorded observations. At this writing, our database only includes observations for 149,368 different plants and animals. ZipcodeZoo draws these observations from many primary sources, but normally via a distribution portal, such as GBIF or IOBIS. To be included in the ZipcodeZoo database, an observation must include a unique latitude+longitude+observation_date, to help reduce the chance that some critter has been counted twice.

ZipcodeZoo continues to add observations to its database, and to map and analyze those observations. Over time, the shape of the distribution shown to the right is likely to change.

Our understanding of the distribution of species is only beginning. For 528,332 different species, our sources have no distribution data at all.

Changing Observation Rates for Mammals, Birds, Reptiles, Amphibians, Fish, and Insects


In the chart to the right, we have shown the number of observations per year for birds (class="Aves"), mammals (class="Mammalia"), reptiles (class="Reptilia"), amphibians (class="Amphibia"), fish (class="Actinopterygii") and insects(class="Insecta"). At this writing, bird observations dominate the data, probably for several reasons:

  • our zealous focus on such records for projects such as BirdFinder,
  • greater public interest in bird watching, and
  • the greater conspicuity of birds than of many other groups of animals.

These differences in observation rates between these 6 Classes of animals make it clear that we must be very careful if we are to use changing observation rates to infer changing populations.

Changing Number of Recorded Observations of the Java Sparrow


In the chart to the right, we have shown the number of observations reported per year for the Java Sparrow, Padda oryzivora. It would appear that there was fairly little change in the number of observations each year between 1960 and 1999, but that after 1999, the number of observations each year climbed dramatically.

But the previous chart shows that observations of all birds also climbed in this period. So we cannot be sure, from this chart, whether the rise in observations was because of an increase in birds or an increase in observation activity.

Changing Percentage of Recorded Observations of the Java Sparrow


In the chart to the right, we show the annual number of observations of the Java Sparrow as a percentage of all bird observations. In the previous chart, the surge in the number of observations of the Java Sparrow could have resulted from more bird watching activity. If the overall bird population is fairly stable, then the percentages in the chart to the right suggest that the Java Sparrow is in decline.

In fact, the IUCN Red List of Threatened Species reports "The popularity of this finch as a cage-bird has resulted (and unless stringent action is taken, will continue to result) in a rapid decline in its population and range as a consequence of intense trapping activity, such that it qualifies as Vulnerable." The IUCN reports that its population trend is downward.

BirdLife International reported that in 1988, it was "Lower Risk/Least Concern", but declared it "Vulnerable" in 2000.

Collar, Crosby and Stattersfield (BirdLife International Red List Authorities) declared the Java Sparrow Vulnerable in 1994.

These conclusions explain why there were no reported sightings in 2005.

This consistency between the statistical trend and the Red List experts suggests that when a species' annual observations decline over time as a percent of the relevant observations (such as that species' Class), that the species might be in trouble. Conversly, it might be that an increase in the annual observation rate for a species suggests a growing population. One means of evaluating these notions is to compare upward and downward trends with conservation status information.

Mean Slope for Three Conservation Statuses


We examined change in annual observations for the period 1960 to 2004 for 130 species that IUCN had defined as Endangered, Vulnerable, or Near Threatened. We then fit a line of best fit to species. The slope of this line is positive when the number of annual observations is increasing relative to that of that species' Class, and negative when these annual observations are becoming less common. We then calculated the mean slope for each of the three groups. As you can see from the chart to the right, the slope is negative for the average Endangered animal, very slightly negative for the Vulnerable animals, and slightly positive for those that are Near Threatened. These results suggest that an analysis of observation data can suggest species that are in need of further scientific study and possible protection.

References