Considering all the birds sampled, identify which species was sampled the most and which was sampled the least. 

Most:

Least:

Using the data from the table, calculate the percentage difference in mean bird mass for the hermit thrushes refueling at Site 1 compared to those refueling at Site 2.

Compare the 17-year summary data for the hermit thrush and the magnolia warbler.

Evaluate the one season data for the hermit thrush and the American robin with regard to average mass change per hour at Site 1.

Describe, using the triglyceride levels graph, the results at Site 1 and Site 2 for all of the birds.

Explain the differences in the triglyceride level and butyrate level for the hermit thrush at Site 1 and Site 2.

Scientists have hypothesized that the food quality is better at Site 1 than at Site 2. Evaluate this hypothesis using the data provided.

Suggest one advantage and one disadvantage for blood sampling rather than weighing birds to assess food quality at stopover sites.

most: white-throated sparrow/WS
least: American robin/AR
(both needed to award the mark)

5% / 5.03% / 5.3% (unit required) (Accept answers in the range of 5 % and 5.3 %)
No indication needed of whether percentage difference is an increase or decrease.

both birds show an increase in mass at Site 1 and a decrease at Site 2;
MW has a greater increase than HT at Site 1; (do not accept larger/greater change)
MW has a greater decrease than HT at Site 2; (accept negative change)
MW has larger mass change at both sites/Site 1 and Site 2;
Do not accept answers quoting only numerical statements.

HT data is reliable whereas AR data is unreliable / differences not significant / uncertainty higher with AR;
(because) error bars/variation/range/standard deviation large for AR / larger for AR than for HT;
(because) smaller sample of AR than of HT;
Do not accept comments about whether the data is accurate or not.

all have a higher concentration of triglyceride at Site 1 than at Site 2;
HT (and WS) highest at both sites/at Site 1;
MW lowest at Site 1 and AR lowest at Site 2;
Do not allow answers quoting only numerical statements.

triglyceride higher at Site 1 because more fat deposition / HT eats more;
butyrate higher at Site 2 because more fat/triglyceride utilized / HT fasts more;

(data supports hypothesis) because mean mass at Site 1 is greater than at Site 2 (for all birds);
because mass gained at Site 1 but mass falls (mostly) at Site 2 (over 17 years);
because triglyceride levels higher at Site 1 / butyrate levels higher at Site 2 / more fat deposited at Site 1 / more fat utilized at Site 2 / more fasting at Site 2;

advantage:
need to capture bird only once to get data / no need to mark and catch birds again;
more informative data can be gathered; (do not accept unqualified “more precise”)

disadvantage:
removal of blood is more stressful/risky for the bird than weighing;
danger of infection / spread of disease / harm to birds;
extra time/money/laboratory equipment is needed to analyse results;
could include fat/triglyceride/butyrate from previous/long-term feeding;
nutrients from food eaten at these sites may not have been absorbed yet;
Award [1] for one advantage and one disadvantage that are not the converse of each other. Do not allow a second advantage or second disadvantage given in the answer.

Part (a) was intended to be an easy start to the question and almost all candidates answered it correctly.

The percentage calculation in (b) was only answered by about half of candidates, perhaps because of the wording of the question, which did not make it clear whether the difference should be calculated as a percentage of that at Site 1 or at Site 2. Candidates were expected to calculate the difference between the two masses by subtraction and then divide either by the mass at Site I or at Site 2. Candidates performed many other calculations, but as only one mark was available, no credit was given for these.

The best answers in (c) made it clear whether the mass changes were increases or decreases, but many answers were vaguer, referring only to mass changes. There was some confusion between mass and mass change, with some some candidates implying that a negative mass change was a low mass. In some cases answers to this question consisted only of figures quoted from the bar chart, rather than a genuine comparison and so did not score any marks.

In (d) candidates were asked to evaluate data. The command term evaluate is defined as assessment of the implications and limitations. In this case it was the limitations of the data that were relevant. Candidates were expected to use the size of error bars and the sample sizes to assess the reliability of the data. Many candidates wrote instead about the differences between the data for the hermit thrush and American robin, without any actual evaluation.

Part (e) of question 1 tested a different skill in data analysis. Candidates were expected to pick out the most significant features of the data and as in (c), answers that merely quoted numerical figures from the bar chart mostly scored few marks. The points that the stronger candidates were made were that the triglycerides level at Site 1 was higher than that at Site 2 in all bird species and that the hermit thrush had the highest levels at both sites, whereas the Magnolia warbler was lowest at Site 1 and the American robin was lowest at Site 2. 

1(f) was another part of the question where it was important to pay attention to the command term. The term explain indicates that causes, reasons or mechanisms are required. In this case the causes of triglycerides levels being higher at Site 1 and of butyrate levels being higher at Site 2 were expected. The stem of the question had given the explanations that should have been given –fat deposition or fat utilisation.

Part (g) involved another evaluation, in this case of a hypothesis. Candidates were expected to conclude that the data supported the hypothesis. No mark was given this and instead marks were awarded for evidence.  

Most candidates only considered the butyrate and triglycerides levels and so scored a maximum of one mark. The second mark was only awarded if candidates gave a broader answer by referring back to differences given earlier in the question for mean mass or mass change between Site 1 and Site 2.

The last part of the question involved suggesting and advantage and a disadvantage of blood sampling. A huge variety of answers were given but few candidates gave both an advantage and a disadvantage that the examiners considered acceptable. The disadvantage was the easier of the two and many candidates wrote about the stress of the procedure for wild birds or harm that the loss of blood might cause. The advantage that was most often given was the opportunity to obtain precise measurements for many different nutrients in blood, compared to the rather blunt assessment of food quality that weighing gives. There was some confusion about the meanings of terms such as precision and accuracy. Birds can of course be weighed accurately with great precision, whereas some candidates implied that blood tests were inherently more accurate and precise.