Biology 302 Field Lab Background – July 2009 Interpreting Egg-damage markings

1. Biology 302 Field Lab Background – July 2009 Interpreting Egg-damage markings

2. Of course you should never handle the nests or eggs bare-handed! Lisa was reflecting on that thought even as she did so in the photo (top right). In this case, however , the nest was being removed at the end of a trial, so human scent was not an issue. Nest 16 was mounted to its tree site with twist-tie fasteners (shown on the previous slide). Nest 1 (lower right), the same size as nest 16, was held in place with string (both are supplied, use whichever works best for the site you have). When you are checking for egg-damage, you may need to roll the eggs around in the nest, or lift them out temporarily – be sure you are wearing a glove when you do so! All your nests should be placed at a height allowing even the shortest member of your group to look down into them – no need to untie a nest on each visit.

3. Cases of Minor Egg Damage In these two nests, you can see several minor types of damage. [Each egg is numbered for your reference.] Eggs 1 and 4 show a series of very fine shallow grooves on the surface – we aren’t quite sure how to interpret these! (Note that the eggs are lying on a smooth foam mat, so the grooves aren’t caused by contact with the inner surface of the nest-basket.) On egg 2 we see what looks like a paw-print left by a mouse or a small rat. Egg 5 bears marks left by the feet of a small songbird, such as a bushtit: three forward-facing toes (clawmark only), and one larger rear-facing toe (its full length leaving a straight-line mark). Such a bird would not be an egg-predator, more likely landing in the basket in search of insects or spiders to eat. Eggs 3 and 6 are more or less undamaged. 1 2 3 4 6 5

4. Cases of Moderate Egg Damage All three eggs in this nest appear to have been handled extensively by a squirrel; you may have observed squirrels with peanuts or other items – they have a tendency to roll the item over and over, and on a soft clay material this handling ends up leaving a series of shallow clawmarks all over the surface (clearly seen on eggs 8 and 9). The damage on egg 7 is also easy to evaluate: the parallel grooved marks (a) look like a paw print, then the raised “crest” of clay (b) obscures beneath it the entry-marks of the animal’s lower incisor teeth. In the reverse-view of egg 7 shown in the lower photograph, you again see the “crest” (b – possibly pushed up by the tongue) and, nearer the camera, the clear marks of the two upper incisor teeth (c). Squirrels are definite egg predators – they are far from herbivorous! 7 b a 8 9 9 b 8 c 7

5. Cases of Substantial Egg Damage These photos show eggs in a single nest, but rolled over for the fullest range of views; the same three eggs, but we did not note which was which. The eggs are so disrupted that it is difficult to determine exactly what happened to them: most of the damage categories visible in the previous slides are present here also, along with some very deep digging-like pawmarks (d), some deep groove features (e; perhaps the result of bird-beaks), and attacks intense enough to have torn chunks out of the clay entirely (f). Since the nest was out at the field site for about 2 weeks, such a variety of damage is not too surprising... but it was in an area of fairly dense, homogeneous, deciduous vegetation (alders, maples, berry-bushes), and not at an ecotone! Go figure. d e f e f d

6. Goodbye for now, from the egg-predator-misleading team. So many squirrels with clay caught in their teeth... we have a lot to answer for. [Gerrit could avoid the group-photo because it was his camera; I could not avoid being photographed holding the wimpy nest. But I created the Powerpoint and it’s my website, so overall I’m not too upset. W ] Gerrit Velema Lisa Allyn Krysta Banack