Bird populations increase during weekends

Yes, the populations of birds increases drastically during weekends. This apparent bias in recording bird sightings during weekends in citizen science databases has been quantified for Europe and North America by Courter et al. They see a decreasing effect of the weekend effect over time for the bird species that they analyzed.

MigrantWatch is a 5 year old citizen science initiative in India that has recorded as many as 22,622 reports as of today. Although the web interface started in 2007, the dataset available for download does have 63 observations that are older, going all the way back to 1910 (Whitehead, CHT. 1911. JBNHS 21).

To get started with analyzing this dataset, it might be interesting to see how the weekend bias has changed over the years. Since, many of these reports are filed by amateur birders it should definitely show a weekend bias. In-fact Dr Jayant Wadatkar fondly remembers a weekend trip to Malkhed Reservoir when he sighted a Common Shelduck for the first time in Maharashtra. While such anecdotal information and common sense would suggest that the weekend effect is real, quantifying its magnitude might be more useful.

So lets tabulate it using the following lines:

 read.csv("migrantwatch_reports.csv",row.names=NULL)->M  
 colnames(M)<-c("Species","Location name","City","State","Reporter","Date","Sighting type","Observation frequency","Start date","On behalf of","Latitude","Longitude")  
 data.frame(Day=format(as.Date(M$Date), format="%A"),Year=format(as.Date(M$Date), format="%Y"))->WD  
 table(WD)  

Tabulation of all observations per day of week from 2007 onward

Day	2007	2008	2009	2010	2011	2012	2013	Total
Monday	48	186	217	226	249	662	277	1865
Tuesday	63	249	208	228	278	562	320	1908
Wednesday	74	228	187	236	363	807	291	2186
Thursday	64	228	252	285	270	722	313	2134
Friday	49	244	300	306	306	646	508	2359
Saturday	123	491	477	614	642	1615	587	4549
Sunday	216	848	835	895	954	2477	1333	7558
	637	2474	2476	2790	3062	7491	3629

The weekend (Sunday more than Saturday) effect does seem rather clear just by eye. Observations for each of the weekdays ranges from 8 to 10% while Saturday has 20% and Sunday has more than 30% of the observations.

While this will obviously affect estimates of first sighting and last sighting for a season in the short term, over time this effect should not affect the larger patterns. However, one has to definitely check the effect of the day of week on all results that are obtained.

Due to the nature of the data collection effort the weekend effect is something that one has to live with.