378 Mr. W. Thompson on the Birds of Ireland, 



than the erection there, this singular locality was again selected in 

 1833, when the nest of the former year was once more used, and 

 the brood escaped from it without any casualty. Two new nests 

 were also built this year and successfully occupied, one of which I 

 remarked on the 10th of August contained eggs for a second brood, 

 and on the 19th of the same month I had the satisfaction of seeing 

 it tenanted by young birds. This nest had for its support the wing 

 of one of the departed falcons, on the centre of which it rested*. 

 The entire height of the shed, which was erected solely for the 

 protection of the hawks, is not above seven feet. The nests are 

 about six feet from the ground, and built against a beam of timber 

 (to this the wing just mentioned is nailed) placed on the top of the 

 low wall supporting the roof. The height of the roof from the ground 

 is four feet two inches, which leaves only two and a half feet clear 

 for the swallow's flight between it and the heads of the hawks as 

 they perch upon their blocks. One of the nests is only six feet from 

 the block occupied by a hawk, and from which this bird has liberty 

 to move to half that distance. The swallows however flew closely 

 past these rapacious birds without being in any way heeded by 

 themf. 



* In White's ' Selborne ' a similar instance is mentioned, 

 f In the Northern Whig (a Belfast newspaper) of July 2, 1829, the fol- 

 lowing paragraph appeared : — " We understand that a pair of swallows have 

 built their nest in Mr. Getty's school-room, at Randalstown ; and notwith- 

 standing there are above forty scholars daily attending, the birds fearlessly 

 went on with their labour, and have now out their young ones. One of tlie 

 windows had been for several nights left down, at which time the swallows 

 found admittance, and after much apparent deliberation commenced their 

 structure, which they carried on chiefly during the hours of the school ; and 

 though they had abundance of time to build, either before the school com- 

 menced, or after it was dispersed, yet they always preferred a few hours 

 about noon for their labour, and seemed to do little at any other time. The 

 scholars, much to their credit, gave them as little annoyance as possible, and 

 the window is still kept down." 



Mr. Blackwall in his ' Researches in Zoology ' mentions the remarkable 

 fact from personal investigation, that swallows, house martins and sand mar- 

 tins not unfrequently leave their last brood of young to perish, and occa- 

 sionally leave their eggs before they are incubated. He speculates on the 

 causes of this *' voluntary act of desertion," and combats the opinion of Dr. 

 Jenner, that it is prompted by "the desire to migvaie, produced by a change 

 in the reproductive system." Having given less attention to the subject 

 than either author, 1 should perhaps be silent, but a few remarks on so ap- 

 parently singular a proceeding may not be considered presumptuous. In the 

 instances alluded to, the young broods and eggs were deserted late in the 

 season, and I should suppose at the migratory period. The pai'amount ob- 

 ject would then seem to be migration, and when favourable weather and 

 wind prevail, the love of oifspring yields to the stronger impulse, and the pa- 

 rents take their departure. Had this favourable time been long enough pro- 

 tracted, they would have continued to tend their offspring and bring them 

 to maturity. It is quite different at the season when the first brood is being 

 produced. The primary principle which then influences them is, the pro- 

 duction of their species ; and no matter how favourable every circumstance 

 may be for migration, they do not leave the country. I have attended to 



